Catalyst Type Effects on Structure/Property Relations of ...

REVIEW

C. Paulik,* C. Tranninger, J. Wang,P. Shutov, D. Mileva,M. Gahleitner . . . . . . . . . . . . . . . 2100302

Catalyst Type Effects onStructure/Property Relations ofPolypropylene Random Copolymers

Random copolymers of isotacticpolypropylene with ethylene and/or higher𝛼-olefins are single-phase materials forwhich crystallinity is reduced and polymor-phism enhanced. Two groups of influencefactors for the structure–property rela-tions are discussed here: The catalystsystem employed for their polymerization,including different Ziegler–Natta genera-tions and metallocenes, and the type ofcomonomer, mostly ethylene, 1-butene,and 1-hexene.

http://crossmark.crossref.org/dialog/?doi=10.1002%2Fmacp.202100302&domain=pdf&date_stamp=2021-10-10

REVIEWwww.mcp-journal.de

Catalyst Type Effects on Structure/Property Relations ofPolypropylene Random Copolymers

Christian Paulik,* Cornelia Tranninger, Jingbo Wang, Pavel Shutov, Daniela Mileva,and Markus Gahleitner

Polypropylene (PP) random copolymers are an important class of commercialmaterials that can be tuned for a wide range of different applications. Thestructure–property relations are mainly discussed in this article focusing ontwo major influencing factors, the catalyst system and the type and amount ofcomonomer. Ziegler–Natta (ZN) catalyst systems still dominate theproduction of polypropylene and todays sixth-generation ZN catalysts arebased on postphthalate donor systems. Metallocene (MC) catalysts offerpossibilities to exactly control the microstructure of the polymer even better.Mostly, ethylene is used as comonomer being randomly distributed for up to7.3 mol% when using ZN catalysts. For single site catalysts, homogenous(single phase) materials can be achieved up to ethylene contents of20.8 mol%. The incorporated comonomer reduces the crystallization speedand the lamellar thickness of the polymer thus affording soft and highlytransparent materials. Random copolymers and terpolymers with higher𝜶-olefins only play a minor role but offer an additional possibility for propertyadjustments. PP random copolymers can also be varied in their performancethrough multistage polymerizations, altering the comonomer content and orthe molecular weight in the different polymerization reactors.

1. Introduction

Among the multiple copolymers of isotactic polypropylene (iPP),which have contributed massively to the success of this polymerwith a global production volume of more than 60 million tons

C. PaulikInstitute for Chemical Technology of Organic MaterialsJohannes Kepler University LinzAltenberger Str. 69, Linz 4040, AustriaE-mail: [email protected]. Tranninger, J. Wang, P. Shutov, D. Mileva, M. GahleitnerBorealis Polyolefine GmbHInnovation HeadquartersSt. Peterstr. 25, Linz 40921, Austria

The ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/macp.202100302

© 2021 The Authors. Macromolecular Chemistry and Physics publishedby Wiley-VCH GmbH. This is an open access article under the terms ofthe Creative Commons Attribution-NonCommercial-NoDerivs License,which permits use and distribution in any medium, provided the originalwork is properly cited, the use is non-commercial and no modificationsor adaptations are made.

DOI: 10.1002/macp.202100302

per year,[1] random copolymers have a spe-cial position. While heterophasic copoly-mers, mostly based on an iPP homopoly-mer matrix and elastomeric inclusions, de-rive their properties from the phase struc-ture with its combination of rigid and elas-tic elements, random copolymers show asingle-phase structure.[2] In comparison toiPP homopolymers, the crystallinity is re-duced by chain disturbances resulting fromcomonomer incorporation, enhancing theinherent polymorphism of iPP.[3,4] This ishighly relevant for industrial applications,since several of the crystal modifications of-fer specific properties, frequently in connec-tion with nucleation.[5] When structured byincreasing melt flow rate (MFR), the mainusage of iPP random copolymers covers therange from pressure pipes for hot and coldwater as well as industrial media throughmono- and multilayer films to thin-wall in-jection molded articles.

Two groups of influence factors for thestructure–property relations of iPP random

copolymers will be mainly discussed in the present review: Thecatalyst system employed for their polymerization, and the typeof comonomer. Section 2 deals with the various catalyst gen-erations for iPP developed since the elementary discoveries ofZiegler and Natta in the 1950s. From the original titanium trichlo-ride catalysts used in combination with slurry processes, severalgenerations of ZN catalysts up to the present post-phthalate cat-alysts have continuously increased productivity, simplified pro-duction and expanded the composition range. In addition, single-site (MC) catalysts offer a further expansion and new propertycombinations. Section 3 concentrates on the most widely pro-duced class of random copolymers with ethylene, which also havethe longest history.[6] In Section 4, copolymers with higher 𝛼-olefins like 1-butene or 1-hexene are discussed, which furtherexpand the property and application range.[7,8] Here, also terpoly-mers with ethylene are considered. In both sections, the effect ofcatalyst type and generation on comonomer content range anddistribution, crystallinity and performance is discussed, and con-sequences for processing and applications are highlighted.

2. Catalyst and Process Generations for iPP

Two types of catalysts are commonly applied to produce iPP to-day: ZN types and MC types. In this section, a brief overview of

Macromol. Chem. Phys. 2021, 2100302 2100302 (1 of 21) © 2021 The Authors. Macromolecular Chemistry and Physics published by Wiley-VCH GmbH

http://www.mcp-journal.de

mailto:[email protected]

https://doi.org/10.1002/macp.202100302

http://creativecommons.org/licenses/by-nc-nd/4.0/

www.advancedsciencenews.com www.mcp-journal.de

Table 1. ZN catalyst generations and performance.

Generation Year Solid components Internal Donor Productivity IIa)

Deashing Process

[kg PP /g Cat]

First 1958 TiCl3*AlCl3+ClAlEt2 None 2–4 60 Yes Diluent

Second 1970 TiCl3+ClAlEt2 Ether, ester 10–15 92–98 Yes Diluent, Bulk

Early thirdb)

1968 MgCl2/TiCl4+AlEt3 None 15 40 No Bulk/Gas

Third 1971 MgCl2/TiCl4+AlEt3 Ethyl benzoate 15–30 95–97 No Bulk/gas

Fourth 1980 MgCl2/TiCl4+AlEt3 Dialkyl phthalate 40–70 95–99 No Bulk/Gas

Fifth 1988 MgCl2/TiCl4+AlEt3 2,2’-Dialkyl-1,3-dimethoxypropane 70–130 95–99 No Bulk/Gas

Sixth 1999 MgCl2/TiCl4+AlEt3 Dialkyl succinate and other types 40–70 95–99 No Bulk/Gas

a)II: Isotactic Index, originally based on heptane (C7) hot extractables

b)The early MgCl2/TiCl4 catalyst systems had activity and stereospecificity lower than what the industry

considers third generation.

their development will be presented, combined with the paralleldevelopment of production processes.

2.1. ZN Catalysts

Heterogeneous ZN catalyst systems largely dominate commer-cial production of iPP as of today. The catalyst system consistsof a solid transition-metal halide, usually TiCl4, a Lewis Base (re-ferred to as internal electron donor) on a MgCl2-support (mostly),and an organo-aluminum compound such as triethyl aluminum(TEA) and a second Lewis Base (usually called external donor)added separately to the polymerization mixture. There are gener-ally accepted six generations of ZN PP catalysts (Table 1).[9]

2.1.1. First- and Second-Generation ZN Catalysts—Slurry Processes

The first-generation ZN PP catalysts are agglomerates of TiCl3crystals, sometimes with co-crystals of AlCl3. The very first cata-lyst, capable of polymerizing olefins, was a mixture of titaniumtetrachloride and triethyl aluminum, commonly referred to as“the Ziegler catalyst.”[10] TiCl3 can form four different crystallinemodifications (i.e., 𝛼, 𝛽, 𝛾 , and 𝛿). The 𝛼, 𝛾 , and 𝛿 forms are pur-ple, while the forth form (𝛽) is brown. Performing TiCl4 reduc-tion with triethyl aluminum at low temperatures forms a brown𝛽-modification of TiCl3. This polymorph is not preferred becauseof its low activity and low stereospecificity,[11,12] while the violetpolymorphs of TiCl3 (𝛼, 𝛾 , and particularly 𝛿) are much bettersuited for production of iPP. The Ziegler catalyst makes PP ofmoderate isotacticity (60% insoluble in heptane), discovered andpatented by G. Natta and co-workers as “isotactic polypropylene”in 1954.[13] In the same year, Edwin J. Vandenberg at the Her-cules Powder Inc. made the same discovery and patented it asthe “process for polymerizing olefins” in 1955.[14]

The first commercial processes for the production of PP werebatch polymerization processes using TiCl3-catalysts activated bydiethyl aluminum chloride (DEAC) in a hydrocarbon medium.The hydrocarbon, usually hexane or kerosene, maintained theiPP in suspension and dissolved the undesirable atactic fraction.After polymerization, the suspension was treated with alcohol todeactivate and solubilize the catalyst residues, and filtered to sep-arate the residues and atactic fraction from the desirable poly-

mer, which is then dried. The alcohol and diluent were recov-ered by multiple distillations, and the atactic fraction was soldas a by-product. As the demand for PP increased, these batchpolymerization processes were rapidly replaced by continuousones, such as the Hercules process performed in several con-tinuous stirred tank reactors (CSTR) with deashing. In this pro-cess, typical for those used throughout the 1960s and 1970s, asuspension of a first-generation ZN TiCl3-catalyst in DEAC andkerosene diluent was continuously supplied to the first of a se-ries of continuous stirred overflow reactors. Monomer was fed tothe first few reactors and allowed to react out in the later ones,making it unnecessary to recycle the monomer. Typical polymer-ization temperatures were in the range of 60–80 °C and maxi-mum pressures as high as 15 bar. Other similar processes, suchas Montedison’s, were operated at pressures as high as 13 barwith monomer recycling.[15] Hydrogen was added to the reac-tors as required to achieve the desired polymer molecular weight,another famous discovery of Vandenberg.[16] Following polymer-ization, the slurry was contacted with isopropyl alcohol, thenaqueous caustic to decompose and neutralize catalyst residues.The aqueous phase containing the alcohol and catalyst residueswas separated from hydrocarbon polymer slurry phase. The sus-pended isotactic polymer was separated from the diluent con-taining the atactic polymer by continuous filtration or centrifu-gation and then dried. Atactic polymer was dried using a thin-film evaporator and sold as a by-product. The products availablefrom this technology were limited to homopolymers with rela-tively high molecular weights, with MFR2 (230 °C and 2.16 kg)below 15 g/10 min, random copolymers containing low amountsof ethylene, and impact copolymers of high molecular weight andlow amounts of copolymer with high ethylene (C2) content. Ex-cessive production of soluble polymer, causing fouling of heat-transfer surfaces, was the primary cause of this limitation, moreso than the loss of monomer to the production of less valuableby-products.

In the early 1970s, Solvay introduced an advancedsecond-generation TiCl3-catalyst with high activity andstereoregularity.[17] The novel steps of Solvay were to add acomplexing agent during the reduction of TiCl4 into TiCl3, andthen again TiCl4 to promote the polymorphic transformation of𝛽-TiCl3 to 𝛿-TiCl3 at 60–70 °C. The level of atactic polymer wassufficiently low so that its removal from the product was notrequired. When this catalyst was used in liquid monomer (bulk)


http://www.advancedsciencenews.com



processes, residues were reduced to the extent that simplifiedsystems for post-reactor treatment were sufficient.

2.1.2. Third-Generation ZN Catalysts—MgCl2-Support

Research on supported polyolefin (PO) polymerization catalystsstarted in the 1950s,[18] and Solvay patented the idea to use Mgcompounds as support for TiCl4 in 1964.[19] The discovery andexploitation of MgCl2-supported systems in 1968 by Kashiwaet al.[20] of Mitsui Petrochemical Industries and by Mayr et al.[21]

of Montecatini is of huge significance, due to the unprecedentedcontrol and advantages they can offer for both polymer andprocess design. The development of the MgCl2-supported tita-nium catalysts was largely supported by collaboration and cross-licensing between the two companies (now Mitsui Chemicalsand LyondellBasell). Starting in 1968 with finely milled MgCl2,which has a similar structure to violet TiCl3, new routes to cre-ate highly active and highly stereospecific catalysts were foundin the following years. Though other supports with layered struc-tures (e.g., MgBr2, MnCl2 and others) can also be used in princi-ple to make stereospecific catalysts for PP, MgCl2 has been usedalmost exclusively, because it allows catalysts the highest activityand stereospecificity.

Montedison and Mitsui Petrochemical introduced high yieldMgCl2-supported catalysts in early 1970s.[22–25] The first versionsof these catalysts were without any internal electron donor. Theiruse reduced the level of corrosive catalyst residues to the extentthat neutralization or removal from the polymer was not requiredanymore, but stereospecificity was insufficient to eliminate theneed for atactic PP (aPP) removal. These catalysts were used inthe Montedison high yield slurry process (a second-generationcontinuous hydrocarbon slurry PP process), simpler and moreeconomic than the first-generation slurry processes due to elimi-nation of the sections required for alcohol treatment, neutraliza-tion, and diluent purification.[15]

Several generations of catalysts for PP have been developedsince based on the MgCl2-TiCl4 system, all involving internallyincorporated electron donor molecules. In polymerization, suchsystems are usually used in combination with both TEA cocat-alyst and an external electron donor. The catalysts differ mainlyin the nature of the internal–external donor couple, with over-all catalyst performance, especially activity and isotacticity, be-ing largely improved when replacing the first family of internal–external donors (both aromatic monoesters, third-generation ZNcatalysts) by the couple aromatic diester (phthalate)–alkoxysilane(fourth-generation ZN catalysts).[26]

Third-generation supported ZN PP catalysts are used in com-bination with a second aromatic monoester, typically para-ethoxy-ethylbenzoate (PEEB) or methyl-para-toluate (MPT),[27] as exter-nal donor. The use of aromatic monoesters both as internal andas external donors (1971) increased the isotactic index (II) up to95% (MgCl2-TiCl4-ethylbenzoate/TEA-MPT catalyst); activities ofsuch catalysts varied between 15 and 30 kg PP/g cat.h and thepolydispersity (i.e., ratio between weight and number average ofthe molecular weight distribution, MW/MN) of the polymer wastypically 8–10. A large part of the internal donor is removed fromthe catalyst on contact with the cocatalyst, the role of the sec-ond aromatic monoester being to effectively substitute the in-

ternal donor in the solid catalyst, maintaining high stereospeci-ficity. Third-generation ZN catalysts have a very high initial poly-merization activity but also a high decay rate, limiting the finalpolymer yield. The rapid decay of the activity can at least partiallybe ascribed to the aromatic monoester reaction with Ti-H bondsformed in chain transfer with hydrogen, generating Ti-O bonds,inactive for chain propagation.[28]

2.1.3. Fourth-Generation ZN Catalysts—Gas-Phase, Bulk, andHybrid Processes

The use of phthalate esters as internal donors and alkoxysi-lanes as external donors (1980) increased the II up to 97–99%(MgCl2-TiCl4-diisbutyl phthalate/AlR3-alkoxysilane catalyst). Ph-thalates tend to react with the TEA cocatalyst during polymeriza-tion and thus are easily displaced from the solid catalyst surface,whereas silanes tend to react with TiCl4 during catalyst prepara-tion and thus can only be used as external donors. In particular,dimethoxysilanes having bulky alkyl groups on the silicon atom,e.g., cyclohexyl or cyclopentyl, are the preferred ones. Activities ofthese fourth-generation ZN catalysts are already between 40 and70 kg PP/g cat.h, with MW/MN between 6 and 8. The catalysts alsodemonstrate low rate of catalyst decay during the polymerization.

The invention of the fourth-generation ZN catalysts in the1980’s formed the base for an intense process development, alsoresulting in an exponential growth of the worldwide PP capacity.Key requirements for state of the art technologies from the pro-cess side are as follows: impact copolymer capability (requires agas phase reactor in series to the matrix producing reactor(s));flexibility (broad range of MFR for homo- and random copoly-mer); reliability (process and catalyst robustness); high single linecapacity (>500 kton a−1). Catalysts should have high mileage andrather low cost, giving access to products of high crystallinity (ho-mopolymers), high transparency (random copolymers), and highimpact resistance (heterophasic copolymers with high content ofamorphous ethylene–propylene copolymer).

Table 2 shows nine of the major licensors of PP technologyin the world with their respective processes. There are two gen-eral types of production processes dominating today: Gas phase(both homo- and copolymerization performed in gas phase re-actors, GPR) and hybrid (propylene homo- and low comonomercontent copolymerization performed in a bulk of liquefied propy-lene, loop reactor or continuous stirred tank reactor (CSTR), highcomonomer content heterophasic copolymerization performedin gas phase). The main polymerization (homo- or random(co)polymer) can be carried out in one reactor, but at least tworeactors are needed to produce impact copolymers. Heterophasiccopolymers are nearly exclusively produced in gas-phase becauseof the solubility of the amorphous propylene-ethylene copolymerin the liquefied monomer. Often two reactors of the same type areconnected in series in order to produce polymer products with amore complex multimodal structure.

Bulk propylene polymerization is carried out in CSTR’s ormore commonly in tubular loop reactors. The first bulk pro-cess utilizing CSTR was developed by El Paso Polyolefins Co.in the 1960’s (so called Rexene or El Paso process), whileChevron Phillips developed the loop process for the productionof HDPE,[38] which was quickly adapted for production of PP.





Table 2. Major Licensors of PP technology worldwide and their respective technologies (VSB: vertical stirred bed; HSB: horizontal stirred bed; FB: fluidizedbed; MZCR: multizone circulating fluidized bed reactor).

Licensor Technology Main reactor Copolymer reactor Developed by First plant Reference

Lummus Novolen Novolen VSB GPR (condensed) VSB GPR BASF 1966 [29]

INEOS Innovene PP HSB GPR (condensed) HSB GPR Amoco 1979 [30]

Lyondell Basell Spheripol Loop (bulk) FB GPR Montedison 1982 [31]

Mitsui Hypol CSTR (bulk) FB GPR Mitsui 1984 [32]

Mitsui Hypol II Loop (bulk) FB GPR Mitsui 1995 [32]

Grace Unipol PP FB GPR (condensed) FB GPR Union Carbide 1986 [33]

Japan PP Corp. JPP Horizone HSB GPR (condensed) HSB GPR Chisso 1987 [34]

Sumitomo Sumitomo FB GPR (condensed) FB GPR Sumitomo 1990 [35]

Borealis Borstar PP Loop (bulk) & FB GPR FB GPR Borealis 2000 [36]

ExxonMobil ExxonMobil Loop (bulk) FB GPR ExxonMobil 2000 [37]

Lyondell Basell Spherizone MZCR FB GPR Basell 2002 [31]

The loop design provides maximum surface area for the most ef-ficient heat removal leading to an increase of the reactor through-put. Nowadays, loop reactors produce more than 50% of all PP.[36]

Gas-phase processes utilize fluidized bed reactors (FBR) orstirred bed reactors (SBR). In FBR, a gaseous stream of monomerand/or nitrogen and/or propane is used to fluidize the polymerparticles in the reactor, whereas in SBR mechanical stirring isused to agitate the polymer particles. FBR’s have the advantageof simple design (no stirrer needed), easy production split ad-justment (by bed level control) and lower takeout of fines withthe gas stream, but are prone to wall sheeting/fouling due to theabsence of mechanical agitation. A unique example of the FBR isthe circulating multizone reactor (MZCR), featured in the Lyon-dellBasell’s Spherizone process.[31] The growing particle repeat-edly circulates between two distinct reaction zones with smoothchange of process conditions, allowing production of bimodalhomo- and random PP products in one reactor. SBR’s are typi-cally smaller than FBR’s, therefore they allow for faster polymergrade transitions and require less energy than FBR’s. The SBR’scan have either horizontal or vertical configurations. The big ad-vantage of the horizontal reactor layout is the plug-flow-like re-actor performance, which allows for very narrow residence timedistribution and fast polymer grade transitions.[39]

Hybrid processes combine bulk and gas-phase processes forthe production of the full range of PP products. The main poly-merization section consists of at least one reactor (not consid-ering the optional pre-polymerization reactor) operating in bulkmode (loop or a CSTR), while the second (optional) section con-sists of at least one fluidized bed (FB) GPR for the production ofimpact copolymers. Both sections are connected in series, whilebeing separated by a flash tank to remove unreacted monomersand hydrogen from the first section, thus achieving a better con-trol over the polymer properties in the different sections. Thehybrid processes are very versatile and are suitable for the pro-duction of a wide range of polymer grades, even if being morecomplex and costly.[36,40]

The Borealis Borstar PP hybrid process is unique in that themain polymerization section consists of one bulk loop reactorand at least one big gas-phase fluidized bed reactor (FBR) for theproduction of polymer matrix, connected in series. This allows

achieving a much higher bimodality of both molecular weightand chemical comonomer distribution of the produced polymer.The direct monomer and polymer feed from the loop into thegas-phase FBR simplifies the process as well as improves heatremoval capacity of the FBR, even if setting some limitations onthe product design. The Borstar process can be operated in su-percritical conditions, thus allowing full homogenization of theloop reactor content. Higher temperature and pressure as wellas high concentration of hydrogen in loop reactor are possiblewithout gas bubble formation (extended operation window).[41]

Currently, the hybrid Spheripol process has the largest shareof installed capacity accounting for over 23 382 kt a−1 (14%) ofglobal PP capacity in 2018, followed by gas-phase Unipol PP andNovolen processes.[42]

2.2. Postphthalate ZN Catalysts: Fifth and Sixth Generations

Until recently, fourth-generation phthalate-based ZN catalyst sys-tems have been considered as the most versatile, practical andcost effective commodity PP catalysts, applicable in many dif-ferent polymerization process types. However, phthalates canact as endocrine disruptors and cause moderate reproductiveand developmental toxicities. Furthermore, phthalates can passthrough the placental barrier and affect the developing fetus.Thus, phthalates have ubiquitous presence in food and envi-ronment with potential adverse health effects in humans.[43,44]

These concerns have placed many of the phthalates used inthe preparation of the fourth-generation catalyst systems on thelist of substances of high concern, and some of them (suchas dibutyl phthalate (DBP) and di(ethylhexyl)phthalate (DEHP))have already been banned in the EU and the US. Despite thefact that the phthalate-based catalysts produce PP with a ph-thalate content far below the 0.3 wt% concentration limit thanallowed by the REACH Regulation (EC) 1907/2006, nonphtha-late solutions are highly encouraged and becoming a competitiveadvantage.

This has motivated extensive research in the area of nonphtha-late catalysts in the past decade. Some companies, such as Lyon-dellBasell, had already been concentrating on the development





of alternative, post-phthalate catalyst systems since the late1980’s. The so-called fifth- and sixth-generation ZN catalysts(1988, Himont) uses 1,3-diethers (typically a 2,2-disubstituted-1,3-dimethoxypropane) as internal donors, respectively.[45–47]

These diethers are capable to coordinate MgCl2 also in the pres-ence of TiCl4 and TEA and do not undergo side reactions nei-ther with TiCl4 during the catalyst synthesis nor with Al-C, Ti-Cand Ti-H bonds during the polymerization. For these reasons,diethers-type ZN catalysts are able to produce iPP even in theabsence of any external donors.[48] Catalysts based on dietherscan provide polymers with very low molecular weight and lowMW/MN, but with high isotacticity. In the absence of externaldonors (MgCl2-TiCl4-1,3-diether/TEA catalyst), the II is typicallyabout 95–96%, the activities are high (100–130 kg PP/g cat.h) andMW/MN is between 4 and 5. Addition of alkoxysilanes to suchcatalysts allows improving isotacticity to 98–99% at the cost ofdecreased productivity (70–100 kg PP/g cat.h).

The next generation of MgCl2-TiCl4 systems (1999, Mon-tell) was developed based on succinate diesters (typically 2,3-disubstituted diethyl succinates) as internal donors.[49–51] The cat-alysts of this type are able to provide both controlled polymerstereoregularity (either very high or low) and high polydispersity(MW/MN 10–15). Succinate-based catalysts are used together withalkoxysilane external donors to give about the same productivityand polymer isotacticity as fourth-generation catalysts.

A combination of these two families resulted in themixed donor catalysts of LyondellBasell, based on the di-ether (9,9-bis(methoxymethyl)fluorene) – succinate (diethyl 2,3-diisopropylsuccinate) internal donor pair.[52] The company de-scribed these as a drop-in nonphthalate solution for the Spheripolplants. Tweaking the ratio between the two donors affects the cat-alyst performance and the product properties, thus minimizingthe differences with the previous generation catalysts and reduc-ing the need for product requalification.

Lately, also other types of internal donor compounds basedon, e.g., aliphatic dicarboxylic esters (glutarates, citraconates,cyclohexane- and 1-cyclohexene 1,2-dicarboxylates), phenyleneand naphthalene diesters, and polyol esters have been devel-oped (see Figure 1 for an overview of structures). The Dow (nowGrace) nonphthalate solution featuring 1,2-phenylene diben-zoate esters[53–55] is one of the most advanced developments ofthe next-generation ZN PP catalysts. The donors are used in theConsista and HYAMPP Grace nonphthalate catalyst families. Thecatalysts show moderate stereoselectivity (89–90%) and high ac-tivity also without the use of alkoxysilane external donors.

Polyol diester internal donors developed by BRICI/Sinopechave a similar polymerization performance to succinate-basedsystems. However, unlike the succinates, this catalyst systemyields high stereoselectivity even without alkoxysilane externaldonors.[56]

Both Mitsui[57] and INEOS[58] have patented cyclohexane-1,2-dialkyl dicarboxylates as internal donors. Toho patentedmalonates[59] and 2,2’-biphenyldicarboxylic acid diesters,[60] andBASF patented 1,8-naphthyl diaryloate compounds.[61] Bore-alis patented a series of catalysts based on alkylene glycoldibenzoates, maleates as well as 1-cyclohexene-1,2-dicarboxylicdialkylesters.[62–64] More on the recent developments in areaof nonphthalate ZN catalysts can be found in the review bySevern.[65]

2.3. MC Catalysts

Although ZN type catalyst systems are dominating the commer-cial PO production, more than 80% of the overall PO manufac-turing processes still using ZN catalysts,[65] single-center MC cat-alysts have attained great importance.[66,67] Metallorganic com-pounds have already been studied for more than 30 years asmodel compounds for ZN reactions. However, they were notapplicable for commercial PO production because of their ex-tremely low activity and poor stereo control. During the mid-1970’s several groups found out, that traces of water improve thecatalyst activity of MC based homogenous catalysts in the pres-ence of trimethyl aluminum (AlMe3). It was Sinn and Kamin-sky who first identified the potential of AlMe3/H2O activatorsfor MC catalyzed ethylene polymerization.[68] With beginningof the 1980’s the performance of MC based catalyst systemshas been improved to afford isotactic, syndiotactic, and pos-sibly even stereoblock PP on an industrial scale.[69] MC cata-lysts suitable for iPP manufacturing generally seem to be basedon zirconocenes supported on inert solids to preserve parti-cle size and shape. The heterogenization makes the MC cat-alysts suitable for advanced process technologies of the majorlicensors.

Narrow molecular weight distributions, typically with MW/MNin the range of 2–4, are a characteristic feature of PO’s pre-pared by single-site catalysts as well as defined regio- and stere-oregularity, and molar mass independent random or sequencedcomonomer incorporation (Figure 2).[70]

The production volume growth of MC catalyst based iPP hasbeen delayed by a number of factors, ranging from the inherenttendency toward regio-defect generation through the issue of het-erogenization to the complex patent situation. Recent develop-ments in complexes capable of combining high isotacticity withlow regio-defect content and thus enabling melting points closeto the “normal” level of ZN catalyst-based iPP (165–167 °C) areonly slowly arriving in industrial processes.[71,72] While Zr andHf are likely to dominate the development as coordination met-als, also titanocenes may make a comeback.[73] Details of MC cat-alyst capacity for copolymer production will be discussed in thefollowing sections.

3. Ethylene–Propylene Random Copolymers

When talking about random copolymers, first a look at the mean-ing of the term „random“ is necessary. Commonly, randomcopolymers of propylene are meant to be largely homogeneousand single-phase polymers with a preferentially isolated insertionof the comonomer. As, however, in case of the still dominant ZNtype catalysts, the reactivity of ethylene is significantly higher—in most studies and for most catalysts by a factor of 5 to 10,[74,75]

formation of adjacent insertions or “blocks” can be expected withincreasing concentration. In practice, this results in a limitationof the ethylene (C2) content for ZN based copolymers at about5 wt% resp. 7.4 mol%, which is already much higher than for pre-vious catalyst and process generations.[76] Already in that range,the content of amorphous fraction soluble in xylene at ambienttemperature (xylene cold soluble – XCS – fraction) increases sig-nificantly, and this increase has been shown to be parallel to adecrease in isolated C2 insertion, as determined by infrared (IR)





Figure 1. Examples of postphthalate internal donors.





Figure 2. Correlations between MC structures and PP architecture. Adapted with permission.[68] Copyright 2003, Wiley-VCH GmbH.

Table 3. Effect of comonomer content on chain structure, crystallization parameters and stiffness of C2C3 random copolymers; data from Gahleitneret al.,[82] Agarwal et al.,[79] and Cavallo et al[83,84].

Polymer C2 C2 [PPP] [PEP] I[E] XCS XC,WAXS ∂T/∂tmeso Flex. mod. Film mod.

[mol%] [wt%] [mol%] [mol%] [%] [wt%] [%] [°C s−1] [MPa] [MPa]

PP-H 0.0 0.0 100.0 0.0 n.d. 1.3 40.5 215 1300 650

PP-R1 4.1 2.8 90.6 2.4 73 3.3 36.2 105 1000 500

PP-R2 5.9 4.0 86.0 3.9 67 4.7 – – 800 420

PP-R3 7.1 4.8 83.3 4.5 65 6.8 31.6 55 605 350

spectroscopy,[77] commonly called “randomness.” A more reli-able and fundamental method for assessing the chain structureand comonomer distribution is, however 13C-NMR spectroscopyin solution or melt.[78,79] The C2 content calculation of Wang &Zhu[80] and the triad analysis for C2/C3 copolymers developedby Kakugo et al.[81] are commonly applied in both academia andindustry, providing the necessary information.

3.1. Monomodal C2C3 Copolymers Based on ZN Catalysts

To give an overview for monomodal ZN based systems, Table 3and Figure 3 present the respective data for a series of onehomo- and three copolymers analyzed in the papers of Gahleit-ner et al.,[82] Agarwal et al.[79] and Cavallo et al.[83,84] Nonlinearityis found for all of the correlations to the comonomer content, but

strongest for the triad-based content of isolated C2-units, calcu-lated by normalizing the [PEP] content like

I [E] =[PEP]

[EEP] + [PPE] + [EEE]∗ 100% (1)

and in the XCS fraction. It appears logical that both are con-nected. Blocky C2 structures, especially with 3 or more unitsin a rows, are more likely to also contribute to the amorphousfraction. Isolated C2 units acting as defects will rather reducecrystallization speed and lamellar thickness, while retaining crys-tallinity (see also the discussion of phase separation in Sec-tion 3.3). The reduced crystallinity is not alone responsible forthe stiffness reduction, but rather in combination with lamel-lar thickness, demonstrated in the nucleation studies of Pukán-szky et al.[85] As shown especially by Cavallo et al.,[83,84] the criti-cal cooling rate for transition from 𝛼-crystalline to mesomorphic





Figure 3. Effect of C2 content on isolated C2 fraction I[E] and flexural mod-ulus of C2C3 random copolymers based on a phthalate-type ZN catalyst(data from ref. [82]).

phase (∂T/∂t(meso) in Table 3) is also reduced significantly withincreasing defect concentration, making these materials easier to“quench” into a less crystalline and more transparent form like incast film processing,[86] a phenomenon which will be discussedin detail below.

Even within different types of ZN catalysts with phthalates asinternal donors, structural variations with a clear effect on finalproperties exist. The emulsion-type catalysts of Borealis with di-rect use of bis(2-ethylhexyl)phthalate as internal donor has beencompared to earlier, conventionally supported generations in sev-eral papers and patents.[80,87,88] For this catalyst type, all compo-nents are combined in liquid phase, generating an emulsion ofdefined droplet size in a second liquid and solidifying them sub-sequently. This results in a catalyst of nearly perfectly sphericalshape and very narrow particle size distribution, with no obviousporosity.[77]

When combined with the same external donor, cyclohexyl-dimethyl-dimethoxysilane (CHMDMS, commonly called “donorC”), C2C3 random copolymers based on the emulsion type showa higher so-called “randomness” (isolated C2 insertion) based onIR spectroscopy. Figure 4, in which unpublished data are com-bined with those from Grein & Schedenig[87] as well as Gahleit-ner et al.,[85] shows the complexity of polymer and applicationproperty effects: Deviations in the melting point and the stiffness,represented by the flexural modulus determined on injection-molded specimens (ISO 178) are very limited, rather within therange of experimental error. In contrast to that, optical proper-ties both on molded plaques and on cast films vary significantly,and especially in sterilization of the latter specimens a massiveeffect related to post-crystallization was found. The Δ haze in Fig-ure 4b indicates the relative increase of film turbidity in a stan-dard steam sterilization process (30 min at 121 °C), a highly rel-evant parameter for medical and other packaging applications,which was found to be considerably worse for products from theconventional catalyst. This change is much stronger for rapidlycooled articles like cast films, and results from a combinationof meso-to-𝛼 transformation and lamellar thickening, the effectgetting stronger with comonomer content simply because of in-creased mobility due to the lower melting point (Tm).[89] This

phenomenon probably results from a stronger tendency to phaseseparation in the polymers with a more blocky C2 insertion, fa-cilitated by the higher mobility of originally well dispersed amor-phous fractions at the sterilization temperature of 125 °C.

The reasons and mode for the replacements of phtha-lates, long-time dominant as internal donors, has been dis-cussed in the previous section. The consequences of the post-phthalate internal donor types for PP homopolymers in termsof molecular weight distribution (MWD) and isotacticity are welldocumented,[51] but systematic studies in case of random copoly-mers are missing. While Busico et al.[90] present the results ofa comparison of phthalate and diether for C2 random copoly-merization, data for a series of copolymers with different C2 con-tent can be found in one of Basell’s patents.[91] At Borealis, cata-lysts using a citraconate as internal donor[62,63] have been devel-oped and found to be suitable for the commercial production ofiPP homopolymers[92] as well as copolymers with ethylene[93,94]

and other comonomers.[95] Also here, an emulsion process isused, which can be used for heterophasic copolymers despite itsapparent nonporosity.[96] Figure 5 shows that both the meltingpoint and amorphous (soluble) fraction are affected quite differ-ently with the two different nonphthalate catalyst systems, evenif the melting points of the respective homopolymers differ onlymarginally. These differences most probably result from varia-tions of the C2 incorporation, but molecular weight distributionmay play a role as well, especially for XCS.

Further variations are possible in combination with differentexternal donors, as shown for example by Chadwick et al.,[97]

where differences in lamellar thickness distribution resultingfrom ZN type variation are evidenced for homopolymers alreadyby temperature rising elution fractionation (TREF). This broad-ness in elution and similarly in melting, as shown before,[82,98]

results from an overlay between molecular weight and isotactic-ity distribution, and becomes increasingly complex for copoly-mers with increasing C2 content. Next to TREF, the differentialscanning calorimetry (DSC) based stepwise isothermal segrega-tion technique (SIST) has been used to demonstrate and analyzesuch heterogeneity. Especially the latter results clearly indicatethat crystallization and processing behavior will be affected bythis heterogeneity.

3.2. Monomodal C2C3 Copolymers Based on MC Catalysts

An even bigger step in terms of structure and performance ismade when moving from ZN catalysts to single-site catalysts(SSC) like MC. While their application for the production of iPPhomo- and copolymers is presently still limited, their potentialhas been studied since the mid-1990s. The earliest example of adirect comparison between ZN and MC based random copoly-mers with C2 is the paper of Fujiyama & Inata,[99] where onlycrystallization has been studied. Two differences to ZN catalystdata presented above are evident in Figure 6a: The MC homopoly-mer has a lower melting point (Tm) related to the regio-defects re-sulting from the MC catalyst leading to a lower of the homopoly-mer, and the dependence of Tm and melting enthalpy (Hm) onC2 content is fully linear in the investigated range. It shouldbe noted that the correlation for the ZN catalyst reference prod-ucts matches the data presented in Figure 4a for the standard





Figure 4. Effect of C2 content on a) melting point (Tm) and tensile modulus, and b) on haze and change of haze in sterilization C2C3 random copolymersbased on conventional (full symbols) and emulsion-based (open symbols) ZN catalysts (data from ref. [87,88]).

Figure 5. Effect of C2 content on melting point (DSC, squares) and XCSfraction (triangles) for nonphthalate ZN catalysts with diether (open sym-bols, data from ref. [91]) and citraconate (full symbols, data from ref.[93,94], with one previously unpublished data point at 2.1 wt% C2).

catalyst nearly perfectly. A much wider range of composition hasbeen studied by Jeon et al.,[100] with a catalyst giving an about 8°C higher melting point for the homopolymer than in the pre-vious case and increasing the C2 content in single-step poly-merization up to 20.8 mol% (i.e., 14.9 wt%). NMR spectroscopystructure was used here to determine stereo- and regio-defects(2,1-misinsertions only), finding a slight increase with C2 con-tent. The still maintained linearity for Tm and the glass transi-tion temperature (Tg) indicates homogeneity even at concentra-tions where phase separation would be expected for ZN catalystproducts (see Figure 6b). Crystallization is affected more strongly,and the morphology images by atomic force microscopy (AFM)indicate the formation of high amounts of inter-lamellar meso-morphic or amorphous phase when crystallizing the copolymerswith more than 10 mol% C2 at lower temperatures. In parallelto that, the formation of 𝛾-phase (discussed in detail below) be-comes dominant.

These two studies already show the potential, but also the effectof catalyst structure, in case of MC based random copolymers.The next logical evolution stage are SSC post-MC catalysts, whichwere compared to MC for C2C3 random copolymers by Stephenset al.[101] A concentration range of up to 19.2 wt% (for post MC)resp. 30.8 wt% C2 (for MC) was studied, finding a more drastic re-duction in melting point and crystallinity in the former case. Thetype of catalyst (developed by DOW Chemical Co.) is, unfortu-

Table 4. Characteristics of a series of monomodal bench-scale homo- andcopolymers based on an emulsion-type MC catalyst (previously unpub-lished data).

Polymer PPR-1 PPR-2 PPR-3 PPR-4 PPR-5 PPR-6 PPH-ref.

MFR2 [g/10 min]a)

19.3 12.6 11.5 9.8 7.9 6.4 6.2

C2 [wt%] 2.2 3.1 4.1 4.5 4.6 5.5 0.0

C2 [mol%] 3.3 4.5 6.0 6.6 6.8 8.0 0.0

I[E] [%] 71 81 79 73 73 68 n.d.

Tm [°C]b)

141 133 126 123 118 111 152

Tc [°C]b)

98 92 86 84 79 72 106

XCS [wt%]c)

0.76 0.61 1.27 0.69 0.71 1.21 0.44

MW [kg mol−1] 180 188 189 184 191 188 247

MN [kg mol−1] 65 73 73 69 71 70 102

MW/MN [–] 2.8 2.6 2.6 2.7 2.7 2.7 2.4

a)230 °C/2.16 kg

b)DSC at 10 °C min−1 c)

xylene cold soluble fraction (ISO 16152);n.d.: not defined.

nately, not disclosed in the paper, but it enables “plastomer-like”copolymers with Tm as low as 44 °C and Tg at −20 °C, with a ten-sile modulus of ≈10 MPa. About 50% more C2 is needed withthe studied MC catalyst, and then Tm is still ≈5 °C higher.

To get a more complete image of the mechanical performanceof MC random copolymers, also in relation to conventional ZNcatalyst based products, we present some own data based onsingle-stage bench-scale polymerization with an emulsion-basedheterogenized MC catalyst,[102] using a zirconocene with bridgedand substituted indenyl ligands. The data in Table 4 result froman extensive molecular characterization by 13C-NMR,[76] DSC,XCS and high temperature size-exclusion chromatography (SEC,trichlorobenzene (TCB) at 135 °C). 2,1-regio-defects were in therange of 0.4 to 0.8 mol%, and the isolated C2 fraction I[E] staysat a high level over the whole range. As the MWD is compara-ble, it also makes sense to directly compare the results of the ad-ditional mechanical characterization on injection-molded spec-imens (flexural test according to ISO 178 and Charpy notchedimpact strength at 23 °C according to ISO 179 1eA).

As Figure 7 shows, the stiffness (flexural modulus) scalesrather linearly with C2 content, and not too differently from pre-viously discussed standard grades based on ZN catalysts. Thesereference polymers[82] are visbroken PP types, i.e., modified byperoxide-induced controlled degradation[103] to achieve a nar-rower MWD facilitating processing, e.g., in film casting and fiber





Figure 6. Effect of C2 content on a) melting point (squares) and enthalpy (diamonds) of C2C3 random copolymers based on MC (open symbols) andZN (full symbols) catalysts (data from ref. [99]), and b) on transition temperatures of C2C3 random copolymers based on MC catalyst (data from ref.[100]).

Figure 7. Effect of C2 content on stiffness (blue) and Charpy notchedimpact strength (NIS) (red) of C2C3 random copolymers based on anemulsion-type MC catalyst (previously unpublished data); black squaresare modulus values for the ZN catalyst-based polymers from Table 3.

spinning. The polydispersity MW/MN is ≈3.4 in case of the ZNcatalyst references, and even lower for the MC polymers, com-monly seen as one of the advantages of these catalysts. NarrowMWD goes together with a reduction of oligomer content, re-flected by the low XCS level, which may be an important factor forthe comparably high stiffness. Thus, a totally different relationbetween melting point and stiffness is achieved, while impactstrength is rather low up to a C2 content of ≈4.5 wt%. Tough-ness increase above that results from a combination between Tgand crystallinity reduction, but 𝛾-phase formation may play a roleas well.

3.3. Bimodal C2C3 Copolymers

Next to varying catalyst systems, PP copolymers can also be variedin their performance through multi-stage polymerization. Whilethis is normally rather associated with heterophasic copolymers,also homopolymers and random copolymers can be optimizedthrough bi- or trimodality.[104] This multimodality can be in termsof molecular weight, comonomer content or both, resulting in awide range of design options. In terms of C2 content, homopoly-mers and random copolymers are largely miscible in a range up

to 5 wt% comonomer content, making both sequentially poly-merized reactor blends[105,106] and melt blends[107] with homo-geneous structure down to lamellar morphology level (see Fig-ure 8a) and high transparency possible. Such compositions arenot only relevant in pure form, but also as matrices for heteropha-sic (high-impact) systems, enhancing for example the stability inheat sterilization as shown in Figure 9.[104,108]

The same advantage in the application phase can also be seenin case of elastomer-free materials, and it clearly affects notonly sterilization resistance, i.e., the structural change at elevatedtemperatures (annealing), but also the physical ageing behaviorat ambient temperatures. This process changes the stiffness /toughness relation of molded articles, films and pipes over timetoward higher modulus and lower impact resistance and affectsrandom copolymers more than homopolymers.[89] A bimodalcomonomer distribution, as achieved with a ZN catalyst in a loop/ gas phase reactor combination, is obviously capable of limitingthe toughness loss over time, as demonstrated by Wang et al.[109]

and shown in Figure 10b. The three copolymers studied here allhave a comparable C2 content of ≈3.5 wt%. A2 has a monomodalC2 distribution and is less impact resistant already after molding,while for the two bimodal polymers the catalyst type appears tobe relevant for maintaining higher toughness. A1 is based on acitraconate-type ZN catalyst as described before[63] and remainson a high level, while A2 from a conventional phthalate type losesits toughness more rapidly. In all cases, the crystallinity increaseat 23 °C is comparable (see Figure 10a).

If the C2 content of the second component is set too high,phase separation will occur due to miscibility limits, first dur-ing solidification and, at higher differences, also in the meltstate. Even at moderate total C2 content, heterophasic poly-mers also called impact copolymers are achieved then, whichdiffer completely from random types in terms of structure andmechanics.[110,111] The two-phase structure of rigid matrix andelastic inclusions results in high ductility and impact resistance,down to sub-zero temperatures because of the low glass transi-tion temperature of the C2C3 copolymer particles. At the sametime, these inclusions scatter light and reduce transparency ac-cordingly, and the interfacial damages at limited deformationsresult in stress whitening.

For ZN catalysts, no study covering the actual transition frombimodal random to heterophasic copolymers could be found, butthe papers of Grein et al.[112] and Santonja-Blasco et al.[113] show





Figure 8. Comparison between the morphology of ZN catalyst-based a) random copolymer with 4.0 wt% C2 and b) random-heterophasic copolymerwith total C2 content 8.8 wt% and XCS 23 wt% (transmission electron micrographs after RuO4 contrasting).

Figure 9. Evolution of a) melting temperature and b) molten fraction at 121 °C as a function of the C2 content of Homo/Random (H/R) matrices(squares) and theoretical pure C2C3 random copolymers (dashed line, interpolated. Adapted with permission.[104] Copyright 2019, Springer Nature.Data from ref. [108]).

the structure in case of low C2 content in the disperse phase forhomopolymer matrices, with relatively small particles and diffuseinterfaces. Random-heterophasic copolymers with softer matrix,further enhancing ductility and eliminating stress whitening,have also been developed[114] and find application for example inthe medical packaging area. Enhanced compatibility allows finedispersion of the elastomeric particles into the range of 1 μm,as can be seen in Figure 8b, resulting in good transparency. A

similar phase structure and performance range is observed forextruder blends of PP homo- or random copolymers with specialelastomeric C2C3 copolymers of low C2 content, like Vistamaxxof ExxonMobil.[115]

Using MC catalysts for producing multimodal random copoly-mers even increases the design space. The comonomer distri-bution both along the chain (intra-chain homogeneity,[100] seealso Table 4) and over the MWD (inter-chain homogeneity[116])

Figure 10. Bimodality effect on the long-term stability of C2C3 random copolymers: a) Density evolution as measure for crystallinity and b) toughnesschanges as measured by the instrumented puncture test (IPT, ISO 6603) at 23 °C; polymers A1 and A3 have a bimodal C2 distribution (data from ref.[109]).





Figure 11. Stiffness/toughness relation of bimodal MC random copoly-mers (full squares) in relation to monomodal ZN catalyst referencepolymers (open squares); all grades have an MFR2 in the range of 8–10 g/10 min (data from ref. [118]).

is clearly improved, allowing a clearer separation between thefractions. This allows a higher C2 content in the second (highercontent) fraction of bimodal polymers without phase separation,which for MC catalysts in case of a two-stage polymerization hap-pens between 10 and 22 wt% C2 in the second component, asindicated both by particle formation on the μm-scale and the ap-pearance of a second Tg for this phase.[117] As Figure 11 shows,this enables the production of transparent single-phase copoly-mers with high impact strength.[118] The polymers based on asimilar catalyst as the ones in Table 4 have a double bimodalitywith lower C2 content and higher molecular weight in the first(loop) fraction, and vice versa in the second (GPR) fraction, result-ing in MW/MN in the range of 3.1–3.5, above the typical range formonomodal MC PPs. In the diagram, their performance is com-pared to mono- and bimodal ZN catalyst-based polymers withcomparable MFR, demonstrating the superiority in impact per-formance.

An important aspect for processing and application of PP ingeneral, but specifically so for random copolymers, is the poly-morphism and its control by nucleation and processing.[86,119–121]

Specifically, the change from predominant 𝛼-modification to 𝛾-modification with increasing C2 content has been discussed byseveral authors, also pointing out the fact that region-defectscaused by MC catalysts act in a similar way, resulting in aneven higher 𝛾-phase content for such polymers.[100,119] As shownspecifically by De Rosa in several papers, this is also the casefor random copolymers with higher 𝛼-olefins, which will be dis-cussed in the next section.

High cooling rates, as commonly occurring in many conver-sion processes like injection molding or film casting, are unfa-vorable for 𝛾-phase formation, but this can be compensated bynucleation, where 𝛼-nucleating agents work fine due to the iden-tical basic crystal lattice structure.[122] For a ZN catalyst copoly-mer with 3.1 wt% C2, the content of 𝛾-modification is increasedfrom less than 10% to 20% at a cooling rate of 1 °C s−1 by nu-cleation with the soluble (clarifier) type di(benzylidene)sorbitol(DBS). At even higher cooling rates, the main competition is be-tween 𝛾- and mesomorphic phase, the critical cooling rate forrandom copolymers to become fully mesomorphic being signifi-cantly lower than for homopolymers (see Table 3).[83,84]

In terms of practical application, nucleation of C2C3 randomcopolymers gives positive effects on both transparency and im-pact resistance.[86,123,124] The difference toward homopolymersis significant for haze over a wide range of MFR, making suchgrades ideal materials for thin-wall packaging, while the impactimprovement is limited to higher molecular weights (i.e., lowerMFRs, see Figure 12a). For transparency resp. haze of injec-tion molded articles, the correlations are more complex, as nextto concentration and polymer type also geometry and process-ing conditions play a significant role. The formation of flow-induced superstructures like shish-kebabs and oriented skin lay-ers is definitely positive for stiffness,[125] while increasing hazedue to an additional interface inside the specimen. Higher MFR,narrower MWD and higher comonomer content are thus ad-ditionally positive for haze reduction, as the formation of ori-ented structures is reduced.[126,127] As no full analysis of thecombined effect of concentration and geometry could be foundin the literature, we present new data for this in Figure 12b:With the soluble nucleating agent 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol (TBPMN, commercial typeMillad NX8000), saturation of the haze reduction is only reachedat > 3000 wt-ppm, and the relation between the different thick-nesses changes with concentration.

In the cast film process, together with subsequent orientationand stretching processes another important application area forC2C3 random copolymers, the possibility to “quench” these poly-mers into predominantly mesomorphic structure is particularlyappreciated.[86] By choosing a suitable combination of melt tem-perature, extrusion speed and chill-roll temperature, highly trans-parent cast films with a haze level of less than 5% at 50 μm can bereached, surface roughness caused by a combination of local crys-tallization effects and additives (especially antiblocking agents)becoming the limiting factor for transparency.[128] A recent sys-tematic study by Di Sacco et al.[129] has demonstrated the possi-bility of achieving high transparency also in case of MC-catalyzedhomopolymers, the regio-defects acting in a similar fashion asdiscussed above.

4. Random Co- and Terpolymers with Higher𝜶-Olefins

In contrast to ethylene propylene random copolymers, copoly-mers of propylene with 1-butene (C4) or other higher 𝛼-olefinslike 1-pentene (C5), 1-hexene (C6) or 1-octene (C8) have a ratherminor commercial importance. An exception are ethylene–propylene–butene (C2/C3/C4) terpolymers that are commonlyproduced and used as sealing materials, balancing good opticalproperties with low sealing initiation temperatures.

Next to the achievable property-profile of propylene copoly-mers with higher 𝛼-olefins that enable their use mainly in niche-applications, it is definitely also the reduced reactivity of ZN cat-alysts toward higher 𝛼-olefins causing their lower industrial im-portance. However, constant improvement and development inthe area of MC catalysts is enabling the incorporation of higher𝛼-olefins at sufficient conversion rates and therefore MC cata-lysts allow a precise control of the micro-structure, in turns en-abling systematic analyses of the synthesized polymers, theirstructure and properties. Therefore, this group of materials is





Figure 12. Effect of nucleating agent concentration on a) haze (squares) and toughness (diamonds) for a PP homopolymer (black) and a randomcopolymer (blue) with 2.8 wt% C2 (both MFR 2.0) nucleated with 1,3:24-bis(3,4-dimethylobenzylideno)sorbitol (DMDBS) (Millad 3988, data from ref.[124]), and (b) haze at different specimen thicknesses for a random copolymer (3.7 wt% C2, MFR 12) molded at 230 °C melt and 40 °C mold temperature(previously unpublished data).

well described in literature—often in combination with possi-bilities arising from various MC types, but is still mainly focus-ing on discussions of the crystal structure and partitioning of thecomonomers of these materials.

Increasing the comonomer length from butene to hexene andoctene or even higher, the resulting property profile of the copoly-mer changes from stiff polymers of limited toughness towardthat of thermoplastic elastomers. This change of properties iscaused by the disturbance of chain regularity due to the in-corporation of the comonomer to the polymer’s backbone. De-pending on the amount and type of comonomer, crystal struc-tures and crystallinity are heavily affected.[121,130–137] The parti-tioning of 1-hexene in propene copolymers is discussed exten-sively in scientific literature, whereas it is generally acceptedthat 1-octene and longer comonomers are rejected and 1-buteneeasily incorporated into the crystal structure or PP.[134,137–139]

Comparing the crystallinity of random copolymers with hexeneand octene comonomers for comonomer contents higher than10% it is found that 1-hexene copolymers exhibit a crystallinityhigher than that anticipated for a comonomer completely ex-cluded from the crystal lattice as it is found for propylene/1-octene copolymers.[138] Therefore a new crystallographic formwas proposed for C3C6 copolymers with 10–25 mol% hexene anddescribed for the first time in 2005 and re-evaluated later on bythe same group.[138,139] It was concluded that this 𝛿-modificationof PP has a trigonal unit cell containing six 3-fold helices. A sim-ilar crystal modification is found in propylene/1-pentene (C3C5)copolymers and C3/C5/C6-terpolymers.[95] At low hexene con-tents, De Rosa and coworkers concluded that the comonomer canpartly be included into the crystal lattice of PP.[134]

Depending on the bulkiness of the comonomer, the meltingand crystallization temperatures are decreasing when changingthe comonomer from butene to hexene or octene.[132,133,136] How-ever, with further increasing the comonomer length, this effectdiminishes and hardly any differences are found in the melt-ing temperatures of copolymers of propene with C8, C10, C12,C16 and C18.[130,137,140] Next to comonomer type and concentra-tion, the melting temperature is also affected by the catalyst sys-tem used (and processing as well as testing conditions). WhereasZN catalysts lead to materials with a gradient distribution of thecomonomer, MC catalysts are capable of highly random incor-poration of the comonomer. This results in a more pronounced

reduction of lamellae length and thickness, further reducing themelting temperatures.[134,141]

The reduced crystallinity and crystal size resulting from theincorporation of comonomers is also reflected in a shift ofthe 𝛼-transition temperature as a consequence of comonomerincorporation.[133,136,142] As consequence of the increase of thefree volume upon the incorporation of n-alkyl branches in propy-lene copolymers also the 𝛽-transition is decreasing with increas-ing comonomer length.[136,143,144] Only 1-butene copolymers de-viate from this behavior due to C4 being readily incorporated intothe PP crystal structure.

A number of studies have been devoted to establish structure–property relationships in random copolymers of propylene withhigher 1-alkenes. It has been demonstrated that the crystalthickness can successfully be controlled by the incorporation ofcomonomers along the propylene chain.[142] The different affin-ity of comonomer units to participate in the crystallization resultsin formation of crystals with different perfectness, leading to dif-ferent mechanical performance.

Figure 13 shows the yield stress of iPP homopolymer (ZN) andcopolymers with 1-butene (iPP-But, ZN) and 1-octene (iPP-Oct,MC) as a function of the volume fraction of the ordered phaseestimated by wide angle X-Ray scattering (WAXS).[146] Sampleswith different crystallinity were generated by variation of thepathway of crystallization (slow cooling, fast cooling and sub-sequent annealing) and the comonomer concentration. The redsymbols represent data of samples, which contain lamellar crys-tals obtained on slow cooling from the melt. The black symbolsstand for samples with mesomorphic nodular domains obtainedby fast cooling from the quiescent melt . Further, the prepara-tions with lamellar (red nonfilled symbols) and nonlamellar crys-tals (black nonfilled symbols) were annealed at elevated temper-atures for 60 min. Annealing caused increase of crystal size andcrystallinity in all preparations.

Increase of the comonomer content or the commoner lengthfrom 1-butene to 1-octene, triggers decrease of the yield stressand the modulus of elasticity as shown by Mileva et al.[146] Thistrend is directly related to change in the degree of crystallinityand crystal geometry. At identical cooling rate, the degree of crys-tallinity and crystal length are influenced by the amount and typeof the comonomer. Due to their partial inclusion into the orderedphase, addition of 1-butene comonomers trigger less reduction





Figure 13. Yield stress as a function of the fraction of ordered phase for iPP homopolymer and copolymers of iPP with 1-butene (But.6, But.11) or 1-octene (Oct.1, Oct.3); the right-hand side shows atomic force microscopy (AFM) images collected on films of iPP-But.11. Adapted with permission.[146]

Copyright 2010, Springer Nature.

Figure 14. Light transmission of iPP and random copolymers of propylene with ethylene (iPP-Eth), 1-butene (iPP-But), 1-hexene (iPP-Hex), and 1-octene(iPP-Oct) as a function of the light wavelength (left). Light microscopy images were collected from slowly cooled samples of iPP-Eth or iPP-But (bottom),iPP-Hex or iPP-Oct (middle); fast cooled samples (top); data for the iPP, iPP-Eth, and iPP-But. Adapted with permission.[146] Copyright 2010, SpringerNature.

in stiffness and yield stress in comparison to 1-octene. Beside themacromolecular structure, the change of the yield stress dependson the crystal geometry, i.e., lamellae or nodules. Comparison ofthe yield stress at identical crystallinity shows that samples con-taining lamellar crystals have higher values than samples withglobular crystals. The effect of the amount and geometry of crys-tals on final properties of films prepared either from the quies-cent or nonquiescent melt has been demonstrated in differentstudies.[129,147–149]

Figure 14 shows the light transmission as a function of thewavelength of iPP homopolymer and random copolymers withethylene, 1-butene, 1-hexene and 1-octene. The samples wereprepared by melt-crystallization at largely different rates of cool-ing. The light transmitted through slowly cooled films was mea-

sured between 50% and 80%, with the higher values obtained forthe copolymers. The increase of the transparency in the copoly-mers can only be due to a reduced crystallinity in combinationwith a reduced spherulite size. Quenched films show a trans-parency of about 90% being independent on the concentrationof comonomer units.

The increase of transparency with increase of the comonomerlength from ethylene to 1-octene in slowly cooled preparations ofrandom copolymers of propylene can be explained by decreaseof the spherulitic size. In case of the quenched preparations,the absence of spherulites and/or changes of the crystals fromnonisometric monoclinic lamellae to isometric mesomorphicnodules triggers light transmission close to 98%. Such a struc-ture, optically, is less heterogeneous than a spherulitic structure.





Figure 15. Amount of XCS fraction as function of the comonomer con-tent for different types of propylene—𝛼-olefin copolymers. Adapted withpermission.[2] Copyright 2019, Springer Nature.

Consequently, there is less light scattering and increased percent-age of transmitted light.

Considering the property profile as described above it becomesobvious that propylene butene copolymers (C3C4), which are alsoat industrial scale accessible via ZN and MC catalysts, take a spe-cial position. However, their cost to property performance is stilllimiting a full commercial success and interest but allowing theiruse in household (injection molding) or pipe applications. Thesematerials crystallize over their full composition range, showing arelatively high degree of crystallinity that passes through a mini-mum at intermediate butene-concentrations. Depending on theamount of butene incorporated, the crystal structure formed is ei-ther the 𝛼 or 𝛾-form of iPP, a mixture of these forms or the stableform I of isotactic polybutene (iPB).[150] The trigonal form of iPPis accessible in these materials only via deformation/stretchingstarting from 𝛼 or 𝛾 crystallized form, but not from purely meltcrystallized samples.

These materials have a melting temperature comparable tothose of C2C3-random copolymers, but a higher stiffness, a bettertransparency and at similar comonomer content a lower amountof XCS fraction. The amount of the XCS fraction, which is formedin propylene-𝛼-olefin copolymers due to the formation of an ad-ditional noncrystallizable fraction, is for C3C4-copolymers in-dependent of the comonomer content. Among all studied ran-dom copolymers of propylene, this observation is exclusivelymade for propylene copolymers with butene. For other randomcopolymers of propylene, there is an exponential increase of theXCS-fraction with increasing comonomer content, indicating thechange of the material type from a random copolymer to a het-erophasic material. This special feature of C3C4-copolymers is aconsequence of the ability of the butene monomer to be incorpo-rated in the crystal lattice of PP (see Figure 15). The same obser-vation was made by Dlubek et al.[144] who found the amount ofamorphous phase and local free volume to increase with increas-ing comonomer content for propylene-𝛼-olefin copolymers ex-cept for C3C4-copolymers. It should be noted here that MC based

homopolymers and random copolymers of low comonomer con-tent always have a lower XCS content than their ZN catalyst coun-terparts, but this is hardly visible in the diagram.

Propylene hexene random copolymers with low amounts ofcomonomer show a rare combination of high clarity, relativelyhigh melting temperature and flexibility. An example for com-mercial use of this material class is the Hostalen PP-XN gradefrom LyondellBasell, which is marketed for hot and cold waterpipe applications.[151] Comparing the glass transition of C3C6polymers to that of conventional C2C3 random copolymers, simi-lar effects of the comonomer incorporation are found. Therefore,differences in the ability of the comonomer to be included in thecrystal lattice do not affect the mobility of the amorphous phase,which is determining the glass transition temperature. The in-creased intensity of the 𝛽-transition of hexene copolymers is in-dicating better impact resistance at lower temperatures.[137,143]

However, this increase is accompanied by a significant decreaseof the material’s rigidity. C3C6-copolymers with comonomer con-tents of 10–25 mol% show due to their ability to crystallize in 𝛿-modification different mechanical behavior.[144] In binary blendswith iPB which crystallizes in form I that is isomorphous tothe trigonal form of iPP, retarded crystallization of the materi-als from the melt in form II of iPB takes place. Ageing at roomtemperature induces transformation to form I and crystallisationof the C3C6 copolymer.[152]

Copolymers of propylene with octene or even higher olefinsare rarely investigated and described in literature. There are in-dications that these polymers may be useful as plastomers or inbarrier films. The low crystallinity of these materials is associatedwith an increase in flexibility and a change of the deformationprocess toward a ductile and more elastomeric-like mechanism.

Terpolymers of propylene with ethylene and butene take anexceptional position among the copolymers with higher 𝛼-olefinsand are of commercial importance, especially in the flexible pack-aging area where a combination of good thermal and opticalproperties with sealing performance is required. However, thisclass of polymers is rarely discussed in the scientific literature.Due to the presence of two comonomer units, the extent of dis-tortion of the crystal structure is more pronounced than in buteneor ethylene copolymers. The more pronounced shortening ofthe crystallizable sequence is additionally causing the formationof 𝛾-modification in these materials. Consequently, ethylene–propylene–butene terpolymers have compared to C4C3 or C2C3copolymers lower crystallinity, lower melting and crystallisationtemperatures resulting in changed mechanical and optical prop-erties. While the stiffness and strength of these polymers is com-parably low, they are highly transparent and their broad meltingrange makes them suitable for sealing applications in the pack-aging area.[153,154]

In addition to the macromolecular structure, the processingand in particular the cooling conditions are parameters thatshould be taken into consideration for controlling the final ma-terial properties.

Figure 16a shows some of the main processing technologieswith the characteristic cooling rates for solidification of the qui-escent melt into a final product. Each technique offers a rangeof cooling rates, which can be controlled by variation of parame-ters like mold/film thickness, cooling temperature, etc. The cool-ing rate at which the quiescent polymer melt is solidified is a





Figure 16. Processing effects: a) Typical cooling rates of processing of iPP; b) modulus of elasticity as a function of chill roll temperature of iPP castfilms.[155]

crucial technological parameter, which affects the final crystalstructure, morphology and material properties like stiffness andtransparency. Figure 16b shows the modulus of elasticity as afunction of the final cooling temperature in a 50 μm thick film ofiPP. Decreasing the chill roll temperature, i.e., the final tempera-ture of solidification, results in an increase of the supercooling ofthe material. The higher the supercooling (T0

m − Tc), the faster thecrystallization rate, which will result in formation of thinner lessperfect crystals. The insufficient time for crystallization at largesupercoolings results in generation of transparent film with lowstiffness, due to the decreased crystallinity and smaller size of thecrystals.

Together with the pathway of crystallization, synthesis of ran-dom isotactic copolymers of propylene and 1-alkenes is themain approach of controlling the structure, the amount andthe morphology of the ordered phase. Research in this fieldincluded, among others, the analysis of the effect of the typeand amount of co-units on the formation of different crys-tal polymorphs, on the partitioning of comonomers in crys-tals and in the amorphous phase, or on the kinetics of crys-tallization of the quiescent melt at processing relevant coolingrates.[83,84,100,121,122,130–138,145,150,152,156–166] In these studies, it hasbeen shown that quenching the quiescent melt of such copoly-mers allows similar mesophase formation at high supercoolingas in case of the iPP homopolymer; however, in the copolymersstudied the mesophase formed already on cooling at distinctlylower rate than in the homopolymer.[83,84,148,149] Furthermore, ithas been shown that the mesophase constitutes of nodular do-mains not organized into spherulites. The nodular morphologyhas been associated with the large number of homogeneous nu-clei, which form on large supercoolings. It is assumed that atrapid cooling, extensive lateral growth of nuclei is not alloweddue to geometrical constrains. Such constrains do not exist oncrystallization at low supercooling or on slow cooling which al-lows the growth and development of lamellar crystals orderedinto spherulites.

Inclusion of 1-hexene or 1-octene comonomer units into theiPP chain decreased significantly the cooling rate required to al-low formation of the mesophase, i.e., from 50 K s−1 for the iPPhomopolymer to 4 K s−1 for the copolymers with 1-hexene or 1-octene.[167] Prior investigation of the effect of 1-butene co-units

on the condition of crystallization and mesophase formation sug-gests that distinctly larger concentration of co-units than in caseof 1-hexene or 1-octene may be required to achieve similar de-crease of the critical cooling rate to obtain mesophase. While ad-dition of only 2–3 mol% 1-hexene or 1-octene permits mesophasedevelopment already on cooling between 1 and 10 K s−1, addi-tion of 6 mol% 1-butene co-units still requires cooling at ratesbetween 10 and 100 K s−1. This observation may be linked todifferent degree of inclusion of co-units into crystals/mesophaseand/or different specific energy of defects in the ordered phase,both affecting the kinetics of segregation at the crystal growthfront.

5. Conclusions and Outlook

Random copolymers of iPP with ethylene and higher 𝛼-olefinscan cover a wide range of properties and applications (see Ta-ble 5). The property variations inside each material class resultmostly from comonomerr content and molecular weight resp.MFR variation, but, as shown in the previous sections, their com-binations can be optimized by catalyst and comonomer distri-bution choice. In that respect, most data are available for C2C3copolymers due to their long history, wide-spread application andthe massive effect of moving from ZN to MC catalysts.[99,100]

Here, also most processing and application related propertieshave been studied, while for C3C4 and C3C6 copolymers the fo-cus has so far been on basic crystallization behavior and the de-velopment of new crystal modifications.[8,139]

From an industrial perspective, however, this focus is clearlyjustified, as for practically all applications the specific advantagesof these copolymers are based on crystal structure and polymor-phism. Mono- and multilayer films derive their excellent trans-parency from a significant mesomorphic content, their sealingbehavior from the onset of melting defining the sealing initia-tion temperature (SIT), and their stability in sterilization fromthe distance between SIT and melting point, Tm.[5,86,104] Ductil-ity and long-term resistance of pressure pipes result from thereduced lamellar thickness and enhanced tie-molecule density,especially in case of bimodal C2C3 compositions[118] and C3C6copolymers.[148] And finally, for thin-wall injection molded cupsand containers for packaging and food storage in households





Table 5. Typical property ranges for random copolymers of iPP with ethylene and higher 𝛼-olefins (data from various references and authors’ experience).

Polymer ZN-PPHa) SSC-PPHa) ZN-C2C3 SSC-C2C3 Terpo (C2C3C4) C3C4 C3C6

Comonomer [mol%] 0 0 0.5–5.5 1.0–8.0 2.0–10.0 (total) 2.0–6.0 1.0–3.0

MFR2 [g/10 min]b) 0.3–5000 1.0–1000 0.3–100 1.0–100 5.0–20 1.0–150 0.5–10

Tm [°C]c) 161–167 145–160 135–158 110–145 120–155 135–155 125–150

XCS [wt%]d) 1.0–2.5 0.3–1.0 2.0–12 0.4–8 2.0–10 2.0–5 2.0–15

Tens. moduluse) [MPa] 900–2200 800–1600 500–1000 400–1100 600–1200 800–1500 600–1200

Yield stresse) [MPa] 25–45 20–40 15–30 12–32 17–35 n.a. 15–30

NIS 23 °Cf) [kJ m−2] 2.0–25 2.0–25 5.0–50 4.0–65 5.0–15 4.0–8.0 5.0–10

NIS −20 °Cf) [kJ m−2] 0.5–8 1.0–10 2.0–15 2.0–20 n.a. n.a. 1.0–5

HDT ISO 75B [°C] 70–110 65–95 55–80 45–85 n.a. n.a. n.a.

a)References b)230 °C/2.16 kg c)DSC d)Xylene cold soluble fraction (ISO 16152) e)Tensile test acc. ISO 527 on injection-molded specimens f)Charpy notched impact strengthacc. ISO 179 1eA, n.a.: not available.

both transparency and toughness are clearly related to the 𝛾-phase formation, further enhanced by nucleation.[123–125]

In most cases, a change from C2 to C4 or C6 as well as fromZN to MC catalysts enables an expansion of the property rangetoward lower crystallinity and melting point, with the catalystchange also reducing the amount of hexane (C6) extractablesmassively (for XCS, the effect is limited to low comonomer con-tents). This development will continue in the future, driven bymarket trends like purity requirements, mono-material packag-ing systems with enhanced recyclability and the quest for en-hanced flexibility, for examples in fibers for hygienic applicationsand films in the medical segment. Next to their pure application,also the use of random heterophasic copolymers (RAHECO) andblend matrices is bound to increase in relevance, consequently.

Conflict of InterestThe authors declare no conflict of interest.

Keywordscatalysts, copolymers, crystallization, mechanics, optics, polypropylene

Received: August 11, 2021Revised: September 25, 2021

Published online:

[1] D. Jubinville, E. Esmizadeh, S. Saikrishnan, C. Tzoganakis, T. Mekon-nen, Sustainable Mater. Technol. 2020, 25, e00188.

[2] M. Gahleitner, C. Tranninger, P. Doshev, in: Polypropylene Handbook:Morphology, Blends and Composites (Eds: J. Karger-Kocsis, T. Bárány),Springer International, Berlin 2019, pp. 295–355.

[3] S. Brückner, S. V. Meille, V. Petraccone, B. Pirozzi, Prog. Polym. Sci.1991, 16, 361.

[4] J. Garbarczyk, D. Paukszta, S. Borysiak, J. Macromol. Sci., Part B:Phys. 2002, 41, 1267.

[5] M. Gahleitner, D. Mileva, R. Androsch, D. Gloger, D. Tranchida, M.Sandholzer, P. Doshev, Int. Polym. Proc. 2016, XXXI, 618.

[6] M. Avella, E. Martuscelli, G. D. Volpe, A. Segre, E. Rossi, T. Simon-azzi, Makromol. Chem. 1986, 187, 1927.

[7] C. De Rosa, F. Auriemma, O. Ruiz de Ballesteros, L. Resconi, I. Ca-murati, Chem. Mater. 2007, 19, 5122.

[8] F. Auriemma, C. De Rosa, R. Di Girolamo, A. Malafronte, M. Scotti,C. Cioce, Adv. Polym. Sci. 2017, 276, 45.

[9] E. Albizzati, G. Cecchin, J. C. Chadwick, G. Collina, U. Giannini,G. Morini, L. Noristi, in Polypropylene Handbook (Ed: N. Pasquini),Hanser, Munich 2005, pp. 15–17.

[10] K. Ziegler, E. Holzkamp, B. Breil, H. Martin, DE 973626 A, 1953.[11] G. Natta, I. Pasquon, A. Zambelli, G. Gatti, J. Polym. Sci. 1961, 51,

387.[12] G. Natta, P. Corradini, G. Allegra, J. Polym. Sci. 1961, 51, 399.[13] G. Natta, P. Pino, G. Mazzanti, US 3112300 A, 1954.[14] E. J. Vandenberg, US 3058969 A, 1955.[15] G. DiDrusco, R. Rinaldi, Hydrocarbon Process. 1981, 60, 153.[16] E. J. Vandenberg, US 3051690 A, 1955.[17] J. P. Hermans, P. Henrioulle, DE 2213086 A1, 1972.[18] C. L. Thomas, US 3153634 A, 1956.[19] P. Dassesse, R. Dechenne, US 3400110 A, 1964.[20] N. Kashiwa, T. Tokuzumi, H. Fujimura, US 3642746 A, 1969.[21] A. Mayr, P. Galli, E. Susa, G. DiDrusco, E. Giachetti, GB 1286867 A,

1968.[22] L. Luciani, P. C. Barbe, N. Kashiwa, A. Toyoda, DE 2643143 A1, 1975.[23] U. Giannini, E. Albizzati, S. Parodi, DE 2735672 A1, 1976.[24] U. Scata, L. Luciani, P. C. Barbe, DE 2822783 A1, 1977.[25] A. Toyoda, N. Kashiwa, US 4069169 A, 1978.[26] P. C. Barbe, U. Giannini, R. Nocci, S. Parodi, U. Scata, EP 0045975

A2, 1982.[27] M. Kioka, H. Kitani, N. Kashiwa, US 4330649 A1, 1982.[28] E. Albizzati, M. Galimberti, U. Giannini, G. Morini, Makromol.

Chem. 1991, 48–49, 223.[29] J. F. Ross, W. A. Bowles, Ind. Eng. Chem. Prod. Res. Dev. 1985, 24,

149.[30] L. Luo, N. Zhang, Z. Xia, T. Qi, Chem. Eng. Sci. 2016, 143, 12.[31] G. Mei, E. Beccarini, T. Caputo, C. Fritze, P. Massari, D. Agnoletto,

S. Pitteri, J. Plast. Film Sheeting 2009, 25, 95.[32] Z. H. Luo, P. L. Su, D. P. Shi, Z.-W. Zheng, Chem. Eng. J. 2009, 149,

370.[33] S. P. Sawin, C. J. Baas, Chem. Eng. 1985, 92, 42.[34] I. Kouzai, K. Fukuda, Macromol. Symp. 2009, 285, 23.[35] H. Sato, H. Ogawa, Review on development of polypropylene manufac-

turing process, Sumitomo Chemical Co., Ltd., Process & ProductionTechnology Center, R&D Report, “SUMITOMO KAGAKU,” Vol. 2,2009.

[36] M. Gahleitner, C. Paulik, Ullmann’s Polymers and Plastics: Productsand Processes. Vol. 2, Part 2, Organic Polymers. Polypropylene, Wiley-VCH, Weinheim 2016.





[37] B. B. Singh, F. Syed, J. Shah, ExxonMobil Enters the Global Polypropy-lene Technology Licensing, CMR Inc. Analysis, CMR, Houston 2005.

[38] P. Galli, G. Vecellio, Prog. Polym. Sci. 2001, 26, 1287.[39] M. Caracotsios, Chem. Eng. Sci. 1992, 47, 2591.[40] J. B. P. Soares, T. F. McKenna, Polyolefin Reaction Engineering, Wiley-

VCH, Weinheim 2012.[41] V. Kanellopoulos, C. Kiparissides, in Multimodal Polymers with Sup-

ported Catalysts. Design and Production (Eds: A. R. Albunia, F. Prades,D. Jeremic), Springer Nature, Cham 2019, pp. 155–203.

[42] Global Polypropylene Report 2, Townsend Solutions, Houston 2018.[43] H. Fromme, T. Küchler, T. Otto, K. Pilz, J. Müller, A. Wenzel, Water

Res. 2002, 36, 1429.[44] A. J. Martino-Andrade, I. Chahoud, Mol. Nutr. Food Res. 2010, 54,

148.[45] E. Albizzati, P. C. Barbe, L. Noristi, R. Scordamaglia, L. Barino, U.

Giannini, G. Morini, EP 0361494 A2, 1990.[46] P. C. Barbe, L. Noristi, R. Scordamaglia, L. Barino, E. Albizzati, U.

Giannini, G. Morini, EP 0362705 A2, 1990.[47] J. C. Chadwick, G. Morini, G. Balbontin, I. Camurati, J. J. R. Heere,

I. Mingozzi, F. Testoni, Macromol. Chem. Phys. 2001, 202, 1995.[48] V. K. Gupta, M. Ravindranathan, Polymer 1996, 37, 1399.[49] G. Morini, G. Balbontin, P. A. A. Klusener, WO 0157099 A1, 2001.[50] G. Morini, G. Balbontin, WO 0230998 A1, 2002.[51] J. C. Chadwick, Macromol. React. Eng. 2009, 3, 428.[52] M. Galvan, R. Pantaleoni, O. Fusco, B. Gaddi, A. Neumann, A. Maz-

zucco, G. Collina, M. Ciarafoni, US 20140316069 A1, 2014.[53] L. Chen, T. W. Leung, T. Tao, G. A. Roth, K. Gao, US 2010174105 A1,

2010.[54] L. Chen, T. W. Leung, T. Tao, US 20128288585 A1, 2012.[55] J. W. van Egmond, WO 2015081254 A1, 2015.[56] M. Gao, H. Lui, Z. Li, J. Wang, J. Yang, T. Li, US 2010222530 A1,

2010.[57] K. Matsunaga, H. Hashida, T. Tsutsui, K. Yamamoto, A. Shibahara,

T. Shinozaki, US 2008125555 A1, 2008.[58] A. B. Ernst, J. A. Streeky, W. L. Oliver, US 2008113860 A1, 2008.[59] T. Ozumi, S. Yamada, N. Nakamura, K. Hisano, M. Hosaka, T. Sug-

ano, US 2014221583 A1, 2014.[60] M. Hosaka, JP 2013028704 A, 2013.[61] C. Main, WO 2010014320 A1, 2010.[62] H. J. Kakkonen, J. Pursiainen, T. A. Pakkanen, M. Ahlgrén, E. Iiskola,

J. Organomet. Chem. 1993, 453, 175.[63] A. Haikarainen, P. Denifl, T. Leinonen, EP 2415790 B1, 2012.[64] P. Denifl, T. Leinonen, WO 2013098149 A1, 2013.[65] J. R. Severn, in Multimodal Polymers with Supported Catalysts. Design

and Production (Eds: A. R. Albunia, F. Prades, D. Jeremic), SpringerNature, Cham 2019, pp. 1–53.

[66] V. Busico, Dalton Trans. 2009, 41, 8794.[67] A. J. Teator, T. P. Varner, P. C. Knutson, C. C. Sorensen, F. A. Leibfarth,

ACS Macro Lett. 2020, 9, 1638.[68] R. Mühlhaupt, Macromol. Chem. Phys. 2003, 204, 289.[69] W. Kaminsky, Catal. Today 2002, 62, 23.[70] M. Stürzel, S. Mihan, R. Mühlhaupt, Chem. Rev. 2019, 116, 1398.[71] M. R. Machat, D. Lanzinger, A. Pöthig, B. Rieger, Organometallics

2017, 36, 399.[72] P. S. Kulyabin, G. P. Goryunov, M. I. Shakirov, V. V. Izmer, A.

Vittoria, P. H. M. Budzelaar, V. Busico, A. Z. Voskoboynikov, C.Ehm, R. Cipullo, D. V. Uborsky, J. Am. Chem. Soc. 2021, 143,7641.

[73] M. R. Machat, C. Jandl, B. Rieger, Organometallics 2017, 36, 1408.[74] Y. V. Kissin, D. L. Beach, J. Polym. Sci., Polym. Chem. Ed. 1983, 21,

1065.[75] M. Seth, T. Ziegler, Macromolecules 2004, 37, 9191.[76] M. Avella, E. Martuscelli, G. D. Volpe, A. Segre, E. Rossi, T. Simon-

azzi, Makromol. Chem. 1986, 187, 1927.

[77] T. Vestberg, M. Parkinson, I. Fonseca, C.-E. Wilén, J. Appl. Polym. Sci.2012, 124, 4889.

[78] A. Tynys, I. Fonseca, M. Parkinson, L. Resconi, Macromolecules 2012,45, 7704.

[79] V. Agarwal, T. B. van Erp, L. Balzano, M. Gahleitner, M. Parkinson,L. E. Govaert, V. Litvinov, A. P. M. Kentgens, Polymer 2014, 55, 896.

[80] W.-J. Wang, S. Zhu, Macromolecules 2000, 33, 1157.[81] M. Kakugo, Y. Naito, K. Mizunuma, T. Miyatake, Macromolecules

1982, 15, 1150.[82] M. Gahleitner, P. Jääskeläinen, E. Ratajski, C. Paulik, J. Reussner, J.

Wolfschwenger, W. Neißl, J. Appl. Polym. Sci. 2005, 95, 1073.[83] D. Cavallo, F. Azzurri, R. Floris, G. C. Alfonso, L. Balzano, G. W. M.

Peters, Macromolecules 2010, 43, 2890.[84] D. Cavallo, G. Portale, L. Balzano, F. Azzurri, W. Bras, G. W. Peters,

G. C. Alfonso, Macromolecules 2010, 43, 10208.[85] B. Pukánszky, I. Mudra, P. Staniek, J. Vinyl Addit. Technol. 1997, 3,

53.[86] D. Mileva, D. Tranchida, M. Gahleitner, Polym. Cryst. 2018, 1,

e10009.[87] C. Grein, T. Schedenig, EP 2195355 B1, 2009.[88] M. Gahleitner, C. Grein, R. Blell, J. Wolfschwenger, T. Koch, E. In-

golic, eXPRESS Polym. Lett. 2011, 5, 788.[89] M. Gahleitner, J. Fiebig, J. Wolfschwenger, G. Dreiling, C. Paulik, J.

Macromol. Sci., Part B: Phys. 2002, 41, 833.[90] V. Busico, J. C. Chadwick, R. Cipullo, S. Ronca, G. Talarico, Macro-

molecules 2004, 37, 7437.[91] G. Collini, G. Morini, EP 0822945 B1, 1997.[92] J. Wang, J. Lilja, T. Horill, M. Gahleitner, P. Denifl, T. Leinonen, EP

3071606 B1, 2014.[93] J. Wang, J. Lilja, M. Gahleitner, J. Braun, EP 3013902 B1, 2014.[94] J. Wang, M. Gahleitner, M. Aarnio-Winterhof, T. Horill, M. Wach-

holder, EP 2965908 B1, 2015.[95] L. Boragno, L. Resconi, M. Hoff, S. Das, K. Alastalo, M. Vahteri, D.

Tranchida, WO 2018122031 A1, 2018.[96] R. Pellecchia, P. Shutov, J. Wang, M. Gahleitner, Macromol. React.

Eng. 2020, 14, 2000022.[97] J. C. Chadwick, G. Morini, G. Balbontin, I. Camurati, J. J. R. Heere,

I. Mingozzi, F. Testoni, Macromol. Chem. Phys. 2001, 202, 1995.[98] Z. Horváth, A. Menyhárd, P. Doshev, M. Gahleitner, J. Varga, C. Tran-

ninger, B. Pukánszky, J. Therm. Anal. Calorim. 2014, 118, 235.[99] M. Fujiyama, H. Inata, J. Appl. Polym. Sci. 2002, 85, 1851.

[100] K. Jeon, Y. L. Chiari, R. G. Alamo, Macromolecules 2008, 41, 95.[101] C. H. Stephens, B. C. Poon, P. Ansems, S. P. Chum, A. Hiltner, E.

Baer, J. Appl. Polym. Sci. 2006, 100, 1651.[102] K. Hakala, E. Mansner, P. Denifl, I. Lehtiniemi, J. Kauhanen, L. Huh-

tanen, EP 2355926 B1, 2010.[103] C. Tzoganakis, J. Vlachopoulos, A. E. Hamielec, Polym. Eng. Sci.

1988, 28, 170.[104] C. Grein, in Multimodal Polymers with Supported Catalysts. Design

and Production (Eds: A. R. Albunia, F. Prades, D. Jeremic), SpringerNature, Cham 2019, pp. 205–241.

[105] P. Jääskeläinen, N. Hafner, P. Pitkänen, M. Gahleitner, O. Tuominen,W. Töltsch, EP 1434810 B1, 2003.

[106] G. Hallot, J.-M. R. G. Vion, EP 2686382 B1, 2012.[107] P. Lodefier, M. Dufrenoy, J. Dubuisson, A. Buffard, C. Boukalidis EP

3180398 B1, 2017.[108] C. Grein, T. Schedenig, EP 2176340 B1, 2008.[109] J. Wang, M. Gahleitner, J. Braun, D. Tranchida, AIP Conf. Proc. 2018,

1981, 020049.[110] P. L. Fernando, J. G. Williams, Polym. Eng. Sci. 1981, 21, 1003.[111] M. Gahleitner, P. Doshev, C. Tranninger, J. Appl. Polym. Sci. 2013,

130, 3028.[112] C. Grein, M. Gahleitner, B. Knogler, S. Nestelberger, Rheol. Acta

2007, 46, 1083.





[113] L. Santonja-Blasco, W. Rungswang, R. G. Alamo, Ind. Eng. Chem.Res. 2017, 56, 3270.

[114] J.-U. Starke, G. H. Michler, W. Grellmann, S. Seidler, M. Gahleitner,J. Fiebig, E. Nezbedova, Polymer 1998, 39, 75.

[115] Y. Li, Y. Li, C. Han, Y. Yu, L. Xiao, Polym. Bull. 2016, 76, 2851.[116] I. Suárez, M. J. Caballero, B. Coto, Eur. Polym. J. 2010, 46, 42.[117] M. Aarnio-Winterhof, P. Doshev, J. Seppälä, M. Gahleitner, eXPRESS

Polym. Lett. 2017, 11, 152.[118] L. Boragno, L. Resconi, J. Lilja, M. Gahleitner, EP 2978782 B1, 2014.[119] K. Busse, J. Kressler, R.-D. Maier, J. Scherble, Macromolecules 2000,

33, 8775.[120] R. G. Alamo, A. Ghosal, J. Chatterjee, K. L. Thompson, Polymer 2005,

46, 8774.[121] C. De Rosa, F. Auriemma, O. Ruiz de Ballesteros, L. Resconi, I. Ca-

murati, Macromolecules 2007, 40, 6600.[122] T. Foresta, S. Piccarolo, G. Goldbeck-Wood, Polymer 2011, 42, 1167.[123] Z. Horváth, A. Menyhárd, P. Doshev, M. Gahleitner, G. Vörös, ACS

Appl. Mater. Interfaces 2014, 6, 7456.[124] Z. Horváth, A. Menyhárd, P. Doshev, M. Gahleitner, D. Friel, J. Varga,

B. Pukánszky, J. Appl. Polym. Sci. 2016, 133, 43823.[125] J.-W. Housmans, M. Gahleitner, G. W. M. Peters, H. E. H. Meijer,

Polymer 2009, 50, 2304.[126] Z. Ma, L. Fernandez-Ballester, D. Cavallo, T. Gough, G. W. M. Peters,

Macromolecules 2013, 46, 2671.[127] B. Schammé, E. Dargent, L. Fernandez-Ballester, Macromolecules

2017, 50, 6396.[128] K. Resch, G. M. Wallner, C. Teichert, M. Gahleitner, Polym. Eng. Sci.

2007, 47, 1021.[129] F. Di Sacco, M. Gahleitner, J. Wang, G. Portale, Polymers 2020, 12,

1636.[130] M. Arnold, O. Henschke, J. Knorr, Macromol. Chem. Phys. 1996, 197,

563.[131] R. Quijada, J. L. Guevara, G. B. Galland, F. M. Rabagliati, J. M. Lopez-

Majada, Polymer 2005, 46, 1567.[132] P. Stagnaro, G. Costa, V. Trefiletti, M. Canetti, F. Forlini, G. C. Al-

fonso, Macromol. Chem. Phys. 2004, 207, 2128.[133] H. Palza, J. M. Lopez-Majada, R. Quijada, J. M. Perena, R. Be-

navente, E. Perez, M. L. Cerrada, Macromol. Chem. Phys. 2008, 209,2259.

[134] C. De Rosa, F. Auriemma, O. Ruiz de Ballesteros, D. De Luca, L.Resconi, Macromolecules 2008, 41, 2172.

[135] I. L. Hosier, R. G. Alamo, P. Esteso, J. R. Isasi, L. Mandelkern, Macro-molecules 2003, 36, 5623.

[136] J. Arranz-Andrés, I. Suárez, B. Pena, R. Benavente, E. Perez, M. L.Cerrada, Macromol. Chem. Phys. 2007, 208, 1510.

[137] K. Jeon, H. Palza, R. Quijada, R. G. Alamo, Polymer 2009, 50, 832.[138] B. Poon, M. Rogunova, A. Hiltner, E. Baer, Macromolecules 2005, 38,

1232.[139] B. Lotz, J. Ruan, A. Thierry, G. C. Alfonso, A. Hiltner, E. Baer, E.

Piorkowska, A. Galeski, Macromolecules 2006, 39, 5777.[140] A. J. Van Reenen, Macromol. Symp. 2003, 193, 57.

[141] P. Locatelli, M. C. Sacchi, I. Tritto, G. Zannoni, Makromol. Chem.,Rapid Commun. 1988, 9, 575.

[142] J. M. Majada-Lopez, H. Palza, J. L. Guevara, R. Quijada, M. C. Mar-tinez, R. Benavente, J. M. Perena, E. Perez, M. L. Cerrada, J. Polym.Sci., Part B: Polym. Phys. 2006, 44, 1253.

[143] H. Lovisi, M. I. B. Tavares, N. M. de Silva, S. M. C. de Menezes, L.C. de Santa Maria, F. M. B. Coutinho, Polymer 2001, 42, 9791.

[144] G. Dlubek, D. Bamford, A. Rodriguez-Gonzalez, S. Bornemann, J.Stejny, B. Schade, M. A. Alam, M. Arnold, J. Polym. Sci., Part B:Polym. Phys. 2002, 40, 434.

[145] B. Poon, M. Rogunova, S. P. Chum, A. Hiltner, E. Bear, J. Polym. Sci.,Part B: Polym. Phys. 2004, 42, 4357.

[146] D. Mileva, Q. Zia, R. Androsch, Polym. Bull. 2010, 65, 623.[147] F. Bédoui, J. Diani, G. Régnier, Polymer 2004, 45, 2433.[148] D. Mileva, M. Gahleitner, D. Gloger, D. Tranchida, Polym. Bull. 2018,

75, 5587.[149] D. Mileva, R. Androsch, H. J. Radusch, Polym. Bull. 2009, 62, 561.[150] C. De Rosa, F. Auriemma, P. Vollaro, l. Resconi, S. Guidotti, I. Ca-

murati, Macromolecules 2011, 44, 540.[151] LyondellBasell Industries Holdings B.V., Hostalen PP “XN” Series

Pipe, Leading the way, Information Brochure 2016, available onlineat: https://www.lyondellbasell.com/globalassets/documents/polymers-technical-literature/hostalen-pp-xn-series-pipe-brochure.pdf

[152] B. Ruiz de Ballesteros, C. De Rosa, F. Auriemma, A. Malafronte, M.Scoti, Polymer 2019, 183, 121826.

[153] R. Benavente, S. Caveda, E. Perez, E. Blaszquez, B. Pena, R. vanGierken, I. Suarez, Polym. Eng. Sci. 2012, 52, 2285.

[154] S. Caveda, W. Perez, E. Blazquez-Blazquez, P. Pena, R. van Grieken,I. Suarez, R. Benavente, Polym. Test. 2017, 62, 23.

[155] V. L. Carrubba, V. Brucato, S. Piccarolo, Macromol. Symp. 2002, 180,43.

[156] A. Turner-Jones, Polymer 1966, 7, 23.[157] S. Cimmino, E. Martuscelli, L. Nicolais, C. Silvestre, Polymer 1978,

19, 1222.[158] H. J. Zimmermann, J. Macromol. Sci., Part B: Phys. 1993, B32, 141.[159] S. Hosoda, H. Hori, K. Yada, S. Nakahara, M. Tsuji, Polymer 2002,

43, 7451.[160] C. De Rosa, S. Dello Iacono, F. Auriemma, E. Ciaccia, L. Resconi,

Macromolecules 2006, 39, 6098.[161] I. L. Hosier, R. G. Alamo, J. S. Lin, Polymer 2004, 45, 3441.[162] C. De Rosa, F. Auriemma, R. Di Girolamo, L. Romano, M. R. De

Luca, Macromolecules 2010, 43, 8559.[163] H. Janani, R. G. Alamo, Polym. Cryst. 2020, 3, e10111.[164] D. Mileva, R. Androsch, H. J. Radusch, Polym. Bull. 2008, 61, 643.[165] D. Mileva, R. Androsch, S. S. Funari, B. Wunderlich, Polymer 2010,

51, 5212.[166] D. Mileva, Q. Zia, R. Androsch, H. J. Radusch, S. Piccarolo, Polymer

2009, 50, 5482.[167] D. Mileva, R. Androsch, D. Cavallo, G. C. Alfonso, Eur. Polym. J. 2012,

48, 1082.




https://www.lyondellbasell.com/globalassets/documents/polymers-technical-literature/hostalen-pp-xn-series-pipe-brochure.pdf




Christian Paulik is head of the Institute for Chemical Technology of Organic Materials at the JohannesKepler University (JKU) Linz (Austria). He earned his Ph.D. in chemical engineering in the field ofpolymer science. In 1995, he started his career in the polymer industry and after various positionshe moved back to academia in 2010 accepting an offer by the JKU. Presently, he is focusing on poly-merization and structure–property relations of polyolefins and specialty polymers, e.g., melaminebased materials, recycling of polymers, and high-pressure biotechnology. He also works on polymeradditives and bio-based resources.

Cornelia Tranninger studied at JKU Linz (Austria) where she got a master’s degree in chemistry in 2006followed by a doctor’s degree in technical science in 2009. Already during this time she started workingon structure–property relationships of polypropylene and was employed at the Polymer CompetenceCenter Leoben, Austria, and right afterward as a senior scientist at the Borealis. For many years, shewas dealing mainly with designing new, innovative heterophasic polypropylene copolymers. Since2015, she moved to the position of a group leader and is now responsible for a group of researchersworking on the development of low-pressure polyolefins.

Jingbo Wang studied material science at the Nanjing University of Technology (China) and obtainedhis Ph.D. degree at DWI and ITMC at RWTH Aachen (Germany), in the field of self-organization ofpolymers. Since 2011, he has been working as a scientist at Borealis and involved in various projectsin developing and upscaling of next-generation polyolefin catalysts and materials. He is a co-authorof 20 papers and more than 50 patents.

Pavel Shutov studied chemistry at the Lomonosov Moscow State University in Moscow (Russia) andearned his Ph.D. degree in 2003 in the field of inorganic and metalorganic chemistry at the PhilippsUniversity of Marburg (Germany). After a two-year postdoctoral fellowship at the University of Gronin-gen (the Netherlands), he started his industrial career at the Dow Chemical in Terneuzen (the Nether-lands). Since 2012, he is employed as a polymerization scientist at Borealis Polyolefine GmbH, with afocus on bench, semi high-throughput and pilot plant scale olefin polymerization, catalyst testing andpolyolefin product design. He co-authored 20 papers and 17 patents.





Daniela Mileva studied polymeric material science at the University of Chemical Technology and Met-allurgy in Sofia (Bulgaria) and obtained her Ph.D. degree in 2013 for research in the field of structure–property relations of random copolymers of polypropylene at the Martin-Luther-University Halle-Wittenberg (Germany). Major research interests concern structure, crystallization, morphology, andrelated properties of polyolefins. Since 2012, she works as a research scientist at Borealis. She is acoauthor of about 40 papers and inventor of a couple of patents.

Markus Gahleitner, born 1963, studied chemical engineering at the JKU Linz (Austria), graduatingwith a Ph.D. thesis on polymer rheology. Since 1992, he works in the InnoTech department of Borealisin the development of polyolefin materials. He also has been organizing external co-operations, andhas spent some years in the patent department. Markus is teaching at several Austrian universities;he is the author of more than 75 papers in international journals, several book contributions, andinventor of more than 60 patents.




Catalyst Type Effects on Structure/Property Relations of ...

Documents

Transcript of Catalyst Type Effects on Structure/Property Relations of ...