Polymer Lectures08 Given
Transcript of Polymer Lectures08 Given
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SYNTHETIC ORGANICPOLYMERS
Convenor: Dr. Fawaz Aldabbagh
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Polymersare large molecules made up of repeating units called Monomers
The synthetic process isPolymerization.
E.g.
CH2
CH2 CH2 CH2
OCH
2CH
2O
Monomer
Polymerizat ion
Polymer
n
Monomer
Polymerizat ion
Polymern
Notedefine repeating unit in terms of monomer structure
Degree of Polym erizationis the number of monomer units in a Polymer
However, for synthetic polymers it is more accurate to state average degree of
po lymerizati on ( )DP
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A polymer prepared from a single monomer is a homopolymer
If two or more monomers are employed, the product is a copo lymer
Linear polymer has no branching
Graft copolymer is an example of a branched network
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Two main classifications of Polymerization
Additionreaction or ChaingrowthMolecular weight increases by successively adding monomers to a reactive polymer
chain end resulting in high molecular weights at low conversions.
STEPreaction or growthPolymers are formed by linking monomer molecules to form dimers, trimers and
higher species in a step-wise fashion. The most abundant species react, and thus
high molecular weight formed only beyond 99% conversion.
Polymerization Conversion (p)
=M0- Mt
M0P
M0= initial number of monomer molecules
Mt = Number of monomer molecules at time t
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Ionic Chain (addition)-Growth Polymerization
The choice of ionic procedure depends greatly on the electronic
nature of the monomers to be polymerized
CO2R CO2R CN CO2R
CN
OR SR
N
Vinyl monomers with electron-donating groups
Vinyl monomers with electron-withdrawing groups
Monom ers and reagents shou ld be scrupu lous ly pu r i f ied; water and oxygen
shou ld be removed.
Polymerizat ions carr ied out at very low temperatures
Anion ic Polymer ization
Cat ion ic Polymerizat ion
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Anionic Polymerizations
In i t iators include alkyl l i th iums and so dium amide
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Cationic Polymerization -- the formed carbocation must be quite stable
OROR
H+
+
H+
+
Stable tertiary carbocation
stable oxonium ion
BF3/H2O
n
E.g. proton initiates polymerization of isobutane (2-methylpropene)
Adhesive, sealant, insulating oil, lubricating oil
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CNCNCN
OHH
CNCNCN
H
acid
nn
+ OH_
_
OMe OMe OMe
H H
OHH
OMe OMe OMen
+
base
n
+ H3O+
React ion s of water with react ive carbanion s and carboc at ions
Noteviable substrates for anionic polymerizations do not have -protons
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Chain Reaction: Free Radical Polymerization
RO OR
Ph
Ph
RO
2 RO
RO
+
Ph
RO
Ph
RO
n
Ph
Ph
n
Initiation
Propagation
Random Termination
Dead ch ains
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Conventional Radical Polymerization
Advantages
1/wide range of vinyl monomers polymerizable
2/can be carried out in bulk, water, organic solvents and other solvents
3/no rigorous purification or drying of reagents required
Conditions: Usually heat required for initiation
Initiator decomposition time should be considered-Amount of initiator, reaction temperature and initiator half-life (slow decompos i t ion)
Initiation Rate = Termination Rate - steady state kinetics apply
Overall,
[radical concentration] = low
Since termination (disproportionation and coupling mechanism) is random, a broad
MWD results. This polymer is dead (cannot initiate new monomer additions).
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Examples of Polymers Prepared by Radical Polymerization
H
H
H
H
H
H
CN
H
H
H
O
MeO
H
H
H
O
Me O
CH2CH
CH2CH
CN
CH2CH
O
OMe
C
CH2CH
O
C O
Me
n
n
n
n
Poly(styrene)
Poly(acrylonitrile)
Poly(vinylacetate)
Poly(methylacrylate)
Monomer Polymer
n
n
n
n
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Advantages of Radical Polymerization
1. Wide variety of vinyl monomers can be polymerized (electron rich and
deficient DBs)
2. Can be carried out in bulk and in a wide variety of solvents, which includewater and organic solvents
3. No rigorous purification of reagents or drying of solvents required
4. Rapid formation of high molecular weight polymer after small conversions of
monomer to polymer ( chain (addition) polymerization)
5. Living/controlled polymerizations enable easy formation of block copolymersand sophisticated architectures
75% of commercial polymers are made by radical polymerizations
Some monomers can only be polymerized by radical means, e.g. acrylic acid (AA)
C C
C
HH
H
O
OH
H
C
H
C
H
COOH
n
AIBN
Ion-exchange resins, smart polymers
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Polar Effects are important in radical polymerizations, and can give
alternating copolymers
Ph
R
Ph
R
CN
CN
Ph
PhR
CN Ph CNn
Radical Polarity
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Chain Reactioninitiation, propagation, termination
DP
50 100
conversion
DP
50 100
conversion
Chain polymerization with termination
Chain polymerization without termination
Living
e.g. conventional radical polymerization
e.g. nitroxide-mediated radical polymerization(NMP)
DP =[monomer]
[Initiator]
Life time of polymer radical chain is about 1 second
Initiator added so to slowly decompose throughout
polymerization time
Typically, rate of initiation = rate of termination
Therefore, [propagating radical] remains constant
Steady State
Initiator decomposes quickly, and polymer chains have long life times
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P T P + T
Nitroxide-mediated Controlled/living Radical Polymerization (NMP)
propagat ion
T= Nitroxide
P= Propagating radical
Features:
1. Molecular weight increases linearly with conversion2. Narrow molecular weight distributions obtained
3. Polymer chains contain living ends enabling chain extension or block
copolymer synthesis
A TAAAAn
A BBBBAAAA
n
n
B T
AAAAAn
B n
+ T propagation
Block copolymer synthesis
Tis sterically congested
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TT
T
TT
T
Conventional Radical Polymerization
Controlled Radical Polymerization
Broad MWD
Dead Polymer
Narrow MWD
Liv ing Polymer
Life time of radicals extended from 1 second to hours, as the radicals
do not get involved in irreversible bimolecular termination reactions,
since radicals are trapped by nitroxide reversibly
Initiator must decompose quickly to insure narrow MWD
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Example of Block Copolymer Formation
Ph
Ph
Ph
N
O
P
O
OEt
OEt
Ph
Ph
O
N P
O
OEt
OEt
O
OMe
Ph
Ph
O
O OMe
N
PO
O
O
AIBN, heat
SG1
n-1
n
+
SG1
n-1
m
n-1 m
D: n = 60
: m = 20
propagation
n = 60
m = 20
heat
Ph
PhO OMe
n-1 m
D: n = 60 : m = 20
Please correct block copolymer structure in questions
Reversible trapping added to
propagation to prevent
irreversible termination
First living poly(styrene) block
heated in the presence of methylacrylate to give diblock D
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C C
H
H C
Me
O
MeO
CH2
C
O
OMe
C
Me
n
n
Poly(methyl methacrylate)perspex
Nitroxides cannot control MMA Polymerizations
N
O
P
O
OEt
OEtC C
CH3
CO2Me
H
H
H
H
C C
CH2
CO2Me
N
OH
P
O
OEt
OEt
+
PMMASG1
PMMA=
+
SG1-H
disproportionation
MMA
AIBN
McHale, Ald abbagh, Zetterlun d, J. Polym . Sci. Part A: Polym . Chem.2007, 45, 2194-2203
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Recent Example of a Graft Copolymer Synthesis
+ Copolymerization
macromonomer monomerGraft copolymer
Poly(AA) NIPAM
C
H
CH2
C
H
CH2
CH2n
Br
CO
OH
CO
OH
C
C
HH
C
O
OCH2CH
3
+
CH2
CH
C O
NCH
CH3
CH3
H
N-Isopropylacrylamide
NIPAM monomer (excess)
McHale, Ald abbagh, Carroll, Yamada, J. Polym . Sci. Part A: Polym. Chem .2007, 45, 4394-4400
Poly(acrylic acid) macromonomer
Inso luble in w ater above th e lower cr i t ical solu t ion temperature (LCST)
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Insolublein water Soluble in NaOH (aq)Graft copolymerin NaOH solution(40C)
Graft copolymer
in NaOH (50C)
Poly(NIPAM)in water(40C)
+
Copolymerization
macromonomer MonomerGraft copolymer
Poly(AA) NIPAM
Dual-Responsive Smart Graft Copolymer
McHale, Ald abbagh, Carroll, Yamada, J. Polym . Sci. Part A: Polym. Chem .2007, 45, 4394-4400Gibb ons , Carroll, Ald abbagh, Yamada, J. Polym. Sci. Part A: Polym. Chem.2006, 44, 6410-6418
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Ziegler-Natta Addition Polymerization
Isotactic polymerization
R
Cl
R
Cl3Ti R AlR
2Cl
Cl3Ti
R
Cl3Ti R
R
Cl3Ti
R
Cl3Ti
Cl3Ti
R
Cl3Ti
R
Cl3Ti
R
TiCl4/ AlR3
1-4 atm, rtn
TiCl4+ AlR3 Cl3Ti AlR2
+
n
s complex
p complex
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Stereochemistry and Polymers
Many useful polymers, such as poly(styrene),
poly(acrylonitrile) and poly(vinyl chloride) are atact ic as
normally prepared. Customized catalysts that effect
stereoregular polymerization of poly(propylene) and
some other monomers have been developed, and the
improved properties associated with the increased
crystallinity of these products has made this an
i m p o r t a n t f i e l d o f i n v e s t i g a t i o n .
The properties of a given polymer will vary considerably with its tacticity. Atact ic poly(propylene)
is useless as a solid construction material, and is employed mainly as a component of adhesives
or as a soft matrix for composite materials. In contrast, isotact icpolypropylene is a high-melting
solid (ca. 170 C) which can be molded or machined into structural components.
Because poly(propylene) rope is so light, it is the only rope that floats. For
this reason, it is very popular among ropes for pool makers and water
sports. Also when wet it is flexible and does not shrink.
Amorphous polymermelts to
a hard rubbery, glassy state
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Step-growth Polymerization
Step-polymers are made by allowing difunctional monomers with
complementary funct ional groups to react with one another
Condensation between two molecules
C C
O O
OCH2CH
2O
n
O O
OMeMeO
OH
OH
+
Poly(ethylene terephthalate)terephthalic acid ethylene glycol
PETThis is an example of a poly(ester)
The reaction is a t ransesteri f icat ion Recyclable plasticbottles and textile
fabrics
Using a co ndensat ion react ion
Th l ( id ) b i tl f t thb i h
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Step-growth Polymerization
Self-Condensation or Ring-Opening Polymerization
First patented by Dupont
Nylon 6 is made by heating caprolactam to about 250 C with about 5-10% water
These are poly(amides) bristles of toothbrishes,
s t o c k i n g s , r o p e , t i r e s , c a r p e t f i b r e
First patented by BASF
260-280 C
250 psi
- H2O
MW = 10,000, m.pt. 250 C, fibres stretched (to increase strength) to 4 times their length
High temp. to drive off waterAlso opened by
cations & anions
Molten nylon spun
into fibres
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Step-growth Polymerization
1. Polymers retain their functionality as end groups at the
end of the polymerization
2. Only a single reaction is responsible for polymer formation3. Molecular weight increases slowly even at high
conversion. This is given by the Carothers equation,
where conversion is (p)
DP =
1
1 - p
At 98% conversion, the degree of polymerization is only 50%
4. Exact stoichiometric balance and very pure monomers
are required to achieve high molecular weights
Larger chains react only at very high c onvers ion
5. Equilibrium reactionsnecessary to remove by-product
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Step-growth Polymerization
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Step-additionno by-products
CH2
O
O
O
O
CH2
6
+6
n
CH2N2 [ CH2] + N2nBF3
Chain-growth condensation
NN CC OOOH
OH
NN
H
O
H
O
OO
+
nPoly(urethane)
Insulation foam, HP adhesives, sealants,
carpet underlay
180 C
Bayer-patented
Lower Temp. than condensation reactions
Impurity found in diazomethane
bisdienebenzoquinone
Cyclic diene heldcis is very reactive
e.g. dicyclopentadiene
rt
Ti f litt t bi d d
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Time for litter to biodegradeProduct Time to biodegrade
Paper 2-5 months
Wool socks 1 to 5 years
Plastic coated paper milk cartons 5 years
Plastic bags 10 to 20 years
Nylon fabric 30 to 40 years
Aluminum cans 80 to 100 years
Plastic 6-pack holder rings 450 years
Glass bottles 1 million years
Plastic bottles Forever
Plastic resin identification codes (1)
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Plastic resin identification codes (1)
Codes Descriptions Recycled products
Polyethylene terephthalate (PET, PETE)is clear, tough, and
has good gas and moisture barrier properties. Commonly
used in soft drink bottles and many injection molded. Otherapplications include strapping and both food and non-food
containers. Cleaned recycled PET flakes and pellets are in
great demand for spinning fiber for carpet yarns, producing
fiberfill and geo-textiles.
Fiber, tote bags, clothing,
film and sheet, food and
beverage containers, carpet,strapping, fleece wear,
luggage and bottles.
High Density Polyethylene (HDPE)is used to make bottles for
milk, juice, water and laundry products. Unpigmented bottlesare translucent, have good barrier properties and stiffness,
and are well suited to packaging products with a short shelf
life such as milk. Because HDPE has good chemical
resistance, it is used for packaging many household and
industrial chemicals.
Bottles; pipe, buckets,
crates, flower pots, gardenedging, film and sheet,
recycling bins, benches,
dog houses, plastic lumber,
floor tiles, picnic tables,
fencing.
Polyvinyl Chloride or PVChas excellent chemical resistance,
good weatherability, flow characteristics and stable electricalproperties. The vinyl products can be broadly divided into
rigid and flexible materials. Bottles and packaging sheet are
major rigid markets, but it is also widely used as pipes and
fittings, siding, carpet backing and windows. Flexible vinyl is
used in wire and cable insulation, film and sheet, floor
coverings synthetic leather products, coatings, blood bags,
medical tubing and many others.
Packaging, binders, decking,
paneling, gutters, mud flaps,film and sheet, floor tiles
and resilient flooring, cables,
mats, cassette trays,
electrical traffic cones,
boxes, garden hose, mobile.
Pl ti i id tifi ti d (2)
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Plastic resin identification codes (2)Codes Descriptions Recycled products
Low Density Polyethylene (LDPE)used predominately in film
applications due to its toughness, flexibility and relativetransparency, making it popular for use in applications where
heat sealing is necessary. LDPE is also used to manufacture
some flexible lids and bottles and it is used in wire and cable
applications.
Shipping envelopes,
garbage can liners, filmand sheet, furniture,
compost bins, paneling,
trash cans, landscape
timber, lumber
Polypropylene (PP)has good chemical resistance, is strong, and
has a high melting point making it good for hot-fill liquids. PP isfound in flexible and rigid packaging to fibers and large molded
parts for automotive and consumer products.
Automobile battery cases,
signal lights, batterycables, brooms, brushes,
oil bins, funnels, bicycle
racks, trays pallets,
sheeting.
Polystyrene (PS)is a versatile plastic that can be rigid or foamed.
General purpose polystyrene is clear, hard and brittle. It has a
relatively low melting point. Typical applications include
protective packaging, containers, lids, cups, bottles and trays.
Light switch plates, vents,
thermal insulation, desk
trays, rulers, license plate
frames, foam packing,
foam plates, utensils
Other. Use of this code indicates that the package in question is
made with a resin other than the six listed above, or is made of
more than one resin listed above, and used in a multi-layer
combination.
Bottles, plastic lumber
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Recycling of plastic containers and wrapping
Chemical Recycling by Eastman Kodak
C C
O O
OCH2CH
2O
C C
O O
OMeMeO
OH
OHn
+
CH3OH
These monomers are purified by distillation or recrystallization and used
as feedstocks for further PET film manufacture.
H
+
methanolys is
PET
Representative Exam Questions
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Representative Exam Questions
1. Using one appropriate monomer for each polymerization classification, discuss the mechanism and
kinetics;
(a) Step-growth, b) conventional (non-living) chain (addition), c) living chain (addition) polymerizations.
In your answer give details of reaction conditions and reagents required.
2. (a) Discuss the stability of nitroxide radicals, and there use in living radical polymerizations.(b) Why is it not possible to control the radical polymerization of methyl methacrylate with nitroxides?
3. How would you prepare the following polymers? Give reaction conditions, reagents and detailed
mechanisms for each polymerization. Name polymers A-D.
Ph
PhO OMe
n n n
A
B Cn-1
m
D: n = 60 : m = 20
4. Draw structures of the polymers obtained from the following reactions;
CO2Me
MeO2C OH OH
O
+H+
KOH
5. Give one example of an isotatic polymer and block and alternating copolymer. Provide reactions (with
conditions) and mechanisms for their synthesis