Chem 471 Part 4. Industrial Polymers

4.1 Polymer Terminology

4.2 The Big Six Industrial Polymers

4.3 Step- and Chain-Growth Polymerization

4.4 Co-Polymers

4.5 Thermoset Polymers

4.1 Polymer Terminology

Polymer a large molecule composed of many repeating units called

monomers (from poly meaning many and meros meaning unit)

Monomer a subunit making up a polymer

Oligomer a polymer with a small number of repeating units

Thermoplastic a polymer that softens or melts when heated and

dissolves in suitable solvents

Thermosets polymers with elaborately cross-linked three-dimensional

structures which are set or hardened by undergoing a chemical

process during the manufacturing of the final product,

decompose on heating, insoluble in any solvent

length of the chain (number of monomer units)

three-dimensional arrangement of polymer chains in the solid

chain branching

chemical composition of the monomer units

bonding between chains (cross linking)

orientation of monomer units within the chain

for copolymers, the ordering of different monomer units in the chains

( ABABABABA, AAABBAAABBAAABB, etc.)

endless possibilities for manufacturing different kinds of polymers

Factors influencing polymer properties

4.2 Industrial Polymers: The Big Six

1

2

3

4

5

6

HOOC COOH HOOH

terephthalic acid ethylene glycol

Symbol Monomer(s) Polymer Properties

H

HH

H

ethylene

H

HH

H

ethylene

vinyl chloride

H

ClH

H

H

CH3H

H

propylene

H

PhH

H

styrene

Name

polyethylene terephthalate (PET or PETE)

polyethylene (HDPE)

polyvinyl chloride (PVC)

polyethylene (LDPE)

polypropylene (PP)

polystyrene (PS)

transparent, high impact strength,

impervious to acid and air, not subject to

stretching, most costly of the six

similar to LDPE (low density polyethylene), more

opaque, denser, tougher, more crystalline and rigid

rigid thermoplastic, impervious to oils and most

organic materials, transparent, high impact strength

opaque, white, soft, flexible, impermeable to water

vapor, unreactive toward acids and bases, absorbs oils

and softens, melts at 100 to 125 oC, does not become

brittle until –100 oC, oxidizes on exposure to sunlight.

opaque, high melting point (160 to 170 oC), high

tensile strength and rigidity, lowest density commercial

plastic, impermeable to liquids and gases, smooth

surface with high luster

glassy, sparkling clarity, rigid, brittle, easily fabricated,

upper temperature use 90oC, soluble in many organic

materials

Industrial Polymers (“Plastics”)

Big Six production / millions of tonnes per year

polyethylene 100

polypropylene 60

polyethyleneterephthalate 60

polyvinylchloride 40

polystyrene 15

Other common polymers polyurethanes polyesters

polymethylmethacrylate (acrylic) polycarbonates

polyacrylonitrilebutadienestyrene (ABS) polyamides (e.g., nylons)

polystyrenebutadiene (synthetic rubber) poylisoprene (rubber)

Uses of industrial polymers about 1/3 for construction (insulation, pipes, siding, flooring, framing, etc.)

about 1/3 for packaging (bottles, pails, bags, wraps, etc.)

other consumer products (textiles, automotive, electronics, etc.)

Importance of industrial polymers

100 kg of plastics produced per person per year (much higher in “developed” countries)

Ever considered a world without plastics? Clothing only from cotton, wool,

leather, fur? Other items only from wood, metal, stone, glass or ceramics?

4.3 Chain- and Step-Growth Polymerization Chain Growth Polymerization

intermediates in the process are transient free radicals, ions or metal complexes

and cannot be isolated

once the chain is initiated, the monomer units add on very quickly and the

molecular weight builds up in a fraction of a second

the monomer concentration decreases steadily throughout the reaction

long reaction times have little effect on the molecular weight, but do affect the yield

at any time the reaction mixture contains monomer and fully grown polymer, but a

low concentration of growing chains

the monomers frequently contain carbon-carbon double bonds, but can contain

cyclic ethers and aldehydes

there is no net loss of atoms in the polymerization reaction

examples:

n

CH2 OCH2=Onorn

nO

XO

X

orn

n

X

X

occurs between molecules containing different functional groups

can be stopped at any time and low molecular weight oligomers can be isolated

the concentration of monomer does not decrease steadily in the reaction, but

disappears early because of oligomer formation

long reaction times gradually build up the molecular weight

after the early stages, there is neither much reactant nor much fully grown product

but a wide distribution of slowly growing oligomers

a small molecule such as water is frequently lost in the reaction

E.g.

hexamethylene diamine

adipic acid

Nylon 66n

NNH

O

O

H

-H2O

H2NNH2

HOOH

O

O

Types of polymerization Step Growth Polymerization

Chain Growth Polymerization Free radical Initiation

General mechanism:

chain transfer

disproportionation

coupling

branching

R'

n

R'RO

R' H

RO

R'

R'

R' R'n

++

n

RO

R'

R'

R' R'

R'RO

R'n

or

++R'

OR

R'Hnn

R'RO

R'n

R'OR

R'

R'RO

R'

H

n

ornnn

RO

R'

RO

R' R' R'

2R'

RO

R'

etc.

Termination

R'RO

R'

+ R'R'RO

Propagation

Initiation

R'RO

+ R'RO

RO2RO OR

Other types of chain transfer

intramolecular chain transfer

addition of a chain transfer agent

n

R'RO

R'

+ CCl4

R'RO

R' Cln

CCl3+

CCl3 R'+R'

Cl3Cetc.

R'

1)

2)

Mercaptans (RSH) and phenols (PhOH) also work as chain transfer agents.

CH2=CH2

HH

Chain Growth Polymerization

Common mono-olefin polymers

n n

Cl

F F

F F

nn

CN

polyethylene poly(vinyl chloride)

polyacrylonitrile(Orlon)

polytetrafluoroethylene(Teflon)

poly(methyl methacrylate)(Lucite, Plexiglass)

polystyrene

n n

H3C CO2CH3

Chain Growth Polymerization

Free radical polymerization of dienes

Conjugated dienes polymerize readily by a free radical mechanism:

n

n

polybutadiene

1,3-butadiene

ROOR 2 RO

Initiation

RO

Propagation

+ RO

RO+ RO

etc.

Termination(as before)

polybutadiene

n

S

heat

S

S

n

nVulcanization

polyisoprene

polychloroprene(Neoprene, Duprene)

CH3

n

nCl

Chain Growth Polymerization

Ionic Initiation

Olefins with an electron withdrawing group on the double bond can undergo ionic

polymerization by an anionic initiation mechanism:

Ionic polymerization can also occur with cationic initiation using a protic acid or a

Lewis acid:

H+

n

etc.

n

termination

(- H+

)

H2O

+ Li+

+ OH-

CNBu

CN H

nn

CNBu

CN

CNBu

CNCN

Li+

CNBu

CN+Bu

-Li

+

Chain Growth Polymerization

Metal Complex Initiation (Ziegler-Natta Catalysis)

catalysts discovered by Karl Ziegler and Giulio Natta in 1950 (Nobel Prize)

polymerize olefins and dienes with stereoregularity to give an isotactic polymer

for example, polypropylene:

isotactic atacticsyndiotactic

The mechanism is somewhat understood:

R

Ti

Cl

Cl Cl

Cl+

R

Ti

Cl

Cl Cl

ClTi

Cl

Cl Cl

Cl

R

Ti

Cl

Cl Cl

Cl

R

=Ti

Cl

Cl Cl

Cl

R

Ti

Cl

Cl Cl

Cl

R n n

Chain Growth Polymerization

Polyamides (Nylons) work began on synthetic polyamides in 1929 by Carothers (Dupont)

interested in replacing silk ( a natural polyamide)

first industrially prepared polyamide was Nylon 66

Nylons are usually prepared condensing a dicarboxylic acid with a diamine

the first number in a nylon’s name is the number of carbon atoms in the amine, the

second is the number in the carboxylic acid

other methods for making polyamides use amino acids or ring-opening lactams

n

N

O H

NH

O

H2NOH

O

-H2O

Nylon 6caprolactam

6-aminohexanoic acid

-H2O

Nylon 66 (MW = 10,000 - 25,000, n= 40 - 100)

n

NHN

O

O

hexamethylenediamineadipic acid

+H2N

NH2

HOOH

O

O

H

Step Growth Polymerization

block copolymers are another type of copolymers

a low molecular weight polymer is extended by reaction with a new monomer

using a “living polymer”

imagine we have a styrene polymer and then add some butadiene and polymerized

it further

we would end up with a number of styrene units bundled together and a number of

butadiene units also together

S S S S S B B B S S S B B S S S S

graft copolymers result when a polymer chain of one monomer is grafted onto an

existing polymer backbone by creating a free radical site along the

backbone which initiates growth of a polymer chain

e.g., styrene chains can be grafted onto a butadiene rubber backbone

4.4 Copolymerization

4.5 Thermoset Polymers Phenol-Formaldehyde Polymers (Phenolic Resins)

discovered in 1910 by Leo Baekland

given the tradename Bakelite

first fully synthetic polymer

the first step in the synthesis is to prepare an initial resin under basic conditions:

OH

OH-

O-

+ H2O

CH2=O

OH

CH2 O-

O-

CH2OH

OHOH

CH2OH

+ di and tri-substituted derivatives

under acidic conditions these compounds can be cross-linked:

H+OH

CH2

OH

OH

CH2

H

OH

OH

OH

CH2

OH

CH2OH2H

+

OH

CH2OH

Phenolic Resins the final product is highly branched

most linkages between aromatic rings are CH2 groups, but some CH2OCH2

linkages exist OH

OH HOOH OHA phenolic or Bakelite resin

a second method uses an acid catalyst to give a linear polymer

these compounds have no free hydroxymethyl groups for cross-linking

OH

CH2

OH OH

HO

HOH

OH H+

OH

OH2

OH

OHOH

OH

HOH

OH

higher molecular weightpolymers and crosslinkedthermosets

Urea Formaldehyde Resins urea gives cross-linked resins with formaldehyde

urea reacts with formaldehyde under basic conditions to produce a “methylolurea”

prolonged heating under acidic conditions results in a complex thermoset of

poorly defined structure which includes ring formation

reaction of this compound (these compounds) under acidic conditions gives a

fairly linear low molecular weight polymer

O

NHH2N OH

H+

-H2O

O

NHH2N

O

NHH2N OH

O

NHN OHNH2N

HH

OH

O

NHN OHNH2N

HH

OO

NHN OHNN

HH

O

Hn

O

NHH2N OH

O

NHH2N O-

H2COH2O+

O

NH-

H2N-OH+

O

NH2H2NH2O

+ HO-

Melamine-Formaldehyde Resins

N N

N NH2

NH2

H2N

+ H2CHON N

N NH

NH2

H2N CH2OH

N N

N NH2

NH2

H2N

N N

N NH

NH2

H2N

N N

N NH2

NH2

HN

N N

N N

N

N

N N

N N

N

N

N N

NN

N N

NN

N

N N

N

a melamine orFormica resin

melamine has three amino groups and six labile hydrogens and will form

thermoset resins with formaldehyde

the chemistry is similar to that for the urea resins

Polyurethane Foams

the important reaction here is the formation of a urethane linkage from an isocyanate and an alcohol

most useful polyurethanes are cross-linked

those commonly used in foams start with a diisocyanate like toluene diisocyanate (TDI) and a low molecular weight polyether

one way of ensuring crosslinking is to use a triol in the polymerization mixture

water is added to the mixture to produce a foam by reaction with some of the isocyanate

+RNCO H2O RNH2 + CO2

n

n

CH3

N

NH

O

O

O

O

CH3

NCO

NCOn

HOO O

OHx.s.+O

HOOH

H