Organic
Polymer
Chemistry
29-1
Some Definitions
 Polymer:
From the Greek, poly + meros, many
parts.
• Any long-chain molecule synthesized by bonding
together single parts called monomers.
 Monomer:
From the Greek, mono + meros, single
part.
• The simplest nonredundant unit from which a polymer
is synthesized.
 Plastic:
A polymer that can be molded when hot
and retains its shape when cooled.
29-2
Continued
 Thermoplastic:
A polymer that can be melted and
molded into a shape that is retained when it is
cooled.
 Thermoset plastic: A polymer that can be molded
when it is first prepared but, once it is cooled,
hardens irreversibly and cannot be remelted.
29-3
Notation & Nomenclature
 Show
the structure by placing parens around
the repeat unit:
• n = average degree of polymerization.
synthesized
from
n synthesized
from
Cl
Polystyrene
Styrene
n
Poly(vinyl chloride)
(PVC)
Cl
Vinyl
chloride
 To
name a polymer, prefix poly to the name of
the monomer from which it is derived.
• For more complex monomers or where the name of
the monomer is two words, enclose the name of the
monomer in parens, for example poly(vinyl chloride).
29-4
ab
Molecular Weight
 All
polymers are mixtures of individual polymer
molecules of variable MWs.
• number average MW: Count the number of chains of a
particular MW (Ni moles), multiply each number by the
MW (Mi), sum these values, and divide by the total
number of polymer chains.
• weight average MW:
29-5
Example
Sample has the unique chains
Chain
MW, Mi
Moles
Present, Ni
Chain
Mass, MiNi
120
0.10
12g
140
0.20
28
140
0.10
14
160
0.30
48
160
0.40
64
180
0.20
36
200
0.10
20
29-6
Example
Now for weight averaged MW
Chain
MW, Mi
Moles
Present, Ni
Chain
Mass, MiNi
120
0.10
12g
140
0.20
28
140
0.10
14
160
0.30
160
0.40
64
180
0.20
36
200
0.10
20
140
48
29-7
Polydispersivity Index
PDI = Mw/Mn measures the extent of
different molecular weights.
PDI greater than or equal to 1.0
29-8
Morphology
 Polymers
tend to crystallize as they precipitate or
are cooled from a melt.
 Acting to inhibit crystallization are that polymers
are large molecules. Complicated and irregular
shapes prevent efficient packing into ordered
structures.
 As a result, polymers in the solid state tend to be
composed of
• ordered crystalline domains
• disordered amorphous domains
29-9
Morphology: Crysatline
 High
degrees of crystallinity are found in
polymers with
• regular, compact structures
• strong intermolecular forces, such as hydrogen bonds
and dipolar interactions.
 As
the degree of crystallinity increases, the
polymer becomes more opaque due to scattering
of light by the crystalline regions.
 Melt transition temperature, Tm: The temperature
at which crystalline regions melt.
• As the degree of crystallinity increases, Tm increases.
29-10
Morphology: Amorphous
 Highly
amorphous polymers are sometimes
referred to as glassy polymers.
• Lacking crystalline domains that scatter light,
amorphous polymers are transparent.
• They are weaker polymers, both in terms of their
greater flexibility and smaller mechanical strength.
• On heating, amorphous polymers are transformed
from a hard glassy state to a soft, flexible, rubbery
state.
 Glass
transition temperature, Tg: The
temperature at which a polymer undergoes a
transition from a hard glass to a rubbery solid.
Put polystyrene cup in boiling water.
29-11
Morphology
• Example: poly(ethylene terephthalate), abbreviated
PET or PETE, can be made with crystalline domains of
0% to 55%.
O
O
O
O
n
Poly(ethylene terephthalate)
29-12
Morphology
 Completely
amorphous PET is formed by quickly
cooling the melt.
• PET with a low degree of crystallinity is used for
plastic beverage bottles.
 More
crystallline formed by slow cooling, more
molecular diffusion occurs and crystalline
domains form as the chains become more
ordered.
• PET with a high degree of crystallinity can be drawn
into textile fibers and tire cords.
29-13
Step-Growth Polymers

Step-growth polymerization: A polymerization in which chain growth
occurs in a stepwise manner between difunctional monomers. Many
chains initiated at same time. All monomeric -> mostly dimeric ->
mostly trimers. Etc.

five types of step-growth polymers:
• Polyamides
• Polyesters
• Polycarbonates
• Polyurethanes
• epoxy resins
29-14
Polyamides Nylon 66

Nylon 66 (from two six-carbon monomers).
O
HO
OH +
O
Hexanedioic acid
(Adipic acid)
H 2N
N H2
heat
1,6-Hexanediamine
(Hexamethylenediamine)
O
O
N
H
Nylon 66
H
N
n
• During fabrication, nylon fibers are cold-drawn to
about 4 times their original length, which increases
alignment, crystallinity, tensile strength, and
29-15
stiffness.
Nylon 66, source of Hexanedioic Acid
• The raw material base for the production of nylon 66 is
benzene, which is derived from cracking and reforming
of petroleum.
3 H2
catalyst
Benzene
O2
catalyst
Cyclohexane
OH
O
+
Cyclohexanol
Cyclohexanone
HN O 3
COOH
COOH
Hexanedioic acid
(Adipic acid)
29-16
Nylon 66, source of the 1,6 hexanediamine
• Hexanedioic acid is the starting material for the
synthesis of hexamethylenediamine.
O
NH4
+ -
O
O- NH4 +
heat
O
Ammoniu m h exanedioate
(Ammoniu m ad ipate)
O
H2 N
NH2
O
Hexanediamide
(Ad ipamide)
4 H2
catalyst
H2 N
NH2
1,6-Hexanediamine
(Hexameth ylen ediamine)
29-17
Polyamides, Nylon 6
 Nylons
are a family of polymers, the two most
widely used of which are nylon 66 and nylon 6.
• Nylon 6 is synthesized from a six-carbon monomer.
O
n
N H 1. partial hydrolysis
Caprolactam
H
O
N
2. heat
n
Nylon 6
• Nylon 6 is fabricated into fibers, brush bristles, highimpact moldings, and tire cords.
29-18
Polyamides, Kevlar
 Kevlar
is a polyaromatic amide (an aramid).
O
nHOC
O
COH + nH2 N
1,4-Benzenedicarboxylic
acid
(Terephthalic acid)
O
C
N H2
1,4-Benzenediamine
(p-Phenylenediamine)
O
CNH
NH
n
+
2 nH2 O
Kevlar
• Cables of Kevlar are as strong as cables of steel, but
only about 20% the weight.
• Kevlar fabric is used for bulletproof vests, jackets, and
raincoats.
29-19
Polyesters, PET
 Poly(ethylene
terephthalate), abbreviated PET or
PETE, is fabricated into Dacron fibers, Mylar
films, and plastic beverage containers.
O
O
HO
OH
1,4-Benzenedicarboxylic acid
(Terephthalic acid)
+
O
HO
OH
heat
1,2-Ethanediol
(Ethylene glycol)
O
O
O
n
+ 2 nH2 O
Poly(ethylene terephthalate)
(Dacron, Mylar)
29-20
PET, source of glycol and terepthalic acid
• Ethylene glycol is obtained by air oxidation of
ethylene followed by hydrolysis to the glycol.
CH2 = CH2
O
O2
catalyst
CH2 -CH 2
H+ , H2 O
1,2-Ethanediol
(Ethylene glycol)
Oxirane
(Ethylene oxide)
Ethylene
HOCH2 CH2 OH
• Terephthalic acid is obtained by catalyzed air
oxidation of petroleum-derived p-xylene.
H3 C
CH3
p-Xylene
O2
catalyst
O
HOC
O
COH
Terephthalic acid
29-21
Polycarbonates, Lexan
• To make Lexan, an aqueous solution of the sodium
salt of bisphenol A (BPA) is brought into contact with a
solution of phosgene in CH2Cl2.
O
CH3
+
Na - O
CH 3
Disodium salt
of Bisphenol A
O- Na + + Cl
Cl
Phosgene
O
CH3
O
CH3
Lexan
(a polycarbonate)
O
+ 2 NaCl
n
29-22
Phase transfer catalysis.
The sodium salt of bisphenol A is water soluble
while the phosgene is not. Immiscible. No
reaction.
Solution: Phase transfer catalysis. NBu4+ and a
negative ion can go back and forth between the
two phases.
 NBu4+
brings bisphenolate ion into organic phase
 Reaction occurs with phosgene producing Cl NBu4+ brings chloride ion into water phase.
29-23
Polycarbonates, Lexan
 Lexan
is a tough transparent polymer with high
impact and tensile strengths and retains its
shape over a wide temperature range.
• It is used in sporting equipment, such as bicycle,
football, and snowmobile helmets as well as hockey
and baseball catcher’s masks.
• It is also used in the manufacture of safety and
unbreakable windows.
29-24
Polyurethanes
A
urethane, or carbamate, is an ester of carbamic
acid, H2NCH2COOH.
• They are most commonly prepared by treatment of an
isocyanate with an alcohol.
O
Addition to
RN = C= O + R' OH
RN HCOR' the N=C
An isocyanate
A carbamate bond
 Polyurethanes
consist of flexible polyester or
polyether units alternating with rigid urethane
units.
• The rigid urethane units are derived from a
diisocyanate.
29-25
Polyurethanes
• The more flexible units are derived from low MW
polyesters or polyethers with -OH groups at the ends
of each polymer chain.
CH 3
O=C=N
N=C=O + nHO-polymer-OH
Low -molecu lar-w eight
polyester or polyeth er
2,6-Toluene
diis ocyanate
O
CNH
CH 3
O
NHCO-p olymer-O
n
A p olyurethane
29-26
Epoxy Resins
 Epoxy
resins are materials prepared by a
polymerization in which one monomer contains
at least two epoxy groups.
• Epoxy resins are produced in forms ranging from lowviscosity liquids to high-melting solids.
29-27
Epoxy Resins
• The most widely used epoxide monomer is the
diepoxide prepared by treating one mole of bisphenol
A with two moles of epichlorohydrin.
CH3
O
Cl
+ Na + - O
O - Na +
CH3
the disodium salt of
bisphenol A
Epichlorohydrin
CH3
O
O
O
O
CH3
A diepoxide
29-28
Epoxy Resins
• Treatment of the diepoxide with a diamine gives the
resin.
CH 3
O
O
O
O
CH3
A diepoxide
NH 2
H2 N
A diamine
CH3
OH
O
Note the
regioselectivity
OH
O
CH3
An epoxy resin
H
N
N
H n
29-29
Thermosets
 Bakelite
was one of the first thermosets.
29-30
Chain-Growth Polymers
 Chain-growth
polymerization: A polymerization
that involves sequential addition reactions, either
to unsaturated monomers or to monomers
possessing other reactive functional groups.
 Reactive intermediates in chain-growth
polymerizations include radicals, carbanions,
carbocations, and organometallic complexes.
29-31
Chain-Growth Polymers
 We
concentrate on chain-growth polymerizations
of ethylene and substituted ethylenes.
R
An alkene
R
n
• On the following two screens are several important
polymers derived from ethylene and substituted
ethylenes, along with their most important uses.
29-32
Polyethylenes
Monomer
Formula
Common
Name
Polymer N ame(s) and
Common Us es
CH2 =CH2
Ethylene
Polyethylene, Polythene;
break -res istant contain ers
and packaging materials
CH2 =CHCH3
Propylene
Polypropylene, Herculon;
textile an d carpet fibers
CH2 =CHCl
Vinyl chlorid e
Poly(vinyl chlorid e), PVC;
con struction tub ing
CH2 =CCl2
1,1-D ichloroeth ylen e
Poly(1,1-dichloroethylene),
Saran ; food packaging
29-33
Polyethylenes
CH2 =CHCN
Acrylonitrile
Polyacrylon itrile, Orlon ;
acrylics and acrylates
CF2 =CF2
Tetrafluoroeth ylen e
Poly(tetrafluoroeth ylen e),
PTFE; nonstick coatings
CH2 =CHC6 H5
Styrene
Polystyrene, Styrofoam;
in sulatin g materials
CH2 =CHCOOEt
Ethyl acrylate
CH2 =CCOOCH3
CH3
Meth yl
methacrylate
Poly(ethyl acrylate);
latex p aints
Poly(methyl methacrylate),
Plexiglas ; glas s sub stitutes
29-34
Radical Chain-Growth
 Among
the initiators used for radical chaingrowth polymerization are diacyl peroxides,
which decompose on mild heating.
O
O
O

O
D ib enzoyl
peroxid e
O
2
O
A b enzoyloxy
radical
2
+
2 CO2
A p henyl
radical
29-35
Radical Chain-Growth
 Another
common class of initiators are azo
compounds, which also decompose on mild
heating or with absorption of UV light.
 or h 
N C
2
:
:
N N
C N
Azoisobu tyronitrile (A IBN )
+
N N
N C
Alk yl radicals
29-36
Radical Chain-Growth
 Radical
polymerization of a substituted ethylene.
• chain initiation
 or h 
In-In
In
2 In
In
+
R
R
• chain propagation
In
In
+
R
In
+
R
R
R
R
In
n
R
R
R
n
R
etc.
29-37
Radical Chain-Growth
• chain termination.
radical
coupling
In
R
2 In
R
n
n
R R
In
n
R
R
disproportionation
In
R
n
H
+ In
R
R
n
R
29-38
Radical Chain-Growth
 Radical
reactions with double bonds almost
always gives the more stable (the more
substituted) radical.
• Because additions are biased in this fashion,
polymerizations of vinyl monomers tend to yield
polymers with head-to-tail linkages.
R
R
R
R
R
R
R
R
head-to-tail linkages
R
R
head-to-head linkage
29-39
Radical Chain-Growth
 Chain-transfer
reaction: The reactivity of an end
group is transferred from one chain to another,
or from one position on a chain to another
position on the same chain.
• Polyethylene formed by radical polymerization exhibits
butyl branches on the polymer main chain.
H
A six-membered tran sition
state leadin g to
1,5-hydrogen ab straction
H
nCH2 =CH2
n
29-40
Radical Chain-Growth
 The
first commercial polyethylenes produced by
radical polymerization were soft, tough polymers
known as low-density polyethylene (LDPE).
• LDPE chains are highly branched due to chain-transfer
reactions.
• Because this branching prevents polyethylene chains
from packing efficiently, LDPE is largely amorphous
and transparent.
• Approx. 65% is fabricated into films for consumer
items such as baked goods, vegetables and other
produce, and trash bags.
29-41
Ziegler-Natta Polymers
 Ziegler-Natta
chain-growth polymerization is an
alternative method that does not involve radicals.
• Ziegler-Natta catalysts are heterogeneous materials
composed of a MgCl2 support, a Group 4B transition
metal halide such as TiCl4, and an alkylaluminum
compound.
CH2 =CH2
Eth ylen e
TiCl4 / Al( CH2 CH3 ) 2 Cl
MgCl2
n
Polyethylen e
29-42
Ziegler-Natta Polymers
 Mechanism
of Ziegler-Natta polymerization.
Step 1: Formation of a titanium-ethyl bond
Mg Cl2 / TiCl 4
particle
Ti
Cl
+
Cl A l
Ti
+
Cl
Cl A l
Diethylaluminum
chloride
Step 2: Insertion of ethylene into the Ti-C bond.
Ti
+
CH2 = CH2
Ti
29-43
Ziegler-Natta Polymers
 Polyethylene
from Ziegler-Natta systems is
termed high-density polyethylene (HDPE).
• It has a considerably lower degree of chain branching
than LDPE and a result has a higher degree of
crystallinity, a higher density, a higher melting point,
and is several times stronger than LDPE.
• Appox. 45% of all HDPE is molded into containers.
• With special fabrication techniques, HDPE chains can
be made to adopt an extended zig-zag conformation.
HDPE processed in this manner is stiffer than steel
and has 4x the tensile strength!
29-44
Polymer Stereochemistry
 There
are three alternatives for the relative
configurations of stereocenters along the chain
of a substituted ethylene polymer.
R H R H R H
R H R H
Isotacti c pol ymer
(i dentical confi gurations)
R H
H R R H
H R R H
Syndi otacti c pol ymer
(al ternating configurati ons)
R H R H R H
R H
H R
Atacti c pol ymer
(random confi gurations)
29-45
Polymer Stereochemistry
 In
general, the more stereoregular the
stereocenters are (the more highly isotactic or
syndiotactic the polymer is), the more crystalline
it is.
• Atactic polypropylene, for example, do not pack well
and the polymer is an amorphous glass.
• Isotactic polypropylene is a crystalline, fiber-forming
polymer with a high melt transition.
29-46
Ionic Chain Growth
 Either
anionic or cationic polymerizations
• Cationic polymerizations are most common with
monomers with electron-donating groups.
OR
Styrene
Is obutylene
Vinyl ethers
SR
Vinyl thioethers
• Anionic polymerizations are most common with
monomers with electron-withdrawing groups.
CN
Styrene
COOR
Alkyl
methacrylates
COOR
CN
Alkyl
Acrylonitrile
acrylates
COOR
Alkyl
cyanoacrylates
29-47
Anionic Chain Growth
 Anionic
polymerization can be initiated by
addition of a nucleophile, such as methyl lithium,
to an alkene.
R'
R'
R
Li +
R'
R
+
Li
+
R'
R
R'
etc.
29-48
Anionic Chain Growth
 An
alternative method for initiation involves a
one-electron reduction of the monomer by Li or
Na to form a radical anion which is either
reduced or dimerized to a dianion.
Li
+
Li
A radical anion
Butadiene
radical coupling
to form a dimer
Li
+
Li
+
Li
Li
A dimer dianion
+
Li
+
+
A dianion
29-49
Anionic Chain Growth
 sodium
naphthalide may be used.
+ Na
THF
N a+
:
Naphthalene
Sodium naphthalide
(a radical anion)
The naphthalide radical anion is a powerful
reducing agent and, for example, reduces
styrene to a radical anion which couples to give a
dianion.
29-50
Anionic Chain Growth
N a+
Styrene
N a+
N a+
N a+
A styryl
radical anion
A distyryl dianion
• The styryl dianion then propagates polymerization at
both ends simultaneously.
29-51
Anionic Chain Growth
 Propagation
of the distyryl dianion.
1. 2n
N a+
N a+ 2 . H O
2
A distyryl dianion
n
n
Polystyrene
29-52
Anionic Chain Growth
 Living
polymer: A polymer chain that continues
to grow without chain-termination steps until
either all of the monomer is consumed or some
external agent is added to terminate the chains.
• after consumption of the monomer under living
anionic conditions, electrophilic agents such as CO2 or
ethylene oxide are added to functionalize the chain
ends.
29-53
Anionic Chain Growth
• Termination by carboxylation.
:
n
Na
+
CO 2
n
COO- Na +
H3 O +
n
COOH
29-54
Anionic Chain Growth
• Termination by ethylene oxide.
n
+
Na
O
n
-
CH2 CH2 O Na
+
H2 O
n
CH2 CH2 OH
29-55
Cationic Chain Growth
 The
two most common methods for initiating
cationic polymerization are:
• Addition of H+. Reaction of a strong proton acid with
the monomer.
• Ionization, as in SN1. Abstraction of a halide from the
organic initiator by a Lewis acid.
 Initiation
by a proton acid requires a strong acid
with a nonnucleophilic anion in order to avoid
completion of the addition to the double bond
• Suitable acids include HF/AsF5 and HF/BF3.
29-56
Cationic Chain Growth
• Initiation by a protic acid.
R
R
R
H+ BF 4 -
H3 C
R
+ BF4 R
R
H3 C
R R RR
n
+ R
BF4 -
R
• Lewis acids used for initiation include BF3, SnCl4,
AlCl3, Al(CH3) 2Cl, and ZnCl2.
29-57
Cationic Chain Growth
• initiation
Cl + SnCl 4
+ SnCl 5 -
2-Chloro-2-phenylpropane
• propagation
+
+
+
2-Methylpropene
n
+
n
+
29-58
Cationic Chain Growth
• chain termination
H2 O
n
+
SnCl 5 -
n
OH
+ H+ SnCl 5 -
29-59
Ring-Opening Metathesis Polymerization
• During early investigations into the polymerization of
cycloalkenes by transition metal catalysts, polymers
that contained the same number of double bonds as
the monomers used to make them were formed.
• for example:
n
TiCl4 ,
LiAl( C7 H1 5 ) 4
1,2-Ad dition polymer
N orborn ene
n
ROMP polymer
• this type of polymerization is known as ring-opening
metathesis polymerization (ROMP).
29-60
Ring-Opening Metathesis Polymerization
• ROMP polymerizations involve the same
metallocyclobutene species as in ring-closing alkene
metathesis reactions.
M CH2
M
A metal
carben e
CH2
con tinued
polymerization
M CH2
M CH2
M CH2
redraw
n
n
ROMP polymer from cyclop entene
29-61
Ring-Opening Metathesis Polymerization
• all steps in ROMP are reversible, and the reaction is
driven in the forward direction by the release of ring
strain that accompanies the opening of the ring.
>
Ring strain
[kJ (kcal)/mol]
125 (29.8)
113 (27)
>>
24.7 (5.9)
5.9 (1.4)
29-62
Ring-Opening Metathesis Polymerization
• ROMP is unique is that all unsaturation present in the
monomer is conserved in the polymer.
• polyacetylene is prepared by the ROMP technique.
metal-n ucleophilic
carben e catalys t
n
Cyclooctatetraene
Polyacetylene
29-63
Ring-Opening Metathesis Polymerization
• poly(phenylene vinylene) is prepared as follows.
OAc
OAc
AcO
OAc
H
H
ROMP
heat
-2 nCH3 COOH
n
n
Poly(ph enylene vin ylen e)
29-64