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William H. Brown
Christopher S. Foote
Brent L. Iverson
Eric Anslyn
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Chapter 29
Organic Polymer Chemistry
William H. Brown • Beloit College
29-1
Organic Polymer Chemistry
 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
Organic Polymer Chemistry
 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
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, multiply each number by the MW, sum
these values, and divide by the total number of
polymer chains.
• weight average MW: Record the weight of each chain
of a particular length, sum these weights, and divide
by the total weight of the sample.
29-5
Morphology
 Polymers
tend to crystallize as they precipitate or
are cooled from a melt.
 Acting to inhibit crystallization are that polymers
are large molecules, often with complicated and
irregular shapes, which prevent efficient packing
into ordered structures.
 As a result, polymers in the solid state tend to be
composed of ordered crystalline domains and
disordered amorphous domains.
29-6
Morphology
 High
degrees of crystallinity are found in
polymers with regular, compact structures and
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.
29-7
Morphology
 Highly
amorphous polymers are sometimes
referred to as glassy polymers.
• Because they lack crystalline domains that scatter
light, amorphous polymers are transparent.
• In addition 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.
29-8
Morphology
• Example: poly(ethylene terephthalate), abbreviated
PET or PETE, can be made with % crystalline domains
ranging from 0% to 55%.
O
O
O
O
n
Poly(ethylene terephthalate)
29-9
Morphology
 Completely
amorphous PET is formed by cooling
the melt quickly.
• PET with a low degree of crystallinity is used for
plastic beverage bottles.
 By
prolonging cooling time, 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.
29-10
Step-Growth Polymers
 Step-growth
polymerization: A polymerization in
which chain growth occurs in a stepwise manner
between difunctional monomers.
 We discuss five types of step-growth polymers:
•
•
•
•
•
polyamides
polyesters
polycarbonates
polyurethanes
epoxy resins
29-11
Polyamides

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
crystallinity, tensile strength, and stiffness.
29-12
Polyamides
• 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)
29-13
Polyamides
• Adipic acid is in turn 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
NH 2
O
Hexanediamide
(Ad ipamide)
4 H2
catalyst
H2 N
NH2
1,6-Hexanediamine
(Hexameth ylen ediamine)
29-14
Polyamides
 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.
29-15
Polyamides
 Kevlar
is a polyaromatic amide (an aramid).
O
nHOC
O
COH +
1,4-Benzenedicarboxylic
acid
(Terephthalic acid)
O
C
nH2 N
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.
29-16
Polyesters
 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)
29-17
Polyesters
• 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
29-18
Polycarbonates
• 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
CH3
Disodium s alt
of Bisphenol A
O- Na + + Cl
Cl
Phosgene
O
CH3
O
CH3
Lexan
(a polycarbonate)
O
+ 2 NaCl
n
29-19
Polycarbonates
 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.
29-20
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
RN = C= O
An isocyanate
+ R' OH
RN HCOR'
A carbamate
 Polyurethanes
consist of flexible polyester or
polyether units alternating with rigid urethane
units.
• The rigid urethane units are derived from a
diisocyanate.
29-21
Polyurethanes
• The more flexible units are derived from low MW
polyesters or polyethers with -OH groups at the ends
of each polymer chain.
CH3
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
CH3
O
NHCO-p olymer-O
n
A p olyurethane
29-22
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.
29-23
Epoxy Resins
• The most widely used epoxide monomer is the
diepoxide prepared by treating one mole of bisphenol
A with two moles of epichlorohydrin.
CH 3
O
Cl
+ Na + - O
O - Na +
CH 3
the disodium salt of
bisphenol A
Epichlorohydrin
CH 3
O
O
O
O
CH 3
A diepoxide
29-24
Epoxy Resins
• Treatment of the diepoxide with a diamine gives the
resin.
CH 3
O
O
O
O
CH 3
A diepoxide
NH 2
H2 N
A diamine
CH3
OH
O
OH
O
CH3
An epoxy resin
H
N
N
H n
29-25
Thermosets
 Bakelite
was one of the first thermosets.
29-26
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.
29-27
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.
29-28
Polyethylenes
Monomer
Formula
Common
Name
Polymer N ame(s) and
Common Us es
CH2 =CH 2
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
29-29
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
29-30
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
29-31
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
29-32
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.
29-33
Radical Chain-Growth
• chain termination.
radical
coupling
In
R
2 In
R
n
n
R R
In
n
R
R
disproportionation In
R
n
+
R
H
In
R
n
R
29-34
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
29-35
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
29-36
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.
29-37
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
29-38
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
29-39
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 blow-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!
29-40
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
Isotactic polymer
(identi cal confi gurations)
R H
H R R H
H R R H
Syndi otactic polymer
(alternating confi gurations)
R H R H R H
R H
H R
Atacti c pol ymer
(random configurati ons)
29-41
Polymer Stereochemistry
 In
general, the more stereoregular the
stereocenters are (the more highly isotactic or
syndiotactic the polymer is), the more crystalline
it is.
• The chains of atactic polypropylene, for example, do
not pack well and the polymer is an amorphous glass.
• Isotactic polypropylene, on the other hand, is a
crystalline, fiber-forming polymer with a high melt
transition.
29-42
Ionic Chain Growth
 May
be either anionic or cationic polymerizations
• Cationic polymerizations are most common with
monomers with electron-donating groups.
OR
Styrene
Isobutylene
SR
Vinyl ethers
Vinyl thioethers
• Anionic polymerizations are most common with
monomers with electron-withdrawing groups.
CN
Styrene
COOR
Alkyl
methacrylates
COOR
Alkyl
acrylates
CN
Acrylonitrile
COOR
Alkyl
cyanoacrylates
29-43
Anionic Chain Growth
 Anionic
polymerization can be initiated by
addition of a nucleophile, such as methyl lithium,
to an activated alkene.
R'
R'
R
Li +
R'
R
+
Li
+
R'
R
R'
etc.
29-44
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
29-45
Anionic Chain Growth
 To
improve the efficiency of anionic
polymerizations, soluble reducing agents such
as sodium naphthalide are 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.
29-46
Anionic Chain Growth
N a+
Styrene
N a+
N a+
N a+
A s tyryl
radical anion
A dis tyryl dianion
• The styryl dianion then propagates polymerization at
both ends simultaneously.
29-47
Anionic Chain Growth
 Propagation
of the distyryl dianion.
1. 2n
N a+
N a+ 2 . H O
2
A distyryl dianion
n
n
Polystyrene
29-48
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.
29-49
Anionic Chain Growth
• Termination by carboxylation.
:
n
Na
+
CO 2
n
COO- Na +
H3 O +
n
COOH
29-50
Anionic Chain Growth
• Termination by ethylene oxide.
n
Na+
O
n
-
CH2 CH2 O Na
+
H2 O
n
CH2 CH2 OH
29-51
Cationic Chain Growth
 The
two most common methods for initiating
cationic polymerization are:
• Reaction of a strong proton acid with the monomer.
• 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
addition to the double bond
• Suitable acids include HF/AsF5 and HF/BF3.
29-52
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.
29-53
Cationic Chain Growth
• initiation
Cl + SnCl 4
+ SnCl 5 -
2-Chloro-2-phenylpropane
• propagation
+
+
+
2-Methylpropene
n
+
n
+
29-54
Cationic Chain Growth
• chain termination
H2 O
n
+
SnCl 5 -
n
OH
+ H+ SnCl 5 -
29-55
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).
29-56
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
29-57
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)
29-58
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
29-59
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)
29-60
Organic
Polymer
Chemistry
End Chapter 29
29-61