15
Introduction to
Organic
Chemistry
2 ed
William H. Brown
15-1
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15
Organic
Polymer
Chemistry
Chapter 15
15-2
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Organic Polymer Chem.
 Polymer:
from the Greek, poly + meros, many
parts. Any long-chain molecule synthesized by
linking 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
15-3
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Organic Polymer Chem
 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
15-4
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Notation & Nomenclature
 Show
the structure by placing parens around the
repeat unit
 n = average degree of polymerization
Cl Cl Cl Cl Cl
Poly(vinyl chloride)
(PVC)
is synthesized
is written as
from
Cl
Vinyl chloride
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
Cl
n
15-5
Notation
&
15
Nomenclature
 To name a polymer, prefix poly to the name of
the monomer from which the polymer is derived
• if the name of the monomer is one word, no parens
are necessary
• for more complex monomers or where the name of the
monomer is two words, enclose the name of the
monomer is parens, as for example
poly(vinyl chloride)
poly(ethylene terephthalate)
15-6
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Morphology
 Polymers
tend to crystallize as they precipitate
or are cooled from a melt
 Acting to inhibit crystallization are their very
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
15-7
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Morphology
 High
degrees of crystallinity are found in
polymers with regular, compact structures and
strong intermolecular forces such as hydrogen
bonds
• 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
15-8
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 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 high flexibility and low mechanical strength
• on heating, amorphous polymers are transformed
from a hard glass 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
15-9
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Morphology
 Example:
poly(ethylene terephthalate) (PET) can
be made with % crystalline domains ranging
from 0% to 55%
O
O
O
O
n
Poly(ethylene terephthalate)
(PET)
15-10
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 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
15-11
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 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
15-12
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polyamides

Nylon 66 (from two six-carbon monomers)
O
O
heat
nHOC(CH 2 ) 4 COH + nH2 N(CH 2 ) 6 NH2
Hexanedioic acid
1,6-Hexanediamine
(Adipic acid)
(Hexamethylenediamine)
O
O
C(CH 2 ) 4 CNH(CH 2 ) 6 NH n + 2 nH2 O
Nylon 66
• during fabrication, nylon fibers are cold-drawn to
about 4 times their original length, which increases
crystallinity, tensile strength, and stiffness
15-13
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polyamides
 The
raw material base for the production of
nylon 66 is benzene, which is derived from
cracking and reforming of petroleum
air
catalyst
3 H2
catalyst
Benzene
Cyclohexane
OH
O
+
HNO3
Cyclohexanol Cyclohexanone
O
O
HOC( CH2 ) 4 COH
Hexanedioic acid
(Adipic acid)
15-14
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polyamides
 Adipic
acid is in turn the starting material for the
synthesis of hexamethylenediamine
O
O
+-
-
NH4
OC(CH 2 ) 4 CO NH4
Ammonium hexanedioate
(Ammonium adipate)
O
O
H2 NC(CH 2 ) 4 CNH 2
Hexanediamide
(Adipamide)
+
heat
4 H2
catalyst
H2 N(CH 2 ) 6 NH2
1,6-Hexanediamine
(Hexamethylenediamine)
15-15
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 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
NH
1. partial
hydrolysis
2. heat
Caprolactam
O
NH(CH 2 ) 5 C
n
Nylon 6
• nylon 6 is fabricated into fibers, brush bristles, highimpact moldings, and tire cords
15-16
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polyamides
 Kevlar
O
nHOC
is a polyaromatic amide (an aramid)
O
COH + nH 2 N
1,4-Benzenedicarboxylic
acid
(Terephthalic acid)
O
C
NH2
1,4-Benzenediamine
(p-Phenylenediamine)
O
CNH
Kevlar
NH
n
+
2 nH 2 O
• 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
15-17
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polyesters
 Poly(ethylene
terephthalate) (PET) is fabricated
into Dacron fibers, Mylar films, and plastic
beverage containers
O
nHOC
O
COH
1,4-Benzenedicarboxylic
acid
(Terephthalic acid)
+
nHOCH 2 CH2 OH heat
1,2-Ethanediol
(Ethylene glycol)
O
O
C
COCH2 CH2 O
n
Poly(ethylene terephthalate)
(Dacron, Mylar)
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
+ 2 nH 2 O
15-18
15 Polyesters
• ethylene glycol is synthesized from ethylene
CH2 = CH2
Ethylene
+
O
H , H2 O
CH2 - CH2
HOCH2 CH2 OH
O2
catalyst
Ethylene oxide
Ethylene glycol
• terephthalic acid is synthesized from p-xylene,
which is obtained from petroleum refining
O
H3 C
CH3
p-Xylene
O
O2
HOC
COH
catalyst
Terephthalic acid
15-19
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polycarbonates
O
CH3
Na + - O
O- Na + + Cl
Cl
Phosgene
CH3
Disodium salt of Bisphenol A
O
CH3
O
CH3
Lexan
(a polycarbonate)
O
n
+ 2 Na Cl
15-20
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 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
15-21
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polyurethanes
A
urethane, or cabamate, is an ester of carbamic
acid, H2NCH2CO2H
• they are most commonly prepared by treatment of an
isocyanate with an alcohol
O
RN=C=O
+
An isocyanate
R'OH
RNHCOR'
A carbamate
 Polyurethanes
consist of flexible polyester or
polyether units (blocks) alternating with rigid
urethane units (blocks)
• the rigid urethane blocks are derived from a
diisocyanate
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15-22
15 Polyurethanes
• the more flexible blocks are derived from lowmolecular-weight polyesters or polyethers with -OH
groups at the ends of each polymer chain
CH3
O=C=N
N=C=O + nHO- polymer-OH
Low-molecular-weight
polyester or polyether
2,6-Toluene
diisocyanate
O
O
CH3
CNH
NHCO- polymer-O
n
A polyurethane
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15-23
15 Epoxy resins
 Epoxy
resins are materials prepared by a
polymerization in which one monomer contains
at least two epoxy groups
• within this range, there are a large number of
polymeric materials and epoxy resins are produced in
forms ranging from low viscosity liquids to high
melting solids
• the most widely used epoxide monomer is the
diepoxide prepared by treating 1 mol of bisphenol A
with 2 mol of epichlorihydrin
15-24
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Epoxy Resins
CH 3
O
+ Na + - O
Cl
Epichlorohydrin
O - N a+
CH 3
Disodium salt of bisphenol A
CH 3
O
O
O
O
CH3
A diepoxide
15-25
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Epoxy Resins
CH3
O
O
O
O
H3 C
A diepoxide
N H2
H 2N
A diamine
CH3
OH
O
OH
O
CH3
An epoxy resin
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
H
N
N
H n
15-26
15 Chain-Growth Polymers
 Chain-growth
polymerization: a polymerization
in which monomer units are joined together
without loss of atoms. For example:
nCH2 = CH2
Ethylene
catalyst
CH2 CH2
n
Polyethylene
15-27
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polyethylenes
Monomer
Formula
Polymer Name(s) and
Common Uses
CH 2 =CH 2
polyethylene, Polythene;
break-resistant containers
and packaging materials
CH 2 =CHCH 3
polypropylene, Herculon;
textile and carpet fibers
CH 2 =CHCl
poly(vinyl chloride), PVC;
construction tubing
CH 2 =CCl 2
poly(1,1-dichloroethylene) Saran;
food packaging
15-28
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polyethylenes
CH 2 =CHCN
polyacrylonitrile, Orlon;
acrylics and acrylates
CF 2 =CF 2
polytetrafluoroethylene, Teflon;
nonstick coatings
CH 2 =CHC 6 H5
polystyrene, Styrofoam;
insulating materials
CH 2 =CHCO 2 CH 2 CH 3 poly(ethyl acrylate); latex paints
poly(methyl methacrylate), Lucite,
CH 2 =CCO 2 CH 3
Plexiglas; glass substitutes
CH 3
15-29
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Radical Chain-Growth
 Among
the initiators used for radical chaingrowth polymerization are organic peroxides,
which decompose as shown on mild heating
O
O
O

O
Dibenzoyl
peroxide
2
O
O
A benzoyloxy
radical
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
2
A phenyl
radical
+ 2 CO 2
15-30
15 Polymerization
 Radical:
a molecule or ion containing one or
more unpaired electrons
 Fishhook arrow: a curved and barbed arrow
used to show the repositioning of a single
electron
 To account for the polymerization of alkenes in
the presence of peroxides, chemists propose a
three-step radical chain mechanism
15-31
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polymerization
 Step
1: chain initiation
In
In
In •
+ CH2 = CH2
In •
+
In •
In-CH 2 CH2 •
An alkyl radical
• Chain initiation: a step in a radical chain reaction
characterized by the formation of radicals from
nonradical compounds
15-32
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polymerization
 Step
2: chain propagation
In-CH 2 CH2 • + CH2 = CH2
In-CH 2 CH2 • + ( n- 1 ) CH2 = CH2
In-CH 2 CH2 CH2 CH2 •
In-( CH2 CH2 ) n •
• Chain propagation: a step in a radical chain reaction
characterized by the reaction of a radical and a
molecule to give a new radical
• Chain length, n: the number of times the cycle of
chain propagation steps repeats in a chain reaction
15-33
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polymerization
 Step
3: chain termination
CH2 CH2 • +
•
CH2 CH2
CH2 CH2 -CH 2 CH2
• Chain termination: a step in a radical chain
mechanism that involves destruction of radicals
15-34
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 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 chaintransfer 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
15-35
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 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 a number of butyl branches on the polymer
main chain
• these butyl branches are generated by a “back-biting”
chain transfer reaction in which a 1° radical end group
abstracts a hydrogen from the fourth carbon back
• polymerization then continues from the 2° radical
15-36
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Radical Chain-Growth
H •
A six-membered transition
state leading to
1,5-hydrogen abstraction
•
H
nCH2 = CH2
n
15-37
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Polymerization
 Propylene
and other substituted ethylene
monomers can also be polymerized under a
variety of experimental conditions
• radical polymerization of propylene involves 2° radical
intermediates to give polypropylene, with methyl
groups repeating on every other carbon
CH3
nCH3 CH= CH2 initator
Propene
(Propylene)
CHCH2
n
Polypropylene
15-38
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 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 IVB transition
metal halide such as TiCl4, and an alkylaluminum
compound
CH2 =CH 2
TiCl
4 /Al(CH
Ethylene
MgCl 2
2 CH 3 ) 2 Cl
n
Polyethylene
15-39
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Ziegler-Natta Polymers
• Step 1: formation of a titanium-ethyl bond
MgCl 2 /TiCl
particle
Ti Cl
+
Al(CH
4
2 CH 3 ) 2 Cl
Ti CH2 CH3
+
Al(CH
2 CH 3 )Cl 2
15-40
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Ziegler-Natta Polymers
Step 2: insertion of ethylene into the titanium-carbon
bond
Ti CH2 CH3
+ CH2 =CH 2
Ti CH2 CH2 CH2 CH3
15-41
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 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!
15-42
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15 Recycling Codes
Code
1
PET
Polymer
poly(ethylene
terephthalate)
Common Uses
soft drink bottles, household
chemical bottles, films,
textile fibers
2
high-density
HDPE polyethylene
milk and water jugs,
grocery bags, bottles
3
V
poly(vinyl
chloride), PVC
shampoo bottles, pipes,
shower curtains, vinyl
siding, wire insulation,
floor tiles, credit cards
4
LDPE
low-density
polyethylene
shrink wrap, trash and
grocery bags, sandwich
bags, squeeze bottles
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15-43
15 Recycling Codes
Code
Polymer
Common Uses
5
PP
polypropylene
plastic lids, clothing
fibers, bottle caps, toys,
diaper linings
6
PS
polystyrene
styrofoam cups, egg
cartons, disposable utensils,
packaging materials,
appliances
7
all other
plastics, mixed
plastics
various
15-44
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.
15
Organic
Polymer
Chemistry
End Chapter 15
15-45
Copyright © 2000 by John Wiley & Sons, Inc. All rights reserved.