9
CHAPTER
REACTIONS OF
VINYL POLYMERS
9.1 Introduction
9.2 Functional
9.3 Ring-forming reactions
9.4 Crosslinking
9.5 Block and graft copolymer formation
9.6 Polymer degradation
9.1 Introduction
Applications of chemical modifications :
Ion-exchange resins
Polymeric reagents and polymer-bound catalysts
Polymeric supports for chemical reactions
Degradable polymers to address medical, agricultural,
or environmental concerns
Flame-retardant polymers
Surface, treatments to improve such properties
as biocompatibility or adhesion, to name a few
The purpose of this chapter :
To summarize and illustrate chemical modifications of vinyl polymers.
9.1 Introduction
Five general categories
(1) reactions that involve the introduction or modification of functional groups
(2) reactions that introduce cyclic units into the polymer backbone
(3) reactions leading to block and graft copolymers
(4) crosslinking reactions
(5) degradation reactions
Polymer reaction시 고려사항
(1) molecular weight
(2) crystallinity
(3) conformation, steric effect
(4) neighboring group effect
(5) polymer physical form의 변화
9.1 Introduction
neighboring group effect
CH3
CH2C
CH2CH
C O
C O
O
O-
O
CH3
H2
C
CH
CH2C
C
O
O
-
-
OH
+
C
O
NO2
CH3
CH2C
NO2
CO2-
CH2CH
CO2-
(9.1)
9.2 Functional Group Reactions
9.2.1 Introduction of new Functional Groups
Chlorination
CH2CH2
Cl2
(-HCl)
CHCH2
(9.2)
Cl
Cl2, SO2
(-HCl)
Cl2
chlorosulfonation
CH2CH2
(-HCl)
CH2CH2
CH2CH
SO Cl
CHCH22
Cl
CH2CH2
Cl2, SO2
(-HCl)
CH2CH
SO2Cl
(9.3)
9.2 Functional Group Reactions
9.2.1 Introduction of new Functional Groups
Properties of polyethylene by chlorination
① Flammability – decrease
② Solubility – depending on the level of substitution
③ Crystalline – more (under heterogeneous conditions)
④ poly(vinyl chloride) – Tg increase
Chlorosulfonation
– provides sites for subsequent crosslinking reactions
9.2 Functional Group Reactions
9.2.1 Introduction of new Functional Groups
Fluorination
CH2CH
C6H5
F2
(-HF)
CF2CF
C6F11
(9.4)
Teflon
- to improve solvent barrier properties.
Aromatic substitution reactions
(nitration, sulfonation, chlorosulfonation, etc.)
occur readily on polystyrene
useful for manufacturing ion-exchange resins
useful for introducing sites for crosslinking or grafting
9.2 Functional Group Reactions
9.2.1 Introduction of new Functional Groups
introducing new functionalities
Chlorometylation
CH2CH
CH2CH
CH3OCH2Cl
AlCl3
+ CH3OH
(9.5)
CH2Cl
Introduction of ketone groups – via the intermediate oxime
NOH
CH2CH2
NOCl
CCH2
O
H2O
+
H
CCH2
(9.6)
9.2.2 Conversion of Functional Groups
Reason useful
To obtain polymers difficult or impossible to prepare
by direct polymerization.
alcoholysis of poly(vinyl acetate)
CH2CH
OCCH3
CH3OH
CH2CH
OH
+ CH3CO2CH3
(9.7)
O
(unstable enol form of acetaldehyde)
9.2.2 Conversion of Functional Groups
Examples
1. Saponification of isotactic or syndiotactic poly(trimethylsily methacrylate)
to yield isopactic or syndiotactic poly(methacrylic acid)
CH3
CH2C
C
CH3
-
(1) H2O, OH
CH2C
+
O
(2) H
(9.8)
CO2H
OSi(CH3)3
2. Hofmann degradation of polyacrylamide to give poly(vinyl amine)
-
CH2CH
CONH2
Br2, OH
CH2CH
NH2
(9.9)
9.2.2 Conversion of Functional Groups
3. Synthesis of “head-to-head poly(vinyl bromide)”
by controlled brominaion of 1,4-polybutadiene
CH2CH CHCH2
Br2
CH2CH CHCH2
Br
Br
(9.10)
9.2.2 Conversion of Functional Groups
Other types of “classical” functional group conversions
dehydrochlorinaion of poly(vinyl chloride)
LiCl
CH2CH
CH
CH
N,N-dimethylformamide
(9.11)
Cl
hydroformylation of polypentenamer
CH
CO, H 2
CH(CH2)3
catalyst
CH2CH(CH2)3
(9.12)
CHO
hydroboration of 1,4-polyisoprene
CH3
CH3
(1) B2H6
CH2C
CHCH2
(2) NaOH, H2O2
CH2CHCHCH2
OH
(9.13)
9.2.2 Conversion of Functional Groups
Conversion of a fraction of the chloro groups of poly(vinyl chloride) to cyclopentadienyl
(CH3)2Al(C5H5)
CH2CH
CH2CH
+ (CH3)2AlCl
(9.14)
Cl
Converting the end groups of telechelic polymers.
Dehydrochlorination of chlorine-terminated polyisobutylene
CH3
CH2CCl
- +
t-BuO K
CH3
CH
3
- +
t-BuO K
3
CH2CH
CCl
Subsequent epoxidation ArCO3H
CH2CCH3CH2
CH3
CH2C CH2
ArCO3H
CH3
CH2C CH2
(9.15)
CH3
32
CH2C CH
CH
CH2C CH2
O
CH3
CH2C CH2
O
(9.16)
9.3 Ring-Forming Reactions
Introduction of cyclic units
greater rigidity
higher glass transition temperatures
improved thermal stability – carbon fiber (graphite fiber)

C
C
N
C
N
N
N
N

Ladder
graphite-type
polymer
O
O
O2
(-HCN)
(-N2)
N
N
N
N
N
N
N
H
H
H
H
H
H
SCHEME 9.1. Reactions involved in pyrolysis of polyacrylonitrile to form carbon fiber.
highly crosslinked
graphitelike polymer
9.3 Ring-Forming Reactions
Ladder structures
- Poly(methyl vinyl ketone) by intramolecular aldol condensation
-
OH
CH2CH CH2CH CH2CH
C O
C O
C O
CH3
CH3
CH3
CH2
(9.17)
CH3
O
Nonladder structures
- Dechlorination of poly(vinyl chloride)
CH2CHCH2CH
Cl
Cl
Zn
CH2
CH2CH CH
(9.18)
9.3 Ring-Forming Reactions
Cyclization reaction be made to approach its theoretical limits.
CH2CHCH2CH
OH
RCHO
CH2
+
H
OH
O
O
(9.19)
R
when R = C3H7, commonly called poly(vinyl butyral)
Plastic
film
Commercially important cyclization
- epoxidation of natural rubber
CH3
CH3
CH2C CHCH2
H2O2
CH3CO2H
CH2C CHCH2
O
(9.20)
9.3 Ring-Forming Reactions
Rubber and other diene polymers undergo cyclization in the presence of acid
cis-1,4-polyisoprene
+
H
+
etc.
H
(9.21)
+
Quantitative cyclization of 1,2-polybutadiene
- with metathesis catalysts
Metathesis
catalyst
+ 2CH2
CH2
(9.22)
9.4 Crosskinking
9.4.1 Vulcanization
RO
+
CHCH2
+
CHCH2
CH2CH
CHCH2
(9.24)
CHCH2
CHCH
CHCH2
CHCH2
CHCH
CHCH2
CHCH
CHCH2
CHCH
CHCH2
CHCH
+
CHCH2
CHCH
CHCH2
CHCH
CHCH2
CHCH
CHCH2
CHCH2
CHCH
+
+ RO
CH2CH
CH2CH
CHCH2
(9.23)
+ ROH
CHCH2
CH2CH
+ ROH
(9.25)
(9.26)
(9.27)
CHCH2
CHCH
CHCH2
CHCH
CHCH2
+
(9.28)
9.4 Crosskinking
9.4.1 Vulcanization
The oldest method of vulcanization
involving addition to a double bond to form an intermediate sulfonium ion
CH2CH
CHCH2
+
+ S S
CH2CH
CHCH2
+
S
(9.29)
S-
+
then abstracts a hydride ion
CH2CH
CHCH2
+
S
CH2CH
CH2CH2
+
S
CH2CH
+
CHCH2
(9.30)
+
CH2CH
CHCH2
+
CH2CH
CH
CH
+
CH2CH
S
Termination
- by reaction between sulfenyl anions and carbocations
CHCH2
(9.31)
9.4 Crosskinking
9.4.1 Vulcanization
Rate of vulcanization
increase
by the addition of accelerators or organosulfur compounds
accelerator
S
S
2+
(CH3)2NCS-- 2Zn2+
(CH3)2NCS 2Zn
1
zinc salts of dithiocarbamic acids
organosulfur compounds
S
S
S
S
(CH3)2NCSSCN(CH3)2
(CH3)2NCSSCN(CH3)2
2
tetramethylthiuram disulfide
9.4.2 Radiation Crosslinking
When vinyl polymers are subjected to radiation
crosslinking and degradation
priority of reaction
Generally, both occur simultaneously
Degradation predominates with high doses of radiation
With low doses the polymer structure determines which will be the major reaction.
Disubstituted polymers tend to undergo chain scission
With monomer being a major degradation product
9.4.2 Radiation Crosslinking
poly(-methylstyrene), poly(methyl methacrylate), polyisobutylene
- decrease in molecular weight on exposure to radiation
halogen-substituted polymers ~poly(vinyl chloride)
- break down with loss of halogen
most other vinyl polymers
- crosslinking predominates
A limitation of radiation crosslinking
that radiation does not penetrate very far into the polymer matrix
The method is primarily used with films
9.4.2 Radiation Crosslinking
Mechanism of crosslinking
Radiation
CH2CH2
CH2CH2
(neighboring chain)
+ H
CH2CH2
CH2CH2
+ H2
CHCH2
Radiation
+ H
(9.32)
+ H2
CHCH2
+ H2
CHCH2
CHCH2
+ H2 (9.33)
(neighboring chain)
fragmentation reactions
CH2CH
R
CHCH
R
R
+ H
CH
CH
+ RH
(9.34)
9.4.3 Photochemical Crosslinking (Photocrosslinking)
Applications
electronic equipment
printing inks
coatings for optical fibers
varnishes for paper and carton board
finishes for vinyl flooring, wood, paper, and metal
curing of dental materials
Two basic methods
(1) incorporating photosensitizers into the polymer,
which absorb light energy and thereby induce formation of free radicals
(2) incorporating groups that undergo either photocycloaddition reactions
or light-initiated polymerization
9.4.3 Photochemical Crosslinking (Photocrosslinking)
(1) incorporating photosensitizers into the polymer,
which absorb light energy and thereby induce formation of free radicals
When triplet sensitizers (benzophenone) are added to polymer
O
 (들뜬상태)
n
O
UV흡수
radical 생성
Benzophenone
CH2CHCH2CH
CH2CHCH2CH
C O C O
R
R
C O
hv
O
(9.35) -cleavage of the excited
+ RC
R
CH2CH2 +
CH2
C
C O
C
R
R
O
(9.36)
chain cleavage
9.4.3 Photochemical Crosslinking (Photocrosslinking)
Poly(vinyl ester) : -cleavage reaction
CH2CH
C O
hv
CH2CH
OR
(9.37)
O
+
C
OR
(2) incorporating groups that undergo either photocycloaddition reactions
or light-initiated polymerization
2 + 2 cycloaddition
cyclobutane crosslinks
9.4.3 Photochemical Crosslinking
O
(a)
O
OC CH
CHAr
OC
+
ArCH
Ar
hv
CH CO
Ar
O
CO
O
(b)
+
hv
SCHEME 9.2. Photocrosslinking (a) by 2 + 2 cycloaddition and (b) by 4 + 4 cycloaddition.
TABLE 9.1. Group Used to Effect Photocrosslinking21-58
Type
Structure
Alkyne
R
C
C
R
Anthracene
continued
Benzothiophene dioxide
S
O
O
O
Chalcone
ArCH
CHCAr
Cinnamate
ArCH
CHCO2R
R
Coumarin
R
O
continued
TABLE 9.1. (continued)
Type
Structure
R
N
Dibenz[b, f]azepine


Diphenylcyclopropenecarboxylate
CO2S
Episulfide
H 2C
CH2
O
R
N
Maleimide (R=H, CH3, Cl)
R'
R
O
continued
TABLE 9.1.
Type
Structure
+
Stilbazole
R N
CH CHR
Y-
Stilbene
ArCH CHAr
CH CH2
Styrene
R
N
1,2,3-Thiadiazole
R
N
S
O
CH3
NH
Thymine
O
N
H
9.4.3 Photochemical Crosslinking
Photo – reactive groups 의 도입 방법
① 중합 반응 동안에 고분자에 도입
CH2
CH
O
OCH2CH2OCCH
BF3 etherate
CH
toluene
3
(9.38)
CH2CH
OCH2CH2OCCH
CH
② 미리 형성된 고분자에 반응기를 첨가
O
CH2CH
+
N
CH2Cl
SnCl4
CH2CH
O
O
4
CH2N
O
(9.39)
9.4.4 Crosslinking Through Labile Functional Groups
Reaction between appropriate difunctional or polyfuntional reagents
with labile groups on the polymer chains - Crosslinking
H2N
Ar NH 2
CH
SO2NH
Ar
NHSO 2CH
CH2
CH
2
CH2
(9.40)
SO2Cl
CH2
CH
HO
R
OH
SO2OROSO2 CH
CH2
H2C
(Friedel-Crafts reaction)
CH
2
CH2
(9.41)
+ Cl
R
Cl
SnCl 4
(9.42)
CH
CH2
R
CH
H 2C
9.4.4 Crosslinking Through Labile Functional Groups
Cyclopentadiene-substituted polymer의 Diels-Alder reaction
(9.43)
+

Thermoplastic Elastomers ( 열에 의해 재 가공이 가능)
9.4.5 Ionic Crosslinking
The hydrolysis of chlorosulfonated polyethylene with aqueous lead oxide
CH2CH
PbO, H2O
CH2CH
CHCH2
SO2-Pb2+-O2S
SO2Cl
CH3
CH2CH2
5
CH2C
CO2H
poly[ethylene-co-(methacrylic acid)]
상품명 :
ionomer
(9.44)
9.4.5 Ionic Crosslinking
Properties of Ionomers
① Introduction of ions causes disordering of the semicrystalline structure,
which makes the polymer transparent.
② Crosslinking gives the polymer elastomeric properties,
but it can still be molded at elevated temperatures.
③ Polarity
, adhesion
9.4.5 Ionic Crosslinking
Application of Ionomers
coatings
adhesive layers for bonding wood to metal
blow-molded and injection-molded containers
golf ball covers
blister packaging material
binder for aluminosilicate dental fillings
9.5 Block and Graft Copolymer Formation
9.5.1 Block Copolymers
1. Polymer containing functional end groups 사용
O
CHCH2OH + OCN
CHCH2
Ph
Ph
(9.45)
OCNH
2. Peroxide groups introduced to polymer chain ends 사용
CH3
CH3
O2
CHCH2OC
R
CH3
CH3
CH
CH3
CHCH2OC
R
(9.46)
CH3
CH3
C
OOH
CH3
개시제의 역할
9.5 Block and Graft Copolymer Formation
9.5.1 Block Copolymers
3. Peroxide units 사용
2xCH2 CH + O2
initiator
CH2CH
X
X
CH2CH
X
O
x
O
O
CH2CH
X
x
(9.47)
x
CHY
+ 2yCH2
CH2CH
X
O
x
(9.48)
2
CH2CH
X
O
x
O
CH2CH
X
y
9.5 Block and Graft Copolymer Formation
9.5.1 Block Copolymers
4. Another way to form chain-end radicals
- mechanical degradation of homopolymers
(using ultrasonic radiation or high-speed stirring)
EX) Polyethylene-block-polystyrene
9.5.2 Graft Copolymers
A. Three general methods of preparing graft copolymers
(1) A monomer is polymerized in the presence of a polymer with branching
resulting from chain transfer.
(2) A monomer is polymerized in the presence of a polymer having reactive
functional groups or positions that are capable of being activated
(3) Two polymers having reactive functional groups are coreacted.
9.5.2 Graft Copolymers
(1) Chain transfer
1) Three components
polymer, monomer, and initiator
2) The initiator may play one of two roles
① It polymerizes the monomer to form a polymeric radical
(or ion or coordination complex), which, in reacts with the original polymer
② it reacts with the polymer to form a reactive site on the backbone which,
in turn, polymerizes the monomer.
9.5.2 Graft Copolymers
3) Consideration
① reactivity ratios of monomers
② To take into account the frequency of transfer
determine the number of grafts.
4) Grafting sites
: That are susceptible to transfer reactions
At carbons adjacent to
double bonds in polydienes
At carbons adjacent to
carbonyl groups
9.5.2 Graft Copolymers
At carbons adjacent to
carbonyl groups
EX
.
(CH2CH2)y
CH2CH
CH2CH
OCCH3
CH 2
CH 2
CH2C
OCCH2(CH2CH2).x
(9.49)
OCCH3
peroxide
O
O
Mixture of poly(vinyl alcohol)-graft-polyethylene and long-chain carboxylic acids
5) Grafting efficiency improvement
Group that undergoes radical transfer readily
(mercaptan is incorporated into the polymer backbone.
9.5.2 Graft Copolymers
6) Cationic chain transfer grafting
CH2CH+BF3OHPh
CH2CH
CH2CH
+
(9.50)
HCH2C
Friedel-Crafts attack
OCH3
Ph
OCH3
Styrene is polymerized with BF3 in the presence of poly(p-methoxystyrene)
9.5.2 Graft Copolymers
(2) Grafting by activation by backbone functional groups
CH2CH
CH2CH
CH2CH
CH 2
Na-naphthalene
CHCN
(9.51)
tetrahydrofuran
Cl
Na
CH2CH
CN
Synthesis of poly(p-chlorostyrene)-graft-polyacrylonitrile
9.5.2 Graft Copolymers
Irradiation – provide active sites
with ultraviolet or visible radiation
with or without added photosensitizer
with ionizing radiation
Major difficulty
substantial amounts of homopolymerization
= grafting
settlement
This has been obviated to some extent by preirradiating the polymer
prior to addition of the new monomer.
9.5.2 Graft Copolymers
Direct irradiation of monomer and polymer together
Best combination
Polymer – very sensitive to radiation
Monomer – not very sensitive
( Sensitivity measurement – G values)
TAB.9.2.
Irradiation grafting of polymer emulsions - effective way to minimize
9.5.2 Graft Copolymers
TABLE 9.2. Appoximate G Values of Monomers and Polymersa
Monomer
Butadiene
G
Very low
Polymer
Polybutadiene
G
2.0
Styrene
0.70
Polystyrene
1.5-3
Ethylene
4.0
Polyethylene
6-8
Acrylonitrile
5.0-5.6
-
Methyl methacrylate
5.5-11.5
Poly(methyl methacrylate)
6-12
Methyl acrylate
6.3
Poly(methyl acrylate)
6-12
Vinyl acetate
9.6-12.0
Poly(vinyl acetate)
6-12
Poly(vinyl chloride)
10-15
Vinyl chloride
aData
10.0
-
from Chapiro.72 G values refer to number of free radicals formed per 100 eV of energy absorbed per gram of material.
Good Combination
Poly(vinyl chloride) and butadiene
9.5.2 Graft Copolymers
(3) Using two polymers
O
N
+ HO2C
O
CNHCH2CH2OC
(9.52)
O
Grafting of an oxazoline-substituted polymer with a carboxyl-terminated polymer
9.6 Polymer Degradation
9.6.1 Chemical Degradation
Breakdown of the polymer backbone
No involving pendant groups.
No functional groups other than
Limit to oxidation ( with oxygen)
9.6 Polymer Degradation
9.6.1 Chemical Degradation
Saturated polymers
Very slowly by oxygen
Autocatalytic
Speed up – heat or light or by presence of certain impurities
Reaction Product – numerous and include water, carbon dioxide,
carbon monoxide, hydrogen, and alcohols
Tertiary carbon atoms – most susceptible to attack
(polyisobutylene>polyethylene>polypropylene)
Crosslinking – always degradation
Decomposition of initially formed hydroperoxide groups
- mainly responsible for chain scission
OOH
O
CH2CHCH2CCH2CH
R
R
R
CH2CHCH2 + CCH2CH
R
R
+
OH
R
Decomposition of initially formed hydroperoxide groups
(9.53)
9.6 Polymer Degradation
9.6.1 Chemical Degradation
Unsaturated polymers
Much more rapidly (by complex free radical )
Allylic carbon atoms – most sensitive to attack
(resonance-stabilized radicals)
very susceptible to attack by ozone
9.6.2 Thermal Degradation
Three types of thermal degradation
(1) nonchain scission
(2) random chain scission
(3) depropagation
(1) nonchain scission
① refers to reactions involving pendant groups
CH
CH2CH
2CH
CH
OCCH
+ HOCCH
OCCH333
CH

CH
CH
CH
OO
O
HOCCH3
++ HOCCH
3
O
O
(9.54)
elimination of acid from poly(vinyl esters)
CH2CH
O
C
OCH2CH2R
CH2CH
O
+ CH2
CHR
C
OH
elimination of alkene from poly(alkyl acrylate)s
(9.55)
9.6.2 Thermal Degradation
② Use – approach to solving the problems of polyacetylene’s intractability
CF3
CF3
CF3
WCl6
CF3
(9.56)
Sn(CH3)4
7 tricyclic monomer
8 precursor polymer
Thermal degradation
8
Durham
route

CF3
+
(9.57)
CF3
coherent films of polyacetylene
Disadvantage of the Durham route
: That a relatively large molecule needs to be eliminated.
Yield polyacetylene without the necessity of an elimination reaction
CH
CH
Hg2+
CH
CH
CH
CH
CH
CH
(9.58)
9.6.2 Thermal Degradation
③ Useful of Nonchain scission reactions
: Characterizing copolymers
(when the amount of a volatile degradation product can be correlated
with the concentration of a given repeating unit)
(2) Random chain scission
: Result from homolytic bond-cleavage reactions
at weak points in the polymer chains
CH2CH2CH2CH2
CH2CH2 +
CH2CH2
CH
CH2 + CH3CH2
(9.59)
9.6.2 Thermal Degradation
(3) Depropagation
Initiation
Chain end Poly(methyl methacrylate)
Random site along the backbone
Poly(-methylstyrene)
In both case
R
R
R
CH2CCH2C
CH2C
R
R
R
R
+ CH2 C
R
(9.60)
9.6.3 Degradation by Radiation
Radiation
crosslinking or degradation
Ultraviolet or visible light
Elevated temperatures - 1,1-disubstituted polymers to degrade to monomer
Room temperature – crosslinking and chain scission reactions
Ionizing radiation
much higher yields of monomer from 1,1-disubstituted polymers
at room temperature.
At comparable levels of radiation
polyethylene and monosubstituted polymers – mainly crosslinking
All vinyl polymers – tend to degrade – under very high dosages of radiation.
9.6.3 Degradation by Radiation

SCHEME 9.3. Random chain scission of polyethylene.