9REACTIONS OF
VINYL POLYMERS
CHAPTER
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
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
Applications of chemical
modifications :
The purpose of this chapter :
To summarize and illustrate chemical modifications of vinyl polymers.
Five general categories
9.1 Introduction
(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 reaction 시 고려사항
(1) molecular weight
(2) crystallinity
(3) conformation, steric effect
(4) neighboring group effect
(5) polymer physical form 의 변화
CH3
C CH2CH
C O
O-
C
O
NO2
CH2
O
CH3
C
CO
C
CHC
O O
H2
CH2 +
O-
NO2
OH-
CH2C
CH3
CO2
CH2CH
CO2- -
(9.1)
neighboring group effect
9.1 Introduction
9.2 Functional Group Reactions
9.2.1 Introduction of new Functional Groups
chlorosulfonation
(9.3)
CH2CH2Cl2
(-HCl)CHCH2
Cl
(-HCl)Cl2, SO2CH2CH2 CH2CH
SO2Cl
Chlorination
(9.2)CH2CH2Cl2
(-HCl)CHCH2
Cl
(-HCl)Cl2, SO2CH2CH2 CH2CH
SO2Cl
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
CH2CH2NOCl CCH2
NOHH2OH
+ CCH2
O(9.6)
introducing new functionalities
CH2CHCH3OCH2Cl
AlCl3
CH2CH
CH2Cl
+ CH3OH (9.5)
Chlorometylation
Introduction of ketone groups – via the intermediate oxime
9.2.2 Conversion of Functional Groups
CH2CH
OCCH3
O
CH3OH CH2CH
OH
+ CH3CO2CH3(9.7)
Reason useful
To obtain polymers difficult or impossible to prepare by direct polymerization.
alcoholysis of poly(vinyl acetate)
(unstable enol form of acetaldehyde)
9.2.2 Conversion of Functional Groups
CH2CH
CONH2
Br2, OH-
CH2CH
NH2(9.9)
(9.8)CH2C
CH3
C O
OSi(CH3)3
(1) H2O, OH-
(2) H+
CH2C
CH3
CO2H
Examples
1. Saponification of isotactic or syndiotactic poly(trimethylsily methacrylate) to yield isopactic or syndiotactic poly(methacrylic acid)
2. Hofmann degradation of polyacrylamide to give poly(vinyl amine)
9.2.2 Conversion of Functional Groups
CH2CH CHCH2Br2 CH2CH CHCH2
Br Br
(9.10)
3. Synthesis of “head-to-head poly(vinyl bromide)” by controlled brominaion of 1,4-polybutadiene
9.2.2 Conversion of Functional Groups
CH2CH
Cl
LiCl
N,N-dimethylformamideCH CH
(9.11)
CH2C
CH3
CHCH2
(1) B2H6
(2) NaOH, H2O2
CH2CHCHCH2
OH
CH3
(9.13)
Other types of “classical” functional group conversions
dehydrochlorinaion of poly(vinyl chloride)
hydroformylation of polypentenamer
hydroboration of 1,4-polyisoprene
(9.12)CH CH(CH2)3
CO, H2
catalystCH2CH(CH2)3
CHO
9.2.2 Conversion of Functional Groups
CH2CH
Cl
(CH3)2Al(C5H5)CH2CH + (CH3)2AlCl
(9.14)
Conversion of a fraction of the chloro groups of poly(vinyl chloride) to cyclopentadienyl
Converting the end groups of telechelic polymers.
(9.16)
CH2CCl
CH3
CH3
t-BuO-K
+
CH2C
CH3
CH2
CH2C
CH3
CH2ArCO3H
CH2C
CH3
CH2
O
(9.15)CH2CCl
CH3
CH3
t-BuO-K
+
CH2C
CH3
CH2
CH2C
CH3
CH2ArCO3H
CH2C
CH3
CH2
O
Dehydrochlorination of chlorine-terminated polyisobutylene
Subsequent epoxidation
9.3 Ring-Forming Reactions
Introduction of cyclic units
greater rigidity
higher glass transition temperatures
improved thermal stability – carbon fiber (graphite fiber)
C C CN N N
N N N
N N N
H H H
N N N
H H H
O O
O2(-HCN)
(-N2)
Laddergraphite-type
polymer
SCHEME 9.1. Reactions involved in pyrolysis of polyacrylonitrile to form carbon fiber.
highly crosslinkedgraphitelike polymer
C C CN N N
N N N
N N N
H H H
N N N
H H H
O O
O2(-HCN)
(-N2)
Laddergraphite-type
polymer
SCHEME 9.1. Reactions involved in pyrolysis of polyacrylonitrile to form carbon fiber.
C C CN N N
N N N
N N N
H H H
N N N
H H H
O O
O2(-HCN)
(-N2)
Laddergraphite-type
polymer
C C CN N N
N N N
N N N
H H H
N N N
H H H
O O
O2(-HCN)
(-N2)
Laddergraphite-type
polymer
SCHEME 9.1. Reactions involved in pyrolysis of polyacrylonitrile to form carbon fiber.
highly crosslinkedgraphitelike polymerhighly crosslinkedgraphitelike polymer
9.3 Ring-Forming Reactions
CH2CH CH2CH
C O
CH3
CH2CH
C CO O
CH3 CH3
OH- CH2
OCH3
(9.17)
CH2CHCH2CH
Cl Cl
ZnCH2CH
CH2
CH (9.18)
Ladder structuresLadder structures - Poly(methyl vinyl ketone) by intramolecular aldol condensation
Nonladder structuresNonladder structures - Dechlorination of poly(vinyl chloride)
9.3 Ring-Forming Reactions
CH2CHCH2CH
OH OH
RCHO
H+
CH2
O O
R
(9.19)
Cyclization reaction be made to approach its theoretical limits.
when R = C3H7, commonly called poly(vinyl butyral)
Plasticfilm
CH2C
CH3
CHCH2H2O2
CH3CO2HCH2C
CH3
CHCH2
O
(9.20)
Commercially important cyclization - epoxidation of natural rubber
9.3 Ring-Forming Reactions
H+
H
+
+
etc. (9.21)
Metathesis
catalyst + 2CH2 CH2(9.22)
Rubber and other diene polymers undergo cyclization in the presence of acid
cis-1,4-polyisoprene
Quantitative cyclization of 1,2-polybutadiene - with metathesis catalysts
9.4 Crosskinking
9.4.1 Vulcanization
RO + CH2CH CHCH2 + ROH
CHCH2
CHCH2
+CHCH2
CHCH2
+ RO CHCH CHCH2 + ROHCH2CH CHCH2
CHCH CHCH2
CHCH CHCH2
+CHCH CHCH2
CHCH CHCH2
CHCH CHCH2
CHCH CHCH2
+CHCH CHCH2
CHCH CHCH2
CH2CH CHCH2
CH2CH CHCH2 +CHCH CHCH2
CHCH CHCH2
(9.23)
(9.24)
(9.25)
(9.26)
(9.27)
(9.28)
9.4 Crosskinking
9.4.1 Vulcanization
CH2CH CHCH2 + S S CH2CH CHCH2
S+
+ S-
+-
(9.29)
CH2CH CHCH2
S+
CH2CH CHCH2
+
CH2CH CH2CH2
S
+ CH2CH CHCH2+
CH2CH CH
S
CH2CH CHCH2CH ++
(9.30)
(9.31)
The oldest method of vulcanizationThe oldest method of vulcanization
involving addition to a double bond to form an intermediate sulfonium ion
then abstracts a hydride ion
Termination - by reaction between sulfenyl anions and carbocations
9.4 Crosskinking
9.4.1 Vulcanization
Rate of vulcanizationRate of vulcanization
2
(CH3)2NCSSCN(CH3)2
S S
(CH3)2NCSSCN(CH3)2
S S
tetramethylthiuram disulfide
1
(CH3)2NCS-
S
2Zn2+
(CH3)2NCS-
S
2Zn2+
zinc salts of dithiocarbamic acids
accelerator organosulfur compounds
increase
by the addition of accelerators or organosulfur compounds
9.4.2 Radiation Crosslinking
When vinyl polymers are subjected to radiation
crosslinking and degradation
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
priority of reaction
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
(9.32)CH2CH2Radiation
CHCH2 + H2
CH2CH2 CHCH2 + H2
(neighboring chain)
+ H
CH2CH
R
CHCH
R
+ H CH CH + RH
R R
(9.34)
Mechanism of crosslinkingMechanism of crosslinking
(9.33)
CH2CH2Radiation
CHCH2 + H2
CH2CH2 CHCH2 + H2
(neighboring chain)
+ H
fragmentation reactions
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)
When triplet sensitizers (benzophenone) are added to polymer
(1) incorporating photosensitizers into the polymer, which absorb light energy and thereby induce formation of free radicals
O O
Benzophenone
UV 흡수n ( 들뜬상태 ) radical 생성
(9.35)
(9.36)
CH2CHCH2CH
C CO
R
O
R
hv
CH2CHCH2CH
C O
R
+ RC
O
CH2CH2
C O
R
+ CH2C
C O
R
-cleavage of the excited
chain cleavage
9.4.3 Photochemical Crosslinking (Photocrosslinking)
CH2CH
C O
OR
hvCH2CH
+ C OR
O (9.37)
Poly(vinyl ester) : -cleavage reaction
(2) incorporating groups that undergo either photocycloaddition reactions or light-initiated polymerization
2 + 2 cycloaddition cyclobutane crosslinks
SCHEME 9.2. Photocrosslinking (a) by 2 + 2 cycloaddition and (b) by 4 + 4 cycloaddition.
OC
O
CH CHAr
+
ArCH CH CO
O
hv
OC
O
CO
O
Ar
Ar
(a)
(b)+ hv
9.4.3 Photochemical Crosslinking
TABLE 9.1. Group Used to Effect Photocrosslinking21-58
Type Structure
R C C R
continued
S
OO
ArCH CHCAr
O
ArCH CHCO2R
R
ORcontinued
Alkyne
Anthracene
Benzothiophene dioxide
Chalcone
Cinnamate
Coumarin
N
R
CO2-
S
H2C CH2
N R'
O
O
R
R
TABLE 9.1. (continued)
Type Structure
Dibenz[b, f]azepine
Episulfide
Maleimide (R=H, CH3, Cl)
Diphenylcyclopropenecarboxylate
continued
NR CH CHR
Y-
+
ArCH CHAr
CH CH2
N
S
N
R
R
NH
N
O
O
H
CH3
TABLE 9.1.
Type Structure
Stilbazole
Stilbene
Styrene
1,2,3-Thiadiazole
Thymine
9.4.3 Photochemical Crosslinking
3 (9.38)
CH2CH + N
O
O
CH2ClSnCl4 CH2CH
CH2N
O
O
4
(9.39)
Photo – reactive groups 의 도입 방법
① 중합 반응 동안에 고분자에 도입
② 미리 형성된 고분자에 반응기를 첨가
CH2 CH
OCH2CH2OCCH CH
O
BF3 etherate
toluene
CH2CH
OCH2CH2OCCH CH
9.4.4 Crosslinking Through Labile Functional Groups
(9.40)
(9.41)
CH SO2Cl
CH2
2
H2N Ar NH2
HO R OH
CH
CH2
SO2NH Ar NHSO2CH
CH2
CH
CH2
SO2OROSO2 CH
H2C
Reaction between appropriate difunctional or polyfuntional reagents with labile groups on the polymer chains - Crosslinking
(9.42)
2CH
CH2+ Cl R Cl
SnCl4
CH
CH2
R CH
H2C
(Friedel-Crafts reaction)
9.4.4 Crosslinking Through Labile Functional Groups
+(9.43)
Cyclopentadiene-substituted polymer 의 Diels-Alder reaction
Thermoplastic Elastomers ( 열에 의해 재 가공이 가능 )
9.4.5 Ionic Crosslinking
The hydrolysis of chlorosulfonated polyethylene with aqueous lead oxide
(9.44)
5
CH2CH
SO2Cl
PbO, H2OCH2CH
SO2-Pb2+-O2S
CHCH2
CH2CH2 CH2C
CH3
CO2H
poly[ethylene-co-(methacrylic acid)]
상품명 : ionomer
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
CHCH2OH + OCN
Ph
CHCH2
Ph
OCNH
O
(9.45)
(9.46)
CHCH2OC
CH3
CH3R
CH
CH3
CH3
O2CHCH2OC
CH3
CH3R
C
CH3
CH3
OOH
1. Polymer containing functional end groups 사용
2. Peroxide groups introduced to polymer chain ends 사용
개시제의 역할
9.5 Block and Graft Copolymer Formation
9.5.1 Block Copolymers
2xCH2 CH
X
+ O2initiator
CH2CH O O CH2CH
XX x x(9.47)
CH2CH O O CH2CH
XX x x
+ 2yCH2 CHY
2 CH2CH O O CH2CH
XX x y
(9.48)
3. Peroxide units 사용
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) 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.
(1) Chain transfer
9.5.2 Graft Copolymers
3) Consideration
4) Grafting sites
At carbons adjacent todouble bonds in polydienes
At carbons adjacent to carbonyl groups
① reactivity ratios of monomers
② To take into account the frequency of transfer
determine the number of grafts.
: That are susceptible to transfer reactions
9.5.2 Graft Copolymers
(9.49)CH2CH
OCCH3
O
CH2 CH2
peroxide
CH2CH CH2C
OCCH2(CH2CH2)x
(CH2CH2)y
OCCH3
O
.
.
At carbons adjacent to carbonyl groups
EX
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
CH2CH+BF3OH-
Ph +
CH2CH
OCH3
CH2CH
OCH3
HCH2C
Ph
(9.50)
6) Cationic chain transfer grafting
Styrene is polymerized with BF3 in the presence of poly(p-methoxystyrene)
Friedel-Crafts attack
9.5.2 Graft Copolymers
(2) Grafting by activation by backbone functional groups
CH2CH
Cl
Na-naphthalene
tetrahydrofuran
CH2CH CH2CH
CH2CH
CN
Na
CH2 CHCN
(9.51)
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 G Polymer G
Butadiene
Styrene
Ethylene
Acrylonitrile
Methyl methacrylate
Methyl acrylate
Vinyl acetate
Vinyl chloride
Very low
0.70
4.0
5.0-5.6
5.5-11.5
6.3
9.6-12.0
10.0
Polybutadiene
Polystyrene
Polyethylene
-
Poly(methyl methacrylate)
Poly(methyl acrylate)
Poly(vinyl acetate)
Poly(vinyl chloride)
2.0
1.5-3
6-8
-
6-12
6-12
6-12
10-15
aData 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
(9.52)
O
N
+ HO2C CNHCH2CH2OC
OO
Grafting of an oxazoline-substituted polymer with a carboxyl-terminated polymer
9.6 Polymer Degradation
9.6.1 Chemical Degradation
Limit to oxidation ( with oxygen)
Breakdown of the polymer backbone
No involving pendant groups.
No functional groups other than
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
CH2CHCH2CCH2CH
R R R
OOH
CH2CHCH2
R
+ CCH2CH
O
+ OH
RR
(9.53)
Decomposition of initially formed hydroperoxide groups
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
(9.54)
CH2CH
OCCH3
O
CH CH + HOCCH3
O
elimination of acid from poly(vinyl esters)
(1) nonchain scission
① refers to reactions involving pendant groups
(9.55)CH2CH
CO
OCH2CH2R
CH2CH
CO
OH
+ CH2 CHR
elimination of alkene from poly(alkyl acrylate)s
CH2CH
OCCH3
O
CH CH + HOCCH3
O
9.6.2 Thermal Degradation
② Use – approach to solving the problems of polyacetylene’s intractability
7
8
CF3
CF3 WCl6
Sn(CH3)4
CF3
CF3
(9.56)
+
CF3
CF3
8(9.57)
tricyclic monomer
precursor polymerThermal degradation
coherent films of polyacetylene
Durhamroute
Disadvantage of the Durham route : That a relatively large molecule needs to be eliminated.
CH CH CHHg2+
CH CH CH CH CH (9.58)
Yield polyacetylene without the necessity of an elimination reaction
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
Initiation Chain end Poly(methyl methacrylate)
Random site along the backbone
Poly(-methylstyrene)
(3) Depropagation
CH2CCH2C
R
R
R
R
CH2C
R
R
+ CH2 C
R
R(9.60)
In both case
9.6.3 Degradation by Radiation
Radiation crosslinking or degradation
All vinyl polymers – tend to degrade – under very high dosages of radiation.
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