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

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



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



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



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)


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)


CH2CH CHCH2Br2 CH2CH CHCH2

Br Br

(9.10)

3. Synthesis of “head-to-head poly(vinyl bromide)” by controlled brominaion of 1,4-polybutadiene


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


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


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


highly crosslinkedgraphitelike polymerhighly crosslinkedgraphitelike polymer


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)


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


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


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


(9.32)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


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


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


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


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



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



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.


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


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


(9.49)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.


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


(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


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.


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


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


(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



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



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


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


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)


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

SCHEME 9.3. Random chain scission of polyethylene.

9.6.3 Degradation by Radiation

Documents

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