9.1 Introduction
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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

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9.1 Introduction

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9 1 introduction

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

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

9.1 Introduction

  • Five general categories

  • reactions that involve the introduction or modification of functional groups

  • reactions that introduce cyclic units into the polymer backbone

  • reactions leading to block and graft copolymers

  • crosslinking reactions

  • degradation reactions

  • Polymer reaction시 고려사항

  • molecular weight

  • crystallinity

  • conformation, steric effect

  • neighboring group effect

  • polymer physical form의 변화


9 1 introduction

  • neighboring group effect

(9.1)

9.1 Introduction


9 1 introduction

(9.2)

(9.3)

9.2 Functional Group Reactions

9.2.1 Introduction of new Functional Groups

  • Chlorination

  • chlorosulfonation


9 1 introduction

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 1 introduction

(9.4)

Teflon

9.2 Functional Group Reactions

9.2.1 Introduction of new Functional Groups

  • Fluorination

- 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 1 introduction

9.2 Functional Group Reactions

9.2.1 Introduction of new Functional Groups

  • introducing new functionalities

  • Chlorometylation

(9.5)

  • Introduction of ketone groups – via the intermediate oxime

(9.6)


9 1 introduction

  • Reason useful

To obtain polymers difficult or impossible to prepare

by direct polymerization.

(9.7)

  • alcoholysis of poly(vinyl acetate)

(unstable enol form of acetaldehyde)

9.2.2 Conversion of Functional Groups


9 1 introduction

  • Examples

  • Saponification of isotactic or syndiotactic poly(trimethylsily methacrylate)

  • to yield isopactic or syndiotactic poly(methacrylic acid)

(9.8)

(9.9)

2. Hofmann degradation of polyacrylamide to give poly(vinyl amine)

9.2.2 Conversion of Functional Groups


9 1 introduction

  • Synthesis of “head-to-head poly(vinyl bromide)”

  • by controlled brominaion of 1,4-polybutadiene

(9.10)

9.2.2 Conversion of Functional Groups


9 1 introduction

  • Other types of “classical” functional group conversions

  • dehydrochlorinaion of poly(vinyl chloride)

(9.11)

  • hydroformylation of polypentenamer

(9.12)

  • hydroboration of 1,4-polyisoprene

(9.13)

9.2.2 Conversion of Functional Groups


9 1 introduction

  • Conversion of a fraction of the chloro groups of poly(vinyl chloride) to cyclopentadienyl

(9.14)

  • Converting the end groups of telechelic polymers.

  • Dehydrochlorination of chlorine-terminated polyisobutylene

(9.15)

(9.16)

  • Subsequent epoxidation

9.2.2 Conversion of Functional Groups


9 1 introduction

  • Introduction of cyclic units

  • greater rigidity

  • higher glass transition temperatures

  • improved thermal stability – carbon fiber (graphite fiber)

9.3 Ring-Forming Reactions


9 1 introduction

  • Ladder structures

  • - Poly(methyl vinyl ketone) by intramolecular aldol condensation

(9.17)

(9.18)

  • Nonladder structures

  • - Dechlorination of poly(vinyl chloride)

9.3 Ring-Forming Reactions


9 1 introduction

  • Cyclization reaction be made to approach its theoretical limits.

(9.19)

when R = C3H7, commonly called poly(vinyl butyral)

Plastic

film

  • Commercially important cyclization

  • - epoxidation of natural rubber

(9.20)

9.3 Ring-Forming Reactions


9 1 introduction

  • Rubber and other diene polymers undergo cyclization in the presence of acid

  • cis-1,4-polyisoprene

(9.21)

  • Quantitative cyclization of 1,2-polybutadiene

  • - with metathesis catalysts

(9.22)

9.3 Ring-Forming Reactions


9 1 introduction

(9.23)

(9.24)

(9.25)

(9.26)

(9.27)

(9.28)

9.4 Crosskinking

9.4.1 Vulcanization


9 1 introduction

  • The oldest method of vulcanization

  • involving addition to a double bond to form an intermediate sulfonium ion

(9.29)

(9.30)

  • then abstracts a hydride ion

(9.31)

  • Termination

  • - by reaction between sulfenyl anions and carbocations

9.4 Crosskinking

9.4.1 Vulcanization


9 1 introduction

  • Rate of vulcanization

increase

by the addition of accelerators or organosulfur compounds

accelerator

organosulfur compounds

1

2

zinc salts of dithiocarbamic acids

tetramethylthiuram disulfide

9.4 Crosskinking

9.4.1 Vulcanization


9 1 introduction

  • 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


9 1 introduction

  • 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 1 introduction

  • Mechanism of crosslinking

(9.32)

(9.33)

  • fragmentation reactions

(9.34)

R

R

9.4.2 Radiation Crosslinking


9 1 introduction

  • 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

  • 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)


9 1 introduction

(1) incorporating photosensitizers into the polymer,

which absorb light energy and thereby induce formation of free radicals

(9.35)

  • When triplet sensitizers (benzophenone) are added to polymer

n

radical 생성

(들뜬상태)

(9.36)

UV흡수

Benzophenone

-cleavage of the excited

chain cleavage

9.4.3 Photochemical Crosslinking (Photocrosslinking)


9 1 introduction

  • Poly(vinyl ester) : -cleavage reaction

(9.37)

(2) incorporating groups that undergo either photocycloaddition reactions

or light-initiated polymerization

2 + 2 cycloaddition

cyclobutane crosslinks

9.4.3 Photochemical Crosslinking (Photocrosslinking)


9 1 introduction

(a)

(b)

SCHEME 9.2. Photocrosslinking (a) by 2 + 2 cycloaddition and (b) by 4 + 4 cycloaddition.

9.4.3 Photochemical Crosslinking


9 1 introduction

TABLE 9.1. Group Used to Effect Photocrosslinking21-58

Type

Structure

Alkyne

Anthracene

Benzothiophene dioxide

Chalcone

Cinnamate

Coumarin

continued


9 1 introduction

TABLE 9.1. (continued)

Type

Structure

Dibenz[b, f]azepine

Diphenylcyclopropenecarboxylate

Episulfide

Maleimide (R=H, CH3, Cl)

continued


9 1 introduction

TABLE 9.1.

Type

Structure

Stilbazole

Stilbene

Styrene

1,2,3-Thiadiazole

Thymine


9 1 introduction

  • Photo – reactive groups 의 도입 방법

① 중합 반응 동안에 고분자에 도입

3

(9.38)

② 미리 형성된 고분자에 반응기를 첨가

(9.39)

4

9.4.3 Photochemical Crosslinking


9 1 introduction

  • Reaction between appropriate difunctional or polyfuntional reagents

  • with labile groups on the polymer chains - Crosslinking

(9.40)

(9.41)

(Friedel-Crafts reaction)

(9.42)

9.4.4 Crosslinking Through Labile Functional Groups


9 1 introduction

  • Cyclopentadiene-substituted polymer의Diels-Alder reaction

(9.43)

Thermoplastic Elastomers ( 열에 의해 재 가공이 가능)

9.4.4 Crosslinking Through Labile Functional Groups


9 1 introduction

  • The hydrolysis of chlorosulfonated polyethylene with aqueous lead oxide

(9.44)

5

poly[ethylene-co-(methacrylic acid)]

상품명: ionomer

9.4.5 Ionic Crosslinking


9 1 introduction

  • 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


9 1 introduction

  • 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

9.4.5 Ionic Crosslinking


9 1 introduction

1. Polymer containing functional end groups 사용

(9.45)

2. Peroxide groups introduced to polymer chain ends 사용

(9.46)

개시제의 역할

9.5 Block and Graft Copolymer Formation

9.5.1 Block Copolymers


9 1 introduction

3. Peroxide units 사용

(9.47)

(9.48)

9.5 Block and Graft Copolymer Formation

9.5.1 Block Copolymers


9 1 introduction

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 Block and Graft Copolymer Formation

9.5.1 Block Copolymers


9 1 introduction

A. Three general methods of preparing graft copolymers

  • 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


9 1 introduction

(1) Chain transfer

1) Three components

polymer, monomer, and initiator

2) The initiator may play one of two roles

  • 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


9 1 introduction

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


9 1 introduction

.

EX

(9.49)

.

Mixture of poly(vinyl alcohol)-graft-polyethylene and long-chain carboxylic acids

5) Grafting efficiency improvement

At carbons adjacent to

carbonyl groups

Group that undergoes radical transfer readily

(mercaptan is incorporated into the polymer backbone.

9.5.2 Graft Copolymers


9 1 introduction

6) Cationic chain transfer grafting

(9.50)

Friedel-Crafts attack

Styrene is polymerized with BF3 in the presence of poly(p-methoxystyrene)

9.5.2 Graft Copolymers


9 1 introduction

(2) Grafting by activation by backbone functional groups

(9.51)

Synthesis of poly(p-chlorostyrene)-graft-polyacrylonitrile

9.5.2 Graft Copolymers


9 1 introduction

  • Irradiation – provide active sites

with ultraviolet or visible radiation

with or without added photosensitizer

with ionizing radiation

substantial amounts of homopolymerization

= grafting

Major difficulty

settlement

This has been obviated to some extent by preirradiating the polymer

prior to addition of the new monomer.

9.5.2 Graft Copolymers


9 1 introduction

  • Direct irradiation of monomer and polymer together

Polymer – very sensitive to radiation

Monomer – not very sensitive

Best combination

( Sensitivity measurement – G values)

TAB.9.2.

  • Irradiation grafting of polymer emulsions - effective way to minimize

9.5.2 Graft Copolymers


9 1 introduction

TABLE 9.2. Appoximate G Values of Monomers and Polymersa

G

Monomer

G

Polymer

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

Butadiene

Styrene

Ethylene

Acrylonitrile

Methyl methacrylate

Methyl acrylate

Vinyl acetate

Vinyl chloride

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


9 1 introduction

(3) Using two polymers

(9.52)

Grafting of an oxazoline-substituted polymer with a carboxyl-terminated polymer

9.5.2 Graft Copolymers


9 1 introduction

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 1 introduction

(9.53)

Decomposition of initially formed hydroperoxide groups

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


9 1 introduction

  • 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 Polymer Degradation

9.6.1 Chemical Degradation


9 1 introduction

9.6.2 Thermal Degradation

  • Three types of thermal degradation

  • nonchain scission

  • random chain scission

  • depropagation

  • nonchain scission

  • ① refers to reactions involving pendant groups

(9.54)

(9.55)

elimination of acid from poly(vinyl esters)

elimination of alkene from poly(alkyl acrylate)s


9 1 introduction

9.6.2 Thermal Degradation

② Use – approach to solving the problems of polyacetylene’s intractability

Durham

route

(9.56)

tricyclic monomer

7

precursor polymer

8

Thermal degradation

  • Disadvantage of the Durham route

  • : That a relatively large molecule needs to be eliminated.

8

(9.57)

Yield polyacetylene without the necessity of an elimination reaction

coherent films of polyacetylene

(9.58)


9 1 introduction

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

(9.59)

9.6.2 Thermal Degradation


9 1 introduction

(3) Depropagation

  • Initiation Chain end Poly(methyl methacrylate)

  • Random site along the backbone

  • Poly(-methylstyrene)

In both case

(9.60)

9.6.2 Thermal Degradation


9 1 introduction

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


9 1 introduction

9.6.3 Degradation by Radiation

SCHEME 9.3. Random chain scission of polyethylene.


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