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

9.2 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

  • 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


  • neighboring group effect

(9.1)

9.1 Introduction


(9.2)

(9.3)

9.2 Functional Group Reactions

9.2.1 Introduction of new Functional Groups

  • Chlorination

  • chlorosulfonation


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


(9.4)

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


9.2 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)


  • 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


  • 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


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

  • by controlled brominaion of 1,4-polybutadiene

(9.10)

9.2.2 Conversion of Functional Groups


  • 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


  • 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


  • Introduction of cyclic units

  • greater rigidity

  • higher glass transition temperatures

  • improved thermal stability – carbon fiber (graphite fiber)

9.3 Ring-Forming Reactions


  • 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


  • 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


  • 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


(9.23)

(9.24)

(9.25)

(9.26)

(9.27)

(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

(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


  • 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


  • 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

(9.32)

(9.33)

  • fragmentation reactions

(9.34)

R

R

9.4.2 Radiation Crosslinking


  • 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)


(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)


  • 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)


(a)

(b)

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

9.4.3 Photochemical Crosslinking


TABLE 9.1. Group Used to Effect Photocrosslinking21-58

Type

Structure

Alkyne

Anthracene

Benzothiophene dioxide

Chalcone

Cinnamate

Coumarin

continued


TABLE 9.1. (continued)

Type

Structure

Dibenz[b, f]azepine

Diphenylcyclopropenecarboxylate

Episulfide

Maleimide (R=H, CH3, Cl)

continued


TABLE 9.1.

Type

Structure

Stilbazole

Stilbene

Styrene

1,2,3-Thiadiazole

Thymine


  • 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


  • 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


  • Cyclopentadiene-substituted polymer의Diels-Alder reaction

(9.43)

Thermoplastic Elastomers ( 열에 의해 재 가공이 가능)

9.4.4 Crosslinking Through Labile Functional Groups


  • The hydrolysis of chlorosulfonated polyethylene with aqueous lead oxide

(9.44)

5

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

9.4.5 Ionic Crosslinking


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


3. Peroxide units 사용

(9.47)

(9.48)

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 Block and Graft Copolymer Formation

9.5.1 Block Copolymers


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


(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


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


.

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


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


(2) Grafting by activation by backbone functional groups

(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

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


  • 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


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


(3) Using two polymers

(9.52)

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

9.5.2 Graft Copolymers


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


(9.53)

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


  • 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


9.6.2 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


9.6.2 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)


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


(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


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


9.6.3 Degradation by Radiation

SCHEME 9.3. Random chain scission of polyethylene.


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