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9.1 Introduction

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  1. 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

  2. 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.

  3. 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

  4. neighboring group effect (9.1) 9.1 Introduction

  5. (9.2) (9.3) 9.2 Functional Group Reactions 9.2.1 Introduction of new Functional Groups • Chlorination • chlorosulfonation

  6. 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

  7. (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

  8. 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. 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

  10. 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

  11. Synthesis of “head-to-head poly(vinyl bromide)” • by controlled brominaion of 1,4-polybutadiene (9.10) 9.2.2 Conversion of Functional Groups

  12. 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

  13. 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

  14. Introduction of cyclic units • greater rigidity • higher glass transition temperatures • improved thermal stability – carbon fiber (graphite fiber) 9.3 Ring-Forming Reactions

  15. 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

  16. 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

  17. 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

  18. (9.23) (9.24) (9.25) (9.26) (9.27) (9.28) 9.4 Crosskinking 9.4.1 Vulcanization

  19. 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

  20. 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

  21. 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

  22. 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

  23. Mechanism of crosslinking (9.32) (9.33) • fragmentation reactions (9.34) R R 9.4.2 Radiation Crosslinking

  24. 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)

  25. (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)

  26. 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)

  27. (a) (b) SCHEME 9.2. Photocrosslinking (a) by 2 + 2 cycloaddition and (b) by 4 + 4 cycloaddition. 9.4.3 Photochemical Crosslinking

  28. TABLE 9.1. Group Used to Effect Photocrosslinking21-58 Type Structure Alkyne Anthracene Benzothiophene dioxide Chalcone Cinnamate Coumarin continued

  29. TABLE 9.1. (continued) Type Structure Dibenz[b, f]azepine Diphenylcyclopropenecarboxylate Episulfide Maleimide (R=H, CH3, Cl) continued

  30. TABLE 9.1. Type Structure Stilbazole Stilbene Styrene 1,2,3-Thiadiazole Thymine

  31. 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

  32. 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

  33. Cyclopentadiene-substituted polymer의Diels-Alder reaction (9.43)  Thermoplastic Elastomers ( 열에 의해 재 가공이 가능) 9.4.4 Crosslinking Through Labile Functional Groups

  34. The hydrolysis of chlorosulfonated polyethylene with aqueous lead oxide (9.44) 5 poly[ethylene-co-(methacrylic acid)] 상품명: ionomer 9.4.5 Ionic Crosslinking

  35. 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

  36. 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

  37. 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

  38. 3. Peroxide units 사용 (9.47) (9.48) 9.5 Block and Graft Copolymer Formation 9.5.1 Block Copolymers

  39. 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

  40. 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

  41. (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

  42. 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

  43. . 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

  44. 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

  45. (2) Grafting by activation by backbone functional groups (9.51) Synthesis of poly(p-chlorostyrene)-graft-polyacrylonitrile 9.5.2 Graft Copolymers

  46. 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

  47. 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

  48. 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

  49. (3) Using two polymers (9.52) Grafting of an oxazoline-substituted polymer with a carboxyl-terminated polymer 9.5.2 Graft Copolymers

  50. 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