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In this chapter, we discuss some of the fundamental principles of polymer chemistry. We begin with a survey of the different kinds of polymers, then consider the reactions used to induce polymerization. Finally, we discuss some of the structural characteristics that determine the physical properties of a polymer. | Chapter 26 Copyright © 2010 Pearson Education, Inc. Organic Chemistry, 7th Edition L. G. Wade, Jr. Synthetic Polymers Chapter 26 Introduction A polymer is a large molecule composed of many smaller repeating units. First synthetic polymers: Poly(vinyl chloride) in 1838. Polystyrene in 1839. Now, 250 billion pounds are produced annually, worldwide. Chapter 26 Classes of Polymers Addition, or chain-growth, polymers. Condensation, or step-growth, polymers. Chapter 26 Chapter 26 Addition Polymers Three kinds of intermediates: Free radicals Carbocations Carbanions Examples of addition polymers: Polypropylene plastics Polystyrene foam insulation Poly(acrylonitrile), Orlon® fiber Poly(methyl -methacrylate), Plexiglas® Chapter 26 Free-Radical Polymerization Initiation step: Propagation step: Chapter 26 Chain Branching Chain branching occurs when the growing end of a chain abstracts a hydrogen atom from the middle of a chain. A new branch grows . | Chapter 26 Copyright © 2010 Pearson Education, Inc. Organic Chemistry, 7th Edition L. G. Wade, Jr. Synthetic Polymers Chapter 26 Introduction A polymer is a large molecule composed of many smaller repeating units. First synthetic polymers: Poly(vinyl chloride) in 1838. Polystyrene in 1839. Now, 250 billion pounds are produced annually, worldwide. Chapter 26 Classes of Polymers Addition, or chain-growth, polymers. Condensation, or step-growth, polymers. Chapter 26 Chapter 26 Addition Polymers Three kinds of intermediates: Free radicals Carbocations Carbanions Examples of addition polymers: Polypropylene plastics Polystyrene foam insulation Poly(acrylonitrile), Orlon® fiber Poly(methyl -methacrylate), Plexiglas® Chapter 26 Free-Radical Polymerization Initiation step: Propagation step: Chapter 26 Chain Branching Chain branching occurs when the growing end of a chain abstracts a hydrogen atom from the middle of a chain. A new branch grows off the chain at that point. Chain branching makes the polymer soft. Chapter 26 Cationic Polymerization Strongly acidic catalysts are used to initiate cationic polymerization. BF3 is a particularly effective catalyst, requiring a trace of water or methanol as a co-catalyst. Intermediate must be a stable carbocation. Chapter 26 Good Monomers for Cationic Polymerization Chapter 26 Anionic Polymerization Alkene must have an electron-withdrawing group like C═O, C N, or NO2. The reaction is initiated by a Grignard or organolithium reagent. Chapter 26 Chain-Growth Step in Anionic Polymerization Effective anionic polymerization requires a monomer that gives a stabilized carbanion when it reacts with the anionic end of the growing chain. Chapter 26 Stereochemistry of Polymers Chapter 26 Properties of Polymers Isotactic and syndiotactic polymers are stronger and stiffer due to their regular packing arrangement. Anionic intermediate usually gives .
