Organic Chemistry,5th Edition L.G.Wade,Jr. Chapter 26 Synthetic Polymers Jo Blackburn Richland College,Dallas,TX Dallas County Community College District ©2003，Prentice Hall
Chapter 26 Synthetic Polymers Jo Blackburn Richland College, Dallas, TX Dallas County Community College District © 2003, Prentice Hall Organic Chemistry, 5th Edition L. G. Wade, Jr
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 produced annually,worldwide. Chapter 26
Chapter 26 2 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 produced annually, worldwide. =>
Classes of Polymers Addition,or chain-growth,polymers repeating unit H CI C- HHHH vinylchloride poly(vinyl chloride) Condensation,or step-growth,polymers dimethyl terephthalate ethylene glycol o o-o-om repeating unit Dacron°polyester Chapter 26 3
Chapter 26 3 Classes of Polymers • Addition, or chain-growth, polymers • Condensation, or step-growth, polymers =>
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 a-methacrylate) Plexiglas. Chapter 26
Chapter 26 4 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 ® =>
Free Radical Polymerization Initiation step:The initiator reacts with the monomer to start the chain. phenyl radicals styrene benzylic radical Propagation step:Another molecule of monomer adds to the chain. many more styrene molecules H growing chain styrene elongated chain polystyrene n=about 100 to 10.000 > Chapter 26 5
Chapter 26 5 Free Radical Polymerization =>