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Step-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers. Many naturally occurring and some synthetic polymers are produced by step-growth polymerization, e.g. polyesters, polyamides, polyurethanes, etc. Due to the nature of the polymerization mechanism, a high extent of reaction is required to achieve high molecular weight. The easiest way to visualize the mechanism of a step-growth polymerization is a group of people reaching out to hold their hands to form a human chain — each person has two hands (= reactive sites). There also is the possibility to have more than two reactive sites on a monomer: In this case branched polymers are produced. ==Step growth polymerization and condensation polymerization== "Step growth polymerization" and condensation polymerization are two different concepts, not always identical. In fact polyurethane polymerizes with addition polymerization (because its polymerization produces no small molecules), but its reaction mechanism corresponds to a step-growth polymerization. The distinction between "addition polymerization" and "condensation polymerization" was introduced by Wallace Hume Carothers in 1929, and refers to the type of products, respectively:〔Paul J. Flory, ("Principles of Polymer Chemistry" ), Cornell University Press, 1953, p.39. ISBN 0-8014-0134-8〕 * a polymer only (addition) * a polymer and a molecule with a low molecular weight (condensation) The distinction between "step-growth polymerization" and "chain-growth polymerization" was introduced by Paul Flory in 1953, and refers to the reaction mechanisms, respectively:〔Susan E. M. Selke, John D. Culter, Ruben J. Hernandez, ("Plastics packaging: Properties, processing, applications, and regulations" ), Hanser, 2004, p.29. ISBN 1-56990-372-7〕 * by functional groups (step-growth polymerization) * by free-radical or ion (chain-growth polymerization) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Step-growth polymerization」の詳細全文を読む スポンサード リンク
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