Step-Growth Polymerizations

This chapter reviews the original classification of polymers and shows why it is no longer generally applicable. It summarizes the current accepted meaning of the terms addition and condensation polymers, and then turns to a useful, alternative classification which focuses on polymerization processes rather than the products of such processes. There are many possible ways to classify polymers. Each may be useful depending on the interests of the classifier. Examples include typing according to the source of the product (naturally occurring polymers, entirely synthetic macromolecules, or those derived by chemical modification of naturally occurring polymers), chemical structure (polyolefin, polyamide, et cetera.), polymer texture during use (rubbery, glassy, partially crystalline), area of application (adhesive, fiber, etc.), and so on. An important classification divides macromolecules into addition and condensation polymers. This distinction was made by W.H. Carothers, who invented nylon-6, 6 and made many fundamental contributions to our knowledge and control of polymerizations. A condensation polymer is one in which the repeating unit lacks certain atoms which were present in the monomer(s) from which the polymer was formed or to which it can be degraded by chemical means. In addition polymers, by contrast, the recurring units have the same structures as the monomer(s) from which the polymer was formed. Examples are polystyrene (1-1), polyethylene (1-3), styrene-maleic anhydride copolymers (1-26), and so on.