20 - Condensation (Step-Growth) Polymer Theory

Abstract

While the relatively young polymer industry was learning much from the modification of natural polymers, production figures were small. As purely synthetic polymers came on stream, the range of valuable applications for plastic materials rapidly increased. Monomers can be joined by means of two principal methods to form polymers, and these methods are used as the broad basis for the classification of synthetic polymers. The first of these, condensation, or step-growth polymerization, involves the use of functional group reactions such as esterification or amide formation to form polymers. In contrast with the usually slow progress of condensation polymerization, the second major classification, addition, or vinyl-type polymerization, usually proceeds so rapidly that it is referred to as chain reaction polymerization. This method of producing synthetic polymers uses the potential dual functionality present in a carbon–carbon double bond. A characteristic common to the monomers of all condensation, or step growth, polymers is that they possess two more or less reactive functional groups. Many useful condensation polymers employ two bifunctional monomers: one having two functional groups of one type and the other having two complementary functional groups. This type of polycondensation is often referred to as an A–A, B–B type and gives only linear polymers. The need for high purity, stoichiometric proportions of reacting functional groups and nearly complete reaction for useful linear polycondensation products change when a 3 or higher functionality component is introduced into the system.