General Aspects of Polymer Synthesis

The formation of synthetic polymers is a process that occurs via chemical connection of many hundreds up to many thousands of monomer molecules. As a result, macromolecular chains are formed. They are, in general, linear but can be branched, hyperbranched, or cross-linked as well. However, depending on the number of different monomers and how they are connected, homopolymers or one of the various kinds of copolymers can result. The chemical process of chain formation may be subdivided roughly into two classes, depending on whether it proceeds as a chain growth or as a step growth reaction (Fig. 3.1). 

The buildup of the polymer chain with monomer conversion differs significantly depending on the class of polyreaction used. In a chain growth process, the molar mass increases rapidly and reaches a plateau value already at low monomer conversion if chain growth is well controlled or living, then a linear dependency of degree of polymerization versus monomer conversion 

Bio- and Multifunctional Polymer Architectures Preparation, Analytical Methods, and Applications, First Edition. Brigitte Voit, Rainer Haag, Dietmar Appelhans, and Petra B. Wetzel. 

FIGURE 3.1 Classification of reaction mechanisms used to build up polymers. 

FIGURE 3.2 Schematic representation of the development of molar mass, for example, M, with monomer conversion for chain growth (free radical), chain growth (living) and step growth mechanisms for the polymer buildup reaction. 

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One other general aspect of polymer synthesis is a novel type of system referred to as a living polymer. A living polymer is one for which, after initiation, monomer (typically an olefin or diene) successively adds to the reactive terminus of the growing chain until all the monomer is exhausted (Figure 13.14). At this point the polymerization stops, but a reactive moiety (typically an anion or a metal complex) is still attached to the end of each chain. Termination has not occurred. The polymer is still "alive", in that if we now add more monomer, the polymerization starts up again. 

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