Preparation of Synthetic Polymeric Materials

The hrst section covers the basic principles and characteristics necessary for polymer preparation by polymerization, being either (a) stepwise polymerization of bifunctional monomers by polycondensation, stepwise polyaddition and ringopening processes, or (b) chain polymerization of vinyl monomers by free radical, cationic, anionic, and coordination addition processes. Both of these polymerization techniques are used for polymer preparation from monomer. The goal of the polymerization technique is to obtain polymers with specific structures and properties -this generally requires specialized polymerization conditions. Also described are the factors affecting the rates of homo- and copolymerizations and the reactivity ratios of different comonomers. 

A and B are the reacting functional groups, C is the by-product, and Z is the group bonding the residues of reacted molecules. Two different functional groups may be borne on a single molecule (Eq. 1.2). 

Alternatively, the bonding functional group can be present in ring form the two different functional groups are present within the ring in condensed form and the by-product is eliminated during ring formation. The chanical compositions of the cyclic monomers and the structural units of the polymers are essentially identical as in addition polymerization, but the stepwise nature and the rate of reaction are more characteristic of condensation polymerization reactions (Eq. 1.3). 

Although the properties of condensation polymers are often superior to those exhibited by vinyl addition polymerization, little attention has been directed toward the introduction of fnnctional groups by polycondensation using appropriately substituted monomer. Polycondensation polymers may contain the reactive functional groups as a part of the polymer backbone or as pendent substituents. 

This is a chain polymerization through multiple bonds and may be regarded as simply the joining together of unsaturated molecules without the formation of byproducts in which there is no difference in the relative positions of the atoms in the monomer and the structural unit of the polymer, Eq. 1.4. 

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