ABSTRACT
We introduce the two main methods of polymerization: Step-Growth and Chain-Growth. Because the former utilizes monomers with two functional groups -X and Y- (X-R-Y) that react to form covalent links -Z- with each other, or a pair of monomers each with two functional groups that are reactive with the other pair of functional groups (X-R-X) and (Y-R′-Y), their resulting microstructures are generally predictable.
On the other hand, molecules with unsaturated bonds possessing weakly held π-electrons may be readily initiated and quickly add additional monomers to form Chain-Growth polymers. Because in Chain-Growth polymerizations the enchainment of monomers may occur in multiple ways, a large variety of microstructures can result. We describe regiosequences (direction of monomer insertion), stereosequences (manner of relative attachments of neighboring side-chains), inadvertent branching from chain-transfer events, comonomer sequences in copolymers, cross-links, and for diene monomers, modes of monomer addition (1,2; 3,4; and 1,4-cis and -trans). The large variety of microstructures produced via Chain-Growth polymerizations is illustrated by example as we work through the number of distinct triad (three repeat unit) microstructures that may be produced during the polymerization of the simple diene monomer 1,3-butadiene (CH2=CH-CH=CH2).
