ABSTRACT
This chapter examines molecular weight averages and distributions in step-growth polymerizations, as these are particularly well-suited to a statistical treatment. It considers the number average degree of polymerization in a linear step-growth reaction. The total number of molecules will equal the number of tetrafunctional units in the system, while the total number of units in the entire molecule, x, depends upon the sum of the y-values of the individual chains. The nature of addition polymerization is such that the statistical approach cannot be readily applied to the analysis of molecular weight distributions, but it is a powerful tool in the study of such aspects of microstructure as copolymer sequence distributions and various types of isomerism. The presence of polyfunctional units nearly always presents the possibility of forming chemical structures of macroscopic dimensions or infinite networks. The chapter defines the critical conditions for the formation of infinite networks and molecular weight distributions for non-linear polymers.
