4. Polymerization and Classification

The discussion in previous chapters has provided a glimpse of the relationship between the molecular structure of polymers and their mechanical behavior. In this chapter the intent is to provide more detailed information about the molecular structure of polymers and the relation of such structure to mechanical performance. Typically materials courses taken by engineering students prior to 1980 contained little, if any, information on the structure of polymers that might be useful in the engineering design of polymer based structures. While now most elementary books on materials do include a chapter or two on polymers they are often omitted on the class syllabus due to the pressures of schedules and/or time constraints. As a result, engineering students often do not obtain a knowledge base that allows the safe design of polymeric structures. All too frequently, the engineering design of structural polymers is based upon principles that are best used for metals. The purpose of the present chapter is to provide a framework for understanding the structure of polymers and hence the structure–property relationships that give rise to their unique mechanical behavior with time, temperature and other environmental parameters as discussed in subsequent chapters. Due to the prevalence of polymers in industrial uses, a general understanding of the concepts outlined in this chapter are essential for an engineer to be able to make informed design decisions on polymeric components and, importantly, to be able to discuss on common ground with synthesis people the type of polymer needed to be produced for a given application.