ABSTRACT
In Chapter 3, it is stated that “the basic structures and characteristics of polymers and plastics are attributable to five main factors such as arrangement, chemical structure, degree of polymerization (size), form, and polymerization method” [1-4]. This infers that the understanding of the behavior and characteristics of polymers and plastics requires basic and fundamental understanding of the concepts of degree of polymerization and molecular weight (MW). This chapter presents a discussion of MW of polymers and the various methods for calculating MW of polymers via the outline:
• Monodispersity • Polydispersity • Molecular weight distribution (MWD) • Number average MW (Mn) • Weight average MW (Mw) • Viscosity average MW (Mv) • Z-average MW
Polymers differ from other chemical compounds in that they have molecules of varying MWs. Chemical compounds have small, discrete molecules; the molecules are of the same size and so have the same MWs. For example, each molecule of a chemical compound like aniline, which has the formula C6H5NH2, has a constant MW of 93 g/g-mol irrespective of the size of the sample. The same is true for a molecule of benzene (C6H6), which has a MW of 78. Such simple compounds like aniline and benzene are said to be monodisperse. Polymers on the other hand have molecules of varying MWs and they are polydisperse.
