Microstructure

Abstract

Abstract The term, microstructure, has been commonly used to describe the average molecular structure of an assembly of polymer molecules, that is, repeat unit structures and mole fractions. With the advent of more detailed structural information, the term microstructure has been broadened to include compositional distributions, chirality (tacticity), average sequence lengths, sequence length distribution, and topology, such as the extent of long chain branching. The average degree of polymerization, molecular weight and molecular weight distribution are not usually included in the definitions of polymer microstructure, but are also necessary to describe completely the average molecular structure of an assembly of polymer molecules. Because of some fundamental differences in polymer structures produced by the modes of polymerization, polymer molecules are also classified by the synthetic routes through which they were obtained. The term microstructure must therefore include all variations in molecular structures from one polymer molecule to the next in addition to describing the overall content of each type of monomer used in copolymerization or each type of homopolymer repeat unit that has different molecular structure. Polymer microstructure is best described from the following viewpoints: topology, repeat unit structures, chirality, variations in sequencing of copolymer repeat units, sequence distributions, and molecular weight and end groups. These are all discussed in detail. Measuring polymer microstructure and chain conformations in amorphous and semicrystalline polymers are also discussed.