Theoretical investigations on some rigid‐rod polymers used as high‐performance materials

This review focuses on a new type of para ‐catenated aromatic polymer being used in the preparation of high‐performance films and fibers of exceptional strength, thermal stability, and environmental resistance, including inertness to essentially all common solvents. Polymers of this type include cis and transpoly( p ‐phenylene benzobisoxazole) (PBO), and the cis and trans forms of the corresponding poly( p ‐phenylene benzobis‐thiazole)(PBT). The purpose of this paper is to summarize the authors' theoretical work on the structures, conformational energies, intermolecular interactions, and electronic properties of PBO and PBT chains, including the protonated forms known to exist in strong acids. The emphasis is on how such studies provide a molecular understanding of the unusual properties and processing characteristics of this new class of materials.