Rigid Aromatic Heterocyclic Polymers: Synthesis of Polymers and Oligomers Containing Benzazole Units for Electrooptic Applications

Abstract

Conjugated organic structures exhibit large, ultrafast nonlinear optical (NLO) responses that arise from excitation of highly charged correlated p-electron states. Highly aligned, high strength films of high molecular weight, rigid rod poly(benzobisazole) (PBZ) polymers have been shown recently to possess oustanding third-order NLO properties.1,2 PBZ polymers, being comprised exclusively of aromatic rings, are conjugated structures with numerous possibilites for structural modification. In addition to ultrafast NLO response, PBZ polymers offer advantages of high damage thresholds, environmental stability, a wide variety of processing options, and excellent mechanical properties. Molecular structures with or without centers of symmetry can be prepared and the molecular weight distribution, electron density, and the molecular morphology can be varied over broad ranges. This tailorability in both molecular structure and supramolecular order provides promise for new materials with optimized NLO properties. This paper describes our recent work on the synthesis of PBZ polymers having controlled molecular weights. By controlling the molecular weight at relatively high levels, we aim to improve the processability and reproducibility of solutions for better optical quality high strength films. By preparing novel lower molecular weight materials, we aim to explore new structures that are specifically designed to maximize their NLO response and may require new methods for obtaining the high degree of molecular order that has become associated with PBZ materials.