Synthesis of high refractive-index melt-stable aromatic polyphosphonates

Abstract

The synthesis of aromatic polyphosphonates based on the step polymerization of various bisphenols and dichlorophenyl phosphine oxide was investigated. The effect of catalyst, type, concentration, and polymerization time were systematically varied to obtain high molecular weight polymers. Very high molecular weight tough, ductile materials with a high degree of optical clarity were synthesized. In contrast with the aromatic polycarbonates, the refractive index was increased from 1.58 to 1.60 (for the bisphenol A-based system) and 1.64 for a biphenol-based system. The latter was still an amorphous soluble polymer as a result of the non-coplanar nature of the phenyl phosphine oxide bond, unlike the analogous polycarbonate. Hydrolytically stable melt-processable cumyl phenol end-capped polyphosphonates were successfully achieved for the first time. Rheological studies show that these end-capped systems are melt-stable at 200°C, whereas the systems of initially higher molecular weight but without any well-defined end capping clearly degraded quickly probably as a result of an acid-catalyzed hydrolysis process. Extensive high char yields were produced upon pyrolysis in either nitrogen or air, suggesting good fire resistance.