Rigid-Rod Polymer Synthesis: Development of Mesophase Polymerization in Strong Acid Solutions

Abstract

ABSTRACTThe development of a method for polycondensation of rigid-rod poly(benzazoles) in poly(phosphoric acid) (PPA) in the lyotropic mesophase has led to an understanding of the synthesis variables that determine the important liquid crystalline product characteristics. These product variables, in turn, control processibility and final fiber or film properties. This paper provides a review of the effects of polymer concentration, solvent composition, polymerization temperature, and monomer purity on two liquid crystalline product characteristics: molecular weight achieved during polymerization, and concentrated solution properties, such as rheological and phase behavior. Central to the understanding of these effects are the factors affecting the polymerization rate. The methods for controlling these synthesis variables are also reviewed. Investigation of alternatives to PPA as the polymerization solvent resulted in a method to obtain high molecular weight poly(2,5-benzoxazole) by adding 40-45 wt % of P2O5 to methanesulfonic acid.