PROCESS TO SYNTHESIZE AB-PBO MONOMER AND PHOSPHATE SALTS THEREOF

摘要

AB-polybenzoxazole monomer, such as 3-amino-4- -hydroxybenzoic acid, can be synthesized in high yields from a hydroxy-benzoic acid or related compound in a three-step process of (1) nitration, (2) hydrolysis of the ester, and (3) reduction of the nitro moiety. The monomer is conveniently recovered as a phosphate salt in high purity by precipitating and recrystallizing from a phosphoric acid solution. The monomer may be polymerized in high concentrations in polyphosphoric acid containing high levels of P2O5 to yield a high molecular weight polymer wihout dehydrohalogenation.