Abstract:The effect of temperature, ultrasonic and environment atmosphere on the stability of poly(p phenyl benzobisoxazole)(PBO) in strong protonic acid solutions, such as poly(phosphoric acid) (PPA) and methanesulfonic acid (MSA), was studied. Results show that in dark environment, PBO-MSA solution is sensitive to the temperature, whereas PBO PPA solution is stable even at high temperature. The degradation process of PBO on the MSA solution is consisted of two steps: first, the o hydroxy amide structure in the PBO molecule degrades; then, the benzoxazole ring openes and formes o hydroxy amide linkage structure, o-hydroxy amide linkage degrades subsequently. The degradation of PBO-MSA solution under ultrasonic belongs to stress induced, which is consistent with the classic ultrasonic degradation mechanism. The results also show that PBO solution is stable under nitrogen, whereas the speed of photo degradation is fast when environment atmosphere is oxygen.