Chain extenders for polyesters. VI. Properties of the polyesters chain‐extended by 2,2′‐bis(4H‐3,1‐benzoxazin‐4‐one)

Some properties of polymers derived by treating poly(ethylene terephthalate) (PET) with such hydroxyl‐addition‐type chain extenders as 2,2′‐bis(4H‐3,1‐benzoxazin‐4‐one) (BNZ) were investigated. Compared with ordinary PET, the chain‐extended PET has a slightly lower melting point and nearly equal molecular size distribution, which indicate that BNZ reacts to form linear chain‐extended polymers without branching. Oxalyl bis(anthranilate) unit copolymerized in the polyester chain showed little influence on thermal and hydrolytic stabilities. In addition, benzoxazinone groups remaining unreacted can act as a heat stabilizer to prevent the decrease in the molecular weight by the chain‐extending reaction in the solid phase. But they showed adverse effect on the hydrolytic stability by promoting hydrolysis of the polymer as much as the carboxyl groups.