Chain extenders for polyesters. V. Reactivities of hydroxyl-addition-type chain extender; 2,2′-bis(4h-3,1-benzoxazin-4-one)

Abstract

In our previous study,1 2,2′-bis(4H-3,1-benzoxazin-4-one) (BNZ) was found to be most effective among the tested chain extenders in coupling hydroxyl terminals of linear polyesters through addition reaction. Detailed studies on BNZ chemistry have been made using poly(ethylene terephthalate) and poly(butylene terephthalate) as the polyester. It has been observed that use of BNZ, equivalent amount to the hydroxyl terminals of the initial polymer, resulted in the highest molecular weight. In contrast with the case of 2,2′-bis(2-oxazoline), which was found to be the most effective carboxyl-addition type chain extender and a wide range of its excess use was allowed,2,3 an excessive use of BNZ resulted in lower molecular weight polymer. Thus, when an equivalent amount of BNZ to the hydroxyl terminals was used, the molecular weight of the resulting polymer could be determined by the carboxyl content of the initial polymer, regardless of its initial molecular weight.