Effect of processing conditions on properties of benzoxazine-urethane copolymers

Abstract

The purpose of this research is to improve performance of polybenzoxazine by alloying with an excellent flexible urethane elastomer which can enhance the flexibility of polybenzoxazine. The polymer alloys of polybenzoxazine and polyurethane was prepared by processing conditions in two methods i.e. Traditional cure method by immediate using thermal treated and Sequential cure method by firstly, moisture in order to produce urethane network following thermal treated. The effects of processing methods were investigated in term of thermal and mechanical properties. In addition, to determine suitable alloy compositions between benzoxazine and urethane resins based on the above processing techniques. The experimental results revealed that the processing window of the BA-a/PU resin mixtures was widened with the amount of the urethane prepolymer. Especially, the synergistic behavior of glass transition temperatures (Tg) of BA-a/PU alloys under both processing conditions is clearly observed. Tg’s of the BA-a/PU alloys under both processing conditions were significantly greater than those of the neat resins, i.e. BA-a (Tg = 186oC) and PU (Tg = -61oC). Tg’s of the BA-a/PU alloys increase with the mass fraction of the PU. The highest value of glass transition temperature was 260 oC under sequential cure method and 252 oC under traditional cure method at BA-a/PU 60/40. Furthermore, the degradation temperature was also about the same up to the PU content of 40 % by weight. The highest value of initial decomposition temperature at 5% weight was 329 oC under sequential cure method and 348 oC under traditional cure method at BA-a/PU 60/40. Moreover, the char yield of the alloys under both processing condition was enhanced with increasing amount of the benzoxazine mass fraction. In addition, the incorporate of benzoxazine structure with polyurethane can reduce their swollen and broken network in chloroform. Finally, the processing conditions of BA-a/PU alloys have no significant effect on above properties. On the other hand, the composition of BA-a/PU in alloys should be considered as the mainly influence.