酚醛型氰酸酯与双酚A型环氧共固化反应的FTIR研究

在恒温固化条件下,通过FTIR跟踪方法,研究了酚醛型氰酸酯与双酚A型环氧共固化反应的路径及其反应机理.共固化体系的反应过程包括在150℃及其以下温度,主要发生的是氰酸酯的三嗪环化固化反应,其中三嗪环化固化反应由于环氧的加入,反应速率被极大地提高了;同时,酚醛型氰酸酯中的氨基甲酸酯类杂质与环氧发生开环聚合反应,引起环氧官能团产生弱而持续的消耗.但在此阶段,酚醛型氰酸酯与环氧之间没有化学反应发生;在180℃及其以上温度,三嗪环和环氧发生反应,异构为异氰脲酸环结构,并进一步反应生成唑啉酮环结构,由于该反应的发生,促进了环氧官能团的消耗速度,在环氧官能团的转化率-时间图中,出现倒S曲线;在三嗪环的转化率图中,出现一个极大值后再降落的曲线.反应温度的提高有利于促进酚醛型氰酸酯与环氧之间的共固化反应,特别是当反应温度为220℃时,氰酸酯官能团和环氧官能团的消耗、三嗪环和唑啉酮环的生成均以较快的速率进行,—OCN生成三嗪环的转化率可以较容易地达到1,而唑啉酮环的转化率不超过0.5.

STUDY ON NOVOLAC CYANATE ESTER CO-CURED WITH EPOXY E-51

The blends of novolac cyanate ester and bisphenol A epoxy resin were expected to attain the high thermal resistance of novolac cyanate ester and the excellent processsablity of epoxy.Little work has been done on novolac cyanate ester/epoxy systems before because the high purity novolac cyanate esters was very difficult to synthesize.In this work,a high purity novolac cyanate ester(M_n=900) and a bisphenol A epoxy(E-51) with an equal molar ratio co-cured system was selected to study the reaction pathway and mechanism by FTIR trace method in the molten state.Isothermal cure conditions include 150,180,200,220℃ were used to conduct the co-cured reactions.The reaction was found to be complex and involve several pathways.When cured below 150℃,trimerization of novolac cyanate ester was the main reaction and the trimerization rate was accelerated after the addition of epoxy.An open ring co-polymerization between epoxy and carbamate,which is an impurity contained in novolac cyanate ester or induced by reaction with water from environment or from epoxy,can always occur.This made a slow dissipation of epoxy in the conversion-time plot.No reactions between epoxy and novolac cyanate ester was found in this stage.When temperature was raised up to and over 180℃,oxazolidinone ring was formed and such a reaction increased the dissipation of epoxy function.As in the case of cyanate function,the transformation of triazine rings quickly reaches it's maximum value and then descent.It was found that increased temperatures facilitated the formation of oxazolidinone.The transformation rate of triazine ring can easily reach 1.0 while the α that value of oxazolidinone formation is less than 0.5.