2-乙基-4-甲基咪唑固化环氧树脂体系动力学模型

由2-乙基-4-甲基咪唑(2,4-EMI)固化双酚A二缩水甘油醚型环氧树脂(DGEBA)的等温差示扫描量热(DSC)实验结果发现固化反应分两阶段进行,催化聚合反应有一诱导期.由DSC测试结果求得催化聚合反应的速率常数.从反应机理出发,以诱导期为边界,建立两阶段的微观固化动力学模型.从扩散的角度在模型中引入临界固化度(αc)和扩散因子,进一步建立扩散控制固化动力学模型,对不同2,4-EMI含量和固化温度(Tc)的体系,计算得到αc.研究发现扩散因素对固化动力学影响较大,固化反应前期由化学动力学控制,后期由扩散因素控制;αc主要由体系的玻璃化转变决定,Tc越高,体系玻璃化转变时对应的固化度越大,cα越大.

CURING KINETIC MODEL OF THE 2-ETHYL-4-METHYLIMIDAZOLE/EPOXY SYSTEM

The system of bisphenol-A diglycidyl ether type epoxy resin(DGEBA) cured with 2-ethyl-4-methylimidazole(2,4-EMI) was studied by means of differential scanning calorimetry(DSC) in isothermal mode.Analysis of DSC curves indicated that the curing reaction could be separated into two stages,the addition reaction and the catalytic polymerization,as proposed in the literatures.The catalytic polymerization reaction has an induction period which decreases with the increasing of curing temperature(T_c).The rate constants for the catalytic polymerization stage were calculated from DSC studies.A curing kinetic model separated into two steps by the induction period was developed based on the reaction mechanism.The model can predict part of the experimental results,but some deviations are observed at the higher values of curing degree(α).A critical value of curing degree(α_c) and a diffusion factor were introduced,and a diffusion controlled curing kinetic model was developed.For the systems of various concentrations of 2,4-EMI cured in the temperature range of 90～120℃,the values of α_c were calculated.The studies show that the diffusion factors affect the curing kinetics greatly in the higher values of α.When the value of α is low,the reaction is controlled by the chemical factors,but it is controlled by diffusion,when α is high.The value of α_c is mainly affected by the glass transition of the system.With the increase of T_c,the curing degree at the glass transition increases and thus the value of α_c increases too.