高转化自由基本体聚合的数学模拟——三段聚合模型Ⅱ.数均相对分子质量和引发剂效率

Mathematical Simulation of Bulk Free Radical Polymerization at High Conversion—Three Stage Polymerization Model Ⅱ.Number-Average Molecular Weight and Initiator Efficiency

基于本研究第一部分中提出的三段聚合模型 ,进一步导得聚合物数均相对分子质量的表达式 ,并首次提出了一种确定聚合各阶段引发剂效率和向单体的链转移常数的方法。将数据处理得到的引发剂效率以及向单体的链转移常数 ,代入导得的表达式 ,计算了数均相对分子质量随转化率的变化规律。结果表明 ,计算值与实验值较为一致。

In this paper,the expressions for the calculation of number average molecular weight based on the three stage polymerization model(TSPM) proposed in part 1 of this study are derived.The method determines the initiator efficiency and the constant of chain transfer to monomer is suggested for the first time.With the use of the method,plots of literature data show that the chain transfer to monomers in each stage for bulk polymerization of MMA and St is negligible and independent of the reaction temperature and initiator concentration.However,chain transfer to monomer for the bulk polymerization of EMA exists.In addition,the initiator efficiency is constant in each stage and also independent of the reaction temperature and the initiator concentration when three monomers mentioned above are polymerized respectively.Compared with low conversion stage,the initiator efficiency in the gel effect stage is reduced slightly for MMA and EMA polymerization,but efficiency decreases obviously for St polymerization.In order to calculate the number average molecular weight at different conversion,the obtained values of initiator efficiency and the constants of the chain transfer to monomers by means of plots of literature data are substituted in the derived expressions.The comparisons between model predictions and literature molecular weight data show that the agreement is satisfactory.