MeOH/BF_3体系引发异丁烯阳离子聚合反应中水含量及聚合温度的影响

研究了水含量和聚合反应温度Tp 对MeOH BF3体系引发异丁烯 (IB)阳离子聚合反应的转化率、产物的分子量及分子量分布的影响 ,求出在不同水含量条件下的Tp 对聚合物分子量影响的数学方程及相应的聚合度活化能Ep ,以期对体系中存在的微量水加以充分利用 .结果表明 ,H2 O]和Tp 两者共同影响IB阳离子聚合反应过程及产物的分子参数 .当Tp 由 - 10 0℃升高至 - 5 0℃时 ,聚合转化率先增加到一定值后再减小 ,在- 80℃～ - 70℃范围内出现峰值 .在 H2 O]较低时 ,Tp 明显影响着聚合产物的分子量及分子量分布 ,Tp 越低 ,分子量越高 ,分子量分布越窄 ;在 H2 O]较高时 ,Tp 对分子量的影响程度较小 ,说明此时水对聚合反应的影响更为突出 .体系中水含量增大对IB阳离子聚合反应呈现不利作用 ,当 H2 O]由 1 5× 10 - 3mol L增加至 4 6×10 - 3mol L时 ,Ep 由 - 4 0kJ mol增大至 - 17kJ mol ,说明随着 H2 O]增大 ,水的负面效应更加明显 ,既促进副反应 ,又阻碍链增长反应 ,增长活化能增大 ,聚合物分子量降低 ,分子量分布变宽 .水的负面作用也随着Tp 升高而变得明显 .

EFFECTS OF WATER CONCENTRATION AND POLYMERIZATION TEMPERATURE ON THE CATIONIC POLYMERIZATION OF ISOBUTYLENE INITIATED BY MeOH/BF3 SYSTEM

The cationic polymerizations of isobutylene (IB) initiated by MeOH/BF 3 system in CH 2Cl 2 were carried out at various temperatures ( T p) from -100℃ to -50℃ in the presence of different concentrations of water (H 2O]) from 1 5×10 -3 ?mol/L to 4 6×10 -3 ?mol/L in the polymerization systems. The effects of H 2O] and T p on the conversion, molecular weight and molecular weight distribution (MWD) of the product polyisobutylene (PIB) were investigated in order to make use of the trace of water which is impossible to remove from the polymerization system. The equations based on molecular weight with T p were obtained and the corresponding active energy of degree of polymerization ( E p) were also calculated at H 2O] of 1 5×10 -3 ?mol/L,2 2×10 -3 ?mol/L,2 9×10 -3 ?mol/L,3 5×10 -3 ?mol/L and 4 6×10 -3 ?mol/L respectively. The results showed that both H 2O] and T p did affect the cationic polymerization of IB and the molecular parameters of PIB. In the cases of different H 2O] of 1 5×10 -3 ?mol/L, 2.2×10 -3 mol/L and 3 5×10 -3 ?mol/L, the conversions increased with T p from -100℃ to -80℃, reached the maximum around -70℃～-80℃, and then decreased with T p from -70℃ to -50℃. It was shown that T p affect on molecular weight more obviously at low H 2O] than that at high H 2O]. Molecular weight increased and MWD narrowed with decreasing T p and/or H 2O]. On the other hand, traces of water in the polymerization systems did the disadvantageous effects on the IB cationic polymerization. All E p was minus at different H 2O] and it increased from -40?kJ/mol to -17?kJ/mol when H 2O] increased from 1 5×10 -3 ?mol/L to 4 6×10 -3 ?mol/L. It indicates that the disadvantageous influences of H 2O on the polymerization processes, the molecular weight and its distribution would become more serious when H 2O] and/or T p increased. H 2O restrained the propagation of polymer chain and accelerated the side reactions of active centers, such as chain transfer reaction and termination, which leading to low molecular weight and broad molecular weight distribution.