H2O/TiCl4/ED 体系引发异丁烯控制正离子聚合中的影响因素研究

在亲核试剂(ED)如吡啶(Py)、N,N-二甲基乙酰胺(DMA)或三乙胺(TEA)存在下,由引发剂H2O和共引发剂TiCl4组成引发体系,在二氯甲烷/正己烷混合溶剂中进行异丁烯(IB)正离子聚合,考察了溶剂极性、聚合温度及异丁烯浓度对聚合反应转化率、产物分子量和分子量分布的影响.试验结果表明,随聚合体系溶剂极性增大,聚合速率加快,相近转化率时聚合产物的分子量分布变窄.随着聚合温度降低,聚合速率明显提高,聚合物的分子量增加,活化能为负值,活性链端发生链转移或链终止等副反应的几率减小,当聚合温度为-60℃时,可以抑制活性链端的β-H脱除反应和链转移副反应,并得到大分子链末端全部为叔氯基团的聚异丁烯(PIB).当[IB]0≤2.5mol/L时,随[IB]0增加,聚合转化率有所增加,聚合产物的GPC谱图均为单峰分布,分子量增大,而分子量分布基本保持不变,对于加入Py的聚合体系,分子量分布指数在1.33~1.45范围内,对于加入TEA的聚合体系,分子量分布指数在1.47~1.60范围内,并求出在加入Py和TEA的聚合体系中活性链向单体的链转移常数CM分别为5.5×10-4和6.6×10-4.

CARBOCATIONIC POLYMERIZATION OF ISOBUTYLENE INITIATED BY H2O/TiCl4/ED SYSTEM

The carbocationic polymerization of isobutylene(IB)with H_2O/TiCl_4 as initiating system in the presence of pyridine(Py),triethylamine(TEA)or N,N-dimethylacetamide(DMA)was conducted in a mixture of methylene dichloride(CH_2Cl_2)and n-hexane(Hex).The effects of solvent polarity,polymerization temperature and monomer concentration on the conversion,molecular weight(MW)and molecular weight distribution(MWD,M_w/M_n)of polyisobutylene(PIB)were investigated.The polymerization rate increased greatly with an increase in solvent polarity.The polymerization rate and the molecular weight of PIB obtained increased obviously with decreasing the polymerization temperature.The corresponding active energy of propagation(ΔE)was calculated to be-28.8 kJ/mol,-25.8 kJ/mol and-29.0 kJ/mol in the presence of Py,DMA and TEA respectively.The chain transfer side-reaction decreased and molecular weight distribution of PIB products became narrow with decreasing polymerization temperature.The polymer with tert-chlorine end group were obtained at-60℃.Both the monomer conversion and molecular weight of PIB increased with isobutylene concentration([IB]_0≤2.5 mol/L)while molecular weight distribution kept relatively narrow and the polydispersity(M_w/M_n)is around 1.4 and 1.5 for the carbocationic polymerization of IB in the presence of Py and TEA respectively.The constant of chain transfer reaction to monomer(C_M)was calculated to be 5.5×10-4 and 6.6×10-4 for the carbocationic polymerization of IB in the presence of Py and TEA respectively.A desirable polymerization of IB with apparent absence of chain transfer reactions could be obtained by H_2O/TiCl_4 initiating system in the presence of Py or DMA at-60℃ under the appropriate reaction conditions.