微量水为引发剂的可控碳阳离子聚合研究

The carbocationic polymerization of isobutylene with impurity "water"/Lewis acids initiating system is considered as a conventional process. On the basis of this conventional cationic polymerization, isobutylene polymerizations by using the adventitious impurity H2O in the polymerization system as initiatoe and Lewis acid as coinitiator were carried out in the absence and presence of additives, such as various nucleophiles (Nu) or common ion salts. The effects of chemical structure and speciality of the additives on the cationic polymerization process, polymerization rate, chian transfer reactions and molecular weight and molecular weight distribution of polymer products were investigated. The kinetics of the IB polymerization with the H2O/Lewis acid/additives initiating system was also investigated. The relationship between the reactivity and donicity of the nucleophiles and their effects on the polymerization were futher discussed..?The polymerization of isobutylene by H2O/Lewis acid was a uncontrolable rapid polymerization process and the polymer products with broad molecular weight distribution,e.g. Mw/Mn=15.0, were obtained. ?The conventional cationic polymerization of IB by "H2O"/Lewis acids initiating system can be converted into an expected polymerization with low polymerization rate, high molecular weight and narrow molecular weight \distribution,e.g. Mw/Mn=1.11 by using certain appropriate H2O/Lewis acids/additives systems. ?It indicated that polymerization rate was first-order with respect both to monomer with H2O/lewis acids/additives system.?It indicated that polymerization rate was first-order with respect both to monomer and to initiator concentrations ([H2O]0) in the presence of strong or weak nucleophiles. The concentration of active centers were propotional to [H2O]0 and only ion-paired species were present in the polymerization system.?It may be seen that the coinitiator Lewis acid exerts a strong effect on the rate of polymerization. The rates increased with [TiCl4]0 in the presence of different nucleophiles. Since the rate of propagation is proportional to the concentration of active species. The first-order in TiCl4 concentration was observed when nucleophiles with strong donicity (Guttman donor number DN≥27) were used, whereas polymerizations exhibited a second-order dependence on TiCl4 concentration in those cases nucleophiles with strong donicity (DN=14.8~18) were used.?The mediation of additives on IB polymerization is relevant to their chemical structure, substituted group, donicity and dosage. Lower additive concentrations were needed for the nucleophiles with high donicity (DN=27.8~61.0) and MWD of the polymer products were relatively narrower (Mw/Mn=1.1～1.3). However, some additives with low donicity and high stereo-hinderance mediated weakly the polymerization process even if their concentration are high, and thus MWD of the polymer products were broader (Mw/Mn=3.2～5.0)?Donorcity of ED obviously affected the reaction order of nucleophilic additives in the polymerization system. The polymerization reactions exhibited first-order dependence on 1/[ED] when DN is from 27.8 to 61.0. The polymerization rate decrased with increasing the concentration of nucleophilic additives. There existed a relationship between the apparent rate constant for propagation( kpA, min-1) and DN (kcal/mol) for various nucleophilic additives: lnkpA=-0.015×(DN) - 1.80..?The sensitivity to air and water decreased by the addition of small amount of additives and thus the stability of initiating system and polymerization system increased. The chain transfer reaction of the propagating species decreased with increasing the donicity of the nucleophilic additives used.?The experimental results show that there existed competitive complexation reactions of various nucleophiles (initiator H2O and nucleophilic additives) with Lewis acid. The mechanistic roles of external ED were to take part in the initiation step by competitive complexation and to modify the reactivity of the growing chain ends in the

本课题立足于调节活性中心阳离子的反应性和稳定性以及反离子对碳阳离子的稳定程度，提出利用聚合体系中难以去除的微量杂质水为引发剂，实现异烯烃可控阳离子聚合，突破现有的碳阳离子聚合的研究现状，开发可产生可控聚合过程、设计分子量与窄分子量分布的新型引发体系，解决体系中杂质水对聚合反应的不利影响，更具工业应用前景。