茂金属催化剂分子设计与苯乙烯间规聚合研究 Ⅱ.单茂钛催化体系苯乙烯间规聚合反应动力学及聚合机理

Molecular Design of Metallocene Catalysts and Study on Syndiospecific Polymerization of Styrene Ⅱ Kinetics and Mechanism of Syndiospecific Polymerization of Styrene with Titanocene Catalyst

研究了茂基三正丙氧基钛［ＣｐＴｉ（ＯＰｒｎ）３］和改性甲基铝氧烷（ｍＭＡＯ）组成的新型单茂钛催化体系进行苯乙烯间规聚合反应动力学规律；在２２～５４ｍｏｌ·Ｌ－１浓度范围内，聚合反应速率对催化剂浓度和单体浓度都呈一级反应关系，表观活化能为３０３５ｋＪ·ｍｏｌ－１，碰撞因子为３１５×１０５ｍｏｌ－１·Ｌ·ｓ－１．推断出苯乙烯间规聚合反应机理，ＣｐＴｉ（ＯＰｒｎ）３和ｍＭＡＯ作用生成对苯乙烯间规聚合有更高活性的［ＣｐＴｉ（Ⅲ）（ＣＨ３）］δ＋…（ＯＰｒｎ）…［ＭＡＯ］δ－弱离子对活性中心；苯乙烯进行链增长反应时，与Ｔｉ配位的单体和增长链上的苯环大π键同时配位到Ｔｉ的２个空轨道上使得钛中心电子云密度增大而促进下一步的插入和链增长反应，并构成苯乙烯的间规聚合机制．

The kinetics of styrene syndiospecific polymerization with η 5 cyclopentadienyltri n propoxy titanium [CpTi(OPr n ) 3] and modified methylaluminoxane ( m MAO) catalytic system was studied Results show that the styrene conversion increases almost linearly with increasing the titanium or monomer concentration The apparent rate of polymerization versus titanium and monomer concentration appears the first order reaction rule, and the apparent rate constant is 1 038×10 -5 mol·L -1 ·s -1 at 333 K The calculated polymerization activation energy (Δ E ) is 30 35 kJ·mol -1 , while the impact fractor is 3 15×10 5 mol -1 ·L·s -1 It is deduced that a weak ionic doublet complexes which can catalyze syndiospecific polymerization of styrene is formed in the catyalytic system by reaction of CpTi(OPr n ) 3 with m MAO The active formed species again by chain transfer is able to re initiate a new polystyrene chain after they are activated by m MAO