膦亚胺半茂钛催化体系合成无规聚丙烯弹性体的研究

Half-titanocenes Catalysts Based on Titamium-phosphinimide for Producing Atactic Elastomeric Polypropylenes with High Molecular Weight

采用2种膦亚胺半茂化合物[(t-Bu)_3P=N]CpTiCl_2(PT1)和[(t-Bu)_3P=N]CpTiMe_2(PT2)为主催化剂,分别以甲基铝氧烷(MAO)或[Ph_3C][B(C_6F_5)_4]为助催化剂用于丙烯聚合研究.详细考察了不同n(Al)/n(Ti)、反应温度、反应压力、反应时间等因素对丙烯聚合活性、分子量与分子量分布及其分子结构的影响.还与典型的(rac-[En(IndH_4)_2]ZrCl_2)(1),CpTiCl_3(2)及Cp_2TiCl_2(3)催化剂的催化效果进行了比较.凝胶渗透色谱(GPC)、核磁共振氢谱与碳谱(1H/13C-NMR)、示差扫描量热分析(DSC)和红外(FTIR)分析结果表明:这2种催化剂催化丙烯聚合的活性可高达3.25×10~6g聚合物/molTi×h,重均分子量高达4.4×10~5,分子量分布<2.0.降低温度及升高反应压力和延长反应时间都能使聚丙烯分子量增加.观察到聚合初期产物分子量随聚合时间线性增大.在-100~200oC范围内没有观察到熔融峰出现,但在-3.7^-2.6oC区间可以观察到有玻璃化转变温度出现.序列结构分析表明,所生成的聚丙烯为无规结构,但二元组r(62.28%)高于m(37.72%),意味着聚合过程中有间规聚合倾向.[mr/(2mm+mr)]+[mr/(2rr+mr)]=1.04的计算结果进一步说明,由此类催化剂体系催化丙烯聚合生成的产物立体结构序列分布服从伯努利统计模型,聚合主要以1,2-插入方式为主,同时含有少量2,1-插入.

Two half-titanocenes, containing a phosphinimide ligand [（t-Bu）3P=N]CpTiCl2（PT1） and [（t-Bu）3P=N]CpTiMe2（PT2） as the main catalysts for olefin polymerization, were examined in propylene polymerization in the presence of methylaluminoxane（MAO） or [Ph3C][B（C6F5）4] as the co-catalyst. The catalytic performance was also compared with typical {rac-[En（IndH4）2]ZrCl2}（1）, CpTiCl3（2） and Cp2TiCl2（3） catalysts. The effects of experimental conditions, including feeding molar ratio of the co-catalyst to the main catalyst [Al]/[Ti], temperature, propylene pressure and reaction time, on the catalytic activity of the polymerization, the molecular weight and molecular weight distribution of the resulting polypropylenes（PPs） were investigated in detail. A maximal activity of 3.25 × 10^6 g PP/mol Ti·h was attained using PT2/[Ph3C][B（C6F5）4] in the presence of MAO at [Al]/[Ti] = 800. Meanwhile, a highest molecular weight of Mw = 4.42 × 10^5 with a molecular weight distribution of 1.73 was reached with PT1/MAO at [Al]/[Ti]=1200. The molecular weights were increased with decreased polymerization temperature, increased reaction pressure and polymerization time（tp）. Interestingly, it was noted that an asymptotic plot of Mw versus tp was almost linear up to 15 min, indicating a ＂single-site＂ catalytic polymerization. 13C-NMR and IR analyses revealed that the resulting polymers were atactic PPs, which were more or less syndiotactically enriched atactic ones with higher diads r（62.28%） than m（37.72%）. Furthermore, a calculated value of 1.04 for [mr/（2mm ＋ mr）] ＋ [mr/（2rr ＋ mr）] indicated that the polymerization was conducted in agreement with the statistical model of Bernoullian. DSC measurements further confirmed the atactic microstructure of the PPs with a glass transition temperature（Tg） ranged from-3.7 ℃ to-2.6 ℃ without any melting endotherm. Accordingly, the PPs produced in this study by the phosphinimide catalysts were mainly made up of 1,2-insertion units together with a small number of 2,1-insertion units.