无机/有机复合载体负载TiCl_3/(n-BuCp)_2ZrCl_2复合催化剂用于宽峰聚乙烯的制备

采用溶胶-凝胶法,将苯乙烯-丙烯酸(PSA)共聚物包覆在以硅胶/MgCl2为载体的TiCl3催化剂上,负载(n-BuCp)2ZrCl2后制得Ziegler-Natta/茂金属复合催化剂。实验在同一反应釜中进行两段反应模拟双釜串联聚合工艺。在第一段反应中制备高分子量高支化度的乙烯/1-己烯共聚物,在第二段反应中,制备低分子量低支化度的聚合物。淤浆聚合结果表明,所得聚乙烯的熔融流动比(MI21.6/MI2.16)较宽,达到79,分子量分布达到18.6。两段反应得到的聚乙烯共混物的结晶度和熔融温度介于第一段、第二段单独反应时所得产物的结晶度和熔融温度之间,且DSC曲线具有单一的熔融峰,说明该两段反应法制备的聚乙烯共混物具有良好的共结晶行为。动力学研究同时表明,苯乙烯-丙烯酸共聚物的引入,使得催化剂的活性缓慢释放,活性持续时间明显长于负载于无机载体的催化剂,有利于灵活地调节各段反应的停留时间。

Novel organic/inorganic support for immobilizing TiCl3/( n -BuCp)2ZrCl2 catalyst to prepare wide distribution polyethylene

A novel organic/inorganic support for immobilizing a hybrid catalyst used in ethylene polymerization was devised.The composition of the hybrid catalyst was as follows：styrene and acrylic copolymer (PSA) was the organic part for binding (n-BuCp)₂ZrCl₂, and SiO₂/MgCl₂ was the inorganic part to immobilize TiCl₃.As an alternative to a tandem or cascade type process, a two-step polymerization method was carried out in a single reactor on a laboratory scale.Utilizing this two-step polymerization process, reactor blends of high molecular weight (made in the first step) copolymer and low molecular weight homo-polymer (made in the second step) were produced that were similar to industrial resins.The results showed that polymer blends had bimodal molecular weight distribution and broad melt flow rate (MI_21.6/MI_2.16=79).Besides, the melting point and crystallinity of the blends were in the range of polymers made separately in the first and second polymerization steps, indicating that the polymer obtained by the hybrid catalyst had good co-crystallinity.Catalyst kinetic curves in each polymerization step showed that the introduction of PSA facilitated gradual generation of the active sites of catalyst.Thus, the activity could be maintained in a long time in each polymerization step.