2,6-二异丙基苯酚改性负载型Ziegler-Natta催化剂及其乙烯-1-己烯共聚反应

研究了新型的改性负载型Ziegler-Natta催化剂,以期制备出组成分布较窄的乙烯-α-烯烃共聚物.通过2,6-iPr2C6H3-OH与TiCl4/ID/MgCl2型负载型钛催化剂在室温下的反应可将芳氧基接到催化剂表面,制得一种改性的烯烃聚合催化剂M-cat.改性催化剂对乙烯聚合及乙烯-1-己烯共聚反应的催化活性与未改性催化剂相近,但共单体效应较弱.前者共聚物的1-己烯含量低于未改性催化剂的产物,但组成分布较窄,分子量较高,且共聚物的沸腾正庚烷可溶级分的序列分布较接近无规分布.三异丁基铝为助催化剂所得聚合活性高于甲基铝氧烷活化的体系.改性催化体系的活性中心分布与未改性体系相比有明显的差别.

ETHYLENE-1-HEXENE COPOLYMERIZATION WITH A 2,6-DIISOPROPYLPHENOL MODIFIED SUPPORTED ZIEGLER-NATTA CATALYST

This work attempts to prepare ethylene-α-olefin copolymer with relatively narrow composition distribution by modification of TiCl4/MgCl2 type supported Ziegler-Natta catalyst.A TiCl4/ID/MgCl2 type catalyst,where ID is a diester,was treated at room temperature with 2,6-iPr2C6H3-OH at phenol∶Ti molar ratio of 1∶1,and the modified catalyst was analyzed for contents of titanium and aryloxy group.It was found that about one third of the titanium atoms in the modified catalyst (M-cat) was connected with an aryloxy group,but its Ti content was decreased to 1.44 wt% from 2.36 wt% of the original catalyst (O-cat).Ethylene-1-hexene copolymerization was conducted in n-heptane with M-cat or O-cat as catalyst and triisobutyl aluminium or methylaluminoxane as cocatalyst.The M-cat showed similar activity as the O-cat in catalyzing the copolymerization,but presented a weaker comonomer activation effect than the latter.The 1-hexene content of copolymer synthesized by M-cat was lower than that of the product of O-cat at the same conditions,but had a markedly narrower composition distribution.Each copolymer sample was fractionated into two fractions by extraction with boiling n-heptane,and the soluble part contains much more 1-hexene units than the insoluble part.The ratio of 1-hexene content in the soluble fraction to that of the insoluble fraction was higher than 18 in copolymer prepared with O-cat,but this ratio was reduced to 3.7 when M-cat was used as the catalyst.On the other hand,the soluble part of copolymer prepared with M-cat showed a more random sequence distribution than that of the O-cat.The distributions of active centers in both the M-cat and O-cat were studied by deconvolution of the polymer's molecular weight distribution curves with multiple Flory most-probable distribution function.Both catalysts showed a broad molecular weight distribution that can be ascribed to 5～6 types of active centers,but the introduction of aryloxy group in the catalyst caused marked changes in the active center distribution.Possible mechanism of the catalyst modification was proposed.