Effect of Ga- and BCl _3-modified silica-supported [t-BuNSiMe _2(2,7-t-Bu _2Flu)]TiMe _2/MAO catalyst on ethylene/1-hexene copolymerization

摘要

In this present study, the copolymerization of ethylene and 1-hexene was conducted over the [t-BuNSiMe _2(2,7-t-Bu _2Flu)]TiMe _2 (CGC)/MAO catalyst immobilized on different supports. The effects of Ga and the Lewis acid BCl _3 modification of the silica support on the copolymerization behavior were investigated based on catalytic activity and polymer properties. It was found that the silica support modified with BCl _3 exhibited the highest activity. However, both Ga and BCl _3 modifiers are capable of enhancing the catalytic activity, probably attributed to stronger interaction between the MAO and support together with the acidic sites exerted by the modification which could assist MAO to activate the catalyst during polymerization. Besides, a role of BCl _3 as a spacer to keep apart the catalyst on the silica surface was proposed as another probable reason for activity increased. This led to the more homogeneous-like behavior with less effect of support and also caused the higher comonomer incorporation content. Moreover, the results revealed that narrow polymer molecular weight distribution can be achieved by the supported CGC catalyst, especially for acidic modified supports. On the other hand, there was no noticeable effect with regards to the melting temperature and copolymer microstructure of the Ga and BCl _3 modification. Therefore, based on the study it may be regarded that the efficient supported CGC catalyst can be accomplished through the acidic modification namely Ga and BCl _3.