MgCl_2/AlEt_n(OEt)_(3-n)负载单茂钛催化剂催化乙烯聚合研究

以MgCl2/AlEtn(OEt)3-n为载体,分别负载五甲基茂基三氯化钛(Cp*TiCl3)和五甲基茂基三苄氧基钛(Cp*Ti(OBz)3),得到两种负载催化剂,在较廉价的AlEt2Cl为助催化剂常压下可以高效地催化乙烯聚合.报道了载体的制备、聚合条件(不同的烷基铝助催化剂、聚合温度、铝钛摩尔比)对催化剂的聚合行为以及聚合物结构的影响.研究结果表明,两种负载催化体系对乙烯聚合具有较高的催化活性,可达105g PE/(molTi·h)数量级,所得聚乙烯的黏均分子量在105以上.经过13C-NMR和DSC分析,两种负载催化剂得到的均为线型聚乙烯.与均相催化剂相比,负载后的单茂钛催化体系的聚合反应动力学表现高效而平稳.这表明载体的微孔结构使活性中心得到了有效的分散,有效地提高了催化剂的活性,同时载体的受限空间有效抑制了聚乙烯增长链的β-H消除反应.

ETHYLENE POLYMERIZATION OVER MgCl2/AlEtn(OEt)3-n SUPPORTED HALF-TITANOCENE CATALYSTS

Half-titanocene catalysts (Cp*TiCl_3,Cp*Ti(OBz)_3) supported on MgCl_2/AlEt_n(OEt)_(3-n) were used for ethylene polymerization with a cocatalyst of common inexpensive AlEt_2Cl.The polymerization conditions such as the cocatalyst,Al/Ti ratio and temperature had significant effects on catalytic activity and properties of the resultant polyethylene.Results showed that the two supported catalysts exhibited high activity in the presence of AlEt_2Cl with 10~5g PE/(mol Ti·h) magnitude of order,and the viscometric molecular weight of the obtained polyethylene was higher than 10~5.In addition,the prepared polyethylene was essentially linear polyethylene according to ~13C-NMR and DSC analyses.Compared with the corresponding homogeneous catalyst system,the kinetic curves of polymerization were quite steady during the reaction process.It is recommended that the surface morphology and the internal porous structure of the supported catalyst were beneficial for the dispersion of active species,resulting in the increase of the activity,and the active species anchored on confined space of MgCl_2/AlEt_n(OEt)_(3-n) pores could inhibit the occurrence of β-H elimination reaction.