【摘要】 考察了TiCl₄-AlC₂H₅Cl₂催化体系中钛的价态对乙烯高聚或低聚的影响。Ti（Ⅳ）与Ti（Ⅲ）形成不同的活性中心,乙烯在Ti（Ⅳ）活性中心上生成低聚物,在Ti（Ⅲ）活性中心上生成高聚物。当这两种活性中心共存时互不干扰,同时生成相应的低聚物和高聚物。链转移速度在Ti（Ⅳ）活性中心上比在Ti（Ⅲ）上至少大两个数量级,而链增长速度则在同一个数量级。说明在此体系中,由于价态变化而改变的β-H转移速度是决定生成高聚物或低聚物的主要原因。更多还原

【Abstract】 By using TiCl4-AlC2H5Cl2 catalyst, the role of Ti valence state in the oligomerization or polymerization of ethylene was investigated. Experimental results show that if titanium of the catalyst is kept as Ti(Ⅳ), only oligomer can be obtained, whereas if Ti(Ⅳ) is deeply reduced to Ti(Ⅲ), the main product will be polymer. When Ti(Ⅲ) and Ti(Ⅳ) coexist in the system, both polymer and oligomer are obtained. It is of interest that the molecular weight of the oligomers produced is almost the same regardless of whether in the catalyst system Ti(Ⅲ) exists or not. Futhermore, a plot of the rate of ethylene absorption versus Ti(Ⅳ)% gives a straight line. It is suggested that different active species are formed on the Ti(Ⅳ) and Ti(Ⅲ).Oligomer is formed on the Ti(Ⅳ) active species while polymer on the Ti(Ⅲ) active species, and these two kinds of active species do not interfere with each other.It is estimated that the chain transfer rate on the Ti(Ⅳ) active species is at least two order of magnitude larger than that on the Ti(Ⅲ) active species, whereas the difference of the chain propagation rates is small and the chain propagation rates on these two different species are within the same order of magnitude. Therefore, the change of valence state which in turn changes the rate of B-hydrogen transfer is the main factor that determines whether polymer or oligomer is formed.更多还原