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本文确立了以硫酸高铈溶液分析钨的价态方法,并应用于研究烷基铝对六氯化钨的还原作用,发现还原能力取决于烷基铝的种类、用量和实验条件。各种烷基铝的还原能力为:i-Bu_2AlH>i-Bu_3Al>Et_3Al_2Cl_3。此外,烷基铝与钨化合物络合生成一种稳定的活性中心是导致引发聚合的重要原因。单体对六氯化钨有还原作用,但是这种还原作用与烷基铝相比还是较弱的。钨的平均价态低于二价时聚合活性降低。在钨的平均价态不低于二价的情况下,聚合活性主要取决于活化剂或活化剂种类,带有吸电子基团的芳香族羟基化合物助催化活性高,带有给电子基团的羟基化合物助催化活性低。一般来说,催化剂陈化都导致聚合活性的明显降低,在四氯苯酚存在下各种加料次序对聚合活性影响不大。本文的一些实验结果更符合于卡宾型反应机理。
In this paper, the method for the determination of tungsten valence by ceric sulfate solution has been established and applied to study the reduction of tungsten hexachloride by aluminum alkyl. The reduction ability depends on the type, amount and experimental conditions of aluminum alkyl. The reducibility of various aluminum alkyls is: i-Bu_2AlH> i-Bu_3Al> Et_3Al_2Cl_3. In addition, aluminum alkyl complexes with tungsten compounds to form a stable active site is the main reason leading to polymerization. Monomers have a reduction of tungsten hexachloride, but this reduction is still weaker than aluminum alkyls. When the average tungsten valence is lower than 2, the polymerization activity decreases. In the case where the average valence of tungsten is not less than two, the polymerization activity mainly depends on the kind of activator or activator, the aromatic hydroxy compound having an electron-withdrawing group has a high cocatalytic activity, Hydroxy compounds have low cocatalytic activity. In general, the catalyst aging resulted in a significant decrease in the polymerization activity, and the various loading sequences in the presence of tetrachlorophenol had little effect on the polymerization activity. Some of the experimental results in this paper are more in line with the Carbin reaction mechanism.