The efficiencies of various types of external electron donors to improve the productivity and molecular weight of the block copolymer, polypropene-block-poly(ethene-co-propene), obtained by a modified stopped-flow method were investigated, directed toward commercial production. Five alkoxysilanes having different structures, and a piperidine compound were employed as external donors. In all cases, an increase in the activity and weight-average molecular weight was observed on addition of the external donor at a Si/Ti mole ratio of ca. 1.0. Diisopropyldimethoxysilane was considered to be the most suitable donor for the synthesis of the block copolymer, due to its higher initial activity and properties, giving a polymer having higher molecular weight. An improvement in the molecular weight with considerable catalyst deactivation was apparently observed by increasing the Si/Ti mole ratio and decreasing the triethylaluminum (TEA) concentration. The results in this paper are an indication that a suitable choice of the kinds of external donors, Si/Ti mole ratio, and TEA concentration are needed to obtain block copolymers with desirable performance.
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Mori et al. (1999) studied this question.
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