Improvement in productivity and molecular weight of polypropene-block-poly(ethene-co-propene) obtained by a modified stopped-flow method using various external electron donors

The efficiencies of various types of external electron donors to improve th e productivity and molecular weight of the block copolymer, polypropene-blo ck-poly(ethene-co-propene) obtained by a modified stopped-flow method were investigated, directed toward commercial production. Five alkoxysilanes hav ing different structures, and a piperidine compound were employed as extern al donors. In all cases, an increase in the activity and weight-average mol ecular weight was observed on addition of the external donor at a Si/Ti mol e ratio of ca. 1.0. Diisopropyldimethoxysilane was considered to be the mos t suitable donor for the synthesis of the block copolymer, due to its highe r 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 p aper are an indication that a suitable choice of the kinds of external dono rs, Si/Ti mole ratio, and TEA concentration an needed to obtain block copol ymers with desirable performance.