Electron donor-induced improvement of the microstructure of polypropene-block-poly(ethene-co-propene) synthesized by a modified stopped-flow polymerization method and correlation with its crystalline morphology

The influence of electron donors on the synthesis of polypropene-block-poly (ethene-co-propene) (PP-b-(PE-co-PP)) using a modified stopped-flow polymer ization method was examined in terms of correlation of the microstructure o f the polymer with its crystalline morphology. The results of propene homop olymerization and ethene-propene copolymerization indicated that the applic ation of suitable internal and external donors induced an improvement in th e stereoregularity of polypropene (PP) without a decrease in the initial ac tivity and a significant change in the monomer composition and monomer sequ ence distribution of the poly(ethene-co-propene) (PE-co-PP). The TiCl4/ethy lbenzoate/MgCl2 - cyclohexylmethyldimethoxysilane catalyst system was found to produce PP-b-(PE-co-PP) having highly isotactic PP segments. The result ing block copolymers were investigated by cross-fractionation chromatograph y and differential scannning calorimetry, suggesting that the improved ster eoregularity of the PP part in the PP-b-(PE-co-PP) had an effect only on th e crystallinity and crystallinity distribution but had no influence on the crystallizability and lamellar thickness of the block copolymer. (C) 1999 E lsevier Science Ltd. All rights reserved.