Synthesis and basic characteristics of polypropene-block-poly(ethene-co-propene) by modified stopped-flow polymerization with an MgCl2-supported Ziegler catalyst

A well-defined diblock copolymer, polypropene-block-poly(ethene-co-propene), was synthesized by modified stopped-flow polymerization with an MgCl2-supported Ziegler catalyst. The copolymer shows a unimodal gel permeation chromatography (GPC) elution curve without any material in the low molecular weight region. The molecular weight can be controlled by the polymerization time (ca. 0.1 to 0.2 s). Furthermore, the elution pattern by cross fractionation chromatography showed that the block copolymer eluted at each temperature region between 0°C to 120°C is composed of a uniform material. After extraction with heptane, the 13C NMR spectra showed that the signals from poly(ethene-co-propene) remain unchanged in the block copolymer but are absent in a corresponding polypropene/poly(ethene-co-propene) blend. The results of differential scanning calorimetry (DSC) and optical microscopic observation indicate not only the formation of a block copolymer with a chemical linkage between the polypropene block and the poly(ethene-co-propene) block, but also the regulation of the crystalline morphology in the block copolymer by changing the composition.