A new approach to increase toughness of synthesized PP/EPR in-reactor blends by introducing a copolymerization step under low ethylene concentration

Complex microstructure of the polypropylene/poly(ethylene-co-propylene) in-reactor blends has been the subject of many studies. In this work simple two-step polymerization procedure was considered and effects of adding another copolymerization step with low ethylene concentration were investigated. The blends microstructure and morphology as well as mechanical properties were studied. The blends were characterized using dynamic mechanical thermal analysis (DMTA), gel permeation chromatography (GPC), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and temperature gradient elution fractionation (TGEF). It was found that adding an extra copolymerization step under low ethylene concentration caused considerable increase in the blends toughness, elongation at break and the number of very small dispersed particles in the polypropylene matrix. The mentioned polymerization step produced copolymers having long polypropylene sequences capable to take part in crystallization of polypropylene matrix, suggested acting as linkage between rubber and polypropylene phases. Although the amorphous copolymer related to the additional copolymerization step had a role in decreasing the average size of dispersed phase, the difference in crystallizable copolymer microstructure suggested had a key role in marked enhancement of mechanical properties.