Structure and morphology of polypropylene/poly(ethylene-co-propylene) in situ blends synthesized by spherical Ziegler–Natta catalyst

Polypropylene/poly(ethylene-co-propylene) (iPP/EPR) in situ blends of different composition were synthesized by spherical Ziegler–Natta catalyst, and were fractionated into three portions: the random copolymer (EPR), the block copolymer, and the iPP matrix. The EPR fraction was characterized by 13C NMR, and the block copolymer fraction was characterized by crystalline segregation and differential scanning calorimetry analysis. The blends showed bi-phase structure with EPR existing in the dispersed phase. Increasing EPR in the blends resulted in increase of the number and diameter of the EPR particles, but there is an upper limit for the particle number. There were only highly irregular spherulites or tiny crystallites in the isothermal crystallized blends. The morphology of the impact fracture surfaces of the blends clearly showed that they were fractured in ductile fashion. There was strong dependence of impact strength of the blends on their morphology, and the sequence distributions of the EPR and segmented copolymer fractions also markedly influenced the mechanical properties.