Mechanisms of nucleation and crystal growth in a nascent isotactic polypropylene/poly (ethylene-co-octene) in-reactor alloy investigated by temperature-resolved synchrotron SAXS and DSC methods

Abstract

The nucleation and lamellar growth mechanisms of nascent isotactic polypropylene/poly(ethylene-co-octene) (N-iPP/PEOc) in-reactor alloy were investigated with temperature-resolved synchrotron small angle X-ray scattering (SAXS), differential scanning calorimeter (DSC) and polarized optical microscopy (POM) methods. We have observed two crystallization peaks (fractionated crystallization behavior) during cooling process in N-iPP/PEOc in-reactor alloy. We also determined that the crystallinities from that two crystallization peaks were dependent on liquid–liquid phase separation (LLPS) time with t0.10 and t−0.28, respectively. It was explained that the fractionated crystallization behavior in the N-iPP/PEOc in-reactor alloy system was caused by crystal nucleation occurring in the iPP rich domain by heterogeneous nucleation and at interface of iPP and PEOc rich domains by the fluctuation assisted nucleation. The fluctuation assisted nucleation only occurred at interface of iPP and PEOc domains by concentration fluctuation through the coupling of liquid–liquid spinodal decomposition and the cross-over to crystal nucleation process. Both lamellar crystals formations from heterogeneous and fluctuation assisted nucleation in N-iPP/PEOc were probed by temperature-resolved SAXS during cooling process. Our results provide the physical model for the multiple nucleation and crystal growth mechanisms in the multi-component, multi-phase polymer systems such as in-reactor alloy or blend.