Fractionated and confined crystallization of polybutene-1 in immiscible polypropylene/polybutene-1 blends*

The crystallization of immiscible polypropylene (PP)/polybutene-1 (PB) blends, in particular the effect of crystal morphology of PP (HTC) on the subsequent crystallization behavior of PB (LTC) was studied. We firstly deemed that PP/PB blends are not complete compatibility but characterized as the LCST-like phase diagram above the melting temperature of PP. Crystallization of PP at different crystallization temperatures brought different PP crystal morphologies and PB was segregated and confined at different locations. Much larger-sized domain of PB component appeared in PP spherulites resulting from the effects of non-negligible phase separation and the slower PP crystallization rate as PP crystallized at high temperature. As temperature continued to fall below Tm of PB, the fractionated and confined crystallization of PB occurred in the framework of PP spherulites reflecting as the decreased crystallization temperature (Tc) of PB and the formation of form I’ beside form II. If PP previously crystallized at high Tc, fractionated crystallization of PB became prominent and confined crystallization of PB became weak due to the much wider droplet-size distribution of PB domains.