Fractionated and Confined Crystallization of Polybutene-1 in Immiscible Polypropylene/Polybutene-1 Blends

In this work, the crystallization of immiscible polypropylene (PP)/polybutene-1 (PB) blends, in particular the effect of crystal morphology of PP (HTC, high T_m component) on the subsequent crystallization behavior of PB (LTC, low T_m component) was studied. Herein, we firstly indicated that PP/PB blends were not completely compatible but characterized as the LCST-like phase diagram above the melting temperature of PP. Crystallization of PP at different crystallization temperatures brought about 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 T_m of PB, the fractionated and confined crystallization of PB occurred in the framework of PP spherulites, reflected by the decreased crystallization temperature (T_c) of PB and the formation of form I′ beside form II. Notably, if PP previously crystallized at high T_c, fractionated crystallization of PB became predominant and confined crystallization of PB became weak due to the much wider droplet-size distribution of PB domains.