Direct formation of form I’ crystals in polybutene-1/polypropylene blend enhanced by cold crystallization

Abstract

During commercial processing of isotactic polybutene-1 (PB-1), crystallization kinetics favor form II while thermodynamics favor the more desired form I/I′, and once the former is adopted, transformation to the latter is extremely slow. In this work, the cold crystallization behavior of PB-1/iPP (isotactic polypropylene) blend (90/10) is investigated with emphasis on the competition between the PB-1 polymorphs. The PB-1/iPP blend is quenched from the melt, annealed first at a low temperature and then at a high temperature, with the ensuing crystallization studied by in-situ Fourier transform infrared spectroscopy, differential scanning calorimetry, and wide-angle X-ray diffraction. It is found that upon annealing at low temperature, form II formation is suppressed and form I′ nuclei prevail, which then develop into crystalline PB-1 dominated by form I′ in the subsequent annealing at room temperature or above. The formation of form I′ as the major polymorph in PB-1/iPP blend containing only a small amount of iPP is attributed mainly to the confinement on PB-1 imposed by the dispersed iPP chains, which hinders form II nucleation.