Polymorph selection during melt crystallization of the isotactic polybutene-1 homopolymer depending on the melt state and crystallization pressure

Abstract

This work investigated the crystalline forms obtained from melt crystallization in the isotactic polybutene-1 (iPB-1) homopolymer via manipulation of the temperature at which samples were melted (T_melt) and crystallization pressure (P_cry). Unlike the results under atmospheric conditions where the molten sample crystallized into the pure form II and the crystallization temperature and kinetics were affected obviously by T_melt, the melted sample crystallized into forms II or I′ under high pressure, depending on T_melt and P_cry. The content of form I′ decreases with increasing T_melt or decreasing P_cry. Meanwhile, the critical pressure for the formation of pure form I′ increases with increasing T_melt. The formation of form I′ is attributed to the memory effect of the melt which preserved some ordered sequence of crystal and the high pressure (P_cry) which suppressed the nucleation and growth of the kinetically favored form II, which results in the formation of form I'. In addition, the melt crystallized form II transforms to form I under high pressure conditions; thus forms I, I′ and II are observed. The relative contents of the three crystalline forms on samples for different T_melt and P_cry are obtained in this work. The result shows that the crystalline forms in melt crystallization of iPB-1 can be customized by regulating the melt state and crystallization conditions.