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

This work investigated the crystalline forms from melt crystallization in isotactic polybutene-1 (iPB-1) homopolymer via manipulating the temperature where samples were melted (Tmelt) and crystallization pressure (Pcry). Unlike the result under atmosphere condition where the molten sample crystallized into pure form II though the crystallization temperature and kinetic was affected obviously by Tmelt, the melted sample crystallized into forms II or I' under high pressure, depending on the Tmelt and Pcry. The content of form I' decreases with increasing Tmelt or decreasing Pcry. Meanwhile, the critical pressure for the formation of pure form I' increases with increasing Tmelt. 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 (Pcry) which suppressed the nucleation and growth of 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 condition, thus forms I, I' and II are observed, the relative content of the three crystalline forms on samples with different Tmelt and Pcry are obtained in this work. The result provides us that the crystalline forms in melt crystallization of iPB-1 can be customized by regulating the melt state and crystallization condition.