Analysis of Formation Mechanism of Crystal Form I in Isotactic Polybutene-1 Based on a Melting Memory Method

Abstract In this paper, the melting memory effect generated by a new protocol of cyclic thermal treatment with form II as “seeds” on the polymorphic transformation in isotactic polybutylene-1(iPB-1) was investigated. Polar Optical Microscope (POM), wide angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR) were used to study the change of morphology and crystal form II→I transition during aging. Selected crystallization temperature (Tsc) and melting temperature (Tsm) were applied to generate residual nuclei of form II. The cycled and uncycled samples were analyzed to demonstrate the formation of crystal I and polymorphic transformation. The results indicate that the melting memory has a significant effect on tetragonal modification, with an increased nucleation density and an accelerated nucleation speed. The ordered chain sequences in crystal II initiated the formation of crystal nucleus of form I, which subsequently induce fast conversion and increased transition degree in the hexagonal crystal growth. Form I was found to have two formation pathways, including the transformation of the unstable crystal form II and the direct formation from residual crystal and melt, which have been rarely discussed before and may shed light on understanding of crystal formation mechanism in polymorphism polybutene-1.