Investigation on the Polymorph Selection during Recrystallization of Isotactic Polybutene-1 Homopolymer

Abstract

The influence of melt structure on the polymorphic selection during recrystallization of isotactic polybutene-1 (iPB-1) was investigated with differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) measurements in this work. The melt with varying ordered structures was prepared by controlling the melt temperature (T_me). The result revealed a significant memory effect on the polymorphic selection in recrystallization, which recrystallized into form I' or II depending on T_me and the initial crystallization temperature of the sample. The T_me range, which was commonly divided into three Domains (Domains I, II, and III) according to the recognized rule, was re-divided. Where the Domain III was further divided into three regions while Domain II was further divided into two regions based on the melting of initial form I and the polymorphic selection in recrystallization. To be specific, only the initial crystal form I is observed in Domain III_c; form I' generated in Domain III_b; while in Domain III_a, a mixture of forms I' and II formed; when T_me reaches Domain II_b, the melt crystallize into form II while no formation of form I' is observed; in Domain IIa, where only form II is shown, the initial crystal form I is not observed. Samples with different initial crystallization temperatures exhibit significant variations in the specific boundary temperatures of Domains, which may be attributed to the lamellar thickness and its distribution in the initial crystals. Overall, the polymorph selection is attributed to the heterogeneous melting of the initial lamellae.