Mechanism of polymorph selection during crystallization of random butene-1/ethylene copolymer

Abstract

Starting from an initial sample of butene-1/ethylene copolymer with stable form I’, we examined the nucleation of different crystalline polymorphs (here metastable form II and stable form I’) at different isothermal crystallization temperatures after being melted at different melt temperature (T melt). When T melt was just above the melting temperature (T m) of the crystallites, self-seeding took place. There, residue crystallites served as nuclei leading to the crystallization of the same crystalline phase. When T melt was a few degrees above the T m, self-seeding was disabled due to complete melting of the initial crystals. Upon crystallization, the selection of the different polymorphs in this random copolymer was found to depend on an interplay between the domain size of segregated long crystallizable sequences and the size and energy barrier of the critical nucleus of the respective crystalline forms. Our results provide a clear understanding of the polymorphs selection during crystallization of a random copolymer as well as homo-polymers under confinement.