Polymorphs Selection in Random Copolymers

Y.F. Men, Y.T. Wang, and J.Y. Zhao

State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, University of Chinese Academy of Sciences, Renmin Street 5625, 130022 Changchun, P.R. China

Many polymers exhibit different polymorphous structure depending on crystallization condition. In random copolymers, the melt state is often structured having segregations of crystallizable chain segments originating from the melting of previous crystals when the system has not been treated at temperature high enough (much higher than the equilibrium melting temperature of the corresponding crystals). Clearly, when being annealed at different melt temperatures, the size of such segregations can be varied so that the followed crystallization can be affected under different confinements. We report in this work a peculiar observation of polymorph selection during crystallization of a butane-1/ethylene random copolymer of 10 mol% ethylene co-units. Depending on previous crystalline size, melt temperature and crystallization temperature, the system showed a systematic variation in polymorphs. It turns out that such polymorphs selection depends on the 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.

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[2] T. Wang, P.R. Liu, Y. Lu and Y.F. Men, Chin. J. Polym. Sci. 34, 1014 (2016). (link)