Interplay between a Strong Memory Effect of Crystallization and Liquid-Liquid Phase Separation in Melts of Broadly Distributed Ethylene-1-Alkene Copolymers
Interplay between a Strong Memory Effect of Crystallization and Liquid-Liquid Phase Separation in Melts of Broadly Distributed Ethylene-1-Alkene Copolymers
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DOI：
10.1021/ma501937c
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发表时间：
2014-11-25
期刊：
影响因子：
5.5
通讯作者：
Alamo, Rufina G.
中科院分区：
文献类型：
--
作者：
Mamun, Al;Chen, Xuejian;Alamo, Rufina G.
Narrow metallocene-made random ethylene copolymers display a strong memory effect of crystallization above their equilibrium melting point akin to the melt memory effect observed in model ethylene1-butene copolymers. The onset temperature for self-nucleation or surviving self-seeds displays a bell shape with increasing comonomer content with a maximum at similar to 2 mol % branches. Self-seeds do not survive at temperatures above the equilibrium melting point for homopolymers and copolymers either with very low branching or with a branching content >4.5 mol %. The self-seeds are associated with clusters of ethylene sequences that remain in the melt in close proximity and accelerate a subsequent crystallization, as observed by higher crystallization peak temperatures and higher nucleation density. Contrasting this behavior, commercial ethylene1-alkene copolymers with a broad, bimodal comonomer distribution display an inversion of the crystallization rate in a range of melt temperatures where narrow copolymers show a continuous acceleration of the rate. The inversion demarcates the onset of a self-seed assisted liquidliquid phase separation (LLPS) between comonomer-rich and comonomer-poor molecules. The interplay between number of self-seeds and chain diffusion during LLPS causes a decrease in the crystallization rate with decreasing melt temperature. When crystallites remain in the melt at temperatures
