Effect of molecular mobility of pre-ordered phase on crystallization in microphase-separated lamellar morphology of strongly segregated crystalline-crystalline diblock copolymers

Publication date: 5 May 2017
Source:Polymer, Volume 116
Author(s): Shiki Nojima, Yuji Higaki, Katsuhiro Kaetsu, Ryohei Ishige, Noboru Ohta, Hiroyasu Masunaga, Tomoyasu Hirai, Ken Kojio, Atsushi Takahara
The effect of molecular mobility of a pre-crystallized phase on the isothermal crystallization in the microphase-separated lamellar morphology of a strongly segregated crystalline-crystalline block copolymer, poly(ethylene glycol)-block-poly(perfluorooctylethyl acrylate) (PEG-b-PFA-C8), was investigated. The diblock copolymer produced a microphase-separated lamellar morphology in the melt state, and the precedent crystallization of PFA-C8 blocks provided the lamellar confinement field. The counter PEG block crystallized within the lamellar confinement field. The molecular mobility of the pre-crystallized PFA-C8 phase was modulated by the thermal history. The structural evolution was monitored by a complementary combination of in situ time-resolved simultaneous small-angle X-ray scattering/wide-angle X-ray diffraction measurements and thermal analyses. The degree of crystallinity and the melting temperature of the PEG crystals were associated with the molecular mobility of the pre-crystallized PFA-C8 phase. The highly packed PFA-C8 phase (higher-ordered phase) constrained the PEG crystallization, whereas the loosely packed PFA-C8 phase (lower-ordered phase) caused a weak restriction in the PEG crystallization to give relatively ordered PEG crystals. Subsequent crystallization in a confinement field of crystalline-crystalline block copolymers was controlled by adjusting the molecular mobility of the pre-crystallized phase.

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