Unusual crystals of poly(ε-caprolactone) by unusual crystallisation: The effects of rapid cooling and fast solvent loss on the morphology, crystal structure and melting

POLYMER

卷:54

Article

Sanandaji, N.¹  Ovaskainen, L.¹  Gunnewiek, M. Klein²  Vancso, G. J.²  Hedenqvist, M. S.¹  Yu, S.³  Eriksson, L.⁴  Roth, S. V.³  Gedde, U. W.¹ 

[1] KTH Royal Inst Technol, Sch Chem Sci & Engn Fibre & Polymer Technol, SE-10044 Stockholm, Sweden

[2] Univ Twente, NL-7500 AE Enschede, Netherlands

[3] HASYLAB DESY, DE-22607 Hamburg, Germany

[4] Stockholm Univ, Arrhenius Lab, SE-10691 Stockholm, Sweden

关键词: Poly(epsilon-caprolactone);    Polymer single crystal;    Rapid expansion of a supercritical (CO2);    solution;   

DOI  :  10.1016/j.polymer.2013.01.014

来源: Elsevier

【 摘 要 】

The lateral habit, unit cell structure and melting behaviour of single crystals of poly(epsilon-caprolactone) (PCL) prepared by the rapid expansion of a supercritical solution technique was studied by AFM at ambient and higher temperatures and by grazing-incident X-ray scattering using a synchrotron source. After dissolving PCL in a solution of supercritical CO2 and 0.1 vol.% chloroform, an extremely fast phase transfer from a supercritical to a gas-like state occurred during expansion into atmospheric conditions, leading to a temporary temperature drop to below -;50 degrees C at the silica surface where the crystals were deposited. Single crystals of a hitherto unreported rectangular lateral habit were observed. Six-sided crystals were also observed, but they were fewer than the rectangular crystals and in addition the angles between the lateral faces were different from the theoretical angles between adjacent {110} faces and {110} and {100} faces. X-ray scattering indicated a polymorphic structure also including the orthorhombic (110) and (200) diffraction peaks. Distinct low angle peaks essentially along the c-axis indicated a stacking on a very fine scale (3.7-4.7 nm) within the crystals. The equatorial diffraction peaks indicated a less dense packing of the PCL stems. Rectangular single crystals with a height according to AFM of 11-27 nm melted between 40 and 45 degrees C, which is lower than the melting points (55 degrees C) recorded for the distorted six-sided crystals. The unusual conditions for crystallisation used gave the polymer molecules a severe limitation to rearrange from the initial random coil state. The facetted crystals consisted of a stack of 4 nm thick blocks; these blocks most probably constituted a regular variation in molecular packing, i.e. molecular order. The pronounced changes in the angles between adjacent faces from those observed in mature PCL crystals and the wide-angle X-ray scattering data indicated the presence of conformational disorder in the crystals. (C) 2013 Elsevier Ltd. All rights reserved.

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