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Unusual crystals of poly(epsilon-caprolactone) by unusual crystallisation: The effects of rapid cooling and fast solvent loss on the morphology, crystal structure and melting
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2013 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 54, no 5, 1497-1503 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2013. Vol. 54, no 5, 1497-1503 p.
Keyword [en]
Poly(epsilon-caprolactone), Polymer single crystal, Rapid expansion of a supercritical (CO2), solution
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:su:diva-88976DOI: 10.1016/j.polymer.2013.01.014ISI: 000315746300005OAI: oai:DiVA.org:su-88976DiVA: diva2:615863
Funder
Swedish Research Council, 2006-3559Swedish Research Council, 2009-3188Knut and Alice Wallenberg Foundation
Note

AuthorCount:9;

Available from: 2013-04-12 Created: 2013-04-08 Last updated: 2017-12-06Bibliographically approved

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Eriksson, Lars
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Department of Materials and Environmental Chemistry (MMK)
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