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Crystallisation behavior and crystal rearrangement of poly(ethylene oxybenzoate)
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2005 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 413/414, no Sp. Iss. SI, 435-441 p.Article in journal (Refereed) Published
Abstract [en]

One complex fact of polymer crystallisation is that polymer crystals have a tendency to rearrange with time. In this paper, poly(ethylene oxybenzoate)s (PEOB) with different degrees of polymerisation ranging from 5 to 30 have been studied by differential scanning calorimetry and polarised microscopy. The samples showed a great tendency for crystal rearrangement during heating to the melting point, even at high heating rates. The relationship between melting point and crystallisation temperature was analyzed and the Hoffman-Weeks method was found to be unsuitable for determining the equilibrium melting point of these polymers. It is proposed that fast crystal rearrangement, which is a characteristic feature of poly(ethylene oxybenzoate), is the reason for the inadequacy of the Hoffman-Weeks method to obtain reliable estimates of the equilibrium melting point. Polarised microscopy showed, remarkably in view of the low molar mass of the polymers, the formation of perfect banded spherulites. Linear growth rate data suggested that the branched polymers crystallised more slowly than their linear analogues, presumably due to differences in the equilibrium melting point.

Place, publisher, year, edition, pages
2005. Vol. 413/414, no Sp. Iss. SI, 435-441 p.
Keyword [en]
Crystal rearrangement, Equilibrium melting point, Melting, Polymer crystallisation
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-5973DOI: 10.1016/j.msea.2005.08.168ISI: 000234202900071Scopus ID: 2-s2.0-29444447766OAI: oai:DiVA.org:kth-5973DiVA: diva2:10525
Note

QC 20100907

Available from: 2006-06-07 Created: 2006-06-07 Last updated: 2016-12-16Bibliographically approved
In thesis
1. Crystallization in Constrained Polymer Structures: Approaching the Unsolved Problems in Polymer Crystallization
Open this publication in new window or tab >>Crystallization in Constrained Polymer Structures: Approaching the Unsolved Problems in Polymer Crystallization
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

The knowledge regarding certain issues in polymer crystallization e.g. the possible existence of short–lived mesophases remains inconclusive due to experimental limitations. Polymers undergo chain folding upon crystallization, which introduces some complications that are not found in crystallization of low molar mass materials. Chain–folded crystals are far from their equilibrium shape and they rearrange rapidly at the crystallization temperature. This, together with the slow experimental techniques traditionally used, impedes the observation of the originally formed structures. To approach this problem, molecularly constrained polymer structures (in which the crystallizing chains are fixed at one end whereas the other end is free to move) have been studied by X–ray diffraction, differential scanning calorimetry, polarized optical microscopy, transmission electron microscopy and atomic force microscopy.

The crystallization studies performed in star–branched polyesters showed that the dendritic cores have a pronounced effect on the crystallization of the linear poly(ε–caprolactone) (PCL) arms attached to them. The star–branched polymers showed slower crystal rearrangement, higher equilibrium melting point, higher fold surface free energy, moderately lower crystallinity, and a greater tendency to form spherulites in comparison with linear PCL. The crystal unit cell was the same in both linear and star–branched PCL. Single crystals of the star–branched polymers were more irregular and showed smoother fold surfaces than linear PCL crystals. No sectorial preference was observed in the crystals of the star–branched polymers upon melting while the single crystals of linear PCL showed earlier melting in the {100} sectors than in the {110} sectors. Some of the differences observed can be attributed to the dendritic cores, which must be placed in the vicinity of the fold surface and thus influence the fold surface structure, the possibility of major crystal rearrangement and the presence of a significant cilia phase during crystal growth causing diverging crystal lamellae and consequent spherulite formation. The attachment of the many crystallizable chains to a single core reduces the melt entropy, which explains the higher equilibrium melting point of star–branched PCL.

The crystallization behavior of a series of poly(ethylene oxybenzoate)s was also studied. The polymers showed a profound tendency for crystal rearrangement during melting even at high heating rates. The Hoffman–Weeks extrapolation method was found to be unsuitable to calculate the equilibrium melting point of the samples studied because the melting point vs. crystallization temperature data were sensitive to the variations in crystallisation time, which led to significant variations in the equilibrium melting points obtained.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 72 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:17
Keyword
Crystallization, Constrained structures, poly(ε–caprolactone), poly(ethylene oxybenzoate).
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-4041 (URN)91-7178-375-X (ISBN)
Public defence
2006-06-16, Sal K2, Teknikringen 28, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100914Available from: 2006-06-07 Created: 2006-06-07 Last updated: 2010-09-14Bibliographically approved

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