A comparison of the morphology and crystallization kinetics of two centrally branched monodisperse alkanes with n-alkanes of equal and half length

Abstract

The isothermal crystallization kinetics and morphologies of two centrally branched monodisperse alkanes have been studied and compared with two long n-alkanes, one of equal and one of half, the molecular length of the branched molecules. The two branched alkanes were C96H193.CHR.C94H189 with R being methyl or butyl, respectively, while the long n-alkanes were C194H390 and C98H198. Both branched molecules invariably crystallize once-folded in contrast to both n-alkanes in which molecules are always fully extended in lamellae, demonstrating that branches are excluded and lie in the folds. At high temperatures, both branched systems form scrolls with all folds on the outer convex surface of quasi-cylindrical lamellae. The crystallization range of the branched alkanes is identical to that of n-C98H198 and the kinetics a little slower, more so for the butyl-branched material; n-C194H390 crystallizes more slowly and at higher temperatures. It follows that the second fold stem of a branched molecule is laid down much faster than the first, as expected for secondary nucleation, a conclusion which splaying data support. Transient ciliation in these chainfolded systems is sufficiently long-lived to yield the same splaying as permanent cilia do in binary blends of n-alkanes and is a pointer to the behavior of polyethylene.

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ORCID for I.L. Hosier: orcid.org/0000-0003-4365-9385

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