| Abstract
| - We synthesized four branched n-alkane samples C35−C1, C35−C4, C35−C6, and C35−C4Ph with the samenumber of carbons as the main chain, n = 35, to which the methyl, butyl, hexyl, and butyl phenyl groupswere respectively attached at the middle, and also the corresponding linear homologue of C35, and studiedtheir crystalline structures from DSC, IR, and Raman spectroscopy, X-ray diffraction measurement, andcomputer simulation. Solid−solid phase transitions characteristic of linear alkane C35 are not observed forany branched alkanes, and their melting temperatures Tm are lowered to 325.2, 318.5, 314.3, and 314.1K,respectively. Main chains of branched alkane molecules are not folded, irrespective of length and chemicalstructure of branches, but are extended to take the planar zigzag form in the solid state. The branches ofC35−C4 and C35−C6 are also aligned inside the crystal in the extended form. Data analyses on solution-grown crystallized samples reveal that, with increasing the branch length, their crystal structures transformfrom polymorphic forms of the orthorhombic (P212121) and the triclinic (P1̄) for C35−C1 and C35−C4 tothe unique triclinic form for C35−C6 and C35−C4Ph, so as to minimize extra surface energy invoked byintroduction of long branches.
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