Low energy crystal structures of poly(di-methyl silane), which is known to have a trans backbone conformation, have been investigated. Energy calculations on isolated molecules show that, like its hexyl counterpart, the lowest energy backbone conformation of the molecule is not all-trans but a helix with the backbone bonds rotated 15 ° away from trans. This corresponds approximately to a 15/7 helix. To determine if the observed trans conformation results from intermolecular interactions, various packing modes of the trans and the 15/7 helix were analysed and their energies compared. Best packing was found for the trans conformation. For the all-trans molecules arranged in an orthorhombic unit cell, the lowest intermolecular energy was found for a = 1.19 and b = 0.78 rim, in good agreement with dimensions found experimentally at room temperature.
Посилання на статтю:
Energy calculations of the crystal structure of poly (di-methyl silane) / S. S. Patnaik and B. L. Farmer // Polymer. – 1992. – Vol 33. – P. 5121-5127.