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Deformation potentials have been calculated for highly extended polymethylene chains containing simple torsional defects. The calculations were performed by using molecular mechanics techniques. The deformation potentials show abrupt discontinuities, which have been identified as gauche-trans transitions of chains containing strained defects into chains in the fully extended zigzag form. The reverse transgauche transition was observed during compression of all-trans chains. The observed discontinuity in the conformational transition is a direct consequence of the input of mechanical energy into the torsional angles and also into the bond lengths and bond angles in the chain. The transition point imposes a limit on the amount of energy stored in chains containing defects; the energy is fully recovered at the transition. It is suggested that abrupt conformational transitions may occur upon drawing crystalline and glassy polymers as a mechanism of avoiding large translational movements of atoms under the conditions of strong constraints from neighboring chains. The Hookean behavior of single chains containing a conformational defect was tested and the effect of this defect on the chain modulus was estimated.

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The report gives molecular-mechanical calculations of potential V(φ) of internal rotation around the central C-C bond in n-hexane with full geometry optimization. Basides the conformational dependence of the potential energy (strain energy), also torsion dependence of vibration entropy, zero point energy (E0) and heat of formation have been calculated for hexane. Limitations of bond-drive technique in application to quantitative static and dynamic characterization of internal rotation are pointed out. Effect of the condensed phase on V(φ) has been assessed on the basis of a simplified model of medium as continuum.