ENERGETICS OF STRAIN-INDUCED CONFORMATIONAL TRANSITIONS IN POLYMETHYLENE CHAINS

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. © 1990, American Chemical Society. All rights reserved.