Molecular deformation of polyethylene

Torsional potential and strain energy distribution in an extended chain under stress

“…The quality of the calculated distribution of elastic energy critically depends on the mutual balance of the force constants and other parameters in the MM method. However, regardless of the quantitative correctness of partition of the elastic energy, our calculations corroborate the conclusion of previous works [4][5][6]: neither of the valence coordinate changes can be neglected in the energetics of chain deformation. Indirect support for the reliability of parametrisation in the method of Boyd comes from a good agreement recently found [5] between the calculations of vibrational shift at deformation, and FTIR and Raman spectra measurements for oriented polyethylene.…”

“…3 and Table 1 gives important information about the sites of major excess of accumulated elastic energy. Together with the results of previous calculations on polyethylene, polypropylene and aromatic polyamides [4][5][6]9], these data should be relevant to the energetics of chain scission, crack propagation and failure of polymeric materials. The quality of the calculated distribution of elastic energy critically depends on the mutual balance of the force constants and other parameters in the MM method.…”

“…Since a stretching of chain to the contour length L corresponds to strain 3.97%, it means that the transition to the extended state proceeds at a chain length slightly exceeding the contour length. A similar type of conformational transition involving the kink defect ...g+tg-... with two gauche states of opposite sign was presumed to occur at the deformation of tie molecules in semicrystaUine polyethylene and related polymers [10], and the abrupt "flip-flop" character of transition was recently confirmed by the MM computations [6]. Our computations for both the gauche and kink defects in a paraffin chain suggest that the gauche-trans transition is connected with a strong coupling of the valence coordinate changes at deformation.…”

“…Currently, the most reliable determination of the potential energy of strained hydrocarbon chains is based on the MM calculations [1, 2]. Boyd's version of this method has been particularly successful in the elucidation of structure and dynamics of polymer chains either undeformed or subjected to the uniaxial stress [3][4][5][6]. Since the details of the method have been given previously [1-7] only a few pertinent facts are reviewed here.…”

Energetics of Stretching of Conformational Defects in Extended Poly(methylene) Chains

“…[3 -7] Calculations have shown that the transition of a defect into a more extended conformation proceeds by an abrupt change of the deformation potential. [3][4][5][6] A flip-flop interconversion of the torsional angles within a defect brings about the change from the shorter (kink) into the longer (all-trans) state. For chains containing the single-kink or jog defects the stored elastic energy was calculated.…”