A molecular-dynamics model of the behavior of a vacancy in the chain of an equilibrium polymer crystal in the 'united atoms' approximation for polyethylene is developed for the first time. It is shown that a defect of this type in a polymer crystal has a soliton mobility, as opposed to vacancies in crystals of low-molecular substances.
Journal of Experimental and Theoretical Physics, vol.88, No.3, pp. 586-589 (1999)

A molecular-dynamics simulation of the behavior of a twist point defect with stretching in a chain of an equilibrium polymer crystal (“united” atoms approximation for polyethylene) is performed for immobile and mobile neighboring chains. It is shown that such a defect in a cold polymer crystal possesses soliton-type mobility. The upper limit of the spectrum of soliton velocities is found, and it is the same for both cases. The maximum possible velocity of defects is three times lower than the theoretical limit of the spectrum (which is equal to the velocity of “torsional” sound in an isolated chain). An explanation of the reason for this discrepancy is proposed: because of the interaction of two “degrees of freedom” of the defect (twisting and stretching) the energy of a nonlinear wave is dissipated in the linear modes of the system, which results in effective friction whose magnitude depends strongly on the velocity of the defect. The “boundary of the spectrum of soliton velocities” determines the transition between regimes of strong and weak braking of defects.
Journal of Experimental and Theoretical Physics vol.91, No.3, pp.515-523 (2000)

The necessary conditions of the applicability of the Frenkel-Kontorova one-dimensional model [the approximation of immobile neighboring chains plus sine-Gordon (continual) equation for nonlinear dynamics of the chain under consideration] to describing the dynamics of vacancies in a polymeric crystal chain are determined. It is shown that these conditions are satisfied for polyethylene crystals. The physical mechanism of model applicability limitations is established.
Journal of Experimental and Theoretical Physics vol.93, No.4, pp.895-902 (2001)