Thermoelastic measurements dealing with adiabatic heating under application of rapid strain (stress) afford a new approach to evaluate important thermal properties of viscoelastic materials. The effects of both dynamic cyclic extension and swelling on the thermoelastic behavior of the acrylonitrile butadiene rubber (NBR) loaded with different concentration of polyvinyl chloride (PVC) have been studied. As the strain amplitude increases, the concentration of the ruptured bonds increases, leading to more enhanced friction between particles and consequently to the observed rise in temperature. This temperature change decreases with increasing PVC concentration up to critical concentration. Swelling behavior of samples was investigated. It was found that swelling as well as diffusion coefficient has a higher level of solvent uptake in a fresh sample than in a strained sample. This can be attributed to the nature of the NBR and PVC blend. Also, the effect of swelling on the thermoelastic temperature change was studied. A remarkable decrease in the temperature change was shown for swelled samples as opposed to fresh samples. Both degradation and crosslinking may occur simultaneously, as was clearly detected for all samples with different sensitivities. (C) 2004 Wiley Periodicals, Inc.