An investigation of the transient thermomechanical behavior of poly(ethylene terephthalate) (PET) is presented with respect to a new composite material system in which shrinkable PET tendons are incorporated into a cementitious matrix to provide a crack-closure mechanism. A series of parametric studies of the effects of the geometry, temperature, and soak time on the mechanical properties of the polymer are presented. In particular, this article focuses on the shrinkage behavior and the development of stresses under restrained shrinkage conditions. A one-dimensional numerical model, which is essentially a modification of Zener's standard linear solid model, is presented with the aim of simulating aspects of behavior of particular relevance to tendons within the composite material system. The model comprises a temperature-dependent dashpot and spring in parallel with a spring and thermal expansion element. The temperature-dependent functions are calibrated with the obtained data, and a final validation example that shows good accuracy in comparison with experimental data not used for the calibration is presented. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2516-2526, 2011