Shrinkage and structural evolution of oriented high-density polyethylene on heating were investigated by a combination of thermomechanical analysis (TMA) and synchrotron small angle X-ray scattering (SAXS) techniques. Under varying load conditions, TMA study was performed to record the continuous length changes as a function of temperature. The value of shrinkage without any load could be evaluated by a linear extrapolation method, which eliminated the influence of the required tension by traditional TMA approach. In addition, the apparent modulus of network was used to describe the nature of entangled molecular network in detail during the shrinkage process. Importantly, it was found that the apparent modulus decreased gradually with increasing temperature. Furthermore, the SAXS data provided a direct evidence for the variation trend of shrinkage stress obtained by the tensile testing stage, and the results confirmed that the shrinkage force mainly originates from interfibrillar networks. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 368-376