We present a new differential formulation of the thermal constraint release phenomenon for linear entangled polymers. This new formulation predicts a relaxation modulus identical to that predicted by the double reptation theory of Tsenoglou [C. Tsenoglou, Viscoelasticity of binary polymer blends, ACS Polym. Prepr. 28 (1987) 185-186] or Des Cloizeaux [J. Des Cloizeaux, Double reptation vs simple reptation in polymer melts, J. Europhys. Lett. 5 (1988) 437-442] for both monodisperse and polydisperse systems. Additionally, we discuss a simple approximation of our approach as well as its possible use for building simple constitutive equations that account for constraint release in a polydisperse environment. (c) 2005 Elsevier B.V All rights reserved.