We consider a mixture of N ideal, polytropic gases. Each species is described by a distribution function f i(t, x, v, I) ≥ 0, 1 ≤ i ≤ N, defined on ${\rm I\!R}_+\times{\rm I\!R}^3\times{\rm I\!R}^3\times{\rm I\!R}_+$, and its evolution is governed by a Boltzmann-type equation. In order to recover the energy law of polytropic gases, the authors of [4] proposed a kinetic model in the framework of a weighted L1 space. Another approach has been developed in [3] in the context of polyatomic gases. Following this previous lead, our model provides a L2 framework in both variables v and I, to eventually perform a mathematical study of the diffusion asymptotics, as it was done in [2] for a model without energy exchange. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]