A nonisothermal microstructure evolution model, governed by a Helmholtz free energy which need not be convex as a function of deformations, is formulated by using a convexified geometry proposed already in [13]. A multidimensional but scalar case is treated. It is shown that, as a special case, this model includes the usual nonlinear thermo-visco-elasticity. In the case of an actual appearance of a microstructure, the existence of a weak solution to a partial linearized model is shown by a semi-implicit time discretization.