The spatiotemporal growth of spherulites in blends of isotactic polypropylene (iPP) and atactic polypropylene (aPP) isomers has been investigated theoretically with the time-dependent Ginzburg–Landau equation, which consists of a nonconserved crystal order parameter and a conserved compositional order parameter. In the description of the total free energy, a local free energy density in the form of an asymmetrical double well, signifying the metastability and latent heat of crystallization, is combined with a nonlocal free energy term representing the interface gradient. In addition, the Flory–Huggins free energy for mixing between iPP and aPP isomers has been employed to account for blend miscibility. Two-dimensional simulations have been carried out, based on the known material parameters of blends of iPP and aPP. The rejection of aPP from the growing spherulitic front has been modeled for comparison with the reported experimental observations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2892–2899, 2004