The structure and properties of a semicrystalline polymer depend sensitively on both its chemico-physical nature and its deformation history. However, the development of structure through crystallization depends strongly on the conditions under which the polymer melt is processed, leading to the phenomenon known as Flow-Induced Crystallization (FIC). In FIC, the rheology of the entangled polymer creates conditions favourable for the nucleation of crystallites in the flowing melt, which in turn accelerates crystallization and alters the final microstructure of the processed material.  At the same time, nucleation and the development of crystallites within the melt alters the rheology of the polymer, making it stiffer and giving rise to an elastic crystallite network, in addition to the temporary network created by entanglements. While the rheology of entanglements and networks is best modelled at the scale of chains and chain segments, the nucleation and growth of an ordered, crystalline phase requires resolution on a very fine spatio-temporal scale better suited to atomistic simulation. In this work, we present a multiscale model that accounts for both the dependence of crystallite nucleation on flow-induced structure in the entangled melt and the evolution of rheology in the crystallizing melt as its topology changes. Finally, the resulting constitutive behaviour is employed in a simple, continuum level model of a prototypical polymer process, the heat-sealing of multilayer packaging films.