Packing and entropy play crucial roles in self-assembly of structured (di-block, triblock) polymers in solvent.  We revisit the random phase reductions of self-consistent mean field models of Choksi-Ren and Uneyama-Doi, including a longer-range interaction associated to partial charges, we  derive the functionalized diblock phase-field model for the free energy.  We show that reductions of this model connect to the scalar models of Gompper-Schick and Gommper-Goos for oil-water-surfactant microemulsions, and then present an analysis of a blend of long and short polymers, identifying a scaling regime in which geometric singular perturbations techniques and simple micro-local analysis can be applied to show that interdigitations of long and short polymers, evocative of the role of sterols in phospholipid bilayers, can have a stabilizing effect.