  We present a theoretical model for predicting the phase behavior of polymer
solutions in which phase separation competes with oligomerization.
Specifically, we consider scenarios in which the assembly of polymer chains
into stoichiometric complexes prevents the chains from phase-separating via
attractive polymer-polymer interactions. Combining statistical associating
fluid theory with a two-state description of self-assembly, we find that this
model exhibits rich phase behavior, including re-entrance, and we show how
system-specific phase diagrams can be derived graphically. Importantly, we
discuss why these phase diagrams can resemble -- and yet are qualitatively
distinct from -- phase diagrams of polymer solutions with lower critical
solution temperatures.
