  Monte Carlo simulations in the grand canonical ensemble were used to obtain
critical parameters and conditions leading to microphase separation for block
copolymers with solvophilic and solvophobic segments. Solvent selectivity was
systematically varied to distinguish between systems that undergo macrophase
separation to ones that microphase separate in the dilute phase, prior to
macrophase separating. Finite-size scaling was used to obtain the critical
parameters. Interestingly, corrections to scaling increase significantly for
systems that form finite aggregates. The threshold value of solvent selectivity
for aggregation was determined for symmetric diblock chains of varying length.
The results indicate that long diblock copolymers form micelles in the dilute
phase prior to macrophase separation, even in marginally selective solvents.
The dependence of critical temperature on solvent selectivity was obtained for
triblock, multiblock, and alternating chains. For highly selective solvents,
strong structuring of both dilute and dense phases makes it harder to reach
equilibrium.
