Miscible block copolymer/homopolymer blends are typically prepared from homogeneous
solutions in a nonselective solvent. During solvent removal and subsequent annealing, the molecular
species comprising such blends organize in such fashion as to lower the system free energy and ideally
attain thermodynamic equilibrium. In this work, we investigate nonequilibrium triblock copolymer/homopolymer (ABA/hB) blends generated by diffusing hB molecules from a hB-selective solvent into a
lamellar ABA copolymer. Since the copolymer is already microphase-ordered during homopolymer
incorporation, we refer to such blends as mesoblends. The mass uptake of hB is found to be strongly
dependent on homopolymer molecular weight (M
hB), with the maximum solubility scaling as M
hB
-1. An
induction period that scales as M
hB
1/2 is also observed. Transmission electron microscopy reveals that
the morphology of these mesoblends appears to be perforated lamellar, which, in some cases, transforms
to cylindrical upon annealing. Dynamic mechanical analysis and differential scanning calorimetry confirm
that the A-rich microdomains in the mesoblends are plasticized. The mechanical properties of these
mesoblends can be improved upon annealing, but nonetheless differ from those of composition-matched
conventional blends.
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