Abstract
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 (MhB), with the maximum solubility scaling as MhB-1. An induction period that scales as MhB1/2 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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