Nanostructural Rearrangement of Lamellar Block Polymers Cured in the Vicinity of the Order-Disorder Transition

The application of large amplitude oscillatory shear (LAOS) to block polymers near their order-disorder transition temperature (TODT) has previously been shown to induce morphological transitions and to promote domain alignment. To kinetically trap these transient shear-induced morphologies, we have utilized reactive poly(styrene-stat-glycidyl methacrylate)-block-polylactide diblock terpolymers that adopt lamellar morphologies in the quiescent state with thermally accessbile TODT's and can readily be cross-linked near the TODT under LAOS. By maintaining a constant curing temperature in the disordered state while varying the strain amplitude, we observed a shear-induced transition from an isotropic fluctuating disordered morphology at low strain amplitude to an aligned parallel-transverse kinked lamellar morphology at high strain amplitude. Additionally, we investigated the effect that cross-linking temperature (distance from the TODT) at a constant strain amplitude had on the occurrence of shear-induced ordering. The large amplitude of composition fluctuations near the TODT was critical for the transition from a disordered to an ordered morphology under LAOS. Conversely, cross-linking temperatures far above TODT revealed the lack of a shear-induced disorder-order transition, possibly because of smaller amplitude fluctuations and/or rapid curing kinetics. These results suggest that careful selection of the strain amplitude and curing temperature during the cross-linking of lamellar block polymers under LAOS may enable the domain anisotropy and continuity to be precisely tailored for a targeted application.