Manipulation of Crystallization Sequence in PEO‑<i>b</i>‑PCL Films Using Solvent Interactions

The physical structure of polymer films is important for understanding the observed macroscopic properties. In crystalline–crystalline block copolymers, the hierarchical nature of assembly is even more influential. Controlling this assembly process is crucial for tailoring film properties. In materials where crystallization of each block occurs nearly simultaneously, the ability to manipulate crystallization order is desirable. Poly­(ethylene oxide)-<i>b</i>-poly­(ε-caprolactone) (PEO-<i>b</i>-PCL) films were monitored via ATR-FTIR to determine the crystallization order during drying from varying solvents. PCL crystallized first from most solvents except toluene and ethyl acetate, where PEO nucleation occurred first. Moreover, after melting the sample to remove solvent–polymer interaction effects, PCL was first to crystallize from the melt, as has been previously reported. Differences in the films’ morphologies based on crystallization order were observed using polarized optical microscopy. These results demonstrate that the order of crystallization and the assembly within the film were controllable when casting symmetric diblock PEO-<i>b</i>-PCL films from different solvents.