Manipulating Crystallization Sequence in PEO-b-PCL Copolymers

Crystalline-crystalline diblock copolymers have a hierarchical crytsallization process based on the relationship among the order-disorder temperature, melting temperature for the first block, and melting temperature for the second block, T_ODT, T_m1, and T_m2, respectively. When T_m1 ≈ T_m2, the crystallization mechanism becomes more complex due to coincident crystallization, where the weight fractions are nearly equal, w₁ ≈ w₂), or sequential crystallization, where w₁ > w₂ and diluent or confinement effects influence nucleation of the second block. In our research, the goal is to understand these mechanisms better and to manipulate them in order to change the microscopic structure, and therefore, the macroscopic properties. A model diblock copolymer for this work is PEO-b-PCL since T_m^PCL ≈ T_m^PEO. One method to manipulate the crystallization mechanism is to use different casting solvents when making PEO-b-PCL films. The work presented here shows that the order of nucleation during drying in PEO-b-PCL films, where w_PCL ≈ w_PEO, can be switched based on selective solvent interactions.