Revisiting Crystallization Pathways in PEO-b-PCL Copolymers

Hierarchical assembly in block copolymers (BCPs) is a critical process and structural component for tailoring macroscopic properties in these diverse materials. Crystallization in BCPs has been studied under a variety of conditions. Poly(ethylene oxide)-b-poly(caprolactone) (PEO-b-PCL) copolymers have received a lot of attention due to their biocompatibility and amphiphilicity. Interestingly, PEO and PCL are miscible and have similar transition temperatures. These features allow for a diverse and robust set of parameters, such as chain weight fraction, thermal history, casting solvent, aging or annealing conditions, etc., to be used for tailoring their physical structure. We have shown that crystallization order and crystallinity can be manipulated using different film preparation conditions. Hydrophobic PCL contains ester bonds capable of hydrolytic cleavage, and hydrophilic PEO promotes water uptake in these amphiphilic materials. Both processes, water uptake and degradation, are dependent on the crystallinity of the two blocks. By preparing films using various solvent casting and thermal preparation techniques, we can begin to correlate structure-property relationships to the hierarchical assembly of crystalline-crystalline copolymers.