Crystallization and phase separation of poly(caprolactone) and poly(ethylene oxide) side chain bearing bottlebrushes

Molecular bottlebrush copolymers have potential applications in the biomedical field due to their unique molecular architecture. Bottlebrush copolymers have been shown to self-assemble into spherical crystalsomes owing to the restriction of the backbone during single crystal growth. In this work, we seek to build on this work by characterizing the crystallization behavior of molecular bottlebrushes with crystalline mixed side chains. A series of mixed side chain molecular bottlebrush was formed using a copper catalyzed grafting-to azide-alkyne cycloaddition click reaction. N₃ functionalized poly(hydroxyethylmethacrylate) was used as backbone, and alkyne-terminated poly(ethylene oxide) and poly(caprolactone) were grafted as side chains (PHEMA-g-PEO_xPCL_y). Differential Scanning Calorimetry (DSC) experiments were performed to investigate the bulk crystallization. Molecular bottlebrush crystalsomes were grown through a solution crystallization process and characterized with Scanning Electron Microscopy (SEM). A systematic study of crystallization behavior through DSC shows a range of crystallization behaviors with a dependence on side chain loading. Peak crystallization temperatures and integrated heat of crystallization were generally decreased with mixed grafting, indicating hindered crystal growth. SEM morphology analysis shows that mixed loading introduces phase separation and influences the shape of the crystalsomes.