Grafting density effect on the crystallization behavior of molecular brushes

Molecular bottlebrushes are a class of grafted block-copolymer containing polymer chains grafted to a semi-flexible backbone. Of particular interest are molecular bottlebrushes containing semicrystalline side chains. In such systems, the grafting density of tethered side chains will significantly influence the development of the final crystalline phase. To investigate this effect in more detail, a series of poly(2-hydroxyethylmethacrylate)-g-poly(ethylene oxide) (PHEMA-g-PEO) bottlebrush polymers were synthesized via a copper catalyzed azide-alkyne cycloaddition reaction. Crystallization behavior, investigated through non-isothermal and isothermal differential scanning calorimetry (DSC), displayed a general increase in crystallization and melting temperature as grafting density increases, suggesting the defect contribution of the backbone is alleviated through increased chain packing. Crystal morphology was investigated through scanning electron microscopy, atomic force microscopy, and polarized light microscopy. Morphological investigations suggest architecture effect on nucleation and radial growth of formed spherulites. This work provides an overview on how grafting density can affect the crystallization behavior of molecular brush systems and provides a framework for future development for semicrystalline brush copolymers.