Versatile strategies to tailor the glass transition temperatures of bottlebrush polymers

Abstract

The glass transition of branched polymers is determined by multiple structural parameters that dictate their inter- and intramolecular interactions, and ultimately, their molecular packing in the amorphous phase. Here we examined the impact of side-chain length, backbone length, blend composition, and topology on the glass transition behavior of bottlebrush polymers. Through examining precision bottlebrush polymer libraries (PBP, Đ_SC = 1.0), we find the infinite molecular weight T_g is reached at a specific brush length after which the effect of the side-chain length dominates. Being a factor more dominant than the backbone, side-chain length affects the T_g of bottlebrush polymers across all sizes and topology variations. To demonstrate the versatility of side chain engineering strategies, a broad range of T_g and glass transition behavior was targeted through judicious choice of side chain length, blend ratios, and brush topology. PBPs yield precise T_g with some values only accessible through making PBP blends at the cost of T_g broadening. Ultimately, multiblock PBPs combine the best features of both approaches; the ability to target arbitrary T_g while maintaining sharp glass transition.