Bottlebrush Polymers by Anionically Growing Poly(ethylene oxide) from Poly(vinyl alcohol) via Azeotrope Enabled Anionic Polymerization

High grafting density bottlebrush polymers with poly(ethylene oxide) (PEO) as side chains were synthesized via a grafting-from strategy. Poly(vinyl alcohol) (PVA) was used as the backbone, with abundant dangling hy-droxy groups on every other carbon-carbon bond. The alkoxide was formed from the hydroxy groups by potas-sium hydroxide with the aid of azeotrope distillation, where the pyrophoric organometallic base was avoided during deprotonation. The composition of bottlebrush polymer PVA-g-PEO was adjusted by changing the backbone choice, reaction time, and the feed ratios of both side chain monomer and initiator with respect to the backbone. The nuclear magnetic resonance (NMR) structure analysis investigated the anionic grafting-from mechanism in bottlebrush polymer. Thanks to the direct linkage of grafting sites to the backbone, the hydroxy proton showed distinguishable chemical shifts before and after grafting. After grafting, the residual hydroxy proton signal on the backbone implied an unfavorable anionic initiation in the isotactic tacticity seg-ment due to the spatial anion repulsion. By repeatedly initiating the synthesis of bottlebrush polymers, the grafting percentage increased, indicating that the grafting-from process was no longer hindered in isotactic segments due to the more spread-out distribution of initiation sites caused by the extended side chains.