Living Anionic Polymerization of 4-(4-(2-Isopropenylphenoxy)butyl)styrene: A New Dual-Functionalized Styrene Derivative Having α-Methylstyrene Functionality

Abstract

The anionic polymerization of a substituted styrene with α-methylstyryl moiety, 4-(4-(2-isopropenylphenoxy)butyl)styrene (1), was carried out in THF at -78 °C with sec-BuLi as an initiator. In the anionic polymerization, only the styryl group of 1 can be selectively polymerized, and on the other hand, the α-methylstyryl moiety remains intact to afford a stable living polymer carrying α-methylstyryl functionality in each monomer unit. The resulting polymers possessed precisely controlled molecular weights and narrow molecular weight distributions. Furthermore, well-defined AB and BA diblock copolymers, poly(1)-block-polystyrene and polystyrene-block-poly(1), could also be synthesized by a two-step sequential monomer addition, namely, 1 followed by styrene, or vice versa. The anionic polymerization of the para-isomeric monomer, 4-(4-(4-isopropenylphenoxy)butyl)styrene (2), proceeded quantitatively within 5 min under similar conditions in THF at -78 °C. The resulting polymers were observed to possess precisely controlled molecular weights and narrow molecular weight distributions, but with small amounts (2-15%) of high molecular weight shoulders, which were presumably arose from the attack of the anionic species on the pendant α-methylstyrene functionality after the conclusion of the polymerization. With use of the meta-isomeric monomer 4-(4-(3-isopropenylphenoxy)butyl)styrene (3) in the polymerization with sec-BuLi, gelation occurred immediately. An insoluble polymer was obtained in 100% yield after 5 min. All attempts to obtain soluble polymers failed in the anionic polymerization of 3. We discussed such different polymerization behaviors of 1-3 in terms of electron-donation to the α-methylstyryl vinyl group via the resonance effect and steric hindrance.