Controlled Functionalization of Crystalline Polystyrenes via Activation of Aromatic C−H Bonds

Abstract

The iridium-catalyzed functionalization of the C−H bond of commercial polystyrenes with three types of tacticities (syndiotactic, isotactic, atactic) using boron reagents is reported. The boronate ester group in the polystyrene was further converted to hydroxy and arene via oxidation and Suzuki−Miyaura cross-coupling, respectively. These functionalizations proceeded without affecting the tacticity or chain length of the starting polymer, and the functional group concentration was easily controlled by changing the ratio of boron reagent to polymer repeating unit. The size and concentration of the functional group in the syndiotactic polystyrenes were found to have huge impacts on the thermal properties of the functionalized polymers. The incorporation of even a small amount (<5 mol %) of the bulky boronate ester group induced complete disappearance of crystallinity for the boryl-functionalized syndiotactic polystyrene. The high crystallinity and melting temperature of syndiotactic polystyrene were not significantly changed, however, until 10 mol % hydroxy group was incorporated into the polymer, presumably owing to the small size of hydroxy group.