Synthesis of Photoisomerizable Block Copolymers by Atom Transfer Radical Polymerization

Abstract

AbstractA series of polystyrene‐block‐poly(n‐butyl methacrylate) (PS‐b‐PnBMA) diblock copolymers (di‐BCPs) with an azobenzene moiety [trans‐4‐methacryloyloxyazobenzene (MOAB)] in the PnBMA segment was prepared by atom transfer radical polymerization (ATRP). P(nBMA‐co‐MOAB) macroinitiators were prepared by activators regenerated by electron transfer (ARGET) ATRP. The MOAB was slightly more reactive than nBMA, resulting in a weak gradient fashion of copolymer. The macroinitiators were subsequently chain‐extended with styrene. Acceleration of the ATRP rate was observed in the presence of a reducing agent. P(nBMA‐co‐MOAB)‐b‐PS di‐BCPs were obtained with relatively narrow molecular weight distributions ($\overline M _{\rm w}$/$\overline M _{\rm n}$ = 1.16–1.49) and the molecular weights were in good agreement with the theoretical values. The efficiency of photoisomerization of the MOAB units was above 80%. DSC traces showed a single Tg suggesting the block copolymers were miscible before UV irradiation. After UV irradiation, the X‐ray reflectivity measurements showed the beating of two frequencies, indicating the formation of island‐hole structure.magnified image