Synthesis of Photoisomerizable Block Copolymers by Atom Transfer Radical Polymerization

Abstract

A 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 ((M) over bar (w)(M) over bar (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 T(g) 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.