Light-responsive block copolymers with a spiropyran located at the block junction

Abstract

Block copolymers with a functional group between their blocks are relatively little explored even though this molecular architecture can reduce the aggregation of the functional groups, promote the phase separation in nanophase-separated materials, and has other interesting effects. Spiropyrans are well-known for their ability to switch to their polar merocyanine form in response to light, force and other stimuli. The synthesis of stimuli-responsive AB-type block copolymers with spiropyran moieties located at the junction of the blocks is presented here. A homopolymer is synthesized from a trimethylindolenine-based atom transfer radical polymerization (ATRP) initiator, followed by its modification to a spiropyran end-functionalized polymer. The spiropyran functionalized polymer is then used as a macro-initiator for the synthesis of a second polymer block by ring opening polymerization (ROP). Alternatively, spiropyran homopolymers are conjugated to other preformed polymers by esterification. The resulting block copolymers reversibly switch under UV and white light irradiation over multiple cycles, and a block copolymer reduced the tendency of the merocyanine to aggregate during switching. The stimuli-responsive block copolymer could be useful for a range of applications, e.g. for bioinspired polymersome nanoreactors, or in membranes with switchable permeability.