Optically active photochromic methacrylic polymers with controlled average molecular weight and defined end-groups by atom transfer radical polymerization

We report a new approach based on atom transfer radical polymerization (ATRP) to produce optically active polymers containing azoaromatic moieties in the side chain with controlled average molecular weights, that can be used to investigate the conformational origin of chirality in this class of synthetic materials. The ATRP technique has been successfully applied to the synthesis of a series of optically active photochromic homopolymers poly[(S)-3-methacryloyloxy-1-(4-azobenzene)pyrrolidine] {poly[(S)-MAP]}, containing a chiral group of one prevailing configuration interposed between the methacrylic moiety and the photochromic azoaromatic chromophore. By just changing the duration of the polymerization process, macromolecules having distinct average chain lengths with low polydispersity values and well defined end-groups have been obtained. l activity and thermal properties of the resulting polymeric derivatives result to depend on their average molecular weight. In particular, a dependence of optical rotation and circular dichroism on chain-length has been evidenced.