Optically active methacrylic polymers bearing side-chain conjugated azoaromatic chromophores

Novel optically active homopolymeric polymethacrylates have been synthesize d by radical polymerization of the corresponding monomers (S)-3-methacryloy loxy-1-(4-azobenzene)pyrrolidine and (S)-3-methacryloyloxy-1-(4'-nitro-4-az obenzene)pyrrolidine. The polymers are characterized by the presence in the side chain of an optically active chiral moiety linked to the trans-azoaro matic system through the pyrrolidine nitrogen atom, which allows the establ ishment of a donor-acceptor conjugated system. The thermal properties of th e polymeric derivatives indicate an appreciable thermal stability and incre ased glass transition temperature values with respect to similar polymeric derivatives bearing in the side chain the conjugated trans-azoaromatic chro mophore. UV and circular dichroism spectra in solution suggest that dipolar interactions between the chromophores are present in the polymeric derivat ives and that the macromolecules assume for chain sections dissymmetric con formations with a prevailing screw sense, induced by the presence of the co nformationally rigid optically active cyclic moiety. This gives rise to muc h higher optical activity of the macromolecular systems with respect to tha t afforded by the structurally related low molecular weight compounds synth esized as models of the polymer repeating units, despite the low stereoregu larity degree of the polymeric main chain. (C) 2000 Elsevier Science S.A. A ll rights reserved.