Optically active methacrylic polymers bearing side-chain conjugated azoaromatic chromophores

Abstract

Novel optically active homopolymeric polymethacrylates have been synthesized by radical polymerization of the corresponding monomers (S)-3-methacryloyloxy-1-(4-azobenzene)pyrrolidine and (S)-3-methacryloyloxy-1-(4′-nitro-4-azobenzene)pyrrolidine. The polymers are characterized by the presence in the side chain of an optically active chiral moiety linked to the trans-azoaromatic system through the pyrrolidine nitrogen atom, which allows the establishment of a donor–acceptor conjugated system. The thermal properties of the polymeric derivatives indicate an appreciable thermal stability and increased glass transition temperature values with respect to similar polymeric derivatives bearing in the side chain the conjugated trans-azoaromatic chromophore. UV and circular dichroism spectra in solution suggest that dipolar interactions between the chromophores are present in the polymeric derivatives and that the macromolecules assume for chain sections dissymmetric conformations with a prevailing screw sense, induced by the presence of the conformationally rigid optically active cyclic moiety. This gives rise to much higher optical activity of the macromolecular systems with respect to that afforded by the structurally related low molecular weight compounds synthesized as models of the polymer repeating units, despite the low stereoregularity degree of the polymeric main chain.