Methacrylic polymers bearing side-chain permanent dipole azobenzene chromophores spaced from the main chain by chiral moieties: synthesis and characterization

Novel optically active polymethacrylates bearing in the side chain a chiral group of one prevailing absolute configuration linked to the trans-azoaromatic chromophore, have been synthesized by radical homopolymerization of the corresponding optically active monomers, prepared in turn from optically active precursors by synthetic methods avoiding any racemization of the chiral center. These polymeric derivatives, namely poly[(S)-3-methacryloyloxy-1-(4′-X-4-azobenzene) pyrrolidine], with X=CN, CHO, CHC(SO2CH3)(CN), CHC(CN)2, are characterized by the presence of the 3-hydroxy-pyrrolidinyl ring as the chiral moiety and the azoaromatic donor-acceptor conjugated system as the moiety with permanent dipole moment. The polymers display optical activity in solution much higher than that afforded by the corresponding low molecular weight models, representative of the monomeric repeating unit, purposely synthesized. Owing to the substantially stereoirregular structure of the main chain, this suggests that the overall optical activity is mainly due to conformational dissymmetry of the macromolecules. Spectroscopic evidence suggests the presence in the above mentioned polymeric derivatives of dipole–dipole interactions between the side-chain azoaromatic chromophores, occurring as a consequence of their anchorage to the polymer backbone, which favors their aggregation.