Optically active polymers bearing side-chain photochromic moieties: synthesis and chiroptical properties of methacrylic homopolymers with pendant trans-azobenzene chromophores bound through L-leucine, L-valine and L-proline amino acid spacers

Full Paper: Novel optically active monomers, based on different L-amino aci d residues such as trans-(S)-4-(2-methacryloylamino-3-methylbutanoylamino)a zobenzene, trans-(S)-4-(2-methacryloylamino-4-methylpentanoylamino)azobenze ne and trans-(S)-4-(N-methacryloyl-2-pyrrolidinoylamino)azobenzene, have be en prepared and homopolymerized by free radical initiation. Circular dichro ism spectra of the resulting polymers, as compared with those of the corres ponding low molecular weight analogues, purposely synthesized, allow one to suggest that the macromolecules assume in solution achiral or chiral confo rmations with a prevailing screw sense, depending on the bulkiness and rigi dity of the L-amino acid residue present in the side chains. The role of in tra- and/or intermolecular hydrogen bonding between side-chain amido groups along the backbone and the structural requirements of the chiral groups in determining the macromolecular arrangement is also discussed.