Optically active polymers containing side-chain photoreactive benzoin methyl ether moieties

Abstract

Optically active copolymers of (−)-menthyl acrylate (MtA) with racemic α-methylolbenzoin methyl ether acrylate (MBA) as well as of (−)-menthyl vinyl ether (MtVE) with racemic α-vinyloxymethylbenzoin methyl ether (MBVE) have been prepared by radical and cationic initiation, respectively. The reactivity of comonomers as well as spectroscopic and fractionation data suggest that acrylic and vinyl ether copolymers show a tendency towards substantial random and block distributions of monomeric units, respectively. Optical activity at 589 nm of the copolymers seems to exclude any stereoselectivity and stereoelectivity during the copolymerization in both systems. Chiroptical properties indicate that in both series of copolymers an induced optical activity on benzoin-derivative chromophores occurs, which is due to a dissymmetric arrangement of the macromolecules. Circular dichroism data, connected with the n → π∗ electronic transition of the keto group, suggest that the observed ellipticity in MBA/MtA copolymers is substantially due to isolated MBA units. In the case of MBVE/MtVE copolymers both isolated and sequential MBVE units give a contribution to the ellipticity, thus suggesting that the induced optical activity is transmitted through short blocks of MBVE units.