ON THE CHIRALITY OF POLYVINYL COMPOUNDS .19. INFLUENCE OF DOUBLE-BONDPOSITION ON THE ASYMMETRIC CYCLO-COPOLYMERIZATION

Cyclocopolymerization of two new monomers, D-mannitol 3,4-O-carbonate 1,2:5,6-bis-O-[(2-vinylphenyl)boronate] (2) and D-mannitol 3,4-O-carbo nate 1,2:5,6-bis-O-[(3-vinylphenyl)boronate] (3), was investigated. Wh ile copolymers of monomer 2, which has the double bond in ortho positi on, do not show optical activity after splitting off the chiral D-mann itol template, optically active copolymers were obtained from monomer 3 with its double bond in meta position. The residual optical activity is due to the configuration of the main chain (main chain chirality). With the aid of circular dichroic (CD) spectra and optical rotation m easurements the configuration of the (3-vinylphenyl)boronic acid diads in the copolymer chain could be determined. When methyl methacrylate (MMA) was used as comonomer, the diads possessed (R,R) configuration. The mechanism of cyclopolymerization of monomer 3, which involves a 17 -membered transition state, could be explained by approximating its co nformations of lowest energy with semiempirical methods (AM1).