Chirality Induction in Cyclocopolymerization Arising from the Chiral Twist of Templates

• Published in: KOBUNSHI RONBUNSHU 1997/10/25, Vol.54(10), pp.684-695
• Main Authors: KAKUCHI, Toyoji, UESAKA, Takahiro, OBATA, Makoto, YOKOTA, Kazuaki
• Format: Article
• Language: Japanese
• Subjects: Absolute Configuration; Asymmetric Polymerization; Chiral; Chiral Diol; Circular Dichroism Spectrum; Computational Chemistry; Cyclic Unit; Cyclocopolymerization; Divinyl Monomer; Exciton; Methacrylate; Racemo; Radical Polymerization; Tamplate; Vinylbenzoate
• ISSN: 0386-2186; 1881-5685
• DOI: 10.1295/koron.54.684

The cyclopolymerization capable of forming monomeric units without planes of symmetry provides one useful means for asymmetric polymerization. Three succharides: L-threitol, α-D-glucose, and D-mannitol, were used as a template for asymmetric induction in radical cyclocopolymerization. The bis (p-vinylbenzoate) monomers (1a-c) (M1) derived from the templates were copolymerized with styrene (M2). The resulting copolymers (2a-c) were canverted into poly [(methyl 4-vinylbenzoate) -co-styrene] s (3a-c). The polymers were optically active; a sourse of chirality was the isolated M1 unit. The exciton chirality method was employed for determining the absolute configuration of the cyclic units. The template having R, R-configuration transmitted its chirality to the main chain in the intramolecular cyclization of the monomer to form an enantiomeric S, S-racemo cyclic unit. The template having S, S-configuration gave the R, R-racemo cyclic unit. The acyclic template, (2S, 4S) -2, 4-pentanediol, was more effective than the cyclic templates such as the D-mannitol and L-threitol. The (2S, 4S) -2, 4-pentanediyl template approximately doubled in effect for the asymmetric induction by comparison with the (S) -1, 3-butanediyl one. The difference in the circular dichroism (CD) spectrum between the monomers from these templates was estimated by calculating the most stable rotational conformation and its energy level. The source of the optical activity in the cyclocopolymerizations was estimated by means of molecular mechanics and semiempirical molecular orbital calculation. The copolymerization of bis (methacryloyloxy) monomer (4a) (M1) from L-threitol with styrene (M2) induced the new chirality due to the isolated M1 unit in the main chain as well. In contrast to the case of the L-threitol template, the copolymerization of bis (methacryloyloxy) monomer (4b) from D-mannitol indicated that the new chirality should be induced by the M1 diad unit rather than the isolated unit.