title: Control of helix sense by composition of chiral-achiral copolymers of N-propargylbenzamides.
abstract: N-Propargylbenzamides 1-7 were polymerized with (nbd)Rh(+)[eta(6)-C(6)H(5)B(-)(C(6)H(5))(3)] to afford polymers with moderate molecular weights (M(n) = 26,000-51,000) in good yields. The (1)H NMR spectra demonstrated that the polymers have fairly stereoregular structures (81-88 % cis). The optically active polymers, poly(1) and poly(2), were proven by their intense CD signals and large optical rotations to adopt a stable helical conformation with an excess of one-handed screw sense when heated in CHCl(3) or toluene. The sign of Cotton effect could be controlled by varying the content in the copolymers of either chiral bulky 1 and achiral nonbulky 3, or chiral nonbulky 2 and achiral bulky 7. The smaller the pendant group in the copolymerization of achiral monomers with 1, the more easily did the preferential helical sense change with the copolymer composition. However, the copolymers of chiral nonbulky 2 and achiral nonbulky 3 did not change the helical sense, irrespective of the composition. The free energy differences between the plus and minus helical states, as well as the excess free energy of the helix reversal, of those chiral-achiral random copolymers were estimated by applying a modified Ising model.
authors.affiliation: Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Katsura Campus, Japan.
authors.forename: Junichi
authors.initials: J
authors.lastname: Tabei
authors.forename: Masashi
authors.initials: M
authors.lastname: Shiotsuki
authors.forename: Takahiro
authors.initials: T
authors.lastname: Sato
authors.forename: Fumio
authors.initials: F
authors.lastname: Sanda
authors.forename: Toshio
authors.initials: T
authors.lastname: Masuda
mesh_terms: D001549:Benzamides / Q000138:chemical synthesis*; D002384:Catalysis; D008968:Molecular Conformation; D008970:Molecular Weight; D009942:Organometallic Compounds / Q000737:chemistry; D012238:Rhodium / Q000737:chemistry; D013696:Temperature
chemical_list: D001549:Benzamides; D009942:Organometallic Compounds; D012238:Rhodium