3 (5) were synthesized and polymerized using (nbd)Rh þ [η 6 -C 6 H 5 B -(C 6 H 5 ) 3 ] (nbd = 2,5-norbornadiene) as a catalyst. Substituted cis-stereoregular polyacetylenes with moderate molecular weights were obtained in good yields. Poly[(R)-1], poly[(S)-1], poly[(S),(R) 0 -2], and poly[(S),(R) 0 -3] exhibited large optical rotations (|[R] D | = 344°-508°), clear CD signals (Δε = 4.8-7.0 M -1 cm -1) in CHCl 3 , and high viscosity indices (0.82-0.87), demonstrating the formation of helical structures with predominantly one-handed screw sense, which were stable up to 55 °C in the solvent. The solution state IR measurement confirmed the presence of intramolecular hydrogen bonding between the pendent carbamate groups of the polymers. Chiral amplification was observed in chiral/achiral [(S)-1/5] and R/S [(R)-1/(S)-1] copolymerizations. Conformational analysis revealed that the polymers adopt a tightly twisted helical conformation with a dihedral angle of 70°at the single bond on the main chain. The molecular mechanics calculation and X-ray diffraction measurement suggested that the diameter of the helix is 25 and 17 A ˚, respectively.
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