Synthesis and helical structure of poly(1-methylpropargyl ester)s with various side chains.

Optically active 1-methylpropargyl esters bearing various substituents were polymerized with (nbd)Rheta(6)-C(6)H(5)B(C(6)H(5))(3) (nbd=norbornadiene) as a catalyst to afford the corresponding poly(1-methylpropargyl ester)s with moderate molecular weights in good yields. The polymers have a cis-stereoregular structure, which was determined by (1)H NMR spectroscopy. Large optical rotations and clear CD signals demonstrated that all these polymers take on a helical structure with a predominantly one-handed screw sense. The polymers exhibited large viscosity indices in the range 1.14-1.75. Chiral amplification was observed in R/S copolymerization. Conformational analysis revealed that the polymers form a tightly twisted helical structure with a dihedral angle of 70 degrees at the single bond of the main chain.