Optical activity and conformation in stereoregular vinyl polymers

Optical rotation, its temperature coefficient, and O.R.D. of isotactic poly-α-olefines, poly-vinyl-ethers and poly-vinyl-ketones in solution and in the solid state, conformational analysis and semiempirical calculation of optical rotation, as well as calculations on the basis of statistical mechanical models, are consistent with the existence of helical conformations of the main chain macromolecules in solution. The large enhancement of [M]D observed in some cases with respect to low molecular models, cannot be ascribed to chromophorie systems peculiar of helical conformations, as no remarkable difference has been found between the spectral absorption regions of the chromophoric systems responsible for the optical activity in polymers and the corresponding low molecular weight compounds. The enhancement of [M]u has been therefore attributed to different positions of the conformational equilibria in the two cases. The linear temperature dependence or [M]D can be taken as an indication that, at least in the experimental conditions used, no sharp conformational transition takes place