Irregular conformations of poly-4-vinylpyridine☆

Additive approximation involving the use of atom-atom potentials provided the means of calculating the irregular conformations of iso- and syndiotactic chain fragments of poly-4-vinylpyridine (P-4VP) as well as the most stable conformations of atactic P-4VP for dddl, ddld, dlld and ddll, i.e. independent tetrads of asymmetrical centres. It was found that the most stable conformations were 31-type helical segments of similar rotational sign for the iso-configuration of asymmetrical centres, and 21-molecular helices for the syndio-configuration, and these conformations link up without any sort of energy losses, while helical segments of dissimilar rotational sign link up successfully via a trans-zigzag“buffer” structure. It is shown that the conformational structures of heterotactic P-4VP may be made up of sequences of regular conformations of chain fragments. A model is proposed for the orientation of macromolecules of non-stereospecific P-4VP. In this model dichroism is brought about by chain segments with a syndiotactic sequence of asymmetrical centres in the trans-zigzag conformation.