Theoretical estimation of the effect of solvent on unperturbed dimensions: 1. Isotactic poly(vinyl alcohol)

The effect of the quality of solvent on the unperturbed chain dimensions $\text{r}{}_0{}^2$ of perfectly isotactic poly(vinyl alcohol) (iso-PVA) was studied by means of some model calculations according to the matrix method of Flory et al. These investigations were based on the assumption that the quality of solvent affected mainly the energy of the intramolecular hydrogen bond, while the magnitude of the interactions between other groups, hardly varied with the change of solvent. The individual conformation energies in a chain of iso-PVA were estimated from the analysis of structurally similar polymers, as well as the results obtained with 2,4-pentanediol. It was found that the characteristic ratio $\text{C =}\text{r}{}_0{}^2\text{nl}{}^2$ increased in non-polar solvents, with energy of the intramolecular hydrogen bond stabilizing the stretched zig-zag conformation of chain. Conversely, the characteristic ratio, monotonously decreased with increasing polarity of solvent to the value of about 6, typical of a flexible random coil. The existence of an analogous relationship, valid for other polymers, able to form an intramolecular hydrogen bond in the chain, was also discussed.