Influences of Polymer Conformation on Acetalization Reaction of Poly(vinyl alcohol): Langevin Dynamics and DFT Approaches

In this work we studied changes in poly(vinyl alcohol) (PVA) conformations with respect to the polymer concentrations, using Langevin dynamics at 300 ± 10 K. Constructed polymer chain consisted of 90 units and the friction coefficient of the solvent (water) was set to 55 ps^-1. We also turned to quantum mechanical calculations, using B3LYP/6-31+G* level of theory in order to investigate the association via hydrogen bonds (HB) between two OH-groups of PVA and between OH-group and water. It was demonstrated that in dilute solutions PVA macromolecules tend to shrink and form more dense coils by comparison with polymers in more concentrated solutions, where two or more chains overlap, entangle and associate via intermolecular hydrogen bonding. We also established that HB between OH-groups and water molecules are less stable than those between two not adjacent OH-groups of one or various chains. The obtained data allow us to consider that in the case of low PVA concentrations, the distances between parts of one chain tend to decrease that leads to the polymer conformation favorable for the intramolecular cross-linking when the acetalization reaction of PVA takes place. As far as the cross-linking occurs within the coil, the resulting product should loss it flexibility. We assumed that the mass-transfer in this system should be slower than the subsequent chemical reaction, so the acetalization of partially modified PVA should proceed with essential retardation.