Study of cryostructuration of polymer systems. XV. Freeze-thaw-induced formation of cryoprecipitate matter from low-concentrated aqueous solutions ofpoly(vinyl alcohol)

Freeze-thaw treatment of low-concentrated (<C*) aqueous solutions of poly(v inyl alcohol) (PVA) results in the formation of a cryoprecipitate fraction. It is shown that the efficiency of such a process (the yield of PVA cryopr ecipitation) depends on the initial polymer concentration in the solution t o be frozen and the conditions of a cryogenic influence. The key factor is defrostation dynamics: The slower the thawing rate, the higher the cryoprec ipitation yield. The iodine-staining method is employed for the quantitativ e analysis of PVA concentrations in the solutions under study and the neces sity of the use of reduced (0-2 degrees C) temperatures throughout such a P VA quantification is demonstrated. Observation of the kinetics of the freez e-thaw-induced formation of cryoprecipitate matter reveals the extreme char acter of the temperature dependence of the efficacy of PVA macromolecule ag gregation, the extreme point being situated in the vicinity of -2 degrees C . (C) 1999 John Wiley & Sons, Inc.