EFFECTS OF SALT ON THE TEMPERATURE AND PRESSURE RESPONSIVE PROPERTIESOF POLY(N-VINYLISOBUTYRAMIDE) AQUEOUS-SOLUTIONS

We examined the effects of salt on the lower critical solution tempera ture (LCST) and lower critical solution pressure (LCSP) of aqueous sol utions of poly (N-vinylisobutyramide), polyNVIBA, and compared them wi th those on poly(N-iso propylacrylamide), polyNIPAAm. We found that th e addition of salt (such as Na2SO4, NaCl, or KCl) decreased the LCST o f aqueous polyNVIBA from 45 degrees C to below 20 degrees C, almost li nearly with the salt concentrations and dependent on the type of salt. We observed a similar concentration-dependent decrease in LCST for po lyNIPAAm. When KI or NaSCN was added to each aqueous polymer solution, some smaller increases in LCST were observed at relatively low salt c oncentrations; higher concentrations of salt gave an almost linear dec rease in LCST. As for LCSP, the addition of most types of salt lowered the transition pressure, but the effects were much more dependent on the type and the valence of the salt (especially of anion) in both pol ymers. Salt with divalent anion showed a larger decrease in LCSP, but those with mono valent anion showed a relatively small decrease, even showed a slight increase at lower salt concentrations in the case of p olyNVIBA. Salt with I- or SCN- showed evident increases in LCSP up to 1 M and was maintained higher than the control even at 2 M. We discuss the interactions of the amide group in the side chains of polymers an d water and their perturbation by ions.