CLOUD POINTS AND PHASE-SEPARATION OF AQUEOUS POLY(N-VINYLACETAMIDE) SOLUTIONS IN THE PRESENCE OF SALTS

Aqueous poly(N-vinylacetamide) (PNVA) solution was found to exhibit th e cloud point in the presence of salt. This cloud point was shown to c orrespond to a liquid-liquid phase separation, as confirmed when the P NVA-salt solutions were maintained at a temperature above the cloud po int. The upper layer had a higher polymer concentration and a lower sa lt concentration than those in the lower layer. Thus interaction betwe en PNVA and salts are repulsive. The lower critical solution temperatu res were estimated to be 18 +/- 1 degrees C for 1.25 molal (NH4)(2)SO4 and 25 +/- 1 degrees C for 0.76 molal Na2SO4. Divalent anions such as SO42-, SO32-, HPO42- and CO32- were effective in causing turbidity wh en examined at 25 degrees C. Dependence of the effect on the cationic species was similar to but significantly different from that for acety ltetraglycine ethylester. The cloud points of PNVA decreased linearly with the increase of the polymer concentration at a fixed salt concent ration or with the increase of the salt concentration at a fixed polym er concentration. A parameter analogous to the salting-out constant wa s empirically derived from the dependencies of the cloud points on the concentrations of polymer and salt.