Effects of hydrophobic unit and its distribution on solution properties ofvinyl pyrrolidone and vinyl acetate copolymer

A series of vinyl pyrrolidone and vinyl acetate copolymers with different m onomer ratios and homogeneity in backbone distribution were synthesized and their solution properties studied. In water, the phase diagram curve is co ncave, with the lower critical solution temperature, due to the cooperation of hydrophobic and hydrophilic hydration. In order to make a substantially homogeneous copolymer, a new method to determine the monomer mole fraction is suggested. When the vinyl pyrrolidone to vinyl acetate mole ratio in th e copolymer is close to unity, sequence distribution plays an important par t in solution behavior. The more homogeneous the structure, the better the solubility in water, and the higher the cloud point. This is attributed to the balance between hydrophobic and hydrophilic forces in solution. Copolym erization kinetic analysis on monomer conversions and turbidity measurement on poly(vinylpyrrolidone/vinyl acetate) solutions give consistent results to confirm this interpretation. (C) 19991999 John Wiley & Sons, Inc.