Crosslinking aqueous poly(vinyl pyrrolidone) solutions by persulfate

Aqueous solutions with 1.5 to 6.5 wt-% poly(vinyl pyrrolidone), PVP, are converted to stable gels by reaction with potassium persulfate. Large quantities of persulfate are needed for high-modulus gels, 50% to 150% of the weight of PVP being required typically. The shear modulus G′ can be measured during reaction by making the gel the restoring element in a simple torsion pendulum. The increase in modulus to a maximum plateau value of G′max can be expressed as a first-order process: Where t is elapsed time of reaction and K increases with the square root of polymer concentration. G′max varies with the second power of the polymer concentration. It also increases rapidly with increasing temperature of reaction and with persulfate/PVP ratio.