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:\documentclass{article}\pagestyle{empty}\begin{document}$$ - \ln [1 - (G'/G'_{\max } )] = Kt $$\end{document} 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.