Pattern formation during polymerization of acrylamide in the presence of sulfide hens

When polyacrylamide gel is prepared from a mixture of acrylamide, N,N'-meth ylene-bisacrylamide and triethanolamine with a peroxodisulfate initiator in the presence of sulfide, spatial pattern formation occurs in the gel if wa ter is spread on top of the gel after it solidifies. These patterns, typica lly arrays of spots or stripes, persist for many hours. Analysis of the eff ects of temperature, composition, stirring, and other factors suggests that the pattern formation occurs during polymerization due to convection drive n by the highly exothermic polymerization reaction. The role of sulfide ion , which is essential for the pattern formation, appears to be to terminate the polymer chain elongation while maintaining the overall exothermic chain reaction.