Polymerization kinetics of polyacrylamide gels. III. Effect of catalysts

The kinetics of photopolymerization, in presence of riboflavin or riboflavin‐5′‐phosphate (FMN), have been studied either spectrophotometrically, at 283 nm, or chemically, by titrating unreacted double bonds with permanganate. The two sets of data are in good agreement and suggest that at least 8 h of light exposure are needed to ensure 95% conversion of monomers into polymers. Up to now, it was generally accepted that photopolymerization should proceed for 1 h. It is not necessary to prolong light exposure for longer than 8 h, because even a 24 h illuminatin period only improves the conversion from 95% to 96%. Although conditions are described which ensure at least 95% conversion of both riboflavin‐and persulfate‐catalyzed gels, their visco‐elastic properties are widely different, suggesting that the final structure of these two matrices must vary considerably as a function of the catalyst used.