Graft copolymerization of methyl methacrylate onto lignosulfonate by H2O2–Fe(II) redox system. I. Preparation and characterization of the graft copolymer

Graft copolymerization of methyl methacrylate onto lignosulfonate in aqueous medium was investigated. It was found that the H2O2–Fe(II) redox system is very effective for the grafting (Ea = 4.4 kcal/mole). The H2O2/Fe2+ ratio was the most important factor in the graft copolymerization and characteristics of the resultant graft copolymers. In most cases, polymerization for 100 min at 30°C was enough to obtain 80% conversion and 50–60% grafting efficiency. The resultant polymer mixture was subjected to extraction alternately with acetone and water, and the graft copolymer was isolated free from homopolymer and unreacted lignosulfonate. With increasing H2O2/Fe2+ ratio, the grafting ratio showed a maximum at 4, whereas the yield of graft copolymer and number of poly(methyl methacrylate) branches for every building unit of lignosulfonate increased up to a ratio of 4, both values, however, remaining constant above 4. The graft copolymer obtained for the case H2O2/Fe2+ = 4 consisted of one part of lignosulfonate and five parts of poly(methyl methacrylate). The number of branches in the graft copolymer was 6 × 10−3/OCH3 or one every 167 guaiacyl nuclei.