The graft copolymerization of styrene and lignin. III. Chain transfer reactions of lignin and lignin model compounds

The effect of addition of lignin model compounds on the polymerization rate and molecular weight of polymer in the radiation‐induced polymerization of styrene was studied. Guaiacol, a model for softwood lignin, reacted slowly with styrene radicals, while 2,6‐dimethoxyphenol, a hardwood lignin model, was a much more efficient chain transfer agent. Studies with isoeugenol indicate that allylic or phenoxy radical stability in a conjugated system may terminate polymerization quite effectively. The results are discussed in the light of new and previous data with isolated lignins; they are consistent with the previously presented grafting scheme.