Graft polymerization of methyl methacrylate onto chemically modified wools using LiBr–K2S2O8 redox system as initiator

Graft polymerizations of methyl methacrylate onto natural, reduced, S‐carboxymethylated, S‐aminoethylated, sulfated, acetylated, and oxidized wools were performed at 30°C using a LiBr–K2S2O8 redox system as initiator. The extent of grafting was found to be dependent on the thiol and amino contents of wool fibers; carboxylic, sulfated groups, and oxidation intermediates had no significative influence on graft yields. The polymethacrylic chains obtained after hydrolysis of the natural part of the copolymer and analyzed by infrared and NMR spectroscopies were characterized by an atactic structure quite comparable to that found for a corresponding homopolymer. There was no stereoregulating effect on methyl methacrylate polymerization due to the crystalline components of the wool structure. A quantitative determination of the number of amino acid residues linked to the end of polymethacrylic chains after hydrolysis indicated that chain termination occurs both by disproportionation and recombination of macroradicals for natural, sulfated, S‐carboxymethylated, and S‐aminoethylated wools; for reduced and oxidized wools, only a recombination by disproportionation was observed in accordance with the open structure of these wool fibers. The chain lengths of the isolated poly(methyl methacrylates) were also found to be consistent with the participation of thiol and amino groups in grafting. It seems, however, that amino groups do not themselves act as initiating sites.