Graft copolymerization of vinyl monomers onto modified cotton. IX. Hydrogen peroxide–thiourea dioxide redox system induced grafting of 2-methyl-5-vinylpyridine onto oxidized celluloses

Cotton cellulose was independently oxidized with potassium periodate, potassium dichromate-sulfuric acid, and potassium dichromate–oxalic acid, and the resulting oxidized celluloses were further modified by treatment with chlorous acid or sodium borohydride. The various modified celluloses so obtained were grafted with 2-methyl-5-vinylpyridine using a thiourea–dioxide–H₂O₂ redox system. It was found that the initiation characteristics of the cellulose samples vary widely with the oxidizing agent used. Further modification of the oxidized celluloses by treating them with chlorous acid enhances considerably their susceptibility toward grafting. The opposite holds true when these oxidized celluloses were modified by sodium borohydride treatment. Excluding thiourea dioxide from the polymerization system offsets grafting onto cotton cellulose while considerable grafting takes place on the various oxidized celluloses and their further modified samples. The work was also extended to study the factors which affect the graft uptake, homopolymer formation, and total conversion. In addition, the reactions involved in initiation of grafting were elucidated.