STUDIES ON THE GRAFT COPOLYMERIZATION OF VINYL MONMERS IN WOOL FIBERS

Abstract

In order to clarify the grafting mechanisms in aqueous lithium bromide-potassium persulfate redox system and potassium persulfate system. Methyl-methacrylate (MMA) grafting was performed onto modified wool and silk fibroin fibers at 30°C and 40°C. In the LiBr-K2S2O8 system, MMA grafton for wool is diminished by pre-treatment with aqueous bromine, peracetic acid, acetic anhydride, diazomethane, 2:4-dinitrofluorobenzene and nitric acid. On the other hand, in the K2S2O8 system, the graft-on is diminished by acetic anhydride, 2:4-dinitrofluorobenzene and nitric acid, but not changed by diazomethane. In the LiBr-K2S2O8 system, MMA graft-on for silk is diminished by the treatment with aqueous bromine, diazomethane, acetic anhydride and nitric acid. In the K2S2O8 system, however, the graft-on is not changed by all the treatments except nitric acid leading to decrease. The grafting onto the wool fibers treated with absolute alcohol solution of bromine is not changed in both grafting system, until almost all the tyrosine is brominated to 3:5-dibromotyrosine. The graft-on, however, is sharply decreased when the oxidation of thiol groups must have occurred. The graft-on is not changed for silk fibers treated with absolute alcohol solution of bromine.Acetylated wool has less graft-on because it has a lower concentration of persulfate inside the fibers compared with unmodified wool. Sharp decrease of graft-on for nitrated wool or silk seems to be due to the “retarder” effect of aromatic nitro compounds. By the treatment with diazomethane on wool fibers, the absorption of potassium persulfate is increased remarkably, but the graft-on does not change in the K2S2O8 system. From these results, it is suggested that graft copolymerization is initiated within the fibers by the free radicals which are formed by the action of the sulfate ion or hydroxyl radicals on thiol groups but not on tyrosine residues. Thus, the thiol groups in wool fibers have an essential role on the grafting and even though a large amount of persulfate is absorbed the grafting is limited by the content of thiol groups. These results lead to the same conclusion as that of the treatment with thioglycollic acid, alkyl halide after reduction, and potassium cyanide in our previous report. Inhibition of homopolymerization in the LiBr-K2S2O8 system is due to the bromination of monomers by liberated bromine. The liberated bromine will act to react with the easily oxidized component of wool or silk fibers. This consumption of bromine will contribute to proceed the graft copolymerization without homopolymerization regulating the bromination of monomers.