ESR study of intramolecular energy transfer in the radiolysis of cellulose thenoates

Abstract

synopsisThe substitution of Zthenoyl, 5-methyl-Zthenoyl, Zthiopheneacryloyl, 5-bromo-2-thenoyl, and 5-bromo-Zthiopheneacryloyl groups on fibrous cotton cellulose increased the radiation resistance of cellulose, as indicated by the retention of the breaking strengths of the modified fibrous celluloses at high dosages of y-radiation, as compared with that of irradiated, unmodified fibrous cellulose. The presence of electropositive or electronegative substituents on the thiophene groups did not reduce the radioprotective effects of these groups for cellulose. Crosslinking of the cellulose thenoates in 1,3-di(4-pyridyl)-propane did not significantly reduce the radiation resistance of the thenoates. Examination of the ESR spectra of irradiated cellulose and cellulose thenoates indicated that the site of the long-lived free radicals on the irradiated cellulose molecules was not changed by the chemical modification. However, the concentration of long-lived free radicals in irradiated cellulose thenoates, at a given radiation dosage, was less than that in irradiated cellulose. The localization of energy on carbon CI or Cr of the cellulose molecule, which leads to depolymerization and loss in breaking strength of fibrous cellulose, was decreased. The radioprotective effects of thiophene groups for cellulose were similar to those of furan and benzenoid groups.

Oxidative reactions of cellulose initiated by free radicals

“…Dehydrogenation and oxidative depolymerization reactions of cellulose are initiated [3] . Chemical modification of cellulose by substitution with groups, which have n-electron-type structures such as benzenoid [23-311, furanoid, [32], and thiophene [33] groups, can minimize the absorption of this electronic energy by the cellulose molecule by selectively absorbing the energy and re-emitting the energy as heat or light. Thus radioprotection of cellulose is effected.…”