SOME MECHANISTIC INSIGHTS IN THE BEHAVIOR OF THIOL-CONTAINING ANTIOXIDANT POLYMERS IN LIGNIN OXIDATION PROCESSES

Modified polyethylene glycol polymers are described in which thiol con taining groups have been added via a simple esterification step. The r esultant thiol end-capped polyethers retain the antioxidant behaviours of the monomeric thiols, but mitigate essentially completely the unde sirable properties of the monomers, including offensive odour, volatil ity, and insolubility in aqueous solvents. This concept substantially enhances the number of potential practical applications of the thiol c ontaining polymers as compared to the monomeric substances. A class of polyethylene glycols substituted with thiolactic acid or thioglycolic acid is described with potential in the pulp and paper industry, for the inhibition of radical induced oxidative processes including bright ness reversion in lignin containing papers. Several techniques are use d to elucidate aspects of the mechanism by which such thiols are effec tive: a novel photoacoustic technique demonstrates the scavenging effe cts of the thiol end capped polyethylene glycols towards alkoxy radica ls. ESR studies demonstrate the ability of these thiol polymers to que nch both the exogenous ''phenoxy'' radicals present in CTMP and TMP pa pers as well as the enhanced radical signal resulting from irradiation of these papers. The strong uv absorbance of these relatively persist ent phenoxy radicals may decrease the optimal initial brightness of pa pers made from mechanical pulps.