OH radical induced depolymerization of poly(methacrylic acid)

Hydroxyl radicals (generated pulse radiolytically in dilute N2O-saturated a queous solutions) react with poly(methacrylic acid) producing two kinds of radicals. The primary radical is converted into a secondary one by H-abstra ction (k = 3.5 x 10(2) s(-1)) as monitored by changes in the UV spectrum. S ubsequently, the secondary radicals undergo chain scission (k = 1.8 s(-1) a t pH 7-9). This process has been followed both by spectrophotometry as well as by conductometry. In competition with the bimolecular decay of the radi cals the ensuing end-chain radicals undergo efficient depolymerization resu lting in the release of monomer. Since the lifetime of the radicals is much longer at high pH, where the polymer attains a rod-like conformation, depo lymerization is most efficient in basic solution. (C) 1999 Elsevier Science B.V. All rights reserved.