STRUCTURE-REACTIVITY STUDIES ON THE CROSS-LINKING OF POLY(VINYL METHYL-ETHER) IN AQUEOUS-SOLUTIONS - A PULSE-RADIOLYSIS STUDY

Pulse radiolysis techniques have been utilized to generate, characteri ze and study the kinetics of crosslinking reactions of the radicals of a temperature-sensitive polymer poly(vinyl methyl ether) (PVME) in aq ueous solutions. The transient species formed on reaction with (OH)-O- . has an absorption maximum at 310 mn with molar absorptivity (epsilon ) = 1060 +/- 330 dm(3) mol(-1) cm(-1). The rate constant for the react ion of (OH)-O-. with PVME has been determined as 3.2 x 10(8) dm(3) mol -l s(-1) by competition kinetics at 296 K. The decay profile of the tr ansient species has been found to vary with the polymer concentration and/or dose rate indicating different modes of recombination under var ious conditions of irradiation. These results have been interpreted in terms of intra- and inter-molecular crosslinking reactions of polymer radicals and it has been shown that when the intramolecular crosslink ing reaction predominates, the decay kinetics deviates from the classi cal second order and shows a time-dependent behaviour. Since the polym er undergoes a coil-globule transition above 307 K, the bimolecular ra te constant for the reaction of (OH)-O-. with the polymer and the deca y kinetics of radicals formed have also been investigated at 318 K.