Pulse radiolysis of poly(vinyl methyl ether) in aqueous solution. Formation and structure of primary radicals I. Janik, P. Ulanski, J.M. Rosiak * Institute of Applied Radiation Chemistry, Technical University, Faculty of Chemistry, Wroblewskiego 15, 93-590 Lodz, Poland Abstract The reactivity of a temperature-sensitive polymer poly(vinyl methyl ether) (PVME) towards OH, e aq , and H atoms in aqueous solution has been investigated by pulse radiolysis. The rate constant for reaction of OH with PVME (1.2 ´ 10 5 Da) has been determined as 2.2 ´ 10 8 dm 3 mol 1 s 1 by competition kinetics at 296 K. Hydrogen atoms are less reactive. The rate constant of the reaction of hydrated electrons with PVME is lower than 1.9 ´ 10 7 dm 3 mol 1 s 1 . Radicals of PVME formed in the reaction with OH have a featureless absorption spectrum with increasing ab- sorption towards shorter wavelengths. Upon OH attack three kinds of radicals are generated: two at dierent a-po- sitions and one at a b-position with respect to the oxygen atom. The a-radicals rapidly reduce tetranitromethane yielding the stable nitroform anion. From the yield of the latter species it is calculated that ca. 54% of the PVME radicals are formed at a-positions. Results are compared with earlier data on low-molecular-weight ethers and simple water-soluble polymers. Ó 1999 Elsevier Science B.V. All rights reserved. PACS: 61.25.H; 61.82.P; 82.30.C; 82.50.G Keywords: Pulse radiolysis; Polymer; Polymer radical; Kinetics; Poly(vinyl methyl ether); Aqueous solution 1. Introduction Poly(vinyl methyl ether) (PVME) is a simple synthetic water-soluble polymer consisting of the repeating units ±CH 2 ±CH(OCH 3 )±. An interesting feature of this polymer is its thermo-sensitivity. Aqueous solutions of PVME undergo phase sep- aration at a lower critical solution temperature (LCST) of ca. 32±38°C [1±3]. It is well known that PVME is easily formed into a water-swellable but insoluble hydrogel, which also shows thermo-re- sponsive characteristics [4±9]. Such responsive gels have been recently the subjects of extensive re- search, motivated by a wide range of potential applications (e.g. thermally activated chemome- chanical devices such as arti®cial muscles, auto- matic separation systems, thermo-sensitive valves etc.). It has been shown that irradiation in aqueous solution is an ecient method of formation and sterilization of polymer hydrogels (e.g. [10,11]). One of the most convenient ways to produce PVME gels is to irradiate its concentrated aqueous solutions by c-rays or electron beam. This method Nuclear Instruments and Methods in Physics Research B 151 (1999) 318±323 www.elsevier.nl/locate/nimb * Corresponding author. Tel.: +48-42-631-3196; fax: +48-42- 636-0246; e-mail: rosiakjm@mitr.p.lodz.pl 0168-583X/99/$ ± see front matter Ó 1999 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 5 8 3 X ( 9 9 ) 0 0 0 7 9 - 8