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Radical annihilation of γ‐ray‐irradiated contact lens blanks made of a 2‐hydroxyethyl methacrylate copolymer at elevated temperatures
Author(s) -
Lin YoungShang,
Ming LiJune,
Peng J. S.,
Fu YingKai,
Lee Sanboh
Publication year - 2010
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.31947
Subject(s) - electron paramagnetic resonance , radical , photochemistry , methylene , chemistry , copolymer , singlet state , polymer chemistry , irradiation , methacrylate , materials science , polymer , nuclear magnetic resonance , organic chemistry , excited state , atomic physics , physics , nuclear physics
The annihilation of the radicals in irradiated 2‐hydroxyethyl methacrylate copolymer was analyzed by the use of electron paramagnetic resonance (EPR) spectroscopy. The EPR spectra were deconvoluted into three radicals: a quartet (Ra), a triplet (Rb), and a broad singlet (Rc). Radical Ra was attributed to coupling with a methyl radical and/or a doublet or triplet with about the same hyperfine coupling due to a methylene radical. Radical Rb was due to a methylene radical produced by main‐chain scission. Radical Rc was attributed to various free radicals without coupling to protons. By comparing the EPR spectra of radicals Ra, Rb, and Rc with the spectrum of a 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) standard with a known spin number, we calculated the spin numbers of the radicals, which decreased with time in the temperature range 25–45°C, regardless of the irradiation dose. The annealing of Ra and Rb and the annealing of Rc at longer times followed second‐order kinetics; these were different from the kinetics for the color formation and defect‐controlled hardening of polymers. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010