ESR Studies on Chain Transfer Reactions: Rate Constants for the Reactions of Model Radicals of Polystyrene Growing Chain Ends with Tetrahalomethanes and Thiophenols

Abstract

Abstract The absolute rate constants for reactions of the model radicals of the growing chain ends of styrene and methacrylonitrile with tetrahalomethanes and thiophenols were determined by spin-trapping methods using ESR spectroscopy. The model radicals were produced by the photodecomposition of 1,1′-diphenylazoethane and 2,2′-azobisisobutyronitrile. In the case of the styrene model radical, the rate constants for the halogen abstraction reaction from CBr4, CBrCl3, and CCl4 were 1.1×107, 2.0×106, and 1.1×105 M−1s−1, respectively, and increased with increasing electron affinity of tetrahalomethanes. The rate constants for the hydrogen abstraction reaction from thiophenols were of the order 106 M−1s−1, independent of the electron-donating and -accepting properties of the para substituents. In the case of the methacrylonitrile model radical, the rate constants for the halogen abstraction reaction from CBr4 and CBrCl3 were 1.1×105 and 4.5×103 M−1s−1, respectively. The rate constants for the hydrogen abstraction reaction from thiophenols with –CH3, –H, and –Cl substituent in the para position were 4.5×104, 2.7×104, and 1.7×104 M−1s−1, respectively. The rate constants decreased with increasing the electron-withdrawing power of the substituent.