Effect of polymer polarity on the positronium formation

Abstract

Positron annihilation lifetime spectra have been measured on styrene–methyl methacrylate, styrene–acrylonitrile, and styrene–butyl methacrylate copolymers. The results show that the longest lifetime τ3 remains constant during extended PALS measurement in all experiment copolymers, and relative intensity I3 decreases to a certain extent with measured time in weak polar copolymers and remain almost unchanged in strong polar copolymers as well as ST–BMA copolymers. The observed decrease in I3 have been found to be unrelated to the microstructural change of copolymers, and, instead, to be more likely a result of the buildup of an electric field inside the copolymers during the prolonged PALS measurement. The field effect can result in the decrease of I3 due to the increase in the positrons and electrons diffusing out of the spur, but the influence of the electric field on I3 decrease with increasing the polarity of the copolymers and the softness of side groups of macromolecular chains in the copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 435–442, 2000