Direct evidence of positron trapping at polar groups in a polymer-blend system

Energy spectra of positron annihilation radiation were measured in polymer blends of polyethylene and ethylene vinyl acetate copolymer (E/VA) by means of the coincidence Doppler broadening technique. Positron annihilation with the core electrons of oxygen was appreciably increased by the addition of small amounts of E/VA to polyethylene and was detected with a sensitivity one order of magnitude higher than would be expected from the number density of the oxygen atoms in the polymer blends. This clearly shows that the positron is sensitively trapped by the polar acetate group of E/VA and demonstrates the usefulness of positrons as a sensitive chemical probe for polar structures in a nonpolar polymer matrix with high positron mobility.