Study on polystyrene via positron annihilation lifetime and Doppler broadened techniques

Positron annihilation lifetime and Doppler broadened annihilation radiation have been measured for six different samples of polystyrene at room temperature in vacuum. The polymerization of styrene was carried out as a free-radical emulsion polymerization in the presence of redox pair initiation system, potassium persulphate/sodium bisulphite as an initiator system and dodecyl benzene sodium sulphate as an emulsifier. The effect of the initiator amount on the viscosity-average molecular weight was also studied. It was found that the viscosity-average molecular weight of the polymer samples decreases with increasing the initiator amount. The ortho-positronium (o-Ps) lifetime decreases with increasing the viscosity-average molecular weight up to 8.56 X 10(4) and increases dramatically after that. The intensity of the o-Ps increases with increasing the viscosity-average molecular weight up to 10.43 X 10(4) and decreases slightly after that. A correlation between the S- and W-parameters, which reflect the electron momentum, and the o-Ps intensity reflecting the electron densities in the free volume sites is obtained. (C) 2001 Elsevier Science Ltd. All rights reserved.