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 temper ature in vacuum. The polymerization of styrene was carried out as a free-ra dical emulsion polymerization in the presence of redox pair initiation syst em, potassium persulphate/sodium bisulphite as an initiator system and dode cyl benzene sodium sulphate as an emulsifier. The effect of the initiator a mount on the viscosity-average molecular weight was also studied. It was fo und that the viscosity-average molecular weight of the polymer samples decr eases with increasing the initiator amount. The ortho-positronium (o-Ps) li fetime 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 t o 10.43 X 10(4) and decreases slightly after that. A correlation between th e S- and W-parameters, which reflect the electron momentum, and the o-Ps in tensity reflecting the electron densities in the free volume sites is obtai ned. (C) 2001 Elsevier Science Ltd. All rights reserved.