Positron annihilation investigations on poly(methyl methacrylate)

Positron lifetime and Doppler broadened annihilation radiation were measure d for seven different samples of poly(methyl methacrylate) at room temperat ure in vacuum. The polymerisation of methyl methacrylate was carried out as a bulk polymerisation in the presence of benzoyl peroxide as an initiator. The effect of the amount of the initiator on the viscosity-average molecul ar weight was studied. It was found that the viscosity-average molecular we ight decreased with increasing amount of the initiator. The average lifetim e and intensity of ortho-positronium (o-Ps) increased with increasing visco sity-average molecular weight up to 6.85 x 10(4) and remained constant afte r that. The S-parameter showed a similar behaviour as that of the o-Ps inte nsity. (C) 2000 Elsevier Science Ltd. All rights reserved.