POSITRONIUM INHIBITION AND FREE-VOLUME IN CHLOROPOLYSTYRENES STUDIED BY POSITRON-ANNIHILATION

Positron annihilation phenomenon has been studied in chloropolystyrene s. PAL and ACAR measurements have been performed in air and at room te mperature for amorphous samples of different chlorine content. The inc rease in the latter is followed by the decrease in both the intensity of the narrow component of ACAR curves and the intensity of the longes t-lived component (I3) in PAL spectra. The latter one, related to the ortho-positronium intensity in polystyrene I-3(0), changes according t o the formula: I3/I-3(0)=[1+(19.93C)0.56]-1 where C denotes the numbe r of Cl atoms per unit of the polymer. The inductive effect produced b y the chlorine in chloropolystyrenes is assumed to be the reason of th e inhibition of the positronium formation in them. In general the chlo rine reactivity towards positrons seems to depend on its position in t he polymer structure. The numerical Laplace inversion technique /1/ ha s been applied to PAL data to recover the radius distribution of free volumes for each sample of the second series. A tendency towards decre ase in mean radius of free volumes is seen when chlorine content incre ases in studied samples. The only exception is the sample in which the highest amount of chlorine atoms has been substituted at alpha-carbon s in the aliphatic chain.