Positronium inhibition and free volume in chloropolystyrenes studied by positron annihilation

Abstract
Positron annihilation phenomenon has been studied in chloropolystyrenes. PAL and ACAR measurements have been performed in air and at room temperature for amorphous samples of different chlorine content. The increase in the latter is followed by the decrease in both the intensity of the narrow component of ACAR curves and the intensity of the longest-lived component (I₃) in PAL spectra. The latter one, related to the ortho-positronium intensity in polystyrene I⁰_3', changes according to the formula : I₃/I⁰₃=[1+(19.93*C)^0.56]^-1 where C denotes the number of Cl atoms per unit of the polymer. The inductive effect produced by the chlorine in chloropolystyrenes is assumed to be the reason of the inhibition of the positronium formation in them. In general the chlorine reactivity towards positrons seems to depend on its position in the polymer structure. The numerical Laplace inversion technique /1/ has been applied to PAL data to recover the radius distribution of free volumes for each sample of the second series. A tendency towards decrease in mean radius of free volumes is seen when chlorine content increases in studied samples. The only exception is the sample in which the highest amount of chlorine atoms has been substituted at α-carbons in the aliphatic chain.