This paper contains a discussion of original and recently published results
on positronium annihilation lifetime studies of elementary free volumes in
the group, of polymer glasses. The results are used for indication of non-
homogeneity of these materials and give some basis for considering a connec
tion of the long-lived component intensities I-3(I-4) with concentrations N
-3(N-4) Of elementary free volumes and, in this way, with fractional free v
olume.