Relations between hole volume and macroscopic volume in various polymers

Different definitions of the free volumes are discussed and related to the total specific volume and to the local free (hole) volume. Positron lifetim e measurements are reported for polyethylene, polytetrafluoroethylene, and CR39-copolymers. Two long-lived components appear in polyethylene and polyt etrafluoroethylene, which were attributed to o-Ps annihilations in crystall ine regions and in holes of the amorphous phase. From a relation between th e coefficients of the thermal expansion of macroscopic and hole volume, the fractional hole volume h and from this the number of holes, N, is estimate d. Values of T-g = 195 K, h(g) = 4.5% (polyethylene) and 5.7% (polytetraflu oroethylene) and Ng = 0.73 nm(-3) (polyethylene) and 0.36 nm(-3) (poly tetr afluoroethylene) were obtained. In semicrystalline polymers these values ag ree with estimates obtained from the densities of the crystalline and amorp hous phases. The effect of cross-linking on the free-volume properties of C R39-copolymer networks was studied. The comparison of the hole volume with the specific volume allowed us to estimate the number density of holes to a pproximate to 1 nm(-3).