Free volume and transport properties of heterogeneous poly(ethylene-co-octene)s

n-Hexane desorption measurements were pet-formed on heterogeneous poly(ethy lene-co-octene)s with hexyl branch contents between 0.8 and 3.9 mol% and cr ystallinities between 30 and 60%, Crystal core contents obtained by Raman s pectroscopy were lower than the density-based crystallinity, particularly F or the samples with the highest degree of branching. A modified Cohen-Tumbu ll-Fujita free volume model adequately described the diffusivity data. The free volume of the penetrable phases was strongly dependent on their total volume fraction, suggesting the presence of an interfacial penetrable compo nent with low fractional free volume. The dependence of the fractional free volume of the penetrable phases on the phase composition suggests that mas s transport takes place from the liquid-like component to the interfacial c omponent and that the penetrant molecules are trapped at the interfacial si tes. The decrease in geometrical impedance factor with increasing crystalli nity may be explained by the presence of extraordinarily wide dominant crys tal lamellae in the heterogeneous low crystallinity samples. The saturation concentration of n-hexane in a wide range of polyethylenes (including the heterogeneous poly(ethylene-co-octene)s, linear polyethylenes and poly(ethy lene-co-butene)s reported earlier; crystallinity range: 30-94%) showed a co mplex non-linear dependence on crystallinity that was qualitative in accord ance with rubber elasticity theory considering also molecular cilia. (C) 20 01 Elsevier Science Ltd. All rights reserved.