EFFECT OF CROSS-LINKING ON THE FREE-VOLUME PROPERTIES OF DIETHYLENE GLYCOL BIS(ALLYL CARBONATE) POLYMER NETWORKS - A POSITRON-ANNIHILATION LIFETIME STUDY

The effect of cross-linking on the free-volume properties of poly(diet hylene glycol bis(allyl carbonate)) networks was studied using a serie s of networks with progressively decreasing density of cross-links. Th e networks were prepared by bulk copolymerization of ethylene glycol b is(allyl carbonate) with an increasing amount of allyl ethoxyethyl car bonate. The mean free-volume hole radius (r) and the hole volume (upsi lon) as well as the hole radius and hole volume density distributions were estimated from positron lifetime measurements. It was found that with increasing concentration of monoallyl comonomer, the mean hole si ze increases from r = 0.250 nm (upsilon = 0.066 nm(3)) for the pure di allyl component to 0.300 nm (0.114 nm(3)) for the 75% concentration of the monoallyl comonomer. Similarly, the hole size distributions shift to larger values. The local free-volume properties were correlated wi th the glass transition temperature and the specific volume. The compa rison of the hole volume with the specific volume allowed us to estima te the number density of holes of similar to 1 x 10(27) m(-3) and a fr ee-volume hole fraction which increases with the concentration of the monoallyl from 0.066 to 0.113.