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(diethylene glycol bis(allyl carbonate)) networks was studied using a series of networks with progressively decreasing density of cross-links. The networks were prepared by bulk copolymerization of ethylene glycol bis(allyl carbonate) with an increasing amount of allyl ethoxyethyl carbonate. The mean free-volume hole radius (r) and the hole volume (v) 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 size increases from r = 0.250 nm (v = 0.066 nm3) for the pure diallyl component to 0.300 nm (0.114 nm3) for the 75% concentration of the monoallyl comonomer. Similarly, the hole size distributions shift to larger values. The local free-volume properties were correlated with the glass transition temperature and the specific volume. The comparison of the hole volume with the specific volume allowed us to estimate the number density of holes of ∼1 × 1027 m-3 and a free-volume hole fraction which increases with the concentration of the monoallyl from 0.066 to 0.113.