Changes In Crosslink Density Research Articles

Composition—property relationships in inorganic oxide glasses

By regarding glasses as oxygen polymers with a cross-linked network structure that can have different packing densities and varying degrees of cross-linking according to which network-forming elements and cations are present, the way in which many of their properties change with composition can be explained, at least qualitatively, in terms of the corresponding changes in cross-link density and network packing. The packing of an oxide network is conveniently measured by the oxygen density of the glass, and this and the cross-link density are readily calculated from the composition and actual density.

Effect of γ‐radiation on the dynamic mechanical properties of silicone rubbers

AbstractDimethyl‐, trifluoropropyl‐, and high phenyl content polysiloxanes were irradiated in a 60Co source to doses of 100 Mrad. The hardness of the specimens increased with dose. Crosslink density changes did not directly reflect the hardness changes. The crosslink density of the dimethyl polymer increased significantly and that of the trifluoropropyl polymer increased only slightly. There was a slight decrease in the crosslink density of the aromatic material. The storage moduli reflected the changes in crosslink density. Loss moduli of the dimethyl‐ and trifluoropropylpolysiloxanes initially decreased and then increased on continuing irradiation. Dynamic moduli of the high aromatic content polymer were essentially unchanged by the radiation. All the dynamic data were correlated by the WLF time–temperature relationship.