STRUCTURE OF RANDOMLY CROSS-LINKED POLY(DIMETHYLSILOXANE) NETWORKS PRODUCED BY ELECTRON-IRRADIATION

The structure of randomly cross-linked poly(dimethylsiloxane) networks is studied as a function of cross-link density. The networks are produced by irradiating a polydisperse polymer melt with 10-MeV electrons. Average molecular weights in between elastically effective links are obtained from macroscopic equilibrium swelling measurements that are interpreted in the framework of classical phantom network models. The values agree with results from a statistical approach based on the Flory-Stockmayer theory assumptions for the cross-linking process. Small-angle neutron scattering measurements were performed on polymer networks swollen to equilibrium in deuterated solvent and on polymer solutions. The scattering from the swollen networks is interpreted by introducing a model that describes the density fluctuations in the swollen network as being fractal at large length scales. The fractal dimension is 5/3. The correlation length of the large-scale density fluctuations is related, through a scaling relation, to the number of monomers in between elastically effective cross-links obtained from the macroscopic swelling measurements and the statistical approach.