Diffusion and equilibrium swelling of macromolecular networks by their linear homologs

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Abstract
Polydimethylsiloxane (PDMS) networks having strands of molecular weight in the range 11,000–36,000 have been prepared by endlinking linear PDMS molecules of these molecular weights with a tetrafunctional linking agent. Absorption of a series of homologous linear PDMS molecules by the resulting PDMS networks has been investigated. The diffusion coefficients at 70°C were found to be rather large, 1 × 10−12–6 × 10−12 m2/s, and approximately inversely proportional to the molecular weight of the diffusing liquid, over the range 5000–38,000. The amount of liquid absorbed at equilibrium was relatively small, 10–80%, in good agreement in all cases with an especially simple version of the Flory–Huggins theory when the heat of mixing is made vanishingly small and only entropic terms are retained.