Molecular Structure and Elastic Behavior of Poly(ethylene oxide) Networks Swollen to Equilibrium

Poly(ethylene oxide) (PEO) networks are prepared by an end-linking procedure upon reacting ±,ω-dihydroxy PEO chains with a plurifunctional isocyanate in stoichiometric amounts. The networks obtained are characterized by their equilibrium swelling degree in dioxane and in water and by the elastic modulus arising from uniaxial compression measurements. For each network, utilizing the Miller-Macosko theory, we have calculated the effective structural parameters, v, the number of elastically active chains, and n, the number of junctions, and the trapping factor Te. This enabled us to compare the predictions originating from the various theories of rubber elasticity with our experimental data. It appears that both the limitation of junction fluctuations and the trapped entanglements are to be considered to account for the behavior of the swollen PEO networks in the range of small strains.