Abstract
Room-temperature-cured simultaneous interpenetrating polymer networks (IPNs), comprising poly(phenylmethylsiloxane) (PPMS) and polyurethanes (PU) have been synthesized. Two PU networks were employed, one based on Adiprene L-100, and one prepared from poly(propylene glycol) (PPG) and toluene diisocyanate (TDI). The cured IPNs were examined by dynamic mechanical analysis. By considering solubility parameters, and prepolymer molecular weight, all compositions were predicted to be compatible on initial mixing, but to phase separate at some degree of network cure. The Adiprene L-100 based system comprised phase separated IPNs. Evidence was found, from 13C n.m.r. linewidth measurements, of mutual interpenetration at the phase boundaries. The PPG/TDI based PU system showed compatible (single T g) IPNs at PU concentrations from 90 to 50%, and phase separation for the 30% PU IPN. The compatibility of the PU-rich IPNs was ascribed to the low M ̄ c of the PU network, causing a kinetic opposition to phase separation. For the compatible IPNs, the plot of T g versus composition could be described by the Gordon-Taylor equation. However, the relationship between modulus and composition for neither system conformed particularly well to empirical mixing equations.
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