Temperature dependence of the zero-shear melt viscosity of oligomeric epoxy resins

The melt viscosities of a homologous series of five epoxy resins based on bisphenol A and epichlorohydrin have been measured over a wide range of temperatures. It is shown that the temperature dependence of the zero-shear viscosity can be well described by the three-parameter Vogel equation. The Vogel parameters B and T_o were found to increase with increasing glass transition temperature, T_g, of the resin, while the ratios $\text{B}\text{T}{}_{\mathrm{<mtext>g</mtext>}}$ and $\text{T}{}_{\mathrm{<mtext>o</mtext>}}\text{T}{}_{\mathrm{<mtext>g</mtext>}}$ remained approximately constant. This constancy of the reduced Vogel parameters implies that T_g can be used as a corresponding states parameter to superimpose the viscosity-temperature data of all five resins onto a single master curve. The existence of such a master curve is of practical use, as it enables melt viscosities of epoxy resins to be predicted over a fairly extensive temperature range from only two quantities, viz. the value of T_g and one single viscosity value at a given temperature.