Rheological behavior of epoxy acrylate prepolymer during UV curing

The effects of sample thickness and curing temperature on the dynamic viscoelastic behavior were investigated during UV curing of an epoxy acrylate prepolymer by the use of an oscillating plate rheometer which was devised in our laboratory. Independent of light intensity, the values of dynamic viscosity plotted against exposure energy lie on a single curve which is approximated by two straight lines. The minimum exposure energy, which corresponds to that at the intersection of two lines, increases with increasing sample thickness and then starts to increase abruptly at a certain thickness. The critical sample thickness is comparable to the penetration depth of a light having a wavelength of 365 nm. The spectral sensitivity shows that the n–π^* absorption at 365 nm by the photoinitiator is of primary importance in polymerization.