hen heated up to160 ° C. From these curves, a Tg value of118 °C and a Young ’s elastic modulus of3973 MPa were obtained for this dispersion-type aromatic polyurethane-acrylate. As polymerization isnot expected to proceed in the glassy state because of severe molecular mobility restrictions, the curing reaction usually stops once the glass transition temperature of the polymer formed reaches the temperature of the sample. The fact that a Tg value as high as118 °C was obtained for a sample which was cured at ambient temperature can be explained by the exothermicity of the acrylate polymerization. The heat that evolved (~80 kJ mo l–1) during the short UV exposure (two second) of the 1-mm thick sample caused a sharp rise of the temperature, which can reach up to160 °Cupon intense illumination.
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