photocalorimetric accessory (DPA) was used for these experiments (Figure 2.18). A short-arc xenon lamp of 450 Watts was used as the light source. A shutter, which was manually controlled, allowed light to irradiate the pans when opened. Desired wavelengths were chosen using the monochromator. Neutral density filters modulated the light intensity.217
Photo-polymerizations were performed in modified aluminum pans (Figure 2.19). Meniscus formation was prevented or greatly minimized due to the step configuration of the pan. Standard aluminum sample pans were pressed into this shape with a retrofitted press.218
The heat of polymerization (Hp) was calculated from the area of the exotherm curve
relative to the baseline (shutter closed). The extent of polymerization (Ep %) was determined by comparing the Hp of the dimethacrylate to the Hp of completely
polymerized methyl methacrylate (-54.8 kJ/mole),219 as shown in equation 2.10. The Ep was as high as 79 % for triethyleneglycol dimethacrylate.220
218 219 220
Gunduz, N., Synthesis and Photopolymerization of Novel Dimethacrylates, M.S. Thesis, Virginia Tech, Blacksburg, VA, 1998. Gunduz, N., ibid. Horie, K., J. Radiat. Curing, 1980, 7(2), 20. Gunduz, N., Op. Cit.