REAL-TIME MONITORING OF POLYMERIZATION QUANTUM YIELDS

Real-time infrared (RTIR) spectroscopy was used to study the polymerization kinetics of a polyurethane-diacrylate photoresist exposed to UV radiation or to a Kr+ laser beam. The conversion versus time curves recorded allow the polymerization rate, i?p, to be determined at any stage of the reaction. Variation of the polymerization quantum yield, φp, upon exposure was monitored in real time from the ratio of Rpto the absorbed light intensity. The effect of atmospheric oxygen on φpis substantial and was quantified. In Oj-free systems, φp reached its maximum value after 130 ms of exposure and a conversion of 6%. A sharp drop of the φpvalue was observed after 25% conversion; it is attributed to a decrease of the initiation quantum yield, φ„ due to segmental mobility restrictions brought on by gelation. The kinetic chain length of the propagation step was evaluated from the ratio φp/φί\ it was found to reach its maximum in the early stages of the polymerization, with values on the order of 7000 mol/radical in the presence of air and up to 50 000 mol/radical in N2-saturated systems. © 1990, American Chemical Society. All rights reserved.