KINETICS OF CATIONIC PHOTOPOLYMERIZATIONS OF DIVINYL ETHERS CHARACTERIZED USING IN-SITU RAMAN-SPECTROSCOPY

In situ Raman spectroscopy experiments were used to determine effectiv e kinetic propagation constants for a series of unsteady-state divinyl ether polymerizations at different isothermal temperatures and light intensities. Raman spectroscopy was found to be ideally suited for mon itoring cationic photopolymerizations because the technique allows iso thermal experiments to be performed with excellent time resolution and allows several spectral features to be observed simultaneously. In ad dition, the Raman experiments provided direct information about the vi nyl bond concentration in situ as the reaction takes place. For these cationic photopolymerizations, the reaction rate and limiting conversi on were both found to increase as the reaction temperature was increas ed. At all temperatures, the profile for the propagation rate constant , k(p), exhibited a dramatic increase at the start of the reaction, pl ateaued at a value between 10 and 40 l/mol s (depending upon temperatu re), and then decreased as the reaction reached a limiting conversion due to trapping of the active centers. Finally, the overall activation energy for polymerization was found to be 25.1 +/- 6.1 kJ/mol. (C) 19 96 John Wiley & Sons, Inc.