Propagation and Termination Kinetics of Cross-Linking Photopolymerizations Studied Using Electron Paramagnetic Resonance Spectroscopy in Conjunction with Near IR Spectroscopy

The use of electron paramagnetic resonance (EPR) in conjunction with Fourier transform near infrared (FT-NIR) spectroscopy to address the complexities associated with the accurate measurement and evaluation of cross-linking polymerization kinetics over the entire conversion range is explored. Experimental protocols are developed providing a more complete picture of the mechanistic and kinetic underpinnings of these radical polymerizations, accessing information that is otherwise unavailable to these techniques individually. The kinetics of two multimethacrylate polymerization systems, one forming a rubbery and the other a glassy polymer network, are compared and contrasted revealing numerous differences in their attributes as characterized by this experimental combination. Steady-state and unsteady-state radical concentration profiles, propagating radical environments during polymerization, and persistent radical populations are explored and utilized to evaluate the underlying propagation and termination kinetics. Subsequently, kinetic parameters obtained with EPR and EPR/FT-NIR are compared with those obtained independently from FT-NIR, enabling evaluation of the assumptions that underlie each technique.