An Investigation of Chain Length Dependent Termination and Reaction Diffusion Controlled Termination during the Free Radical Photopolymerization of Multivinyl Monomers

Recent investigations of dimethacrylate monomers reveal that chain length dependent termination (CLDT) is important during network formation; however, the importance is not a trivial function of double bond conversion or monomer chemistry. Poly(ethylene glycol)-600 dimethacrylate (PEG600DMA) simultaneously exhibits CLDT and reaction diffusion controlled termination and a reaction diffusion coefficient that depends on the cure condition. To investigate this behavior, the impact of light intensity, monomer chemistry, and network formation on the termination mechanism was investigated. The copolymerization of PEG600DMA with increasing di(ethylene glycol) dimethacrylate (DEGDMA) concentrations reveals that the importance of CLDT during reaction diffusion controlled termination is a function of the rubbery or glassy nature of the resulting polymer network. As well, the addition of nonreactive PEG600 to the DEGDMA polymerization increases the importance of CLDT throughout the polymerization and elevates the reaction diffusion coefficient. Finally, electron paramagnetic resonance (EPR) spectroscopy unsteady-state experiments reveal a strong chain length dependence of the termination kinetic constant for long radical chains during the high double bond conversion of both rubbery and glassy dimethacrylates.