Photopolymerization of acrylamide in the very low monomer concentration range

The polymerization kinetics of acrylamide (AAm) initiated by the photoinitiator DAROCUR(2959) (DAR(2959)) under UV light irradiation were investigated. Variations of polymerization rate with AAm concentration and conversion were studied. Under the present low monomer concentrations the gel effect as well the difusion-controlled termination reactions are expected to be postponed or suppressed. The polymerization rate vs. conversion curve of the photoinduced polymerization of AAm was described by two non-stationary rate intervals and the initial rate maximum. In both intervals the polymerization rate decreased with conversion and the decrease was much more pronounced in the low conversion region. Furthermore, the polymerization rate was observed to decrease with increasing monomer concentration. The polymerization behavior was discussed in terms of the intra and intermolecular chain transfer processes (mainly to backbiting) and the decrease of propagation rate coefficient with the monomer concentration. Furthermore, the chain transfer reactions including backbiting step initiate the formation of less reactive radicals and/or the retardation of the polymerizaton.