Magnetic field effects on the free radical solution polymerization of acrylamide

Systematic polymerization experiments quantified magnetic field (MF) influences on the free radical solution polymerization of acrylamide for various polymerization conditions. The type of initiation, the initiator concentration, the monomer concentration, and the viscosity of the aqueous medium were the subject of variation. The initiator efficiency (Φ) increased up to 60% and the initiator exponent of the overall rate expression raised from 0.1 to 0.28 when a weak MF of 0.1 T was applied to photochemical initiation. However, no appropriate effect was observed for thermal initiation. Kinetic analysis proved a reduction of the termination rate coefficient (kt) up to 40%. Photochemically initiated polymerizations in media of enhanced viscosity revealed the highest increment of the initiator efficiency ratio ΦMF/Φ and the most pronounced reduction of ktMF/kt. On the contrary, the propagation rate coefficient (kp) and the monomer exponent were not influenced by MF. Despite considerable increase of the polymerization rate in MF, no reduction of the molar mass was found. Compensation of increased ΦMF and decreased ktMF are suggested as explanation. The singlet-triplet intersystem crossing mechanism for radical pairs served to explain the MF effects.