Studies on the kinetics of inverse emulsion polymerization of acrylamide using α-ketoglutaric acid as photoinitiator

Abstract

The kinetics of the inverse emulsion photopolymerization of acrylamide using the water soluble photoinitiator (triplet radical generator) α-ketoglutaric acid (α-KGA), sorbitan monooleate (Span 80) as the emulsifier and toluene as the oil phase has been studied. The rate of polymerization ( R p) can be represented by: R p ∝ I 0.5[C] 0.5[M] 1.28[E] −0.42, where I, C, M and E represent the light intensity (313 nm u.v. light), photoinitiator, monomer and emulsifier, respectively. The kinetic results suggest that the polymerization of acrylamide is essentially a microsuspension one. The emulsifier apparently acts as a retarder. The overall activation energy is 10.20 ± 1.58 kJ mol −1. The presence of the gel effect is evident from the increase of molecular weight with conversion and also from the nature of the percentage conversion versus time curves. A useful linear relation between high conversion molecular weight and maximum R p was found to exist. The relation yields the upper limit of the viscosity average molecular weight [(7.25 ± 0.48) × 10 6] for 4.5 mol dm −3 acrylamide, 6.3% (w/v) Span 80, toluene:water = 53:47 (v/v), a stirring rate of 425 rev min −1 and a temperature of 30°C.