Sodium acrylate (SA) and its polymer (PSA) are sol-uble in aqueous media. SA can be polymerized by four
methods; bulk (solid state), solution, inverse-emulsion
and inverse-suspension [1].
Inverse-suspension polymerization is defined as a
dispersion of water-soluble monomer in a continuous
organic matrix. The advantage of inverse-suspension
over other methods is that a fine powdery product is
obtained and the particle size can be easily controlled
by controlling the reaction conditions. In recent years,
the inverse-suspension polymerization method has been
successfully used to prepare water soluble/swellable prod-ucts, e.g., thickeners, flocculating agents and super-absorbent hydrogels [2,3].
Emulsifier levels are typically 2–5 wt.% of the organic
phase and are below the critical micelle concentration.
The dispersion is thermodynamically unstable and re-quires both continuous vigorous agitation and the ad-dition of a low hydrophilic–lipophilic balance stabilizer.
The latter forms a condensed electrically neutral inter-facial layer and prevents coalescence. The monomer
droplets are typically 1–100lm in diameter and are
controlled predominantly by the Weber number of the
mixture. The polymerization is often initiated chemically
by free radical azo or peroxide species; these can be lo-cated either in the dispersed (aqueous) or continuous
(organic) phase. If water-soluble initiators are employed,
each particle contains all the reactive species and
therefore behaves like an isolated micro-batch poly-merization with the kinetics proceeding according to the
solution mechanism. Oil-soluble initiators are, however,
more common because they generate higher molecular
European Polymer Journal 39 (2003) 1013–1018
www.elsevier.com/locate/europolj
*
Corresponding author.
E-mail address: m.zohuriaan@proxy.ipi.ac.ir (M.J.
Zohuriaan-Mehr).