Particle formation and gelling behaviour of anionic oligoesters in aqueous solution

Certain oligomeric, phthalate-based polyester molecules, prepared by a melt condensation polymerisation reaction and having a controlled degree of sulfonation, have been shown to form gels in aqueous solution. The inclusion of the sulfonate moieties into the oligoester molecules increases their aqueous dissolution from the melt. Light scattering and rheology studies suggest that the mechanism controlling the gelation is thought to depend on the formation and aggregation of small colloidal particles which themselves result from the association of individual oligoester molecules. Studies of the phase behaviour of these anionic oligoesters in aqueous solution have shown that gels only form for certain levels of sulfonation of the oligoesters and then at higher oligoester concentrations. At lower concentrations liquid/liquid type phase separation may be observed. Increasing NaCl concentration significantly influences the rate of phase separation or gel formation. Optical microscopy studies confirm that the gel-forming systems contain chain-like particulate aggregates.