VISCOSITY EFFECTS OF A GRAFT COPOLYMER WITH A HYDROPHOBIC BACKBONE AND HYDROPHILIC SIDE-CHAINS IN A WATER AOT CYCLOHEXANE OIL CONTINUOUS MICROEMULSION

A graft copolymer, with hydrophilic poly(ethylene glycol) monomethyl e ther (MPEG) side chains grafted onto a hydrophobic poly(dodecyl methac rylate) (PDMA) backbone, has been synthesized. The nonmodified backbon e is soluble in cyclohexane. By contrast, the graft copolymer is solub le neither in cyclohexane nor in water but is well soluble in water/AO T/cyclohexane oil-continuous microemulsions (AOT = sodium bis-(2-ethyl hexyl) sulfosuccinate). Already at low concentrations (1-3 wt %), the copolymer gives rise to a marked (up to 100-fold) increase in the visc osity in the microemulsion/copolymer system. The relative viscosity of the system is dependent on the characteristics of the microemulsion a nd can vary by 1 order of magnitude depending on the volume ratios of AOT, water, and cyclohexane. We interpret the results in terms of poly mer-droplet cross-linking, caused by the solubilization of the hydroph ilic side chains into the water droplets of the microemulsion. There a re thus close analogies between our system and the more well-studied a queous mixtures of hydrophobically modified water soluble polymers wit h micelle-forming surfactants.