Synthesis in microemulsion and characterization of stimuli-responsive polyelectrolytes and polyampholytes based on N-isopropylacrylamide

Series of stimuli-responsive polyelectrolytes and polyampholytes based on N-isopropylacrylamide (NIPAM) have been synthesized by a microemulsion polymerization technique. The formulation of the polymerizable microemulsions was optimized by using cohesive energy ratio (CER) and hydrophile-lipophile balance (HLB) concepts, with special emphasis given to the role of the monomers. Moreover, a semi-continuous process was developed which allowed us to significantly reduce the surfactant level needed for the formulation of the microemulsion. The nucleation mechanism was investigated by dynamic light scattering experiments through the evolution of the particle size with the extent of polymerization. The final inverse latexes are clear and stable, of low particle size (d∼70 nm) and contain up to 20 wt% of high molecular weight NIPAM-based charged polymers. Under the experimental conditions selected, the latter samples are shown to be homogeneous in composition, irrespective of the monomer feed composition.