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 polym erization technique. The formulation of the polymerizable microemulsions wa s optimized by using cohesive energy ratio (CER) and hydrophile-lipophile b alance (HLB) concepts, with special emphasis given to the role of the monom ers. Moreover, a semicontinuous process was developed which allowed us to s ignificantly reduce the surfactant level needed for the formulation of the microemulsion. The nucleation mechanism was investigated by dynamic light s cattering experiments through the evolution of the particle size with the e xtent of polymerization. The final inverse latexes are clear and stable, of low particle size (d similar to 70 nm) and contain up to 20 wt% of high mo lecular weight NIPAM-based charged polymers. Under the experimental conditi ons selected, the latter samples are shown to be homogeneous in composition , irrespective of the monomer feed composition. (C) 2001 Elsevier Science L td. All rights reserved.