Emulsifier-free poly[2-(diethylamino) ethyl methacrylate] microgels with cationic quaternary ammonium monomers

Abstract

Although poly[2-(diethylamino) ethyl methacrylate] (PDEA) microgels are biocompatible and show potential in drug delivery, little research exists with respect to their preparation. Therefore, emulsifier-free PDEA microgels were synthesized in the presence of cationic ammonium salts of 2-(dimethylamino) ethyl methacrylate (DMA) that were quaternized with 1-bromohexadecane, 1-bromooctadecane, 1-bromopentane, or benzyl chloride. These served as both comonomers and polymerizable surfactants, providing colloidal stability to the DEA droplets during polymerization. The stability of the microgel particles in different pH values between 4 and 11 was investigated by turbidity-wavelength measurements. The benzyl group containing monomer was the most stabilizing. The pH-responsive behavior of the microgels in dilute aqueous solution was examined with respect to the amount of DEA, amount of copolymer, type of copolymer, and water content. Most of the microgels remain colloidally stable up to a pH of 9.0, while particles are less than 300 nm in size at pH 8.0. The isoelectric points of the microgels are higher than 8.5 in most cases. In fact, this value exceeds 12.0 by modifying the amount of copolymer