SYNTHESIS OF N-VINYLCAPROLACTAM AND N,N- (DIMETHYLAMINO)ETHYL METHACRYLATE MICROGELS BY POLYMERIZATION WITHOUT STABILIZATOR AND ITS PROPERTIES

Abstract

Stimuli-responsive particles of crosslinked poly-N-vinylcaprolactam and poly-N,N-(dimethylamino)ethyl methacrylate (microgels) have been synthesized in oil-in-water emulsion without using of emulsifier. Dispersions of spherical particles of about 200 nm in size rather narrowly distributed as defined by dynamic light scattering and TEM microscopy were stable in time in case of 50 and more mol. % of N,N-(dimethylamino)ethyl methacrylate. Zeta potential, measured by laser Doppler microelectrophoresis, revealed negative (-4.4 mV) and low positive (+6.6 mV) charges on particle surface. Positive charge in the case of 70 mol. % of N,N-(dimethylamino)ethyl methacrylate is provided by the protonated nitrogen atom of the monomer on the interphase surface. Low positive and negative instead of expected more positive value of zeta potential can be explained by specific sorption SO₄^2- ions on the particle surface during the polymerization, which are formed by decomposition of initiator K₂S₂O₈. Investigation of the effect of pH on the stability and particles size of the microgel with 50 mol. % of N,N-(dimethylamino)ethyl methacrylate showed that they remain stable in a wide range of pH values. An increase in the size of particles caused by polyelectrolyte swelling is observed in an acidic medium. Synthesized microgels exhibit thermosensitive properties. It is shown that, with an increase of N,N-(dimethylamino)ethyl methacrylate units, the volume phase transition temperature shifts to a lower temperatures, while the degree of particle compression is decreasing. It should also be noted that the change in particles size under the effect of temperature is reversible.