POLY(ALKYLCYANOACRYLATE) NANOCAPSULES - PHYSICOCHEMICAL CHARACTERIZATION AND MECHANISM OF FORMATION

Nanocapsules of poly(isobutylcyanoacrylate) and poly(isohexylcyanoacry late) were prepared by addition of the monomer to an organic phase and subsequent mixing of the organic phase to an aqueous phase containing poloxamer 188, 238 or 407. Gel permeation chromatography indicated th at in contrast to literature reports, polymerization occurred in the o rganic phase and nanocapsules were obtained by interfacial precipitati on of the polymer without any significant change of the molecular weig ht. Addition of SO, to the organic phase before the introduction of th e monomer allowed preparation of nanocapsules with a lower molecular w eight. Nanospheres were prepared in a similar way albeit using an orga nic phase that was completely miscible within the aqueous phase so tha t solid spheres were obtained. Density gradient centrifugation reveale d that nanocapsules had a density intermediate between nanospheres and an emulsion prepared in the same way without addition of monomer to t he organic phase. Further, the process used to prepare nanocapsules ha d a high yield since no oil droplets or nanospheres were obtained by t his process. Zeta potential of the nanocapsules and spheres was found to be related to the molecular weight of the polymer: values as high a s approximate to -42 mV were obtained for low molecular weight nanocap sules (MW approximate to 1000) compared to approximate to - 10mV for t he emulsion and the high molecular weight nanocapsules (MW approximate to 100 000). Surface charge of the nanocapsules and molecular weight of their polymeric wall conditioned the adsorption capacity of poloxam ers. Moreover, the highest adsorption was measured with the most hydro phobic poloxamer. These observations agree with previous work conducte d on hydrophobic surfaces.