Acetal-functionalized polymer particles useful for immunoassays. II. Surface and colloidal characterization

Monodisperse polymer colloids with dimethyl and diethyl acetal functionalities were synthesized by a two-step emulsion polymerization process. The first step consisted of a batch emulsion homopolymerization of styrene (St). The dimethyl and diethyl acetal functionalities were obtained by batch emulsion terpolymerization of St, methacrylic acid (MAA), and methacrylamidoacetaldehyde dimethyl acetal (MAAMA) or methacrylamidoacetaldehyde diethyl acetal (MAADA) in the second step, onto the previously formed polystyrene latex particles. The latexes were characterized by TEM and conductimetric titration, in order to obtain the particle size distribution and the amount of carboxyl and acetal groups on the surface, respectively. The chemical stability of the functionalized surface groups during the storage time was analyzed. The hydrophilic character of the surface of the polymer particles was determined by means of nonionic emulsifier titration. The colloidal stability of the synthesized latexes was studied by measuring the critical coagulation concentration (CCC) against KBr electrolyte, and the existence of a hairy layer on the surface of the latex particles was analyzed by measuring the hydrodynamic particle diameter at several electrolyte concentrations. The surface functionalized groups remained stable for 2 years. The relative hydrophilic character and the colloidal stability were affected by the pH of the medium. On the other hand, the higher the surface charge, the larger the thickness of the hairy layer.