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

Monodisperse polymer colloids with dimethyl and diethyl acetal functionalit ies were synthesized by a two-step emulsion polymerization process. The fir st step consisted of a batch emulsion homopolymerization of styrene (St). T he dimethyl and diethyl acetal functionalities were obtained by batch emuls ion terpolymerization of St, methacrylic acid (MAA), and methacrylamidoacet aldehyde dimethyl acetal (MAAMA) or methacrylamidoacetaldehyde diethyl acet al (MAADA) in the second step, onto the previously formed polystyrene latex particles. The latexes were characterized by TEM and conductimetric titrat ion, in order to obtain the particle size distribution and the amount of ca rboxyl and acetal groups on the surface, respectively. The chemical stabili ty of the functionalized surface groups during the storage time was analyze d. The hydrophilic character of the surface of the polymer particles was de termined by means of nonionic emulsifier titration. The colloidal stability of the synthesized latexes was studied by measuring the critical coagulati on concentration (CCC) against KBr electrolyte, and the existence of a hair y 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 hyd rophilic character and the colloidal stability were affected by the pH of t he medium. On the other hand, the higher the surface charge, the larger the thickness of the hairy layer. (C) 1999 John Wiley & Sons, Inc.