COATING WATER-SWELLABLE POLYMER LATEXES BY INTERFACIAL POLYMERIZATION

Two techniques of coating water-swellable polymer latexes (hydrogels) with an inorganic or organic layer were developed, based on interfacia l polymerization. The hydrogel latexes were prepared by inverse suspen sion polymerization. The first kind of interfacial polymerization is h ydrolysis and polycondensation of tetraethyl orthosilicate (TEOS) or 3 -(trimethoxysilyl)propylmethacrylate (TMS-PMA) on the surface of hydro gel latexes. The hydrochloric acid, which is the catalyst for this rea ction, was previously loaded into the hydrogel latexes. The HCl-contai ning hydrogel latexes were then suspended in an organic solution of TE OS or TMS-PMA. The hydrolysis and condensation occur only at the surfa ce of each hydrogel particle and the generated SiO2 or SiO(PMA) networ k covers the hydrogel latexes. The second interfacial polymerization i s polymerization of methylenedi-p-phenyl diisocyanate (MDI) and trieth ylene glycol (TEG) on the surface of hydrogel latexes. TEG was deposit ed on the hydrogel by suspending the hydrogel powder in a tetrahydrofu ran (THF) solution of TEG and evaporating the THF. The TEG-deposited h ydrogel powder was then suspended in an organic solution containing bo th MDI and the catalyst dibutyltin dilaurate (DBTL). The MDI and DBTL molecules react with the TEG molecules only at the surface of the hydr ogel particles, and the polyurethane P(MDI-TEG) thus formed wraps the particles. Based on these two coating procedures, three kinds of mater ials were obtained: SiO2 coated hydrogels, SiO-(PMA) coated hydrogels and P(MDI-TEG) coated hydrogels. Soft polyether brushes were grafted t o the SiO-(PAM) coated latexes. The P(MDI-TEG) coated hydrogels were u sed as reservoirs for beta-hydroethyltheophylline (beta-HETP), and the release of the latter molecules from the coated hydrogels was investi gated. (C) 1995 John Wiley and Sons, Inc.