Effects of sulphonic and phosphonic acrylic monomers on the crosslinking of acrylic latexes with cycloaliphatic epoxide

Two model acrylic latexes were synthesized using methyl methacrylate (MMA) and butyl acrylate (BA) with methacrylic acid (MAA) or 2-hydroxyethyl metha crylate (HEMA). The MAA or HEMA were incorporated to provide the latexes wi th carboxyl and hydroxyl functionality, respectively. A cycloaliphatic diep oxide (3, 4-epoxycyclohexyl methyl-3', 4'-epoxycyclo-hexane carboxylate) wa s used as a crosslinker for both the latexes. The crosslinking of the latex es with the diepoxide was catalyzed using a copolymerizable or free sulphon ic or phosphonic acids. The copolymerizable acids (2sulfoethyl methacrylate (SEM) and acid phosphoxyethyl methacrylate (PEM)) were added during the la tex synthesis. The free acids (p-toluene sulphonic acid (TsOH) and phenylph osphonic acid (PPA)) were added into the latex emulsion shortly before cros slinking. The crosslinked coatings were evaluated in terms of water absorpt ion, gel content, and pull-off adhesion. The crosslinking of the hydroxyl f unctional latex coatings with the cycloaliphatic epoxide required an acid c atalyst, whereas the crosslinking of the carboxyl latex coatings did not ne ed an acid catalyst. Sulphonic and phosphonic acrylic acid monomers not onl y functioned as catalysts for the crosslinking reactions, but also improved the adhesion and freeze-thaw stability of the latex coatings. In addition, neutralization of the acid catalysts led to reduction of the crosslinker h ydrolysis, and consequently enhanced the overall coating properties. (C) 19 99 Elsevier Science S.A. All rights reserved.