Viscoelastic properties and coating performance of acrylic copolymers crosslinked with melamine resin

Abstract

AbstractFor 8 carboxy and hydroxy functional acrylic copolymers crosslinked with melamine resin, glass transition temperature (Tg), molecular weight of chain segments between crosslinked point (Mc), and polymer‐solvent interaction parameters (χg ) were determined by dynamic mechanical measurements and swelling measurements. Tg increases and Mc decreases with the increase of hydroxyl value and the molecular weight of acrylic copolymers. Tg decreases and Mc increases with the increase of alkyl chain length of acrylate in acrylic copolymers. The film hardness, Tg and polarity of methyl methacrylate (MMA) containing acrylic‐melamine‐cured films are higher than those of styrene‐containing acrylic‐melamine‐cured films, but both films are almost the same in the degree of crosslinking (maximum loss tangent, tan δmax, and Mc). Tg increases and Mc decreases with the increase of melamine resin content for acrylic‐melamine coatings. The cured film consists of the acrylic‐melamine segments and the melamine‐melamine segments at crosslinking points. The carboxy group enhances the crosslinking reactions at low temperatures. All films crosslinked have single glass transition temperatures and broad damping peaks, which show good compatibility. The values of χg of acrylic copolymer‐melamine films in polar and nonpolar solvents depend on the polarity of acrylic composition and the degree of crosslinking. χg values of carboxy functional acrylic‐melamine film in any solvents are smaller than that of carboxy and hydroxy functional acrylic‐melamine film. χg values of MMA‐containing acrylic‐melamine film in polar solvents are smaller than those of styrene‐containing acrylic‐melamine film, but χg values of MMA‐containing acrylic‐melamine film in nonpolar solvents are larger than those of styrene‐containing acrylic‐melamine film. χg values of acrylic‐melamine film in polar and nonpolar solvents increase with the increase of alkyl chain length of acrylate. The χg values of acrylic‐melamine coatings in toluene are less than 0.3 and smaller than those of alkyd coatings.