Synthesis and characterization of an acid catalyst for acrylic-melamine resin systems based on colloidal unimolecular polymer (CUP) particles of MMA-AMPS

• Zero-VOC colloidal unimolecular polymer particles with sulfonate groups on the surface were prepared.
• Unlike carboxylate functional CUPs, the sulfonate functional CUPs are stable in water containing 50 ppm calcium ions.
• These CUP systems catalyzed the crosslinking of hydroxyl and carboxyl functional acrylics with melamine resin.
• Commercial catalyst leached out of the crosslinked acrylic-melamine film but the CUP catalyst did not.

Colloidal unimolecular polymer particles (CUPs) based on poly(methyl methacrylate-co-2-acrylamido-2-methylpropane sulfonic acid) were synthesized and characterized and its potential for use as a blocked acid catalyst for curing of acrylic-melamine based resin systems were evaluated. These CUPs were synthesized by the process of water reduction of acrylic copolymers and had zero volatile organic content (VOC). The curing performance of CUPs was evaluated by way of pencil hardness, micro-indentation hardness and solvent resistance measurements. These sulfonic acid containing CUPs catalyzed the curing of acrylic-melamine systems effectively and were found to provide final resin properties comparable to the commercially used blocked acid catalysts. On a molar equivalent basis, the amount of CUP catalyst required for the final cured film properties was lower than the commercial blocked acid catalyst. NMR analysis confirmed that the commercial acid catalyst leached out of the cured film when exposed to water for 24 h while the CUP catalyzed coating did not.

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