Environmentally Benign Formation of Poly(methacrylate ester) Microspheres by Precipitation Copolymerization in Supercritical Carbon Dioxide

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An environmentally benign formation method of polymeric microspheres is reported using supercritical carbon dioxide (SC-CO₂). The polymer microspheres were synthesized by the precipitation copolymerization of glycidyl methacrylate (GMA) with methyl methacrylate, n-butyl methacrylate or diethylaminoethyl methacrylate, methacrylic acid (MAA) or 2-hydoxyethyl methacrylate (2-HEMA) in SC-CO₂. Scanning electron microscopy (SEM) showed that the products were spherical microparticles with the addition of MAA and/or 2-HEMA as the monomer. The mean diameter of the particles is 0.5–5 μm. During the copolymerization of GMA with MAA and/or 2-HEMA in SC-CO₂, it was found that MAA and 2-HEMA served as a stabilizer for GMA. The obtained polymer particles were applied as powder coatings, which have been attracting much attention as environmentally benign coating systems. The resulting coatings have a smooth and coherent film. The particle size and morphology were controlled by changing the pressure, temperature, and initial GMA/MAA and/or GMA/2-HEMA concentration ratio. The initial concentration ratio was more effective than the other factors in controlling the particle size.