Synthesis Of GMA Acrylic Terpolymer Resin And Preparation Of Powder Coating

Epoxy acrylic resins for powder coating were synthesized by solution polymerization and dispersion polymerization methods, respectively. Copolymerization using glycidyl methacrylate (GMA),methyl methacrylate (MMA) and butyl acrylate (BA) as comonomers were initialized by azobisisobutronitrile (AIBN). For solution polymerization, the solvent was toluene and the media was mixture of ethanol-deionized water or 2-methoxyl ethanol-deionized water for dispersion polymerization. After the finish of dispersion polymerization, the terpolymer precipitated naturally as continuous falling of the medium temperature. This new method avoided the introduction of impurities into the synthesized resin and the process of distilling solvent. The used media could be recycled. The curing kinetics of acrylic powder coating systems were investigated by dynamic differential scanning calorimetry.In this study, the methods to control effectively the molecular weight and polydispersity indexes,the glass-transition temperature,the epoxy equivalent weight (EEW) and non volatile organic content of synthesized acrylic resins were studied in detail. The structure of the synthesized acrylic resin was investigated by infrared (IR) spectroscopy and 1HNMR. Molecular weight and polydispersity indexes of the resultant resin were determined by gel permeation chromatography (GPC). The EEW of acrylic resin was determined by titration analysis. The glass-transition temperature (Tg) was determined by differential scanning calorimetry (DSC). The thermostability of the synthesized acrylic resin was measured by thermogravimetry (TG). Diameter distributions and morphology of the GMA-MMA-BA terpolymer particles prepared by dispersion polymerization were characterized with the aid of submicron particle analyzer and scanning electron microscopy (SEM). The acrylic powder coatings were prepared by blending the synthesized resin,curing agents and suitable assistants. The properties of coating film were determined by impacter,vancometer and cross cut test.The study results showed that the synthesized resin which was prepared by dropwise method and at the boiling point of solvent in solution polymerization had a good general performance. The molecular weight and polydispersity could be controlled by adjusting polymerization temperature and the content of initiator effectively. The number average molecular weight of synthesized resin decreased from 14983 to 3922 and the polydispersity was about 1.60. The EEW of synthesized resin could be adjusted from 450g/eq to 550g/eq by the weight content of GMA in comonomers. The Tg of synthesized resin can be controlled from 40℃to 60℃by adjusting the MMA/BA ratio. The non volatile organic content of the synthesized resin was above 98.0%. If the ratio of ethanol to water in dispersion polymerization was suitable, the stability of polymerization will very well and the shape and uniform of the micro-spheres will keep well. The analysis of precipitating phenomena in dispersion polymerization showed the terpolymer maybe followed the mechanism of oligomer precipitating. The other properties of acrylic resin prepared by dispersion polymerization also can be controlled by the similar methods just like in solution polymerization. The results of curing kinetics showed that the tetrabutylammonium bromide had better catalytic effects than ethyl triphenyl phosphorus bromide. The acrylic powder coatings were prepared by blending the synthesized resin,carboxyl functional polyester and suitable assistants. In a good recipe, the direct impact of coating film was 30cm. and the pencil hardness of coating film was 4H. The adhesive power of coating film reached 1 degree. The gloss at 60°was 25.9 which approached the gloss of low gloss powder coating.