Design, synthesis, characterization, and utilization of functionalized solid polymers as ultraviolet curable powder coatings
Ultraviolet (UV) functional solid polymers based on polyepoxide, polyacrylate, and polyester backbones were synthesized as part of an ongoing structure-property relationship study of novel UV curable powder coatings (UVPC) Each of these polymers was either methacrylic or acrylic functional. The polymers were characterized, formulated, and processed into low temperature curable UVPC. The effects of polymer architecture, molecular weight, and functional equivalent weight on storage and thermal stability, process ability, rheology, coating performance, and network formation have been evaluated. Each UVPC was powder and solvent cast in order to compare the effect of application method on coating aesthetics, performance, and crosslinking. Conversion was monitored by FTIR, 1 H NMR, and DSC. DMA was utilized to characterize and quantify the efficiency of the two stage annealing/curing process. The DMA data was used to calculate effective molecular weight between crosslinks. Rheology provided a strong correlation between flow and leveling for polymers exhibiting functional group thermal stability. Polymers not exhibiting functional group thermal stability did produce usable films but were not as reproducible or predictable as thermally stable polymers. Polyacrylate based UVPC exhibited poor thermal stability and high viscosities which limited low temperature flow and leveling. Polyepoxides exhibited hard, solvent resistant films but typically exhibited poor flexibility and impact resistance. A series of silane modified acrylated polyepoxides were synthesized that provided excellent film forming qualities and superior mechanical properties. All polyester based UVPC provided good mechanical performance and typically exhibited good storage stability.