Microgel formation and thermo-mechanical properties of UV-curing unsaturated polyester acrylates

The effect of internal and terminal unsaturation on the properties of the acrylated polyester films was investigated. Four types of acrylated polyester resin were prepared using adipic acid, maleic anhydride, neopentyl glycol, trimethylolpropane, and acrylic acid. Terminal and internal double bond content as well as branching was adjusted by the molar quantities of trimethylolpropane and maleic anhydride, respectively. A reactive diluent, trimethylolpropane triacrylate (TMPTA), was also used. A three-factor, three-level Box-Behnken design was used to investigate complex nonlinear relationships. Dynamic mechanical, fracture toughness, and tensile properties were evaluated with respect to the amount of terminal and internal unsaturation, and reactive diluent concentration. It was found that microgel formation extensively affects the final UV-cured film properties. Small quantities of microgels function as micro-support units, whereas high extent of microgelation causes phase separation through cluster formation and hence, decreases the mechanical properties. It is essential to control the extent of microgelation and phase separation to optimize product performance. (c) 2007 Wiley Periodicals, Inc.