The effects of primary amine catalyzed thio-acrylate Michael reaction on the kinetics, mechanical and physical properties of thio-acrylate networks

Thio-acrylate networks were prepared using two methods. The first method involved the in-situ photopolymerization of a multifunctional thiol mixed with a multifunctional acrylate in the presence of a photoinitiator (photo-cure only), while the second method utilized an extremely efficient thio-acrylate Michael reaction followed by the photopolymerization of unreacted acrylate functional groups (amine catalysis/photo-cure). The thio-acrylate Michael reaction was catalyzed by a primary amine that promoted a rapid 1-to-1 Michael addition reaction of thiol to acrylate. Kinetic analysis via real-time infrared (RTIR) spectroscopy verified the 1-to-1 addition, the rates of the thio-acrylate Michael reaction and the total incorporation of the thiol into the networks at various concentrations when the amine catalyst was used. Differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA) data show very narrow glass transition temperatures for the networks prepared when the amine catalysis/photo-cure sequence was used. The two step sequential process can be used to target network films that can be tailored to have high energy damping properties at a given temperature, e.g., room temperature. Finally, in all cases, whether the photo-cure only or the amine catalysis/photo-cure process was used, the glass transition temperature increased with the initial acrylate feed concentration.