Stabilization of UV‐curable vinyl compositions by transition metal compounds

A UV‐curable composition, which has a shelf life of greater than six months at 60°C for bonding or coating glass surfaces, was developed. The formulation consists of a dimethacrylate monomer, a methacryltrialkoxysilane, a photoinitiator, MEHQ, DLTDP, a water scavenger, and FeCl 3 . In the absence of FeCl 3 , gelation occurs within 24 hr at 25°C. Gelation is caused by the formation of a crosslinked vinyl addition polymer having a methacrylate diester/silane monoester mole ratio of 20:3. Analogous stability is achieved if instead of FeCl 3 a number of heavy metal compounds are used, including CrCl 3 , CoCl 2 , NiCl 2 , RuCl 3 , Pr(fod) 3 , and Eu(fod) 3 . Nontransition metal compounds, e.g., AlCl 3 , BCl 3 , and SnCl 2 , are poor or ineffective stabilizers. Gelation is initiated by free radicals. When MEHQ and DLTDP are present, less Fe 3+ is converted to Fe 2+ than in their absence. This indicates that a complex interaction is operating among these substances. A scheme is presented in which recycling of Fe 3+ and phenolic and thioether antioxidants is proposed.