Photochemical formation of ammonium/thiolate complexes from quaternary ammonium thiocyanates and its use in crosslinking of polymers

1-Phenacyl-(1-azania-4-azabicyclo[2.2.2]octane) thiocyanate (PnDbSCN) and N-phenacyl-4-(N′,N′-dimethylamino)pyridinium thiocyanate (PnDpSCN) were prepared as novel photobase generators. These quaternary ammonium salts (QASs) have higher melting points and decomposition temperatures than corresponding QASs having dithiocarbamate anions. From 1H NMR and UV spectral analyses, it was found that PnDbSCN turned to 1,4-diazabicyclo[2.2.2]octane (DABCO) and phenacylthiocyanate (PnSCN) on irradiation at 254 nm, and the resulting PnSCN was further transformed into 5-phenyloxazole-2-thione (POT) in the presence of DABCO to form ammonium/thiolate complexes. PnDpSCN also showed similar 1H NMR spectral changes on irradiation. Poly(glycidyl methacrylate) (PGMA) films containing amines in the presence of POT crosslinked at lower temperature than those in the absence of POT, and PGMA films containing QASs became insoluble on irradiation followed by post-exposure baking.