A Novel Water-Soluble Photoinitiator for the Acrylic Photopolymerization Type Resist System

A novel water-soluble photoinitiator, sodium 4-[2-(4-morpholino)benzoyl-2-dimethylamino]butylbenzenesulfonate (MBS), was synthesized by sulfonation of 2-benzyl-2-(dimethylamino)-1-(4-morpholinophenyl)-1-butanone (BDMB) for “environmentally friendly” and “completely water-soluble” resist systems. MBS showed sufficient solubility in water and the same high sensitivity as BDMB. Novel water-soluble photopolymerization resist systems, composed of MBS, polyfunctional acrylate monomers, and water-soluble polymers, were also evaluated. Among the commercially available polyfunctional acrylate monomers, a trifunctional epoxy acrylate monomer from glycerol (DA-314) showed good solubility in water. The sensitivity of this resist system to irradiation of 365-nm UV light was 1.5 mJ/cm 2 at 2-μm film thickness. Advantages of the resist are no need for any organic solvent or any alkaline developer. The chemistry of MBS was investigated by IR and photolysis. It was proved that the radical generation mechanism of MBS was the same as for BDMB.