Solubility of thermostable alkyl phosphate ester copper complexes in poly(alkyl methacrylate) for near-infrared-absorbing dyes

To realize thermoplastic near-infrared-absorbing resin materials with weak absorbance in the visible region, the solubility of thermostable alkyl phosphate ester copper complexes in poly(alkyl methacrylate) has been investigated for their use as near-infrared-absorbing dyes. C4–C12 alkyl phosphate ester copper complexes were synthesized and mixed with n -butyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate at 0.10 mol/g copper ion in the monomer solution. The obtained solutions were polymerized to prepare 3 mm resin plates, and the plate transparency was evaluated by a haze meter. 2-Ethylhexyl methacrylate solutions of the 2-ethylhexyl phosphate copper complex and the isodecyl phosphate copper complex maintained their transparency even after polymerization, so these two copper complexes show good solubility in poly(2-ethylhexyl methacrylate). Both of the resin plates have >80% visible light transmittance and