Photoluminescent phenanthroimidazole derivatives as covalently linked UV stabilizers for latex coatings

Synthetic latexes are widely used as binders for outdoor barrier applications, where ultraviolet (UV) protection is of high practical importance. This study reports the synthesis of two novel, highly photoluminescent phenanthroimidazole (PPI) derivatives and their application as covalently linked UV-absorbing stabilizers in waterborne, photostable coatings based on all-acrylic latex polymers. Vinyl-functionalized phenanthroimidazole-based monomers, namely 1,2-bis(4'-vinyl-[1,1'-biphenyl]-4-yl)-1H-phenanthro[9,10-d]imidazole (DV-bPPI) and 1,2-bis(4-vinylphenyl)-1H-phenanthro[9,10-d]imidazole (DV-PPI), were synthesized via Suzuki cross-coupling with high yield up to 85%. The synthesized monomers were characterized by multinuclear NMR, FTIR spectroscopy, and single-crystal X-ray diffraction analysis. PPI derivatives, in amounts ranging from 0.05 to 1 wt% (based on monomers), were copolymerized with methyl methacrylate, butyl acrylate, and methacrylic acid using a standard emulsion polymerization technique. The resulting coatings were fully transparent in the visible region and were characterized by UV-vis and photoluminescence measurements. Dynamic mechanical analysis demonstrated that DV-bPPI and DV-PPI, at concentrations of 0.5-1 wt% and 0.25-0.5 wt%, respectively, effectively prevented UV-induced degradation of the polymer films.