Universal Group 14 Free Radical Photoinitiators for Vinylidene Fluoride, Styrene, Methyl Methacrylate, Vinyl Acetate, and Butadiene

Group 14 (Mt = Sn, Ge, Pb) R₃MtX, R₄Mt, and R₆Mt₂ complexes (R = alkyl, aryl; X = H, halide, etc.) are introduced as novel, universal, visible and black light bulb (BLB)/UV photoinitiators for free radical photopolymerization of alkenes, including vinylidene fluoride (VDF), vinyl acetate, methyl methacrylate, styrene, and butadiene. A comprehensive solvent, ligand and metal comparison for VDF indicates progressively faster BLB photopolymerizations in acetonitrile (ACN) ∼ dimethylacetamide (DMAc) < dimethyl sulfoxide (DMSO) < butanone < propylene carbonate < acetic anhydride ∼ cyclohexanone < dimethyl carbonate and especially in the photosensitizing acetone, where Me₂SnI₂ ∼ Ph₃SnI ∼ Bu₃Sn–N₃ ∼ Bu₃Sn–CH₂–CHCH₂ ≪ Bu₃Sn–S–SnBu₃ < Ph₄Ge < Ph₆Pb₂ < Bu₃Sn–I < Bu₄Sn < Ph₆Sn₂ < Bu₃Sn–Br < Ph₆Ge₂ < Oct₄Sn < Bu₄Ge < Bu₃Sn–Cl < Ph₄Pb < Bu₃Sn–H ≪ Bu₆Sn₂ ≪ Me₆Sn₂ and where M_n is controlled by solvent chain transfer. Photoinitiation results from a combination of R₃Mt·, R·, and solvent (S·, e.g., CH₃–CO–CH₂·) radicals, where R₆Sn₂ (R = Me, Ph) initiates as R₃Sn·, all Bu derivatives, as both Bu₃Sn· and Bu·, and Ph₄Mt and Ph₆Mt₂ (Ge, Pb), only indirectly via S·. Interestingly, while R₃Sn–CH₂–CF₂-poly­(vinylidene fluoride) (PVDF) eliminates R₃SnF to afford CH₂CF–PVDF macromonomers, nonfluorinated alkenes are initiated even in bulk under visible light and do not undergo R₃SnH elimination.