Macromolecules, Vol.52, No.22, 8895-8909, 2019
Universal Group 14 Free Radical Photoinitiators for Vinylidene Fluoride, Styrene, Methyl Methacrylate, Vinyl Acetate, and Butadiene
Group 14 (Mt = Sn, Ge, Pb) R(3)MtX, R(4)Mt, and R(6)Mt(2) 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) similar to dimethylacetamide (DMAc) < dimethyl sulfoxide (DMSO) < butanone < propylene carbonate < acetic anhydride cyclohexanone < dimethyl carbonate and especially in the photosensitizing acetone, where Me2SnI2 similar to Ph3SnI similar to Bu3Sn-N-3 similar to Bu3Sn-CH2-CH=CH2 << Bu3Sn-S-SnBu3 < Ph4Ge < Ph6Pb2 < Bu3Sn-I < Bu4Sn < Ph6Sn2 < Bu3Sn-Br < Ph6Ge, < Oct(4)Sn < Bu4Ge < Bu3Sn-Cl < Ph4Pb < Bu3Sn-H << Bu6Sn2 << Me6Sn2 and where M-n is controlled by solvent chain transfer. Photoinitiation results from a combination of R(3)Mt center dot, R center dot and solvent (S center dot, e.g., CH3-CO-CH2 center dot) radicals, where R6Sn2 (R = Me, Ph) initiates as R3Sn center dot, all Bu derivatives, as both Bu3Sn center dot and Bu center dot, and Ph(4)Mt and Ph(6)Mt(2) (Ge, Pb), only indirectly via S center dot. 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.