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

Abstract

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.

Applications of Halogen-Atom Transfer (XAT) for the Generation of Carbon Radicals in Synthetic Photochemistry and Photocatalysis

“…This has facilitated the development of cascade processes based on radical generation followed by intra-as well as inter-molecular processes 62 and free radical polymerization (FRP). 63 3.1.1.1. Application in Radical Cyclizations.…”

“…The utilization of ditin compounds in synthetic chemistry has proved advantageous as they do not contain a weak Sn–H bond (e.g., Sn–H BDE for Bu 3 SnH is 78 kcal mol –1 ), and therefore minimize unwanted radical reduction reactions which are a common drawback of tin/silicon hydride chemistry. This has facilitated the development of cascade processes based on radical generation followed by intra- as well as inter-molecular processes and free radical polymerization (FRP) …”

Fluoroalkyl Pentacarbonylmanganese(I) Complexes as Initiators for the Radical (co)Polymerization of Fluoromonomers

“…The 19 F NMR spectra of the PVDF obtained from the three activation methods (Figures S10, S12, and S14) also exhibit all the expected resonances of PVDF [6,13,14,31,32,34,35]. The characteristic signal centered at −91.9 ppm (a in Figure 4) is assigned to the regular -CH2CF2-CH2CF2-(head-to-tail, H-T) sequences.…”

Vinylidene fluoride polymerization by metal-free selective activation of hydrogen peroxide: microstructure determination and mechanistic study

“…After the hydroxyl radical was identified as the reactive radical species, and due to the high ability of the released PVDF• macroradicals to abstract a hydrogen from DMC, hence generating carbonate radicals which also initiated the polymerization, it was of interest to highlight the nature of the chain-ends and the molar masses of the resulting polymers. They were characterized by 1 H and 19 F NMR spectroscopy 17,50,55,[57][58][59][60] and MALDI-TOF spectrometry. Several model molecules were synthesized in order to ensure the presence of NMR signals assigned to carbonates, carboxylic acids and alcohols endchains (Figure 2) and to evaluate the regioselectivity of hydroxyl and carbonate radical additions onto VDF.…”

“…17 In addition, a signal at 5.65 ppm ( 19 F NMR: -93.46 ppm) was identified as CH 2 =CFgenerated by the β-F elimination reaction. [60][61][62] In addition, three triplets assigned to the dimethyl carbonate radicals initiated polymerization of VDF 60,63 were identified in the 4.46 to 4.27 ppm range ( 19 F NMR: -93.19 ppm). After the qualitative identification of the chain-end functions of the prepared PVDFs (Table 5, entry 13), the relative quantity of each of them could be estimated based on NMR analysis.…”