New dibenzoylgermanium derivatives are synthesized starting from various dithioacetal protected benzaldehydes by a coupling reaction with different dialkyldichlorogermanes and subsequent oxidative cleavage of the protecting group. The synthesized germanium compounds show a significantly stronger blue light absorption than camphorquinone. During irradiation, the dibenzoylgermanium derivatives undergo photodecomposition under formation of radicals. Therefore, the different dibenzoylgermanium derivatives are used as amine‐free visible‐light photoinitiators for dental cements and composites. Composites based on the different dibenzoylgermanes are storage‐stable and show a significantly improved bleaching behavior over composites with CQ/amine photoinitiators.magnified image

SUMMARY: Acrylic groups containing phosphonic acids were synthesised by ether formation of ethyl achloromethylacrylate with hydroxyalkylphosphonates and subsequent hydrolysis to the corresponding phosphonic acid a-methyl-substituted acrylates. The structure of the synthesised monomers was confirmed by elemental analysis, IR, 1 H NMR, 13C NMR and 31 P NMR spectroscopy. The monomers are stable in aqueous ethanol. The radical polymerisation of the monoacrylates in tetrahydrofuran with 2,29-azobisisobutyronitrile (AIBN) results in soluble polymers, whereas a phosphonic acid diacrylate results in a cross-linked polymer.

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Hydrolytically stable, crosslinking bis(acrylamide)s 1a–1l or bis(methacrylamide)s 2a–2c were synthesized by reaction of acryloyl or methacryloyl chloride using primary or secondary amines. In addition, monomers 3a and 3b were obtained by amidation of 2,6‐dimethylene‐4‐oxaheptane‐1,7‐dicarboxylic acid (DMOHDA) with propylamine and diethylamine, respectively. The structures of the monomers were characterized by IR, 1H, and 13C NMR spectroscopy. All monomers containing N,N′‐monosubstituted carbamide groups were solids. Those containing N,N′‐disubstituted carbamide groups were water‐soluble liquids. Water‐soluble bis(acrylamide) 1d (N,N′‐diethyl‐1,3‐bis(acrylamido)propane) shows a radical polymerization reactivity in the presence of 2,2′‐azobis(2‐methylpropionamidine) dihydrochloride (AMPAHC) similar to that of glycerol dimethacrylate, as revealed by gelation experiments in water. 1d is hydrolytically stable in 20 wt.‐% phosphoric acid and can be used to substitute dimethacrylates in self‐etching dentin adhesives. Furthermore, this monomer was also suitable as a reactive diluent in composites.magnified image

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