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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SUMMARY: Vinylcyclopropanes are important synthetic intermediates in organic chemistry and are mostly synthesized by the simultaneous introduction of the cyclopropane and the vinyl unit, e. g., by the reaction of trans-1,4-dihalobutenes with b -dicarbonyl compounds or the addition of carbenes to dienes. The polymerization of vinylcyclopropane itself results in vinyl polymers with predominantly 1,2-structural units. The radical polymerization of substituted vinylcyclopropanes results in polymers with mainly 1,5-ring-opened units, whereby radical stabilizing substituents or electron-withdrawing groups increase the radical polymerizability and the ring-opening ability. The vinylcyclopropanes undergo a radical copolymerization with other vinyl monomers, such as methacrylates, and, in comparison to the polymerization of these linear vinyl monomers, the vinylcyclopropanes show a significantly lower volume shrinkage during ring-opening polymerization. Hybrid vinylcyclopropanes are polymerized step-by-step under formation of reactive polymers or polymer networks. Multifunctional cross-linking vinylcyclopropanes can be used as new low-shrinking matrix monomers for photopolymerizable materials. In addition, the sol-gel process of trialkoxysilyl-functionalized vinylcyclopropanes affords low shrinking organic-inorganic nanocomposites.

Multifunctional 2-vinylcyclopropanes were synthesized by esterification of the 1 -methoxycarbonyl-2-vinylcyclopropane-1 -carboxylic acid with ethylene glycol, 1,1,1 -trimethylolpropane or 1 ,4-cyclohexanediol in the presence of 1,3-dicyclohexylcarbodiimide (DCC). The structure of the new vinylcyclopropanes was confirmed by elemental analysis, IR, 'H NMR and 13C NMR spectroscopy. The radical polymerization of the 2-vinylcyclopropanes in bulk with 2,2'-azoisobutyronitrile (AIBN) results in transparent crosslinked polymers. The polymerization of the liquid monomers is accompanied by a low shrinkage in volume.

Methyl 2‐(bicyclo[3.1.0]hex‐1‐yl)acrylate (1) was synthesized from methyl 2‐(cyclopentene‐1‐yl)‐2‐hydroxyacetate by cyclopropanation, followed by oxidation to the corresponding bicyclic 2‐oxoacetate and Wittig olefination with methyltriphenylphosphonium bromide. Initiated with 2,2′‐azoisobutyronitrile at 65 °C in chlorobenzene, the radical homopolymerization of 1 occurred with opening of the cyclopropane ring leading to a polymer with a glass transition temperature of 90 °C. The reactivity of 1 in radical copolymerization was higher than that of methyl methacrylate. magnified image