Frank Zeuner

Synthesis and polymerization of vinylcyclopropanes

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 β-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.

Synthesis of bis(3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoyl)(phenyl)phosphine oxide - a tailor-made photoinitiator for dental adhesives.

Summary Because of the poor solubility of the commercially available bisacylphosphine oxides in dental acidic aqueous primer formulations, bis(3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoyl)(phenyl)phosphine oxide (WBAPO) was synthesized starting from 3-(chloromethyl)-2,4,6-trimethylbenzoic acid by the dichlorophosphine route. The substituent was introduced by etherification with 2-(allyloxy)ethanol. In the second step, 3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoic acid was chlorinated. The formed acid chloride showed an unexpected low thermal stability. Its thermal rearrangement at 180 °C resulted in a fast formation of 3-(chloromethyl)-2,4,6-trimethylbenzoic acid 2-(allyloxy)ethyl ester. In the third step, the acid chloride was reacted with phenylphosphine dilithium with the formation of bis(3-{[2-(allyloxy)ethoxy]methyl}-2,4,6-trimethylbenzoyl)(phenyl)phosphine, which was oxidized to WBAPO. The structure of WBAPO was confirmed by 1H NMR, 13C NMR, 31P NMR, and IR spectroscopy, as well as elemental analysis. WBAPO, a yellow liquid, possesses improved solubility in polar solvents and shows UV–vis absorption, and a high photoreactivity comparable with the commercially available bisacylphosphine oxides. A sufficient storage stability was found in dental acidic aqueous primer formulations.

Synthesis and Dental Aspects of Acrylic Phosphoric and Phosphonic Acids

Introduction Achieving a strong and durable bond to dentine is of great importance in restorative techniques. In recent years there has been a lot of debate as to how such a bond may be obtained. Bonding is believed to occur through either mechanical or chemical interaction or possibly a combination of both[1]. In this study we have focused on phosphorus compounds[2−4] which can form complexes with the Ca2+ ions of hydroxyapatite. Most of the hitherto known compounds can not afford a single step procedure in dental adhesion. To overcome this problem several new phosphonic and phosphoric methacrylates have been synthesized. Furthermore, polymerization capabilities and characteristics of physical and adhesive properties are described.

Synthesis and dental aspects of acrylic phosphonic acids

Phosphoric acid esters of 2-hydroxyethyl methacrylate are favorable as components of dentin adhesives because they are able to remove the smear layer on dentin and achieve a strong bond between the restorative material and the tooth substance. However, one disadvantage of these polymerizable phosphoric acids is their low hydrolytic stability. This problem should be overcome with monomers 1 (R2,3=H) containing more hydrolytically stable bonds between the polymerizable methacrylic group and the strong acidic phosphorus group.

Polymerization of cyclic monomers. VII. Synthesis and radical polymerization of 1,3-bis[(1-alkoxycarbonyl-2-vinylcyclopropane-1-yl)carboxy]benzenes

1,3-Bis[(1-alkoxycarbonyl-2-vinylcyclopropane-1-yl)carboxy]benzenes 1 [RO: CH3O (a), C2H5O (b)] were synthesized by the esterification of the corresponding 1-alkoxycarbonyl-2-vinylcyclopropane-1-carboxylic acids with resorcinol. The structure of the new vinylcyclopropanes was confirmed by elemental analysis and infrared (IR), 1H nuclear magnetic resonance (1H-NMR), and 13C nuclear magnetic resonance (13C-NMR) spectroscopy. The radical polymerization of difunctional 2-vinyl-cyclopropanes in bulk with 2,2′-azoisobutyronitrile (AIBN) results in hard, transparent, crosslinked polymers. During the bulk polymerization of the crystalline bis[(1-methoxycarbonyl-2-vinylcyclopropane-1-yl)carboxy]benzene 1a, an expansion in volume of about 1% took place. The radical solution polymerization of 1a resulted in a soluble polymer with pendant 2-vinylcyclopropane groups.

A Simple Method for the Preparation of Functionalized Steric Hindered Methacrylic Acid Esters and Amides

Abstract Methacrylates are obtained by using a one pot method, in which the α‐methyl substituted acrylic acid is converted into the corresponding anhydride in situ by means of carbodiimides or p‐toluenesulfonyl chloride and a further reaction with 2,6‐dialkylphenols in the presence of 4‐(dimethylamino)pyridine (DMAP) as the catalyst.

Synthesis of Novel 2‐Vinylcyclopropane Phosphonic Acids

Abstract 2‐Vinylcyclopropane‐1‐phosphonic acid diesters 1a–d were synthesized by the reaction of trans‐1,4‐dibromo‐2‐butene with α‐substituted phosphonic acid diesters. Esterification of 1‐ethoxycarbonyl‐2‐vinylcyclopropane‐1‐carboxylic acid with dimethyl 2‐hydroxyethyl‐phosphonate gave the 2‐vinylcyclopropane phosphonic acid dimethylester 1e. The silylation of phosphonic acid diesters 1a–e by halotrimethylsilanes followed by solvolysis with methanol or water resulted in the formation of phosphonic acids 2a–e. In the case of steric hinderance of the phosphoryl group, monoesters 3c,d were also formed. Furthermore, ethyl carboxylate 1b could be chemoselectively cleaved by aqueous potassium hydroxide to carboxylic acid 4.

Synthesis and radical polymerization of hydrolytically stable dentin bonding agents

Acrylic groups containing phosphonic acids were synthesized by ether formation of ethyl α-chloromethylacrylate with hydroxyalkyl phosphonates and subsequent hydrolysis to the corresponding phosphonic acid α-methylsubstituted acrylates. Furthermore, phosphonic acids derived from acrylonitrile and acrylamide were synthesized. The monomers are hydrolytically stable in aqueous ethanol. The radical polymerization of the monofunctional phosphonic acids results in water soluble polymers, whereas in case of a phosphonic acid diacrylate a cross-linked polymer was formed. The most radical polymerizable phosphonic acids can be used to promote the adhesion to dentin.