Ester of (meth-)acrylic acid containing perfluor alkyl groups, their preparation and use in dentistry.

The invention relates to new (meth) acrylic acid esters containing fluoroalkyl groups, their preparation and use in dental technology. It relates in particular to those compounds which are suitable as curable polymers in the dental field for relining dental prostheses.

The expression (meth) acrylic acid ester is intended to mean that both methacrylic acid esters and acrylic acid esters are equally covered by the invention.

Fluorine-containing monomeric and oligomeric (meth) acrylates are known from the literature. They are used in the manufacture of dental prosthesis and filling materials and give them reduced water absorption and reduced solubility.

For example, J.Dent.Res., 58, 1981 to 1986 describes the use of 1,1,5-trihydro-octafluoropentyl methacrylate as a polymerizable component in dental filling materials. Then there are fluorine-containing phenylcarbinol acrylates, such as 1,1,1,3,3,3-hexafluoro-2-phenyl-2-acryloyloxypropane from Org.Coat.Plast.Chem. 42, 204 to 207, 1980.

Similar compounds and their use in the dental field are further described in U.S. Patent 4,356,296. US Pat. No. 4,616,072 discloses perfluoroalkyl monomethacrylates as hydrophobic copolymers for dental filling materials. The monomers disclosed in EP-A2-0 201 031 and 0 201 778 with substituted bis-phenyltetrafluoroethane also serve for restorative dentistry.

These previously known monomers have the disadvantage that when they are cured, essentially hard-brittle polymers are formed, which severely limits their possible use in dental technology.

The invention has for its object to provide curable monomers for use in dental technology, which can be used in addition to a reduced solubility and increased mechanical strength of the cured end product, in particular as an underfill material for dental prostheses with increased adhesion to already cured polymethyl methacrylate.

The invention initially relates to new macromonomer fluoroalkyl groups (meth) acrylic acid esters of the general formula<chemistry id="chem0001" num="0001"><img file="EP0373384A1_D0001.tif" /></chemistry> where R 1 is the same or different and is a hydrogen or fluorine radical, R² is the same or different and is a hydrogen or methyl radical, a has a value of 0, 1, 2, 3 or 4, c has a value of 2, 3 or 4, b an average value from 2 to 30, n an average value from 4 to 12 and m has an average value of 3 to 14.

The above formula I is to be understood as an average, general formula of a macromonomer mixture. The individual individuals differ in particular in the number of their oxyalkylene groups, which, with the average value of b as a maximum, corresponds to a Schulz-Flory distribution or is approximated.

The chain length of the fluoroalkyl group is determined by the index n. n has an average value of 4 to 12. The underlying alcohol is R¹C_nF_2n- (CH₂-)_aOH a single compound, the value of n is absolute and corresponds to an integer from 4 to 12. Compounds with an average or absolute value of n = 6 to 10 are preferred.

The hydroxyl function of the fluoroalcohol can be separated from the perfluoroalkyl group by one or more CH₂ groups. The number of such CH₂ groups results from the value of a. a can be an integer, namely 0, 1, 2, 3 or 4.

The index m of the oxyalkylene group C_mH_2mO- has an average value of 3 to 14. The oxyalkylene group can structure<chemistry id="chem0002" num="0002"><img file="EP0373384A1_D0002.tif" /></chemistry> , wherein R³ is an alkyl radical having 1 to 12 carbon atoms, or have CH₂CH₂CH₂CH₂O- when tetrahydrofuran is used for the preparation of the fluorinated alkanol polyether.

Examples of suitable oxyalkylene groups are the oxypropylene, oxybutylene, oxyoctylene, oxydecylene and oxydodecylene radicals. The compounds according to the invention can have the same or different oxyalkylene groups within the individual molecule, so that the index m is to be understood as an absolute numerical value in one case and as an average numerical value in the other case. If there are different oxyalkylene groups next to each other in the same molecule - arranged randomly or in blocks - the molecule should be free of oxyethylene groups. If the molecule has only the same oxyalkylene groups, ie if the value m is to be understood as absolute, it follows from the lower limit of m = 3 that oxyethylene groups are excluded.

Compounds which contain perfluoroalkyl groups are generally poorly soluble or insoluble in customary solvents and are therefore difficult to handle.

The presence of oxyalkylene groups with longer-chain radicals R³ can influence the properties of the compounds according to the invention, in particular after the polymerization, such as hydrophobicity and elastic / plastic behavior, and their solubility and can be adapted to the intended use.

The number of oxyalkylene groups results from the value of b and is on average 2 to 30. A b value of 5 to 20 is preferred.

Particularly preferred compounds according to the invention are those in which at least 50 mol% of the oxyalkylene units in the average molecule are oxypropylene and / or oxybutylene units and the average value of m for the other oxyalkylene units is 5 to 14. It has been shown that these compounds are particularly suitable for the intended use.

Particularly preferred are compounds with the characteristic that in the average molecule at least 90 mol% of the oxyalkylene units are oxypropylene and / or oxybutylene units and the average value of m for the other oxyalkylene units is 5 to 14.

Compounds in which the oxyalkylene units consist exclusively of oxypropylene and / or oxybutylene units combine excellent properties with low cost.

The synthesis of alkoxylated perfluoroalkanols is advantageously carried out by cationic polyaddition using Lewis acids, such as boron trifluoride, boron trifluoride etherate and tin tetrachloride.

Another object of the present invention is the process for the preparation of these compounds. This process is characterized in that a polyoxyalkylene monoether of the general formula

R¹- (C_nF_2n-) (CH₂-)_aO- (C_mH_2mO-)_bH with an isocyanate of the general formula<chemistry id="chem0003" num="0003"><img file="EP0373384A1_D0003.tif" /></chemistry> in a manner known per se at temperatures in the range from 20 to 100 ° C., if appropriate in the presence of a solvent which is inert to isocyanate groups and if appropriate in the presence of a catalyst which is known per se for the reaction of the isocyanate group with the hydroxyl group.

The indices have the meaning already given.

In general, the reaction takes place at low temperatures, such as room temperature. Moderate warming up to about 100 ° C accelerates the reaction. A solvent can be dispensed with in most cases. However, if you do not want to do without a solvent for process engineering reasons, solvents which are inert to isocyanate groups, such as toluene or xylene, are suitable. It is recommended to use a catalyst for the reaction of the isocyanate with the alcohol. Such catalysts are familiar to the person skilled in the art and can be found in the literature. Tin catalysts such as dibutyltin dilaurate and tin octoate are particularly preferred.

To avoid premature polymerization, a sufficient amount of a suitable polymerization inhibitor must be added to the reaction batches. Suitable polymerization inhibitors are hydroquinone, hydroquinone monomethyl ether or t-butyl catechol.

The compounds obtained are distinguished on the one hand by their macromolecular character and on the other hand by their unsaturated end group, which in turn is capable of polymerization; In professional circles, these compounds are therefore also called macromonomers.

Another object of the invention is the use of the compounds according to the invention as curable monomers in the dental field. For this purpose, the compounds according to the invention are compounded with additives customary in dental technology. Such additives can be fillers, such as - in particular hydrophobized - glass ceramic, finely divided silica or pigments or modifiers. The modifiers are used to optimize certain properties that are important in terms of application, such as elasticity, tear resistance, aging resistance, compatibility.

Other suitable modifiers are divinylbenzene, ethylene glycol dimethacrylate, butanediol dimethacrylate, trimethylolpropane trimethacrylate and pentaerythritol tetramethacrylate.

Catalysts for radiation-induced polymerization, such as benzil dimethyl ketal, 2,3-bornanedione, dimethylaminobenzenesulfanic acid bis-allylamide, benzophenone, diethoxyacetophenone, are also added to the preparations in amounts of 0.1 to 3% by weight. The preparation is cured with the aid of lamps customary in dental technology, the radiation of which has a wavelength of 200 to 550 nm.

The curing can also be carried out with peroxidic catalysts or initiators at elevated temperatures. Peroxides such as dibenzoyl peroxide are used for this. At low temperatures, crosslinking is possible with the help of redox initiators. An example of such a redox initiator is the dibenzoyl peroxide / N, N-dihydroxyethyl-p-toluidine system.

The compounding with various additives and the curing of the (meth) acrylic acid esters according to the invention into dental products which are optimal in terms of application technology takes place in a manner known per se and can be found, for example, in the publications cited above, in particular EP-A2-0 201 031 and 0 201 778 .

example

a) Preparation of an α-hydroxy-ω-perfluoroalkylalkanol polyether (not according to the invention)

170 g (approx. 0.37 mol) of perfluorooctylethanol and 9.2 g of tin tetrachloride are heated in a pressure reactor under pure nitrogen to 60 ° C. and 163 g (approx. 2.8 mol) of propylene oxide are added over a period of 3 h. After a post-reaction lasting 0.5 h, the mixture is cooled. The epoxy number of 0.01 determined on a sample of the product indicates that the reaction has largely ended. The product is neutralized with 25 vol .-% ammonia, the water is distilled off at 80 ° C and 10 Torr and finally filtered in the presence of a filter aid.

The hydroxyl number determined by wet analysis is 63, which corresponds to a molecular weight of approx. 890 with an assumed functionality of 1.

b) Preparation of an α-methacryloyl-ω-perfluoroalkanol polyether urethane (according to the invention)

445 0.3 g of 2,6-di-tert-butylcresol are added to g (approx. 0.5 mol) of the α-hydroxy-ω-perfluoroalkanol polyether from a) and the mixture is heated to 45 to 50 ° C. 77.5 g (approx. 0.5 mol) of isocyanatoethyl methacrylate, to which a drop of dibutyltin dilaurate has been added, are then added dropwise with constant stirring. The reaction temperature should not exceed 60 ° C. The course of the reaction is followed in the IR spectrometer until the NCO absorption band has completely disappeared, the time required for this is about 12 h, but can be shortened by adding stannous octoate. The yield is approximately 100%. The molecular weight determined by osmometry is 1040 and thus corresponds to the theoretically determined molecular weight.

c) Production of a soft relining material for dental prostheses

60 Parts by weight of the compound of b) according to the invention are mixed with 30 parts by weight of 2,2,3,3-tetrafluoropropyl methacrylate and 10 parts by weight of 2,2,3,3,4,4-hexafluoro-1,5- mixed pentanediol-dimethacrylate. 1.5% by weight of di-benzoyl peroxide are added to the mixture.

35 parts by weight of hydrophobic silica are added to this solution by intensive mixing under vacuum in a laboratory planetary mixer. The result is a clear, transparent paste that can be used as a soft relining material for dental prostheses both in the press and in the injection process. Curing takes place at 70 to 90 ° C in a water bath within 1 to 3 h.<tables id="tabl0001" num="0001"><table frame="all"><title>table</title><tgroup cols="3" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left">example</entry><entry namest="col2" nameend="col2" align="center">Water absorption mg / cm²</entry><entry namest="col3" nameend="col3" align="center">Shore A hardness 37 ° C</entry></row></thead><tbody valign="top"><row rowsep="0"><entry namest="col1" nameend="col1" align="left">c)</entry><entry namest="col2" nameend="col2" align="right">0,80 ± 0,20</entry><entry namest="col3" nameend="col3" align="right">30 - 35</entry></row><row rowsep="0"><entry namest="col1" nameend="col1" align="left">Commercial product based on silicone</entry><entry namest="col2" nameend="col2" align="right">1,70 ± 0,80</entry><entry namest="col3" nameend="col3" align="right">30 - 35</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">Commercial product based on plasticized methacrylates</entry><entry namest="col2" nameend="col2" align="right">6,90 ± 1,20</entry><entry namest="col3" nameend="col3" align="right">47 - 50</entry></row></tbody></tgroup></table></tables>