Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-11-30
2002-10-01
Lambkin, Deborah C. (Department: 1626)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C558S198000, C526S328000
Reexamination Certificate
active
06458868
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an organophosphate compound (hereinafter may also be referred to as “phosphate monomer”) having a polymerizable group, and a process for preparing the same, and a dental polymerizable composition comprising the organophosphate compound, the dental polymerizable composition exhibiting excellent adhesive strength.
BACKGROUND ART
A dental adhesive has been used to adhere a restorative material to a defective site of teeth or coat the site with the material, and to maintain a restorative material for a long period of time, and thus imparting great merits to present dental care services. As above, the largest reason why clinical techniques using a dental adhesive are widely spread is owing to the development of a technique for adhering to teeth, particularly to dentine tissues.
An active engagement in the studies for adhering to teeth has been made particularly since the 1970's, and particularly there have been tried applications of a polymerizable monomer having an acid group such as phosphate group or carboxylic acid group among compounds having a reactivity to hydroxyapatite, a main component of teeth. However, a phosphate monomer, which had been known at the time, for instance, 2-methacryloyloxyethyl dihydrogenphosphate, has no water resistance at all even though it was used as a dental adhesive, showing no adhesion at all to teeth, particularly to dentine tissues.
However, in the studies made by the present applicant, there have been elucidated that among monomers having a phosphate group, a phosphate monomer having a hydrocarbon group with strong hydrophobicity in the molecular structure exhibits extremely high adhesion to teeth, and high level of adhesion durability even under wet conditions such as oral cavity.
A feature of the phosphate monomers proposed by the present applicant resides in that —P(O)(OH)
2
group or >P(O)(OH) group is bound with a polymerizable group such as a (meth)acrylic group via a hydrocarbon group with strong hydrophobicity which has a large number of carbon atoms. The details of these technique are disclosed in the patent applications filed by the present applicant, such as Japanese Patent Laid-Open Nos. Sho 58-21607 and Sho 58-21687 (corresponding to U.S. Pat. No. 4,539,382).
It is no exaggeration to say that the technique for adhering to teeth has been established for the first time by using these phosphate monomers as a dental adhesive, which were disclosed in the above publications and the like. Since then, various forms of dental adhesives have been proposed by using a group of these phosphate monomers. The above phosphate monomers proposed by the present applicant serve a great role for imparting high adhesion achieved in these techniques.
In the preparation of the above phosphate monomers, for instance, a (meth)acrylic acid monoester monophosphate ester (hereinafter also referred to as “phosphate monoester”), there is mainly employed a preparation process comprising reacting a (meth)acrylic acid monoester, which is a reaction product of a diol and a (meth)acrylic acid, with phosphorus oxychloride, and hydrolyzing the resulting compound having —P(O)Cl
2
group. Such a process has been made known by the present applicant in Japanese Patent Laid-Open No. Sho 59-139392, wherein the process comprises a four-step process, steps (I) to (IV), detailed below.
(I) Preparation of (Meth)acrylic Acid Monoester
A (meth)acrylic acid monoester is prepared by esterification reaction of a diol and a (meth)acrylic acid. In this reaction, a (meth)acrylic acid diester is obtained as a by-product, and an unreacted diol is also contained in the product.
(II) Removal of Unreacted Diol in Reaction Mixture
When the diol is water-soluble, the diol can be usually removed by repeatedly washing the mixture obtained in step (I) with water. On the other hand, when the diol is hardly water-soluble, a non-polar organic solvent, such as n-hexane, cyclohexane, benzene or toluene, in which the diol is insoluble, is appropriately selected, and the reaction mixture is diluted 2- to 10-folds with this organic solvent, and thereby the precipitated diol can be removed by filtration. However, since the (meth)acrylic acid diester obtained as a by-product has solubilities to various solvents similar to those of the (meth)acrylic acid monoester, the separation thereof from the reaction mixture by these processes is difficult. Therefore, in the subsequent process, the monoester is used as a mixture with the diester.
(III) Preparation of Phosphate Monoester
The mixture comprising the (meth)acrylic acid monoester and the (meth)acrylic acid diester is reacted with phosphorus oxychloride or pyrophosphoric acid, to prepare a phosphate monoester. In this process, the phosphate monomer can be quantitatively prepared from the (meth)acrylic acid monoester.
(IV) Isolation of Phosphate Monoester
The reaction mixture is added to a non-polar organic solvent such as n-hexane or toluene, and the (meth)acrylic acid diester, which is a by-product from step (I), is dissolved in the organic solvent, to remove it by extraction, to give a phosphate monoester having high purity. Alternatively, the phosphate monoester is extracted to an aqueous layer by forming a sodium salt or a barium salt thereof, to separate the water-insoluble (meth)acrylic acid diester, and thereafter the aqueous layer is again made acidic to recover a phosphate monoester, thereby giving a phosphate monoester having high purity.
The present applicant has manufactured the above phosphate monomers by themselves, and marketed dental materials comprising the phosphate monomers. In addition, the preparation process concretely disclosed in the above publications can be relatively easily carried out on an industrial scale, and the resulting phosphate monomers have satisfactory performance for practical purposes. However, the present inventors have pursued to further improve the following features, to provide even higher quality phosphate monomers.
1) Improvement in Yield of Phosphate Monomer (Phosphate Monoester)
The reaction mixture obtained in step (I) contains a considerable amount of the (meth)acrylic acid diester, not a desired product, in addition to the unreacted diol, and the (meth) acrylic acid monoester, essential in the subsequent preparation of the phosphate monoester. The studies of the present inventors have revealed that the ratio of monoester/diester/unreacted diol is 0.8-2/1/0.5-1.5. The formation of the (meth)acrylic acid diester merely wastes the diol, which is economically disadvantageous. Particularly when the diol is expensive, there arises a large problem in costs.
Further, in step (IV), if the amount of the (meth)acrylic acid diester admixed in the proportion to the desired phosphate monoester is large, the purity is less likely to increase when the diester is purified by extraction removal with hexane, or the like. In addition, if the purity is tried to increase, the amount of the solvent used in extraction becomes large, or the number of extraction steps repeated becomes large, so that there also arise problems in economic disadvantages and efficiency.
2) Decrease in Coloring
The phosphate monoester obtainable by the preparation process described above has satisfactorily high purity as determined by a liquid chromatography analysis. However, as the phosphate monoester is purified, the coloring ranging from pale yellow to pale brown may be observed in some cases. In a dental adhesive comprising such a colored phosphate monomer, there arise defects that it would be difficult to adjust the color tone of the adhesive to a desirable one having excellent visually acceptable appearance, and that the color of the part restored with the adhesive does not match with the surrounding teeth.
3) Improvement in Storage Stability
When a phosphate monomer per se or a dental adhesive comprising a phosphate monomer is stored for a long period of time, the viscosity thereof may increase, thereby causing gelation or solidification in some cases. Further, there arises a problem of low
Harada Miho
Minami Yasuji
Ohtsuki Junichi
Okada Koichi
Takahashi Koji
Kuraray Co. Ltd.
Lambkin Deborah C.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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