Organic compounds -- part of the class 532-570 series – Organic compounds – Heavy metal containing
Reexamination Certificate
2000-10-17
2002-06-25
Kumar, Shailendra (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heavy metal containing
C252S299010, C252S299640, C552S309000, C556S012000, C560S061000, C560S067000, C560S070000, C525S360000, C525S361000, C525S389000, C523S212000, C523S213000
Reexamination Certificate
active
06410765
ABSTRACT:
BACKGROUND OF THE INVENTION
The instant invention relates to alkene functionalized, metal oxide, manoparticle composites with polymerizable alkene matrix monomers primarily suitable for dental and medical restoration; i.e., dental restoratives and bone repair, and to the method of their use for such purposes and methods of manufacture. Other applications envisioned include optical elements, X-ray photoresists, and repair of materials.
There have been efforts made to generate functionalized metal oxide nanoparticles to make highly uniform composite materials; namely, in U.S. Pat. No. 5,064,877 by R. Nass et al., in U.S. Pat. No. 5,030,608 by U. Schubert et al.(see also H. Schmidt and H. Wolter, J. Non. Cryst. Solids, 121, 428 (1990). They claim a method for producing functionalized, photopolymerizable particles by replacing groups, R, in M(R)
n
with groups A which complex M and further contain functional groups which can be photopolymerized. The dispersed, individual metal oxide particles can be prepared by removing R completely, partially replacing by A and then by hydrolyzing to oxide with water. Alternatively, the oxyhydroxide particles may be preformed as M(O)
z
(OH)
x
R
y
and converted to M(O)
z
(OH)
x
A
y
by the loss of R. The preformed oxyhydroxide is formed by Nass et al. by the hydrolysis of the organometallic M(R)
n
by water directly or by water generated by reaction of acid and alcohol unlike Wellinghoff in U.S. Pat. No. 5,570,583 where the oxide is formed by direct ester exchange between a metal alkoxide and a strong organic acid thereby decreasing the number of required reactants.
There have been other attempts to form organic-inorganic hybrid glasses. However, in one case a silane functionalized polymer is hydrolyzed with water to form a network crosslinked by the resultant silica particles making removal of volatile reaction products difficult [Y. Wei et al., Chem. Mater., 2(4), 337 (1990); C. J. T. Landry et al., Polymer, 33(7), 1487 (1992)]. M. Ellsworth et al. [JACS, 113(7), 2756 (1991); U.S. Pat. No. 5,412043; U.S. Pat. No. 5,254,638] attempted to eliminate the composite shrinkage induced by removal of volatile reaction products by utilizing ring strained alkenoxysilanes and polymerizable solvents where all reaction by products contribute to the SiO
2
network or the resultant interpenetrating, matrix, organic polymer. The expected packing disruption induced by the strained ring opening of the alkenoxysilane was a strategy for compensating for the shrinkage induced by conversion of double bonds to single bonds
Zero polymerization shrinkage is one of the most necessary features of a dental restorative so that accumulated stresses do not debond the dentin-restorative interface or fracture the tooth or restorative which can result marginal leakage and microbial attack. This feature is also important in bone repair and in accurate reproduction of photolithographic imprints and optical elements.
Other attempts have been made to reduce polymerization shrinkage by utilizing nematic liquid crystal monomers. The expected low polymerization shrinkage for such compounds originates from the high packing efficiency that already exists in the nematic state, thus minimizing the entropy reduction that occurs during polymerization. Liquid crystal monomers or prepolymers have another advantage in that the viscosity is lower than an isotropic material of the same molecular weight.
M. Aizawa et al. [JP H 5-178794, Jul. 30, 1993] disclose a bisalkene substituted liquid crystal crystal monomer that is suitable for dental restorative materials in combination with silica particle reinforcement. Latter H. Ritter [EP 0,754,675 A2] et al. also disclose liquid crystal monomers that might be suitable for dental applications; however, in neither of the above two patents was the liquid crystal nematic at room temperature or dental temperature. Reactive diluents were added to the original compounds to generate liquid monomers and it was not clear that liquid crystallinity was present in these mixtures. However, even more recently, J. Klee et al. [WO 97/14674] discuss two liquid crystal monomers that are nematic in the desired temperature range between room temperature and 37° C.
Parent U.S. application Ser. No. 08/721,742, identified above, discloses bisalkene terminated liquid crystal monomers that form stable liquid crystalline melts between room temperature and 37° C. and their composites with functionalized nanoparticles. This disclosure describes the nanoparticles formed by the reaction of trialkylylchlorosilane, formic acid and tantalum alkoxide that are quite acidic in concentrated methanol solution and must be surface functionalized with the base, vinyl imidazole in order to neutralize the excess acidity. The alternative functionalization with an alkene phosphate suffers from the relative hydrolytic instability of the phosphate linkage and the low selectivity of the alkene dimethyl phosphate ester with Ta—OH bonds. While very satisfactory, the composites are, however, hydrophilic, and this mitigates against their complete suitability for dental purposes.
SUMMARY OF THE INVENTION
The forgoing problems and deficiencies of the prior art are overcome by the instant invention which provides workable oxide-monomer mixtures with especially low polymerization shrinkage in the matrix resin while permitting high loading of strengthening materials and high matrix molecular weight, and yet permitting the matrix to strain soften, and flow onto/and or into areas to be cemented, coated, or restored, such as bone and tooth crevices, and to be polymerized between −40° C. and +40° C.
Briefly, the present invention comprises novel functionalized amphoteric nano-sized metal oxide particles, composites thereof, and transparent or translucent acrylate or methacrylate based matrix-metal oxide compositions with photopolymerizable room temperature nematics that have high strength and hardness with essentially zero shrinkage.
The invention also comprises the methods of making, the composites and compositions as hereinafter set forth.
DETAILED DESCRIPTION
While the present invention can be carried out using any metal capable of forming amphoteric metal oxides to form the metal oxide nanoparticles, such as tantalum, niobium, indium, tin, titanium and the like, it will be described in connection with tantalum. Tantalum is particularly desired for dental and medical uses since it will provide X-ray opaque materials necessary for diagnosis by dental and medical personnel.
These tantalum nanoparticles are prepared as set forth in the parent application identified above by ester exchange of tantalum oxide with an acid such as formic acid.
For this invention it is important that such nanoparticles be non-interacting without high surface acidity which is detrimental for dental applications, especially. In addition, it is preferable that the alkene be reacted with the oxide surface through a phosphonate linkage which has good hydrolytic stability and will react with Ta—OH bonds only through the ester bonds. In order to make an especially active phosphonating species we reacted the dimethyl ester of the methacryl phosphonate with a silanating agent to form the hydrolytically unstable vinyl dimethyl silyl ester. The silanating agent can be a chloride, as shown below, or a bromide.
This reaction is quite generic and can be utilized to form the any trialkylsilyl ester (for example, trimethylsilyl) of any functionalized phosphonate, including vinyl phosphonate. Suitable esters have the general formula:
wherein R is a photopolymerizable group, such as a vinyl, acryl, or methacryl group, and R′, R″, and R′″, which can be the same or different, are an alkyl or alkene group.
For purposes of further illustration, in addition to the trialkylsilyl ester of vinyl phosphonate, phosphonates having the following groups can also be used:
1. R is —CH═CH
2
and R′, R″, and R′″ are each —CH
3
;
The silyl phosphonate
Dixon Hong
Norling Barry K.
Rawls Henry R.
Wellinghoff Stephen T.
Kumar Shailendra
Paula D. Morris & Associates P.C.
Southwest Research Institute
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