GB2247685A - Improvements in cross-linked polymers - Google Patents

Abstract

A room temperature curable composition comprises a dimethacrylate monomer, such as 2, 2 bis-4 (2-hydroxy-3- methacryloyloxypropoxy) phenyl propane, a diluent monomer, an initiator, an accelerator and a specified amount (0.05- 0.7 wt% of composition) of an inhibitor, developing high modulus (over 3.4 GPa) on curing. The preferred compositions are indicated for use as dental resins, eg for fissure sealants, or when used with fillers, as dental repair compositions.

Description

IHPROVENENTS IN CROSS-LINKED POLYMERS This invention concerns cross-linked polymers. More especially, it concerns cross-linked methacrylate polymers having high modulus and indicated for use as dental resins.

Bis GMA (2,2 bis-4 (2-hydroxy-3-methacryloyloxypropoxy) phenyl propane) is the basic monomer for a large number of proprietary dental composite filling materials. Reference is made to USP 3,926,906 which describes a polymeric dental filling system based on bis GMA, in a convenient two-pack system, although there are many other patents describing acrylate polymers used with inorganic fillers for dental restorative work. Such known dental composite materials are used for restorative work on anterior teeth, especially since they can be tinted to match a patient's existing teeth. However, known composite materials do not in general have adequate properties for use on posterior teeth, whether as permanent crowns, inlays etc, where teeth are subjected to much higher stresses, apart from one or two proprietary so-called posterior composites.In the posterior region, inorganic materials, such as dental amalgam, remain the materials of choice. We believe, however, that polymeric materials having properties permitting use on posterior teeth, would be popular for several reasons, and it is an aim of the present invention to provide such materials.

Bis GMA is marketed commercially in the UK as "Nupol" (Trade Mark). U.K Patent Application No 2163442 discloses that bis GMA may be copolymerised with tetrahydrofurfuryl methacrylate (THFM), and that modulus goes through a maximum of 5 GNm .2 at approximately 5% by weight of THFM when heat curing at 800C. It is also disclosed that the polymerisation mixture should include an initiator, such as benzoyl peroxide and an accelerator, preferably a tertiary aromatic amine such as N, N-dismethyl morpholine.If curing is done at room temperature, the modulus for a mixture of bis GMA and THFM is in the range 3.1 to 3.2 GNm -2 The present invention provides a room temperature curable composition comprising a dimethacrylate monomer, a diluent monomer capable of increasing the efficiency of conversion of the dimethacrylate monomer, an initiator, an accelerator and an inhibitor in an amount of from 0.05 to 0.7 wt% of composition.

The preferred dimethacrylate monomer is bis GMA, although other monomers such as those described in GB Patent 1267564 (Espe), and other dimethacrylate monomers such as urethane dimethacrylates, may be used.

The diluent monomer is preferably THFM; other monomers such as glycol methacrylates may also be considered. The amount of diluent monomer is preferably 5 to 40X by wt; this gives a mixture of suitable viscosity for most normal uses.

Initiators for curable systems of this type are well known and are generally organic peroxides such as aliphatic acyl or alkyl peroxides, eg lauroyl peroxide or tert-butyl peroxide, or more preferably an unsubstituted or substituted aromatic acyl peroxide such as benzoyl peroxide or 2,4-dichlorobenzoyl peroxide. Suitable amounts of initiator are 1 to 5 by wt, preferably approximately 3X by wt.

Accelerators for acrylate systems are generally known, and amines are preferred. Suitable amines are tertiary amines, for example an N-heteroyclic amine such as N-ethyl morpholine or preferably N,N-dihydroxyethyl-p-toluidine, suitable amounts of accelerator are 1 to 3X by wt, preferably 1.5 to 2.5X by wt.

Suitable inhibitors, and the optimum amount for a given curable composition, may be found by routine experiment. For example, hydroquinone and its methyl ether derivatives, are common inhibitors.

We prefer, however, to use 2, 6 - ditertiary butyl phenol which is marketed under the trade name "Topanol A". Preferred amounts of this inhibitor are 0.05 to 0.3X by wt.

The curable composition according to the invention may include other components, providing that desirable properties are not unduly adversely affected. For use as a dental fissure sealant, for example, it would not normally be necessary to include other components, but if the composition is intended for dental restorative work, it would normally be desirable to include an inert filler. Suitable fillers are finely divided inorganic substances, especially pyrolytic silica, but other materials such as hydroxyapatite, glass beads, metal oxides such as alumina, quartz and the like may be used, also finely divided metal particles such as silver. Suitable particle sizes are 0.05 to 100 microns, and the quantity of such filler is suitably 60 to 80% by weight based on the monomer component.If desired, the inorganic filler may be pretreated with a keying agent to improve the bond between the curable composition and the inorganic filler. Such keying agents as the organosilanes, and aspects of their use are known in the art. The present invention also contemplates using an organic filler, especially comprising particles of the elements of the curable composition, with or without additional comonomers, which have been heat cured to give maximum modulus and hardness. Such organic fillers may not have the performance to replace inorganic fillers in all uses.

The curable compositions may incorporate dyes and/or pigments to give a match to a patient's teeth.

The compositions are desirably formulated in a two-pack form which requires mixing of the components to produce a room-temperature curing composition, but which components have an extended shelf life whilst separate. The components are suitably a first paste with the monomer system, filler, the initiator and the added inhibitor, the second paste would contain the monomer system, filler and the amine accelerator.

The composition desirably cures in 2 to 5 min after mixing, and the proportions of accelerator and inhibitor are adjusted to achieve this.

If desired, the composition may be subsequently heat cured.

The use of a light curing system, incorporating a photoinitiator system as known in the art, may be used together with or in place of the initiators discussed above.

The compositions are described herein in detail in connection with their use as dental resins, but the invention should not be construed as limited thereto. The properties of the composition are such that they may find application as adhesives, potting or sealing compositions, for example in electronic applications. The composition is believed to be substantially inert, and may find uses in items and parts used in medicine or surgery, such as in orthopaedic and neurosurgery.

The invention will now be described by way of example only.

EXAHPLE A monomer system of sufficient fluidity for handling at room temperature was prepared by mixing 70 parts by weight of bis GMA (purchased as "Nupol" from Freeman Chemicals Ltd, Ellesmere Port, South Wirral, UK) with 30 parts by weight of THFM. 3% by weight of benzoyl peroxide was added as a 50/50 masterbatch with dicyclohexyl phthalate (purchased as "Lucidol CH50" from Akzo Chemicals BV), as initiator, and varying amounts of N,N-dihydroxyethyl-p-toluidine (DEHPT) were incorporated as accelerator. Using "Topanol A" as inhibitor at different concentrations based on the weight of the monomer system, the components were well mixed by hand using a spatula and poured into a rubber mould of approximate dimensions 5 x 1 x 0.2 cm and allowed to cure at room temperature for 10 min.

The resulting slabs of cured resin were disengaged from the mould and were tested to destruction using a three-point bending test on a Nene Universal testing machine, at a rate of deflection of Smm/min.

From the linear portion of the plots, the Youngs modulus was determined in known manner.

The results are shown in the accompanying figure. It was surprisingly observed that modulus appeared to go through a maximum, and also that the maximum offered a very useful increase in modulus from the 3.1 G Pa value achieved without the added inhibitor, with room temperature curing, to 3.6 G Pa.

In the figure, open circles represent results for resins with 1 molD DEHPT; open triangles represent 1.5 mol%; crosses represent 2 molX and open squares represent 2.5 mol% DEHPT.

Claims (15)

CLAIHS

1. A room temperature curable composition comprising a dimethacrylate monomer, a diluent monomer capable of increasing the efficiency of conversion of the dimethacrylate monomer, an initiator, an accelerator and an inhibitor in an amount of from 0.05 to 0.7 wt% of composition.

2. A composition according to claim 1, wherein the dimethacrylate monomer is bis GMA.

3. A composition according to claim 1 or 2, wherein the diluent monomer is THFM.

4. A composition according to any one of the preceding claims, wherein the initiator is an organic peroxide in an amount of from 1 to 5 % by wt.

5. A composition according to any one of the preceding claims, wherein the accelerator is a tertiary amine in an amount from 1 to 3 X by wt.

6. A composition according to any one of the preceding claims, wherein the inhibitor is 2, 6 - ditertiary butyl phanol.

7. A composition according to any one of the preceding claims, wherein the amount of inhibitor from 0.05 to 0.3 % by wt.

8. A composition according to any one of the preceding claims, comprising also a filler.

9. A composition according to anyone of the preceding claims, in two-pack form.

10. A two-pack composition according to claim 9, comprising a first paste comprising blended monomers, filler if desired, initiator and inhibitor, and a second paste comprising blended monomers, filler if desired, and accelerator.

11. A composition according - to claim 1, substantially as hereinbefore described.

12. The use of a composition according to any one of claims 1 to 7 or 9, 10 or 11 if the composition contains no filler, as a fissure sealant.

13. The use of a composition according to claim 8 or 9, 10 or 11 if the composition contains a filler, for the repair of teeth or the manufacture of dental replacement parts.

14. A process for the manufacture of dental fillings or dental replacement parts, comprising polymerising a composition according to any one of claims 1 to 11, and simultaneously or subsequently shaping the composition to form the filling or replacement part.

15. A process according to claim 14, wherein the polymerisation is carried out in or on a patients' tooth to form a filling, tooth replacement part or fissure sealant.

15. A process according to claim 14, wherein the polymerisation is carried out in or on a patients' tooth to form a filling, tooth replacement part or fissure sealant.

AMENDMENTS TO THE CLAIMS HAVE BEEN FILED AS FOLLOWS.

'. A room temperature curable composition comprising a dimethacrylate monomer, a diluent monomer capable of increasing the efficiency of conversion of the dimethacrylate monomer, an initiator, an accelerator and an inhibitor in an amount of from 0.05 to 0.7 wt of composition, the composition being such that upon curing at room temperature, the Youngs Modulus of the resulting polymer is ln excess of 3.4 GPa.

2. A composition according to claim 1, wherein the dimethacrylate monomer is bis GMA.

3. A composition according to claim 1 or 2, wherein the diluent monomer is THFM.

4. A composition according to any one of the preceding claims, wherein the initiator is an organic peroxide in an amount of from 1 to 5 % by wt.

5. A composition according to any one of the preceding claims, wherein the accelerator is a tertiary amine in an amount from 1 to 3 Z by wt.

6. A composition according to any one of the preceding claims, wherein the inhibitor is 2, 6 - ditertiary butyl phanol.

7. A composition according to any one of the preceding claims, wherein the amount of inhibitor from 0.05 to 0.3 % by wt.

8. A composition according to any one of the preceding claims, comprising also a filler.

9. A composition according to any one of the preceding claims, in two-pack form.

10. A. two-pack composition according to claim 9, comprising'a first paste comprising blended monomers, filler if desired, initiator and inhibitor, and a second paste comprising blended monomers, filler if desired, and accelerator.

11. A composition according to claim 1, substantially as hereinbefore described.

12. The use of a composition according to any one of claims 1 to 7 or 9, 10 or 11 if the composition contains no filler, as a fissure sealant.

13. The use of a composition according to claim 8 or 9, 10 or 11 if the composition contains a filler, for the repair of teeth or the manufacture of dental replacement parts.

14. A process for the manufacture of dental fillings or dental replacement parts, comprising polymerising a composition according to any one of claims 1 to 11, and simultaneously or subsequently shaping the composition to form the filling or replacement part.