IE51152B1 - Polymerisable methacrylate compositions suitable for dental use - Google Patents

Abstract

A polymerizable composition particularly for dental use, comprises at least one methacrylate monomer having 2 to 4 polymerizable double bonds, from 0 to 400% based on the monomer of inorganic particulate filler, from 0 to 5% based on the monomer or silane coupling agent, an effective catalyst-activating amount of accelerator comprising copper ion and from 0.5 to 5.0% based on the monomer of (a) an organic peroxy compound and (b) reducing agent for said peroxy compound or a mixture of (a) and (b) wherein the concentration of (b) does not exceed 40% of the total quantity of (a) and (b).

Description

The invention relates in general to polymerizable but not exclusively for dental use compositions and particularly/to such compositions/ capable of undergoing a rapid rate of cure to produce a product polymerizate having a relatively higher quantity of insoluble component.

Polymerizable dental compositions based on the use of methacrylate monomers, e.g. the reaction product of the bis glycidyl ether of bis phenol A and methacrylic acid (hereinafter designated BIS-GMA), are commonly used as fillings, pit and fissure sealants and are advantageously adapted to a wide variety of dental restorative techniques. Such compositions typically include one or more methacrylate monomers and at least one component of a free radical liberating (redox) polymerization system for said monomer(s). Usually, the monomer composition so formulated includes the peroxy type catalyst (oxidant) which is later contacted with the reducing agent (reductant) shortly prior to dental use. Upon contact of the oxidant with the reductant compositions, usually for convenience provided as pastes, polymerization occurs leading to the formation of a polymerizate having the physical properties necessary to the maintenance of good structural integrity and within the oral cavity, e.g. high compressive strength /high degree of insolubles. The latter condition is highly desirable to minimize leaching out of vital ingredients and consequent deterioration of the polymerizate. - la 51152 Rapid and complete curing are thus highly desirable objectives. To some extent, increase in catalyst concentration enhances curing rate; however, correlative enhancement in the degree of cure does not necessarily obtain. In fact, it is often the case that large catalyst concentrations impair the degree of cure thus producing a relatively larger percentage of soluble and leachable components in the final polymerizate. Moreover, larger amounts of peroxy catalyst increase the possibility of pre-polymerization of methacrylate monomer, i.e. prior to contact with reductant thereby often necessitating the use of adjuvants, often in unusually large amounts having a stabilizing or polymerization retardant effect. However, such retardant effects are inevitably manifest to some extent during monomer-oxidant-reductant contact thereby depressing the cure rate and, unavoidably the degree of cure.

A primary object of the invention is to provide polymerizable dental compositions wherein the foregoing and related disadvantages are eliminated or at least mitigated to a substantial extent.

Another object of the invention is to provide polymerizable dental compositions capable of undergoing a rapid rate of cure to produce a polymerizate having a relatively high quantity of insoluble component.

Yet another object of the invention is to provide such - 2 152 a composition having good structural stability within the environment of the human oral cavity.

Still another object of the invention is to provide such a composition wherein any requirements for using higher catalyst concentrations to achieve effective rate and degree of cure are obviated.

A still further object of the invention is to provide such compositions wherein stability of monomer in the presence of peroxy catalyst is effectively improved.

Yet a still further object of the invention is to provide a process of utilizing such compositions to prepare a high quality polymerizate.

Other objects and advantages of the invention will become apparent hereinafter as the description proceeds.

According to the present invention, a polymerizable composition consisting of an oxidant portion and a reductant portion separately packaged or a mixture of said portions comprises, in one or both said portions or in said mixture, methacrylate monomers having 2 to 4 polymerizable methacrylate groups, at least 40% by weight of the monomers comprising the reaction product of glycidyl methacrylate and bisphenol A and the monomers comprising 1,6-hexanedioldimethacrylate present in an amount up to 60% by weight, an inorganic particulate filler in an amount up to 400 parts by weight per 100 parts by weight of said monomers, a silane coupling agent in an amount up to 5 parts, preferably at least 0.5 part, by weight per 100 parts by weight of said monomers, and an accelerator comprising copper ion in an amount of from 5 to 100 parts by weight per million parts by weight of said monomers; in said oxidant portion or in said mixture a free radical polymerization catalyst comprising an organic peroxy compound in an amount of from 0.5 to 5.0 parts by weight per 100 parts by weight of said monomers; and in said reductant portion or in said mixture a reducing agent for said peroxy compound in an amount of from 0.3 to 2.0 parts by weight per 100 parts by weight of said monomers but - 3 51152 not exceeding 40% of the total parts by weight of said peroxy compound and reducing agent.

The oxidant portion and the reductant portion of the composition are preferably both in the form of pastes and should be formulated to be storage-stable. The portions are mixed together shortly prior to use, e.g. dental use, to form a pasty mixture in which polymerization is initiated, the mixture solidifying as polymerization proceeds.

The accelerator preferably comprises cupric ions. Cupric ions are most conveniently supplied in the form of copper salts with organic and inorganic acids. Particularly preferred materials for use herein include, cupric acetate, cupric acetyl acetonate, cupric chloride, and cupric sulphate. The compounds may be used singly or in admixture comprising two or more. In addition, cuprous ions may be present with the cupric ions, although the cupric compounds are found to be generally more effective to give both high degree and rate of cure. Accordingly, it is particularly preferred herein that cupric ion (Cu++), constitutes at least 50% of the total copper ion used. However, and as will be hereinafter demonstrated, the use of cuprous salts alone provides significant improvement when compared to test runs omitting entirely the copper ion. Whether this is due to the presence of cupric ions invariably present in available cuprous salts or to the cuprous ion or to the combination has not been clearly established.

The amount of copper ion present in the monomer composition is exceedingly small, ranging from 5 to 100 ppm, preferably 8 to 50 ppm, based on total monomer. Otherwise stated, the amount of copper ion is at least that necessary to provide effective catalyst activating or accelerating effects. The term total monomer as used herein refers to the total monomer which would be present at the time polymerization actually occurs. Thus, in accordance with a preferred embodiment, peroxy catalyst, monomer, filler and silane coupling agent are included in a first paste portion referred to as the “oxidant paste, and the reducing agent for said peroxy SI 1 52 catalyst is included in the second or reductant paste preferably including the same components as the first paste except for the peroxy catalyst. The copper ion may be present in either or both of the paste portions, its presence in the oxidant portion being most preferred. In any event, copper ion concentration in this embodiment has reference to the total monomer present in both the oxidant and reductant pastes.

On the basis of catalyst, the concentration of copper ion generally ranges from about 0.02 to about 0.4% of the peroxy compound.

The copper compound can be added to the composition by dispersing same in the normally liquid monomers component. The requisite dispersion can be achieved by adding the copper compound to the monomer as a solution in a solvent preferably a polar organic solvent of low boiling point such as ether or lower alkanol, e.g. methanol. Since the solvent is merely a carrier for the copper compound it is most desirable that it be of high volatility so that, generally, most if not all of the solvent is removed in subsequent handling operations, e.g. mixing, etc. The amount of solvent used is quite low, thus to provide 80 ppm (Cu++), and using only a 1% solution in methanol, the volume of solvent would be only 12.5% of monomer volume and 2.5% of a suitable paste on a weight basis. Alternatively, the copper compound may be sorbed onto the filler, e.g. silica, for mixing with the monomer component^).

Methacrylate monomers are selected from materials having two to four polymerizable methacrylate groups per molecule in order that the cured composite be crosslinked and thus better suited for use in the oral cavity. The most preferred monomers are those having two polymerizable methacrylate groups per molecule. Desirable characteristics for such monomers include low polymerization shrinkage, low exotherm during polymerization, low water sorption and the ability to cure rapidly and completely in the mouth. It is also desirable that the monomers be low in volatility and non-irritating to the tooth pulp.

Methacrylate monomer materials useful in this invention are well known - 5 51152 in the art. The preferred materials generally include monomers having a central portion containing at least one aromatic ring and at least two acrylic end groups. Of this type, BIS-GMA is one of the essential monomers and in preferred embodiments constitutes at least 50% by weight of the total monomer composition. The commercial BIS-GMA available from Freeman Chemical Co., U.S.A., under the Trade Mark NUPOL is an example of a suitable material.

Methacrylate monomers particularly useful in this invention are those represented by the following general formulae : [ (M - A - 0) - Ar ]2 - B (M - A)b CRp in IV (M - A - OCO)2Ar II (M - A - OCO - NH)iR3 V CH, - M I CH - M' I CHj - M VI wherein M is methacryloyloxy, i.e. CH2 = C(CH3)COO- ; M1 is methacryloyloxy or hydroxyl; A is alkylene having 1-3 carbon atoms, such as methylene, propylene, isopropylene - 6 SI 152 hydroxyalkylene having 1-3 carbon atoms, such as hydroxymethylene, 2-hydroxypropylene or acetoxyalkylene having 3-5 carbon atoms in the alkylene group such as 2-acetoxypropylene, 3-acetoxyamylene etc.; n is 1 to 4 preferably 1 or 2; m is 2 or 3 and p is 1 or 2 with the proviso that the sum of m and p is 4; R is hydrogen, methyl, ethyl or -A-M wherein A and M are previously described; Ar is phenylene, e.g. o-phenylene, m-phenylene or p-phenylene, alkyl substituted phenylene, e.g. tolylene or 5-t-butyl-m-phenylene or cycloaliphatic having 6 to 10 carbon atoms such as 1,3-cyclohexylene; wherein R r5 and R are independently hydrogen, alkyl e alkylene having 2 to etc ., or -R2{0-R2) x carbon atoms such as , or substituted alkyl and R' is carbon atoms such as ethylene, dodecylene 2 2 OR- wherein R is alkylene having 2 or 3 ethylene, propylene or isopropylene and x is - 7 51158 zero to 5; and K·^ ic phenylene, tolylene, metliylene-bls-phenyleiin oi’ alk.'/lnnc having 2 to 12 carbon atoms.

Monomers having the above formulae are well known • and generally commercially available materials. Alternately, tlmy arc readily provided by conventional synthetic routes, for example, by reacting a phenolic compound such as diphenolic acid, phloroglucinol or bisphenol A with glycidyl methacrylate in the presence of various tertiary amines or by reacting methacrylic acid with an epoxide containing compound such as JO the diglycidyl ether of a bisphenol. Some of these monomers also arc made by reacting appropriate alcohols with methacrylic acid, methacrylyl chloride or methacrylic anhydride.

Illustrative monomers having these formulae include: CKg=C (C »3) COOCHgCHg-OCO^^^-COOC^CHgOCOC (0¾ )=0¾ J 0^=0( CH3 )-000 A CHgOCO A 0000(0¾) = 0¾ no CIi3 θπ3 011 £oh2OCOC(CH3) = CHjQjiJ CH3CH2C { CH2-O-C-C=CH2)3; och3 CIt2= 0(0^)000(0^)^0000(01^)=0¾. 0112= 0(0¾) C00C¾C¾0C¾C¾0CH2Ciί20C0C ( CH2 )=CII2 } CH2=C(CH3) COOCH2CH(OH)CIl2-Oe_^^.0-CI^-CH(OH)C^COC(CH3)=CM ci^= c(ch3)coo——0(0¾ )2 -^^-70-000(01^)=0¾ J - 8 5 0.4^=0 (ClipCOO-CItjC^OlQCHg-O- - OCHg CH(OH)CHgOCOC (CH^CH bcH2CH(0H)0C0C(CH3)=CH2 ch3 CJi,= G(ClI3)C00-CK2,CH20C0NH-rHj '''MHCOOCH C . OH 0C0C(CH )=CH 2 2 3 2 OH )Ho=0(0H3)C00-0l(?CH-0C0NH-CH2CH2C-^-C-CH-NHG00CH-CH2-0C0-C(CH3)=CH2 tk ch ch Li Monomers having the formulae I, II, III and IV are preferred in the practice of this invention. Of these monomers, I, II and III arc particularly preferred, monomers IV being employed more often in admixture with or more of monomers I, II and III, although it will be appreciated that the reaction product of glycidyl methacrylate and bisphenol A and 1,6-hexanedioldimethacrylate are always present.

Other useful methacrylate monomers suitable for use in the practice of this invention include those having the following formulae wherein M and Ar are as previously described; (MR^OArjgCiCH^Jg wherein R^is isopropylenej (MR^OAr)2and(MR^0)2Ar wherein is 2-hydroxy6 6 propylene; ΜΛ R M wherein R is liydroxycyclopentyl Or 8- 8 hydroxycyclohexyl, and A is 2-hydroxyethylene; and wherein R i s : (A, Λ CH ic, (u, -ch^o-^ci ->CH CH,- or - 9 51152 Preparative details for many of those monomers are given in and 3,774,305. A terl.lgry eutectic monomer mixture also suitable for use in this invention is described in U.S. Patent No. 3,539,526.

Mixtures of two or more appropriate methacrylate monomers are within the scope of this invention. In fact, mixtures can optimize the characteristics of the resulting dental composition.

Thus, it is preferred that the monomer mixture has a viscosity of from about 100 to about 10,000 centipoises as determined using a Brookfield viscometer at 20 rpm,at room temperature.

The inorganic particulate fillers employed in the compositions of this invention include fused silica, quartz, crystalline silica, amorphous silica, soda glass beads, glass rods, ceramic oxides, particulate silicate glass, radiopaque glasses(barium and strontium glasses), and synthetic minerals such as beta-eucryptic (HAlSiOi)) having a negative co··!* fieiont ot' thermal expansion. It is also feasible to employ finely divided materials and powdered hydroxylapatite., although materials that react with silane coupling agents are preferred. Also available as a filler are colloidal or submicron silicas coated with a polymer. - 1052 Small amounts of pigments to allow matching of the composition to various shades of teeth can be included. Suitable pigments include Iron oxide black, cadmium yellows and oranges, fluorescent zinc oxides, titanium dioxide, etc.. The filler particles would be generally smaller than about 50 microns in diameter and preferably smaller than 30 microns.

The silane coupling agdnts or keying agents are materials that contain at least one polymerizable double bond to react with the methacrylate monomers. Examples of suitable coupling agents are vinyl trichlorosilane, tris(acotoxy) vinyl silane, l-N(vinylbenzylaminoethyl) aminopropyl trimethoxysilane-3,or 3-mcthacryloxypropyl trimethoxy silane. The last named material is preferred for use with methacrylate monomers because of the similarity in reactivity of the double bonds. invention Peroxy catalysts useful in the/ and capable of initiating polymerization of the methacrylate monomers are well known in the art for such use and include conventional peroxy as well as hydroperoxy compounds such an cumene liydropcroxide, p-methane hydroperoxide, diisopropyl benzene hydroperoxide and t-butyl hydroperoxides. - 11 51153 Hydroperoxides are the preferred species of organic peroxy polymerization catalyst with cumene hydroperoxide (CHP) being particularly preferred. If desired, peroxide stabilizers such as ascorbic acid, maleic acid and the like may be included ln small amounts.

Reducing agents useful herein generally include any material capable of reacting with the peroxy compound to form polymerization initiating, free radical species as is known in the art. Particularly useful herein is a substituted thiourea having the formula: ί 5 x- κ-------C- Z wherein X is H or Y and Y is alkyl having 1 to 8 carbon atoms, such as methyl, butyl, octyl; cycloalkyl having 5 or 6 carbon atoms such as cyelopentyl, eyclohexyl; chloro, hydroxy or mercapto substituted alkyl having 1 to 8 carbon atoms such as chloroethyl, mercapto-etbyl, hydroxymethyl and chlorooctyl; alkenyl having 3 to 4 carbon atoms, such as allyl or methallyl; aryl having 6 to 8 carbons, such as phenyl or xylyl, and chloro-, hydroxy-, methoxy-, or sulphonyl substituted phenyl such as ctilorophenyl,.phenylsulfonyl, hydroxyphenyl and methoxyphenyl; acyl having 2 to 8 carbon atoms such as acetyl,butyryl, octanoyl; chloro or methoxy substituted acyl, such as chloroacotyl, chlorobenzoyl, chlorotoluoyl and methoxybenzoyl; aralkyl having 7 to 8 carbon atoms, such - 12 SilSS as benzyl, or chloro oi· methyl substituted aralkyl such as inothoxybensyl; and Z is NH^, NHX or NX^. Examples of ' illustrative compounds suitable for use in the practice of this invention are methyl thiourea, isopropyl thiourea, butyl thiourea,octyl thiourea, benzyl thiourea, acetyl thiourea, benzoyl thiourea, octanoyl thiourea, cyclohexyl thiourea, allyl thiourea, 1,1,3-triphenyl thiourea, 1,1,3trimethyl thiourea, 2,4-xylyl thiourea, p-tolysulphonyl thiourea, l-octyl-3-phenyl thiourea, o-methoxyphenyl thiourea, m-hydroxyphenyl thiourea, 1,1-diallyl thiourea, 1,3-diallyl thiourea, 2-methallyl thiourea, o-methoxybenzyl thiourea, l-(hydroxymethyl)-3-methyl thiourea, 1,1-dibutyl thiourea, 1,3-dibutyl thiourea, l-(p chloro phenyl)-3-methyl thiourea, butyl-3-butyryl thiourea, l-acetyl-3-phenyl thiourea, 1 methyl-3-(p-vinylphenyl) thiourea, l-methyl-3-0 tolyl thiourea, l-methyl-3-pentyl thiourea, 3-methyl-l, 1-diphenyl thiourea and 1-acetyl, 3-(2 metcaptoethyl) thiourea. While any of the aforementioned thiourejas can be employed in the practice of this invention, preferred are the monosubstituted thioureas, that is, those having the aforementioned formula wherein X is H and Z is NH . Particularly preferred are 2 phenyl thiourea, acetyl thiourea and allyl thiourea. Preferably, the composition contains about 0.5 to about 1% by weight of reducing agent.

The following Examples are illustrative of embodiments of of the invention. All parts and percentages are by weight. - 13 S1152 EXAMPLES 1-14 Radiopaque reductant pastes having the following compositions are prepared: Composition % by Weight Ingredient A B C D E F G H1Nupol 10.27 10.24 10.27 10.27 10.27 10.27 10.27 10.272hmdma 10.27 10.24 10.27 10,27 10.27 10.27 10.27 10.2?3A-174 1.03 1.02 1.03 1.03 1.03 1.03 1.03 1.03 Acetyl Thiourea 0.43 0.43 0.43 0.43 0.43 0.43 0.43 0.43 Ascorbic acid __ 0.07 w+ — — .00022 ! .000* 14.0011 .0022 .0033 .00445Imsil A-10 41.86 41.86 41.86 41.86 41.86 41.86 41.86 41.86 ^Corning 7724 36.14 36.14 36.14 36.14 36.14 36.14 36.14 36.14 TOTAL 100 100 100 100 100 100 100 100 1 - Bis (GMA) - 1.6 hexanedioldimethacrylate o * - z-methacryloxy propyl trimethoxy silane 11 - In the form cupric acetate added from methanol solution to monomer mixture - Amorphous silica (Illinois Minerals) - Barium Glass (Corning) Nupol, Imsil and Corning are trade marks.

Radiopaque oxidant pastes having the following compositions are prepared.

Ingredient Composition % by weight I. J Nupol 9-94 9.78 HMDMA 9.94 9-78 A - 174 0.99 0.98 Maleic acid 0,41 Ascorbic, acid 0.07 .4- Cumene hydroperoxide (80%) 1.05 i;$5 Imsil A-10 41.93 41.79 Corning 7724 36.06 36.22 Total 100 100 Oxidant and reductant pastes respectively are mixed in a weight ratio of 1:1 as indicated in the following Examples Curing times are given in minutes and include time required for mixing, approximately 30 seconds. The cessation of the curing reaction is determined by the material no longer being indentable by a spatula. It can also be done by measuring the percent of polymerizate insoluble in methanol upon completion of the curing reaction. Samples of- the polymerforming mass are taken at timed intervals during the curing reaction; cessation of the latter is indicated by the point at which percent insolubles remains substantially constant.

The results are summarized as follows: - 15 51152 Example No. Oxidant Paste Reductant Paste PPM Cu++ Cure in Heductant Minutes Paste Temp °C 1 J C 2.2 3.5-4.3 21 ? II D k.k 2.8-3.2 23 3 If E 11.0 1.8-2.2 23 4 II F 22.0 1.7-2.2 20.5 5 II G 33.0 1.5-1.8 21.5 6 (I H 44.0 1.3-1.8 23 7 11 A none 4,0-5.0 27 8 I C 2.2 3.3-3.8 21 9 II Ό 4.4 2.7-3.5 22.5 10 If E 11.0 1.8-2.2 23 11 11 F 22.0 1.7-2.0 20.5 12 tt G 33.0 1.3-1.7 21 13 It II 44.0 1.25-1.6 23 14 II A none 3.3-4.0 21 In each of the runs, curing is carried out in air, i.e. in an open vessel. Increased concentration of Cu** provides more rapid cures. - 16 51152 In comparison to Examples 7 and 14, which omit the copper accelerator, the data establish marked improvement in curing rate for the present invention.

Similar combinations (1:1) of reductant paste B with I and J 5 produce comparable results to those of Examples 7 and 14.

EXAMPLES 15-28 Each of Examples 1 - 14 is repeated with the exception that the cupric acetate is sorbed onto the filler and then added to the monomer composition. Similar improvement is obtained in curing rate by comparison with control runs omitting the copper compound.

EXAMPLES 29 - 31 The following reductant-containing and oxidant-containing compositions are prepared : - 17 51152 REDUCTANT Composition % by weight Ingredient K L M Nupol 9-9 9.9 9.9 HMDMA 9-9 9-9 9.9 Acetyl Thiourea 0.45 0.45 0.45 Cu++ 0.0002 0.0005 0.0010 Corning 7724a 36.25 36.25 36.25 IMSIL A-10a 42.25 42.25 42.25 Colloidal Silica 1.30 1.30 1.30 a. Silanized OXIDANT COMPOSITION - N Ingredient Nupol HMDMA CUP (80S) Corning 7724a IMSIL A-10a Colloidal Silica a. Silanized Composition % by weight 9.325 9.325 1.05 36.25 42.25 1.80 The Oxidant paste is mixed on a clean glass plate with each of the three reductant pastes in a 1:1 ratio. Curing times for each of three mixes are determined by the - 18 51152 time required for the blended material to be resistant to indentation by a plastic spatula. The results are summarized as follows: PPM Cu++ in Reductant Curea Example No. Oxidant Paste Reductant Paste Paste_ Minutes a. at 23°C 4.2-5.0 2.5-3.0 2.3-2.a In each of the above runs, curing Is carried out in air. (Shorter curing times would result under glass or in a cavity covered by a matrix strip.) It is evident that increasing the concentration of Cu++ results in a shorter cure time.

Similar results are obtained when the foregoing examples are repeated but utilizing, within the ranges hereinbefore specified the following peroxy catalysts and reductant compounds: peroxy catalysts - p-methane hydroperoxide, diisopropylbenzene hydroperoxide and t-butyl hydroperoxide; reductants-allyl thiourea, phenyl thiourea, and 3-allyl-l, 1-diethylthiourea.

Claims (13)

1. A polymerizable composition consisting of an oxidant portion and a reductant portion separately packaged or a mixture of said portions; said composition comprising, in one or both said portions or in said 5 mixture, methacrylate monomers having 2 to 4 polymerizable methacrylate groups, at least 40% by weight of the monomers comprising the reaction product of glycidyl methacrylate and bisphenol A and the monomers comprising 1,6-hexanedioldi-methacrylate present in an amount up to 60% by weight, an inorganic particulate filler in an amount up to 400 parts 10 by weight per 100 parts by weight of said monomers, a silane coupling agent in an amount up to 5 parts by weight per 100 parts by weight of said monomers, and an accelerator comprising copper ion in an amount of from 5 to 100 parts by weight per million parts by weight of said monomers; in said oxidant portion or in said mixture a free radical polymerization 15 catalyst comprising an organic peroxy compound in an amount of from 0.5 to 5.0 parts by weight per 100 parts by weight of said monomers; and in said reductant portion or in said mixture a reducing agent for said peroxy compound in an amount of from 0.3 to 2.0 parts by weight per 100 parts by weight of said monomers but not exceeding 40% of the total parts 20 by weight of said peroxy compound and reducing agent.

2. A composition as claimed in Claim 1 wherein the accelerator comprises cupric ion.

3. A composition as claimed in Claim 1 or Claim 2 wherein the weight ratio of free radical polymerization catalyst to reducing agent is about 25 2:1.

4. A composition as claimed in any of Claims 1 to 3 the reducing agent comprises a substituted thiourea compound.

5. A composition as claimed in Claim 4 wherein the reducing agent comprises an allyl or acetyl - substituted thiourea. - 20 51152

6. A composition as claimed in any of the preceding claims wherein the peroxy compound comprises cumene hydroperoxide and the reducing agent comprises acetyl thiourea.

7. A composition as claimed in any of Claims 1 to 5 wherein the peroxy 5 compound comprises cumene hydroperoxide and the reducing agent comprises allyl thiourea.

8. A composition as claimed in Claim 2 or in any of Claims 3 to 7 when appendant to Claim 2 wherein the cupric ion is present as cupric acetate, cupric acetyl acetonate, cupric chloride or a mixture thereof.

9. 10 9. A composition as claimed in Claim 2 or in any of Claims 3 to 8 when appendant to Claim 2 wherein the concentration of cupric ion is from 5 to 100 ppm based on the monomer. 10. A composition as claimed in Claim 2 or in any of Claims 3 to 9 when appendant to Claim 2 wherein the cupric ion is dispersed in the monomer. 15

10. 11. A composition as claimed in Claim 2 or in any of Claims 3 to 10 when appendant to Claim 2 comprising up to 50% by weight based on the weight of cupric ion of cuprous ion.

11.

12. A composition as claimed in any of the preceding claims wherein both said portions have, or said mixture has, a paste-like consistency. 20

13. A polymerizable composition as claimed in Claim 1 and substantially as described in any of Examples 1 to 6, 8 to 13, 15 to 20, 22 to 27 and