A MULTI-PART ACRYLIC COLD-CURING COMPOSITION

Abstract

A multi-part acrylic cold curing composition for metallography moulds to produce a metallography mount is described. The composition has a storage stable solid part and a storage stable liquid part. The parts are operable to form a mixture which polymerises to a solid mass upon mixing of the parts together. The solid part comprises polymer powder and initiator and the liquid part comprises acrylic monomer and optionally activator or accelerator. The initiator is present in an amount effective to polymerize the acrylic monomer component upon being mixed with the liquid part. The composition comprises a cyclic ester side group containing monofunctional acrylic monomer. The composition liquid part may contain a mixture of monofunctional monomer(s) and polyfunctional monomer(s), wherein the polyfunctional monomers comprise between 12 and 22% w/w of the total monomers in the uncured composition. Metallography mounts and processes for producing the mounts are also described.

Claims

1. A acrylic cold curing composition for metallography moulds to produce a metallography mount comprising: a storage stable solid part and a storage stable liquid part, the parts being operable to form a mixture which polymerizes to a solid mass upon mixing of the parts together, the solid part comprising polymer powder and initiator and the liquid part comprising acrylic monomer and optionally activator or accelerator, the initiator component being present in an amount effective to polymerize the acrylic monomer component upon being mixed with the liquid part, wherein: the acrylic monomer comprises a cyclic ester side group containing monofunctional acrylic monomer, wherein the cyclic ester side group containing monofunctional acrylic monomer comprises between 70 and 96% w/w of the total monomers in the uncured composition.

2. A multi-part acrylic cold curing composition for metallography moulds to produce a metallography mount comprising: a storage stable solid part and a storage stable liquid part, the parts being operable to form a mixture which polymerizes to a solid mass upon mixing of the parts together, the solid part comprising polymer powder and initiator and the liquid part comprising acrylic monomer and optionally activator or accelerator, the initiator component being present in an amount effective to polymerize the acrylic monomer upon being mixed with the liquid part, wherein: the acrylic monomer comprises a cyclic ester side group containing monofunctional acrylic monomer, the liquid part comprises a mixture of monofunctional monomer(s) and polyfunctional monomer(s), and wherein the polyfunctional monomers comprise between 12 and 22% w/w of the total monomers in the uncured composition.

3. A solid metallography mount produced from mixing a multi-part acrylic composition comprising: a storage stable solid part and a storage stable liquid part, the parts being operable to form a mixture which polymerizes to a solid mass upon mixing of the parts together, the solid part comprising polymer powder and initiator and the liquid part comprising acrylic monomer and optionally activator or accelerator, the initiator component being present in an amount effective to polymerize the acrylic monomer upon being mixed with the liquid part, wherein: the acrylic monomer comprises a cyclic ester side group containing monofunctional acrylic monomer.

4. A multi-part cold curing pack for metallography moulds to produce a metallography mount comprising a first container and a second container, the content of the said first and second containers being in accordance with the solid and liquid parts according to claim 1.

5. A solid metallography mount comprising an acrylic polymer at least partially formed from a cyclic ester side group containing monofunctional acrylic monomers.

6. A mount according to claim 5, comprising a further polymer, wherein at least one monomer comprising the cyclic ester side group containing monofunctional acrylic monomer, forming the acrylic polymer is not present in the monomer(s) forming the further polymer.

7. A cold curing composition or a pack according to claim 1 for use as a cold mounting metallography moulding composition to produce metallography mounts.

8. A composition, pack or mount according to claim 1, wherein a suitable cyclic ester side group containing monofunctional acrylic monomer is a methacrylate monomer.

9. A composition, pack or mount according to claim 1, wherein the cyclic ester side group containing monofunctional acrylic monomer is selected from one or more cyclic aliphatic ester methacrylate monomers and/or aryl ester methacrylate monomers.

10. A composition, pack or mount according to claim 9, wherein the cyclic aliphatic ester methacrylate monomers are selected from one or more of cyclohexyl methacrylate, isobornyl methacrylate, dicyclopentenyl methacrylate, dihydrodicyclopentadienyl methacrylate, adamantyl methacrylate, 4-t-butylcyclohexyl methacrylate, 3.3,5-trimethylcyclohexyl methacrylate and tetrahydrofurfuryl methacrylate.

11. A composition, pack or mount according to claim 9, wherein the cyclic aliphatic ester methacrylate monomers are selected from one or more of cyclohexyl methacrylate, isobornyl methacrylate, dicyclopentenyl methacrylate, dihydrodicyclopentadienyl methacrylate, adamantyl methacrylate, 4-t-butylcyclohexyl methacrylate, and 3,3,5-trimethylcyclohexyl methacrylate.

12. A composition, pack or mount according to claim 9, wherein the aryl ester methacrylate monomers are selected from one or more of benzyl methacrylate, 2-phenoxyethylmethacrylate and phenyl methacrylate.

13. A composition, pack or mount according to claim 1, wherein the monofunctional monomer used in the liquid part or monofunctional monomer residues of the acrylic polymer may comprise a mixture of more than one monofunctional acrylic monomer or residue thereof.

14. A composition, pack or mount according to claim 3, wherein the cyclic ester side group containing monofunctional acrylic monomer or residue thereof comprises between 10 and 100% w/w of the total monomers in the uncured composition or monomer residues in the acrylic polymer.

15. A composition, pack or mount according to claim 14, wherein the cyclic ester side group containing monofunctional monomer or residue thereof comprises between 70 and 98% w/w of the total monomers in the uncured composition liquid part or monomer residues in the acrylic polymer.

16. A composition, pack or mount according to claim 1, wherein the balance of monomers is made up of polyfunctional and, optionally, other monofunctional monomer(s).

17. A composition, pack or mount according to claim 3, wherein the-polyfunctional monomers or residues thereof comprise between 0 and 90% w/w of the total monomer in the uncured composition or monomer residues in the acrylic polymer.

18. A composition, pack or mount according to claim 15, wherein the-polyfunctional monomers or residues thereof comprise between 2 and 30% w/w of the total monomers in the uncured composition or monomer residues forming the acrylic polymer.

19. A composition, pack or mount according to claim 1, wherein the acrylic monomer component comprises between 80 and 100% w/w of the liquid part or wherein acrylic monomers form between 80 and 100% w/w of the acrylic polymer.

20. A composition, pack or mount according to any claim 1, wherein the activator or accelerator comprises between 0 and 10% w/w of the liquid.

21. A composition, pack or mount according to claim 1, wherein the liquid part monomer component or acrylic polymer comprises a polyfunctional monomer or residue thereof in addition to a monofunctional monomer or residue thereof and such polyfunctional monomer has at least two polymerizable double bonds per molecule.

22. A composition, pack or mount according to claim 21, wherein suitable bifunctional monomers of the polyfunctional monomer include: ethylene glycol dimethacrylate, hexanediol dimethacrylate, tripropylene glycol dimethacrylate, butanediol dimethacrylate, neopentyl glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, dipropylene glycol dimethacrylate, allyl methacrylate, divinyl benzene and substituted analogues thereof; and trifunctional monomers of the polyfunctional monomer include: tripropylene glycol trimethacrylate, trimethylol propane trimethacrylate, pentaerythritol trimethacrylate; tetrafunctional monomers of the polyfunctional monomer include pentaerythritol tetramethacrylate, and hexafunctional monomers of the polyfunctional monomer include dipentaerythritol hexamethacrylate.

23. A composition, pack or mount according to claim 21, wherein a mixture of more than one polyfunctional monomer is used.

24. A composition, pack or mount according to claim 1, wherein the liquid part or acrylic polymer comprises a mixture of monofunctional monomer(s) and polyfunctional monomer(s) or residues thereof.

25. A compound, pack or mount according to claim 1, wherein the ratio of monofunctional monomers or residues thereof to polyfunctional monomers or residues thereof in the liquid part or acrylic polymer is between 95:5 wt % and 70:30 wt %.

26. A composition, pack or mount according to claim 1, wherein the polymer powder or further polymer is selected from a polymer or copolymer having >100 monomer residue units.

27. A composition, pack or mount according to claim 1, wherein the polymer powder or further polymer is homopolymer of a polyalkyl(alk)acrylate or (alk)acrylic acid or copolymer of a polyalkyl(alk)acrylate or (alk)acrylic acid with one or more other vinyl monomers.

28. A composition, pack or mount according to claim 1, wherein the polymer powder is in bead form having a mean particle size of between 10 microns and 800 microns.

29. A composition, pack or mount according to claim 1, wherein the polymer powder comprises between 60 and 99.9% w/w of the solid part.

30. A composition, pack or mount according to claim 1, wherein the initiator comprises between 0.1 and 15% w/w of the solid part.

31. A composition, pack or mount according to claim 1, wherein the ratio of solid to liquid part or the ratio of the acrylic polymer to the further polymer is in the range 1:2 to 4:1 by weight.

32. A composition, pack or mount according to claim 1, wherein other monofunctional monomers or residues thereof are not present in the liquid part of the composition or the acrylic polymer.

33. A composition, pack or mount according to claim 32, wherein ethyl methacrylate monofunctional monomers or residues thereof are not present in the liquid part of the composition or acrylic polymer thereof.

34. A composition, pack or mount according to claim 1, further comprising a polymerization activator or accelerator selected from a barbituric acid compound present in the storage stable solid part in combination with a transition metal salt present in the liquid part.

35. A composition, pack or mount according to claim 34, wherein the polymerization activator or accelerator comprises 0.1 wt % to 2.0 wt % of barbituric acid in the solid part and 0.005 wt % to 0.05 wt % of copper compound dissolved in the liquid part.

36. A process of producing a metallography mount comprising the steps of: mixing a solid part and a liquid part together to form a liquid or semi-solid paste: the solid part comprising, polymer powder and initiator and the liquid part comprising acrylic monomer and optionally activator or accelerator, the initiator component being present in an amount effective to polymerize the acrylic monomer upon being mixed with the liquid part; pouring the liquid or semi-solid paste into a mould containing a metallography sample to be analysed to at least partially encapsulate the sample; allowing the liquid or semi-solid paste to harden around the sample; and optionally, releasing the mounted metallography sample from the mould for analysis or further preparation, wherein: the acrylic monomer comprises a cyclic ester side group containing monofunctional acrylic monomer, the cyclic ester side group containing monofunctional acrylic monomer comprises between 70 and 96% w/w of the total monomers in the uncured composition.

37. A process of producing a metallography mount comprising the steps of: mixing a storage stable solid part and a storage stable liquid part together to form a liquid or semi-solid paste, the solid part comprising polymer powder and initiator and the liquid part comprising acrylic monomer and optionally activator or accelerator, the initiator component being present in an amount effective to polymerize the acrylic monomer component upon being mixed with the liquid part characterized in that the acrylic monomer component comprises a cyclic ester side group containing monofunctional acrylic monomer; pouring the liquid or semi-solid paste into a mould containing a metallography sample to be analysed to at least partially encapsulate the sample; allowing the liquid or semi-solid paste to harden to form a solid mass around the sample; and optionally, releasing the mounted metallography sample from the mould for analysis or further preparation.

Description

EXAMPLES

[0087] Characterisation Techniques:

[0088] % wt residual dibenzoyl peroxide content of the acrylic polymer beads is determined by a titration method.

[0089] The mean particle size of he acrylic polymer beads is determined using a Coulter LS230 laser diffraction instrument.

[0090] Molecular weight is determined by gel permeation chromatography (GPC) using tetrahydrofuran solvent and a refractive index detector calibrated using poly(methyl methacrylate) standards.

[0091] End of pour time is the length of time from the start of mixing solid and liquid components together until the mixture is too viscous to pour from the mixing container.

[0092] Shore D hardness is measured using a durometer according to ASTM D2240.

[0093] Preparative Method:

[0094] General description of method used to prepare acrylic cold mounting system.

[0095] Acrylic polymer solid and monomer liquid components plus relevant equipment such as beakers, measuring cylinders, spatulas, etc. are conditioned in an incubator at 23 C. before use.

[0096] 10 g of acrylic polymer solid is weighed into a 30 ml capacity plastic beaker and the desired amount of monomer liquid is weighed into a 10 ml capacity glass measuring cylinder. The monomer liquid is then poured into the beaker containing the acrylic polymer solid and mixed for 30 seconds using a spatula. The rate of mixing is relatively slow to minimize the inclusion of air bubbles. After 30 seconds mixing, approximately half the mixture is poured into a 25 mm diameter plastic mounting cup and left to harden at 23 C. The remainder of the mixture is left in the plastic mixing beaker at 23 C. to determine the pour time and set time. The viscosity of the mixture steadily increases with time, an exotherm occurs and the mixture transforms into a hard glassy casting.

[0097] After undergoing an exotherm, the casting in the plastic mounting cup is allowed to cool overnight before testing for Shore D hardness and visible assessment of clarity, colour and relative amount of trapped bubbles compared to a control.

Examples 1 to 4 and Comparative Examples A and B

[0098] The acrylic polymer solid used for examples 1 to 4 and comparative examples A and B was a copolymer of ethyl methacrylate (EMA) and methyl methacrylate (MMA) made by suspension polymerisation using dibenzoyl peroxide (BPO) as initiator. The copolymer composition was 80 wt % EMA and 20 wt % MMA. The mean particle size of the poly(EMA-co-MMA) bead polymer particles was 55 microns and the amount of residual BPO was 2.2 wt %. The weight average molecular weight (Mw) was 274,000 daltons.

[0099] The acrylic monomer liquid used for examples 1 to 4 was a mixture with composition: 88.75 wt % isobornyl methacrylate (iBoMA), 10 wt % triethylene glycol dimethacrylate (TEGDMA) and 1.25 wt % N,N-dihydroxyethyl-p-toluidine (DHEPT).

[0100] Examples 1 to 4 vary in the amount of acrylic monomer liquid used to mix with 10 g of the poly(EMA-co-MMA) bead polymer.

[0101] Comparative examples A and B are control mounts made using an acrylic system typical of that already known in the metallography market.

[0102] Specifically, comparative example A is produced by mixing an acrylic monomer liquid of composition: 76.25 wt % n-butyl methacrylate, 12.50 wt % ethyl methacrylate, 10 wt % triethylene glycol dimethacrylate and 1.25 wt % N,N-dihydroxyethyl-p-toluidine (DHEPT) with poly(EMA-co-MMA) bead polymer in the ratio of 6 g of the acrylic monomer liquid to 10 g the poly(EMA-co-MMA) bead polymer.

[0103] Comparative example B is produced by mixing an acrylic monomer liquid of composition: 71.25 wt % n-butyl methacrylate, 12.50 wt % ethyl methacrylate, 15 wt % triethylene glycol dimethacrylate and 1.25 wt % N,N-dihydroxyethyl-p-toluidine (DHEPT) with poly(EMA-co-MMA) bead polymer in the ratio of 6 g of the acrylic monomer liquid to 10 g the poly(EMA-co-MMA) bead polymer.

TABLE-US-00001 Comparative Comparative Example Example Example Example Example Example 1 2 3 4 A B Mix Ratio 10 g/7 g 10 g/6.2 g 10 g/6 g 10 g/5 g 10 g/6 g 10 g/6 g solid(g):liquid(g) End of pour time, 8 6 6 3.5 3 3 minutes Set time, minutes 22 16.5 16 11.5 11.5 10 Amount of trapped + + + bubbles Shore D hardness 72 75 80 82 75 76

TABLE-US-00002 Appearance in terms of amount of trapped bubbles relative to control mounts (comparative examples A and B) ++ Significant reduction over comparative examples A and B + Marked reduction over comparative examples A and B As per comparative examples A and B Marked increase over comparative examples A and B Significant increase over comparative examples A and B

[0104] Comparison of example 3 with comparative examples A and B shows that an acrylic mount with a marked reduction in trapped bubbles and higher Shore D hardness can be prepared using the monomer liquid based on iBoMA.

Examples 5 to 8

[0105] The following examples show the effect of increasing the amount of DHEPT accelerator on the set time and other properties.

[0106] The acrylic polymer solid used for examples 5 to 8 was the same as in examples 1 to 4

[0107] The acrylic monomer liquid used for examples 5 to 8 varied in the amount of N,N-dihydroxyethyl-p-toluidine (DHEPT) accelerator from 1.25 wt % to 2.50 wt %. The compositions are listed in the following table. 7 g of each acrylic monomer liquid was used to mix with 10 g of the poly(EMA-co-MMA) bead polymer.

[0108] The results show that the set time reduces with increasing amount of DHEPT accelerator as expected. However, an additional benefit was noted in that the shore D hardness also increased with increasing amount of DHEPT.

TABLE-US-00003 Example 5 Example 6 Example 7 Example 8 Monomer liquid iBoMA (wt %) 88.75 88.25 88.00 87.50 composition TEGDMA (wt %) 10.00 10.00 10.00 10.00 DHEPT (wt %) 1.25 1.75 2.00 2.50 Mix Ratio 10 g/7 g 10 g/7 g 10 g/7 g 10 g/7 g solid (g):liquid (g) End of pour time, 8 8 6 7 minutes Set time, minutes 22 16 15 12 Amount of + + + + trapped bubbles Shore D 72 75 75 86 hardness

Examples 9 to 11

[0109] The following examples show the effect of increasing the amount of TPGDMA crosslinker in the acrylic monomer liquid

[0110] The acrylic polymer solid used for examples 9 to 11 was the same as in examples 1 to 4.

[0111] The acrylic monomer liquid used for examples 9 to 11 varied in the amount of triethylene glycol dimethacrylate (TEGDMA) crosslinker from 10 wt % to 20 wt %. The compositions are listed in the following table. 7 g of each acrylic monomer liquid was used to mix with 10 g of the poly(EMA-co-MMA) bead polymer.

[0112] The results show that increasing the amount of TEGDMA crosslinker to 15 wt % and 20 wt % leads to reduced set time and increased hardness. Example 10 with 15 wt % TEGDMA crosslinker also showed a significant reduction in the number of trapped bubbles in the casting compared to comparative example B.

TABLE-US-00004 Example Example Example 9 10 11 Monomer liquid iBoMA (wt %) 88.75 83.75 78.75 composition TEGDMA (wt %) 10.00 15.00 20.00 DHEPT (wt %) 1.25 1.25 1.25 Mix Ratio 10 g/7 g 10 g/7 g 10 g/7 g solid (g):liquid (g) End of pour time, 8 7 7 minutes Set time, minutes 22 13 13 Amount of + ++ + trapped bubbles Shore D hardness 72 82 82

Examples 12 to 14

[0113] The following examples show the effect of varying the identity of the monofunctional monomer containing a cyclic group,

[0114] The acrylic polymer solid used for examples 12 to 14 was the same as in examples 1 to 4.

[0115] The acrylic monomer liquids of examples 12 to 14 used iBoMA, cyclohexyl methacrylate (CHMA) and tetrahydrofurfuryl methacrylate (THFMA), respectively, as the monofunctional monomer containing cyclic group in conjunction with triethylene glycol dimethacrylate (TEGDMA) crosslinker. The compositions are listed in the following table. 7 g of each acrylic monomer liquid was used to mix with 10 g of the poly(EMA-co-MMA) bead polymer.

[0116] The results show that use of CHMA or THFMA as the monofunctional monomer containing a cyclic group gives further enhancements in Shore D hardness.

TABLE-US-00005 Example Example Example 12 13 14 Monomer liquid iBoMA (wt %) 88.75 composition CHMA (wt %) 88.75 THFMA (wt %) 88.75 TEGDMA (wt %) 10.00 10.00 10.00 DHEPT (wt %) 1.25 1.25 1.25 Mix Ratio 10 g/7 g 10 g/7 g 10 g/7 g solid (g):liquid (g) End of pour time, 8 22 6 minutes Set time, minutes 22 27 25 Amount of + + + trapped bubbles Shore D hardness 72 85 83

Examples 15 to 17

[0117] The following examples show the effect of varying the identity of the polyfunctional monomer used for crosslinking.

[0118] The acrylic polymer solid used for examples 15 to 17 was he same as in examples 1 to 4.

[0119] The acrylic monomer liquid of examples 15 to 17 contained iBoMA as the monofunctional monomer containing cyclic group in conjunction with either triethylene glycol dimethacrylate (TEGDMA), trimethylol propane trimethacrylate (TMPTMA) or ethylene glycol dimethacrylate (EGDMA) as the polyfunctional monomer used as crosslinker. The compositions are listed in the following table. 7 g of each acrylic monomer liquid was used to mix with 10 g of the poly(EMA-co-MMA) bead polymer.

[0120] The results show that use of any of these polyfunctional crosslinking monomers gives a fast setting system (set time<22 minutes) to form a hard mount (Shore D hardness>72) with a lower level of trapped bubbles compared to comparative example A.

TABLE-US-00006 Example Example Example 15 16 17 Monomer liquid iBoMA (wt %) 88.75 88.75 88.75 composition TMPTMA (wt %) 10.00 EGDMA (wt %) 10.00 TEGDMA (wt %) 10.00 DHEPT (wt %) 1.25 1.25 1.25 Mix Ratio 10 g/7 g 10 g/7 g 10 g/7 g solid (g):liquid (g) End of pour time, 8 9 8 minutes Set time, minutes 22 17 15 Amount of + + + trapped bubbles Shore D hardness 72 75 74

Examples 18 to 20

[0121] The following examples extend the series of experiments shown in examples 9 to 11 to show the effect of further increasing the amount of TPGDMA crosslinker in the acrylic monomer liquid.

[0122] The acrylic polymer solid used for examples 9 to 11 and 18 to 20 was the same as in examples 1 to 4.

[0123] The acrylic monomer liquid used for examples 9 to 11 and 18 to 20 varied in the amount of triethylene glycol dimethacrylate (TEGDMA) crosslinker from 10 wt % to 40 wt %. The compositions are listed in the following table. 7 g of each acrylic monomer liquid was used to mix with 10 g of the poly(EMA-co-MMA) bead polymer.

[0124] The results show that increasing the amount of TEGDMA crosslinker to 15 wt % and 20 wt % leads to reduced set time and increased hardness. Example 10 with 15 wt % TEGDMA crosslinker also showed a significant reduction in the number of trapped bubbles in the casting compared to comparative example B. However, further increase in the amount of TEGDMA crosslinker from 25 wt % to 40 wt % leads to no further reduction in set time and Shore D hardness is reduced. These results show that the optimum balance of properties (fewest trapped bubbles, lowest set time and highest Shore D hardness) is achieved by example 10 with 15% wt TEGDMA crosslinker.

TABLE-US-00007 Example Example Example Example Example Example 9 10 11 18 19 20 Monomer iBoMA (wt %) 88.75 83.75 78.75 73.75 63.75 58.75 liquid TEGDMA (wt %) 10.00 15.00 20.00 25.00 35.00 40.00 composition DHEPT (wt %) 1.25 1.25 1.25 1.25 1.25 1.25 Mix Ratio 10 g/7 g 10 g/7 g 10 g/7 g 10 g/7 g 10 g/7 g 10 g/7 g solid(g):liquid(g) End of pour 8 7 7 7 7 7.5 time, minutes Set time, 22 13 13 14 13 13 minutes Amount of + ++ + + + + trapped bubbles Shore D 72 82 82 75 75 75 hardness

Example 21

[0125] This example demonstrates the successful preparation of cold mounting specimens for examination by microscope.

[0126] The following specimens were placed in separate mounting cups (25 mm diameter and 20 mm deep) and the two-part cold curing composition prepared according to example 3 was poured into the moulding cups to encapsulate each specimen. The liquid was allowed to harden around the specimens before releasing the mounted metallography sample from the mould for further preparation.

[0127] 1. 20 mm long stainless steel bolt with 13 mm hexagonal head and 8 mm diameter shaft

[0128] 2. Stainless steel nut screwed onto a stainless steel bolt of 12 mm length

[0129] 3. Piece of veined sandstone chipping approximately 20 mm long and 4 mm depth

[0130] 4. Printed circuit board of 15 mm square

[0131] All samples wetted out well and had good adhesion. The Shore D hardness of all samples was 80, the same as example 3 without the encapsulated specimens.

[0132] The mount containing specimen number 2 was selected for further preparation work using a Carlo de Giorgi Polishing/Grinding lathe. The specimen surface was firstly ground to a smooth finish using a grinding wheel and then polished to a final finish ready for microscopic examination using a calico polishing mop with polishing compound.

Example 22

[0133] This example demonstrates the use of a barbituric acid compound in combination with a transition metal salt as polymerisation activator or accelerator.

[0134] An acrylic polymer solid was prepared by mixing 99.5 wt % of the poly(EMA-co-MMA) copolymer of examples 1 to 4 with 0.5 wt % 1-benzyl 5-phenylbarbituric acid . An acrylic monomer liquid was prepared by mixing 79.99 wt % isobornyl methacrylate (iBoMA), 20 wt % triethylene glycol dimethacrylate (TEGDMA) and 0.01 wt % copper acetyl acetonoate (CuAcAc). 7 g of the acrylic monomer liquid was used to mix with 10 g of the acrylic polymer solid according to the preparative method to prepare an acrylic casting for assessment of appearance and Shore D hardness and also determine end of pour time and set time.

[0135] The results are tabulated below. Comparison of example 22 with comparative examples A and B shows that an acrylic mount with a significant reduction in yellow colour, a marked reduction in trapped bubbles and higher Shore D hardness can be prepared using a monomer liquid containing a polymerisation activator or accelerator based on a barbituric acid compound in combination with a transition metal salt.

TABLE-US-00008 Example 22 Mix Ratio solid (g):liquid (g) 10 g/7 g End of pour time, minutes 5 Set time, minutes 12 Amount of trapped bubbles + Yellow colour ++ Shore D hardness 82

TABLE-US-00009 Appearance in terms of amount of trapped bubbles and yellow colour relative to control mounts (comparative examples A and B) ++ Significant reduction over comparative examples A and B + Marked reduction over comparative examples A and B As per comparative examples A and B Marked increase over comparative examples A and B Significant increase over comparative examples A and B

[0136] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0137] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0138] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0139] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.