BOUND-IN CATALYSTS

Abstract: A curable composition for the preparation of a polyurethane material is provided wherein the composition comprises isocyanate prepolymers having a chemically bound-in catalyst.

Description: BOUND-IN CATALYSTS The present invention relates to curable compositions and in particular to isocyanate based resin systems suitable for use in medical applications, such as orthopaedic casting and splinting. Such isocyanate based resin systems react with polyfunctional active hydrogen containing compounds in the presence of a catalyst to form a polyurethane material. Traditionally inorganic carbonate catalysts (US 4,427,003) have been used with isocyanate resin systems but more recently different catalysts based on tertiary amines have been used for example catalysts containing morpholino groups. The use of tertiary amine catalysts for polyurethane formulations is discussed in US 4,239,855, US 4,380,591, US 4,510,269, US 4,590,223, US 4,714,719 and US 5,071,809. Such formulations usually comprise mixing an organic polyisocyanate, an organic compound containing at least two active hydrogen atoms, stabilizers, fillers and additives as required and a tertiary amine catalyst. With all such catalysts however it is important that the catalyst be thoroughly mixed with the isocyanate system for even curing to occur. Furthermore there is the possibility that catalyst may leach out from the cured product or from the resin system during cure. In addition such reactive tertiary amine catalysts may be vapourized by the exotherm generated during the polyurethane reaction. These amines may have a strong odour and the potential inhalation toxicity of tertiary amines is also well known. There is thus a need for an efficient catalyst which does not pose any toxicity problems due to leaching or evaporation. Patent Application WO94/02525 partially addresses the problems encountered with tertiary amine catalysts by modifying reactive tertiary amine catalysts by mixing under reaction conditions a reactive tertiary amine, a polyol and an organic isocyanate compound, to give a catalyst or co-catalyst, which has a higher molecular weight, and may therefore be retained more within an isocyanate resin system. However even such a modified catalyst may still be prone to leaching especially when used in a water curable isocyanate composition. Further the use of a free modified catalyst (where the catalyst is added to the reaction mixture) results in a reaction process with more steps. The present invention seeks to provide isocyanate based water curable compositions which obviate or overcome at least some of the above-mentioned disadvantages of prior art compositions. According to the present invention there is provided a curable composition comprising isocyanate prepolymers wherein said prepolymers contain chemically bound-in catalysts. Further there is provided a curable composition comprising isocyanate prepolymers without any non bound-in catalyst. Preferably said curable composition is a water curable composition. Further said isocyanate prepolymers may comprise a mixture or a single chemical species. Said chemically bound-in catalysts, bound to a curable composition as hereinbefore described may be covaiently bound, ionically bound or may comprise a mixture of ionically and covaiently bound catalysts. In a preferred embodiment said chemically bound-in catalysts comprise tertiary amine groups, most preferably said tertiary amine groups are covaiently bound to the isocyanate prepolymers. Thus according to the present invention there is provided a curable composition suitable for use as a casting or splinting resin comprising a plurality of isocyanate prepolymers having chemically bound-in tertiary amine groups; wherein said prepolymers are the reaction products of polyisocyanates and molecules comprising both a tertiary amine group and an isocyanate reactive group. The term "isocyanate reactive group" refers to a group which forms a covalent bond when reacted with an isocyanate group (-NCO) under appropriate conditions, these include for example hydroxy and amine groups as well as carboxylic acids, thiols, anhydrides, urethanes, ureas and other such groups with an active hydrogen atom known to one skilled in the art. Chemically bound-in tertiary amine groups are defined as including tertiary amine groups bonded covaiently and/or ionically to the isocyanate prepolymer. The water curable composition of the present invention does not require the addition of a free catalyst to catalyse curing since the bound-in tertiary amine groups themselves act as a catalyst. The possible problem of catalyst leaching out from a resin composition is thus avoided and the number of separate components required in the resin may be reduced. The bound-in tertiary amine groups may be present at any appropriate location in the isocyanate prepolymers. For example they may be introduced at an end of the prepolymer molecules via a capping reaction, they may be present on a side chain extending from the main polymer backbone, or may be part of the polymer backbone itself. Further, depending on the nature of tertiary amine groups to be reacted with the polyisocyanates the tertiary amine groups may be present on some or all of the locations as discussed above. The chemically bound-in tertiary amine groups may comprise a single species or mixture of species. Further several species of such bound tertiary amines may be present within the prepolymer composition or within one isocyanate prepolymer molecule. For example some of the prepolymer composition may have one tertiary amine present and the rest may have another species of tertiary amine present. Any one of the prepolymer molecules may contain a single bound-in tertiary amine group, more than one tertiary amine group of a single species or more than one tertiary amine group of a number of species. In addition any one prepolymer molecule may comprise more than one tertiary amine group either present on a side chain, as end groups or part of the polymer backbone, for example when tertiary amine molecules comprise two or more isocyanate reactive groups and act as chain extenders. Appropriate tertiary amine molecules for reacting with the polyisocyanates so as to form the prepolymers of the composition of the present invention include molecules selected from the group comprising the general formula I, π, and πi as illustrated below: FORMULA I FORMULAE FORMULA m Where Ri is typically from the group comprising alkanols, aikylamines and alkylacids where said alkyl group may be branched and is typically Ci to Cio. Examples include -(CH 2 )„NH 2l -(CH 2 ) n OH, -(CH 2 )„-NHR 2 , -(CH 2 )„CH(OH)CH 2 OH, -(CH 2 ) n (CHR 2 ) n OH, -(CH 2 )„(CHR 2 )„NH 2 , -(CH 2 )„(CHR 2 )„NHR 2 , -(CH 2 ) n CH(OH)CH 2 C0 2 H, -(CH 2 )„CH(OH)CH 2 SO 2 OH, -(CH 2 )„CO 2 H, -(CH 2 ) n (CHR 2 )„COOH where n = 1 to 10 Where R 2 and R 3 may be the same or different and are typically C . to Cio of the group comprising alkyls, aryls, alkylenes, aikylamines, branched alkyls or alkylenes. Examples include -CH 3 , -(CH 2 )„NR 2 R 3l -(CH 2 )„CH 3 , -(CH 2 ) n (CHR 2 )„CH 3 where R 2 = R-, where R 3 = ^ where n = 1 to 10 Where Z = -CH 2 - or a bond Where A = >NH, -O-, >NR L >CH 2 , >CHRι, >NR 2l >CHR 2 where n = 1 to 10 Where Y - R, Where Y and G together form a group - (CH 2 ) P - where p = 2 to 6 may be optionally interrupted by, - O -, > NH, -CH- I CH 3 Where M and G together form a group These molecules may be optionally substituted with substituents which do not substantially adversely affect the reaction of the molecules with isocyanate groups or the catalytic effect of the tertiary amine groups when present in the prepolymers of the composition of the present invention. Appropriate molecules for reacting with the polyisocyanates so as to form the prepolymers of the composition of the present invention may include but are not limited to the molecules listed below. 1. 1 -(2-Hydroxyethyl) pyrrolidine CH 2 CH 2 OH 2. 1 -Methyl piperazine H 3. 1-Methyl-2-piperidinemethanol CH 3 1 ,4-Bis(2-hydroxyethyl)piperazine O^CH j CH A"\ / CH-CH-CH Further useful tertiary amine molecules include 2-[2-(Dimethylamino)ethyl]methylamino ethanol. 6. Gramine H 7. 3-Morpholino-1 ,2-propanediol 8. 1 ,4-Bis(3-aminopropyl)piperazine CH CH 2 CH 2 NH. 9. Tropine 10. 3-Aminopropylmorpholine 11. 4-(2-Hydroxyethyl) morpholine 12. 3,3-Diamino-N-methyl dipropylamine. * . CH 2 CH 2 CH 2, NH 2 CH N 3 ^ CH 2 CH 2 CH 2 NH 2 13. 1,4-Bis(2-hydroxypropyl)-2-piperazine CH 3 14. 1-(2-Hydroxypropyl) imidazole CH_____CH 15. 3-Dimethylamino propanol 16. β-Hydroxy-4-Morpholine propane sulphonic acid Tertiary amine containing molecules which are mono- functional with respect to isocyanate groups where the functional groups for example mono-hydroxy or mono-amino molecules are suitable for capping reactions, whereby the tertiary amine groups can be located at or close to chain ends of a polyisocyanate. Such molecules are advantageous in that they can allow the viscosity of the prepolymer to be relatively easily controlled, whereas this may be difficult using multi-functional molecules which act as chain extenders (particularly where the level of tertiary amine is required to be high). Tertiary amine containing molecules which are di-functional with respect to isocyanate groups can be used as chain extenders. Tertiary amine containing molecules which are poly- functional with respect to isocyanate groups can be used as cross linkers. The polyisocyanates used to react with the molecules comprising both a tertiary amine group and an isocyanate reactive group can be any appropriate polyisocyanates well known in the art for casting and splinting applications, for example liquid polymeric MDI's (4,4'-methylene bis (phenyl isocyanate)). Whatever species of tertiary amine containing molecules are utilised to prepare a bound-in catalyst, it is preferred that they comprise less than 10% by weight more preferably from 0.1 to 5% by weight of the curable composition. The polyisocyanates include molecules formed by chain extending polyisocyanates with polyols for example polyethylene glycols (PEG's), as is well known in the art. Apt chain-extended polyisocyanates are disclosed in WO 89/08463. The present invention includes within its scope a flexible substrate having therein and/or thereon a composition of the present invention. The flexible substrate is desirably a fibrous material and is preferably a bandage or tape. Suitable substrates include glass fibre, polypropylene and other materials known to those skilled in the art. According to the invention there is provided an orthopaedic splinting material comprising a substrate carrying a curable composition as hereinbefore described. In an embodiment of the present invention there is provided a method for forming a hardened splint from a splinting material comprising a substrate carrying a curable composition as herein before described wherein said splinting material is shaped around or against a body member and allowed to cure. Further there is provided a process for making a curable composition as hereinbefore described wherein polyisocyanates and molecules comprising both a tertiary amine group and isocyanate reactive group are reacted to give an isocyanate prepolymer. There is also provided the use of a curable composition as hereinbefore described in the preparation of an orthopaedic splinting material. Preferably said curable composition is a water curable composition. The substrate for carrying the curable composition of the invention may have the curable composition applied in any manner conventionally used by someone skilled in the art. These include processes such as coating, dipping, spraying and laminating. The orthopaedic splinting material comprising the flexible substrate having a water curable composition of the present invention therein and/or thereon may be provided in a sealed package and may be sterilised. When it is desired to use the flexible substrate carrying the curable composition of the invention the package can be opened, the substrate may be wet with water for example by dunking or spraying to initiate curing and the substrate can then be shaped as desired against or around a limb of a patient. Extra cushioning may be provided in the form of undercast padding. On curing, a hardened cast or splint is formed. The present invention will now be described without limitation thereof with reference to the accompanying examples: Example 1 The following procedure illustrates the production of a resin formulation containing a bound in catalyst according to the present invention. The substances used in the formulations and the amounts present are indicated in Table 1 below. Table 1 Description Componentfsϊ Weiαht.αϊ Polyol Mix PEG600/PEG3350/Glycerol 17.90 Voranol CP1421 ™ Random co-polymer PEG/PPG 17.95 (obtainable from K & K Greeff Ltd UK) N-Methyl piperazine Mono-functional t-amine catalyst 2.02 (obtainable from Aldrich Chemical Co. Ltd. UK)) Isonate 143™ Polymeric MDI 62.10 (obtainable from K & K Polymerics and K & K Greeff Ltd. UK). Irganox 1010™ Antioxidant 0.4 (obtainable from Ciba Geigy UK LTD, UK) Antifoam MSA™ Antifoaming Agent 0.96 (obtainable from Ellis Everard Inc. USA) Into a dried 700ml flask was weighed out the Irganox 1010™, Antifoam MSA™ and Isonate 143™ The flask was fitted with a stirrer, a dry nitrogen blanket and an inlet port. The flask was heated in a thermostatically controlled water bath at 60° C. After mixing the polyol mix and Voranol CP1421 ™ to homogeneity in a different flask, approx 70% of the resultant homogeneous polyol mixture was added to the components in the 700ml flask. The temperature was raised to 80°C and the mixture was stirred for 1 hour. The catalyst was weighed into the remaining 30% of the homogenous polyol mixture mixed and this mixture was then added to the 700ml flask. The temperature was reduced to 60°C and the reaction mix was stirred for a further 1.5 hours. While still hot the product was poured into a dry 500ml airtight jar. The resultant product was then allowed to cool, poured into a pre-dried airtight container, and could then be used as a resin . Curing of the resin was assayed using a setting rate rheometer as described below: - Curing Assay The rheometer used is illustrated in Fig. 1 a) in plan view and in Fig. 1 b) in a cross-section taken along line x-x shown in Fig. 1. The labelled parts are:- A. Main housing G. Beam B. Low friction ball race H. Coiled springs C. Lower platen I. Movement transducer D. Two grub screws H. Pivot of connecting rod E. Knurled screw K/L. Tension and adjusters F. Eccentric wheel attached M. Upper platen to 10 rpm electric motor This instrument has been fully described by Bovis and Harrington (in British Dental Journal 1964, 131, 352). The basic operation of the setting rate rheometer is that transducer (I) measures the movement of beam (G). The maximum rotary movement of (G) is 1° 12' +/- 2'. This movement is suppressed as the materials sets. If the material sets to a rigid solid, the movement of the beam (G) will be zero. In use, the rheometer was connected to a bench top computer which recorded data representing the decreasing movement of the beam as a resin sets. A small amount of test material (comprising a resin sample and an approximately equal volume of water which had been thoroughly mixed together for a few seconds) was placed on the lower platen (C) a few seconds after mixing. The upper platen (M) was then immediately lowered on its guide into position so that the thickness of the material between the two platens was only a few millimetres. The beam (G) was immediately set into oscillating motion. The output from the transducer was continuously recorded by the computer. From this computer data a graph of the variation of the viscosity of the setting resin with time was obtained. The cure time was taken at the point where the viscosity of the test material became so high that no further changes could be detected by the rheometer. This usually occurred shortly after the largest change was observed (see graph). Cure times were all determined at room temperature (20°C). It was found that a cure time of under 2 minutes was obtained where the resin formulation comprising an N-Methyl piperazine catalyst as described in Example 1 above was used. This is illustrated in the graph shown in Fig. 2, where the cure time can be seen to be about 80 seconds. This compared very favourably with a cure time of 15 minutes for a resin formulation prepared in the same manner but omitting the catalyst. Example 2 The procedure described in Example 1 was repeated using a different catalyst and varying the weights of the materials used in the resin formulation. The components used are as set out in Table 2 below:- (obtained from Aldrich Chemical Co.) Isonate 143™ Polymeric MDI 67.0 Irganox 1010™ Antioxidant 0.4 Antifoam MSA™ Antifoaming agent 0.96 (Suppliers of the products indicated with trade marks are disclosed in Example 1). Example 3 The procedure described in Example 1 was repeated except that different catalysts were used (again at a level of 2% by weight). The results are indicated in Table 3 below. Table 3 Catalyst Used Cure Time ( Mins) 3-Amino propyl morpholine 8 1 ,4-Bis(2-hydroxyethyl)piperazine 3 Example 4 The procedure described in Example 2 was repeated except that different catalysts were used at a different level i.e. 1% by weight. The results are indicated in Table 4 below: - Table 4 Catalyst Used Cure Time.Mins. β-Hydroxy-4-moφholine propane sulfonic acid 10 3-Amino propyl moφholine 10 Example 5 The resin formulation obtained in Example 1 was used to thoroughly impregnate a polypropylene bandage which was then dipped in water, squeezed several times to allow water to impregnate throughout the bandage, and used to bandage around the forearm of an artificial limb (which approximates the contours of a human forearm). It was found that a hard, smooth cast was formed within about two minutes of when the wet, impregnated bandage was applied. The resin had a viscosity which allowed the bandage to be easily worked so that a smooth cast could be formed. Example 6. 7 and 8 The procedure described in Example 1 was repeated using the following formulations, as set out in Table 5, Table 6 and Table 7 below: Table 5 Example 6: Description Component.s) Weight la) PEG 3350 Polyethylene Glycol 4.01 (Mwt 3350) BPA 2EO Ethoxylated Bis-phenol A 4.99 BPA 5EO Ethoxylated Bis-phenol A 7.38 Jeffamine EDR-148™ Diamine chain extender 1.77 (obtainable from Whitfield Chemicals) Methyl-n-piperazine Bound-in catalyst 5.02 Desmodur N3400™ Aliphatic isocyanate 76.83 (obtainable from Huntsman Coφoration) (NCO/OH ratio : 3.44/1) Antifoam MSA™ Silicone based 0.5 antifoaming agent Metatin 812ES Tin catalyst 0.2 Table 6 Example 7 Description Component.s. Weight fg) PEG 3350 Polyethylene Glycol 2.92 (Mwt 3350) PEG 1500 Polyethylene glycol 7.84 (Mwt 1500) BPA 5EO Ethoxylated Bis-phenol A 3.76 Voranol EP2001 ™ Ethyleneoxide end- 10.29 capped polypropylene glycol Methyl-n-piperazine Bound in catalyst 5.23 Desmodur N3400™ Aliphatic isocyanate 23.08 (DN3400/HDB-LV: 1.0/2.0) Tolonate HDB-LV™ Aliphatic isocyanate 46.87 (obtainable from Rhone-Poulenc) (NCO/OH ratio : 4.43/1) Antifoam MSA™ Silicone based 0.5 antifoaming agent Metatin 812ES Tin catalyst 0.2 Example 8 Description Component.s) Weight la) PEG 3350 Polyethylene Glycol 2.51 (Mwt 3350) PEG 1500 Polyethylene glycol 14.59 (Mwt 1500) Voranol EP2001 ™ Ethyleneoxide end-capped 8.84 polypropylene glycol Methyl-n-piperazine Bound-in catalyst 4.49 Desmodur N3400™ Aliphatic isocyanate 22.37 (DN3400/HDB-LV : 1.0/2.0) Tolonate HDT-LV™ Aliphatic isocyanate 47.21 (NCO/OH Ratio : 4.43/1) Antifoam MSA™ Silicone based 0.5 Antifoaming agent Metatin 812ES Tin catalyst 0.2

Claims: CLAIMS 1. A curable composition comprising isocyanate prepolymers characterised in that said prepolymers contain chemically bound-in catalysts. 2. A curable composition as claimed in claim 1 characterised in that said composition is water curable. 3. A curable composition as claimed in claim 1 characterised in that said prepolymers comprise a single chemical species. 4. A curable composition as claimed in claim 1 characterised in that said catalysts are covaiently bound to said prepolymers. 5. A curable composition as claimed in claim 1 characterised in that said chemically bound-in catalysts comprise a mixture of ionically and covaiently bound catalysts. 6. A curable composition as claimed in claim 1 characterised in that said catalysts are tertiary amine groups. 7. A curable composition as claimed in claim 6 characterised in that prepolymers comprise a polymeric backbone with side chains extending from said backbone. 8. A curable composition as claimed in claim 7 characterised in that said tertiary amine groups are covaiently bound to a side chain extending from said isocyanate prepolymer. 9. A curable composition is claimed in claim 7 characterised in that said tertiary amine groups are covaiently bound into the backbone of the isocyanate prepolymer. 10. A curable composition as claimed in claim 6 characterised in that said tertiary amine groups comprise a single chemical species. 11. A curable composition as claimed in claim 6 characterised in that said tertiary amine groups comprise less than 10% of the curable composition. 12. A curable composition as claimed in claim 6 characterised in that said tertiary amine groups comprise molecules selected from the group comprising the general formula, I, II and IE: FORMULA I FORMULA π FORMULA m Where Ri is typically from the group comprising alkanols, aikylamines and alkylacids where said alkyl group may be branched and is typically Ci to C 10 . {Examples include -(CH 2 )„NH 2 , -(CH 2 )„ OH, -(CH 2 )„-NHR 2 , -(CH 2 )„CH(OH)CH 2 OH, -(CH 2 )„(CHR 2 ) n OH, -(CH 2 )„(CHR 2 )„NH 2 , -(CH 2 ) n (CHR 2 )„NHR 2l -(CH 2 )„CH(OH)CH 2 CO 2 H, -(CH 2 ) n CH(OH)CH 2 SO 2 OH, -(CH 2 )„CO 2 H, -(CH 2 )„(CHR 2 ) n COOH where n = 1 to 10 Where R 2 and R 3 may be the same or different and are typically Ci to Cio of the group comprising alkyls, aryls, alkylenes, aikylamines, branched alkyls or alkylenes. Examples include -CH 3 , -(CH 2 ) n NR 2 R 3 , -(CH 2 ) n CH 3 , -(CH 2 ) n (CHR 2 )„CH 3 where R 2 = Ri where R 3 = Ri where n = 1 to 10 Where Z = -CH 2 - or a bond Where A = >NH, -O-, >NRι, >CH 2 , >CHR,, >NR 2 , >CHR 2 where n = 1 to 10 Where Y = Ri Where Y and G together form a group - (CH 2 ) P - where p = 2 to 6 may be optionally interrupted by, O -, > NH, -CH- I CH 3 Where M and G together form a group 13. A curable composition as claimed in claim 6 characterised in that said tertiary amine groups are selected from the group comprising 1- (2-hydroxyethyl)pyrrolidine, 1 -methyl piperazine, 1- methyl-2-piperidinemethanol and, 1-4 bis(2-hydroxy ethyl)piperazine. 14. An orthopaedic splinting material comprising a substrate carrying a curable composition as claimed in claim 1. 15. A process for making curable composition as claimed in claim 1 characterised in that polyisocyanates and molecules comprising both a tertiary amine group and an isocyanate reactive group are reacted to give an isocyanate prepolymer. 16. The use of curable composition as claimed in claim 1 in the preparation of an orthopaedic splinting material. 17. A method for forming a hardened splint from a splinting material comprising a substrate carrying a curable composition as claimed in claim 1 characterised in that said splinting material is shaped around a body member and allowed to cure.

Inventors: SHELVEY MICHAEL FRANCIS, TOWNS CARL ROBERT, SHELVEY, MICHAEL, FRANCIS, TOWNS, CARL, ROBERT
Applicants: SHELVEY MICHAEL FRANCIS, SMITH & NEPHEW, TOWNS CARL ROBERT, SHELVEY, MICHAEL, FRANCIS, SMITH & NEPHEW PLC, TOWNS, CARL, ROBERT
Application year: 1995
Main classification: C08G18
IPC codes: A61L15, C08G18