ADHESIVES

Abstract: Cross-linked polyurethanes wherein the polyurethane comprises acrylated isocyanate groups cross-linked with polyamine or disulphide groups. The cross-linked polyurethanes may be incorporated into pressure-sensitive adhesives.

Description: ADHESIVES The present invention relates to adhesives, their preparation and their use. Adhesives which are suitable for use on the skin and which comprise polyurethane polymers are known from European Patent No.0271292B1. Adhesives described therein are prepared by reacting an isocyanate precursor with an acrylate comprising hydroxyl-containing esters of acrylic or methacrylic acid to produce a prepolymer. The prepolymer so formed may be cross-linked to form a polyurethane polymer by irradiation. In addition, prior art cross- linked polyurethane systems tend to be sensitive to water and when in contact with water produce carbon dioxide which results in bubbles appearing in gels. We have now found that such isocyanate precursors may be reacted with hydroxylated alkyl acrylates to produce a non-cross linked polyurethane hereinafter referred to as the prepolymer. Such prepolymers may then be reacted with a polyamine (i.e. polymer with amine groups) or a disulphide to produce a cross-linked polyurethane. Thus according to the invention we provide a cross-linked polyurethane wherein the polyurethane comprises an acrylated isocyanate cross-linked with polyamine or polysulphide groups. The cross-linked polyurethanes according to the invention are advantageous in that they provide a skin friendly non-self adherent pressure sensitive adhesive which is inherently tacky. The cross-linked polyurethane of the invention absorbs water, eg. from 5 to 95% of the weight of the cross-linked polyurethane, to form a polyurethane gel. The cross-linked polyurethane will absorb water and become hydrated and when hydrated may contain up to 95%, typically from 35 to 95% by weight of water, aptly 50% to 92%, preferably 70 to 90% by weight of water and most preferably 75 to 85% by weight of water. The water absorption of the cross-linked polyurethane can be obtained by taking a known weight of the cross-linked polyurethane and immersing it in water for 24 hours. The resulting polyurethane gel is removed from the water, surface water is removed by lightly blotting with absorbent paper and then the weight of the polyurethane gel is taken. The water absorption of the cross-linked polyurethane (% by weight) can then be calculated. The polyurethane gels are also suited to providing skin friendly non-self adherent pressure sensitive adhesives and such adhesives are a further feature of the present invention. Thus according to a further feature of the invention we provide a skin friendly non-self adherent pressure sensitive adhesive which comprises a cross-linked polyurethane wherein the polyurethane comprises an acrylated isocyanate which is cross-linked with polyamine or disulphide groups. The adhesives of the invention are skin friendly, ie. that they can be removed from the skin without causing discomfort and because of their inherent tackiness can be replaced and adhere again. The adhesives also have the advantage that they are non- self-adherent so that if for example the adhesive surface becomes creased during the application of a dressing the contracting surfaces of the adhesive may be easily peeled apart and the dressing is not wasted. Any isocyanate precursors known βeι §e_ may be used, but the preferred isocyanate precursors are those described in European Patent No.0271292B. The non-cross-linked polyurethane may be prepared using one or more hydroxy alkyl acrylates. In the acrylate moiety, the alkyl group may be C1 to 10, preferably C1 to 6, eg. ethyl. The polyamines or disulphides act as cross-linking agents when reacted with the prepolymer. Thus, preferred polyamines are diamines. Any diamines known Q§L se may be used such as alkyl C1 to 10 diamines such as ethylene diamine. Preferred diamines are the class of compounds known as Jeffamines (Trade Mark) available from Huntsman Corporation in the UK. Jeffamines are high molecular weight diamines with a polymeric backbone. Jeffamines may have a molecular weight ranging from 200 to 6000. The Jeffamine ED-Series products are polyether diamines which are based on a predominately polyethylene oxide backbone. This imparts complete water solubility to each of the members of this series. The Jeffamine ED-Series products have the following structure: H 2 NC . HCH 2 -[ l OCHCH 21 α a -[ l OCH 2 CH 2 ] J b -[ l OCH CH 21 J c -NH 2 CH. CH CH. The Jeffamine DU Series are urea condensates of Jeffamine D-Series products. The DU-Series products are made by coupling a Jeffamine D-Series product with urea, in order to form a diamine product of increased molecular weight. This is exemplified by the following structure: O H 2 NC. HCH 2 -[ l OCH 2 C, H] n -NH-C-NH-[C . HCH 2 O] J n -CH 2 .HNH 2 CH, 3 CH, 3 CH, 3 CH, 3 Preferred disulphides are polysulphides of the following general structure: HS(C2H 4 OCH2θC2H4S x ) n C2H4θCH2θC 2 H4SH wherein x is an integer, and n is an integer from 1 to 30. Polysulphides may vary in molecular weight, eg. when n is 6 the polysulphide may have a molecular weight of about 1000, and when n=23 the polysulphide may have a molecular weight of about 4000. Such polysulphides are known per §e_ and are available from Morton International, Speciality Chemicals Group in the UK. Optionally, the cross-linking reaction may be promoted by the presence of an effective amount of catalyst. The present invention also provides a method of preparation of cross-linked polyurethane as hereinbefore described, which comprises; (i) reacting an isocyanate with an hydroxylated acrylate to produce a prepolymer; and (ii) reacting the prepolymer with a polyamine or a disulphide to produce a cross-linked polyurethane. In another aspect the present invention also provides a process for the preparation of a pressure sensitive adhesive in the form of an inherently tacky polyurethane gel which comprises hydrating a cross-linked polyurethane as hereinbefore described with from 5 to 95% w/w of water. In a further aspect, the present invention provides adhesive products comprising an adhesive gel in accordance with the invention. The adhesives of the present invention are suitable for use in a number of applications such applications include use as an adhesive when coated on a substrate for bandages, absorbent wound dressings, burns dressings, incise drapes, first aid dressings, intravenous catheter dressing, ostomy devices, condom attachment in urinary incontinence devices, transdermal drug delivery devices, adhesive tapes (surgical tapes, wound closure tapes and the like), protection devices such as napkins, diapers, incontinence pads and protection pads, electroconductive gels. However the main use is envisaged to be in dressings and drapes of the types above when the adhesive is in contact with the skin. The adhesives of the invention may be employed in the manufacture of bacteria proof wound dressings such as those which comprise a backing layer which has upon substantially the whole of the wound facing surface thereof a layer of pressure sensitive adhesive in accordance with the invention. The cross-linked polyurethanes of the invention are advantageous in that they may be prepared without the need of a radical initiator or a UV irradiation source. Many medicinal agents may be incorporated into the adhesives of the present invention. By the term agents it is meant pharmacologically active agents and agents including topical anaesthetics such as amethocaine, xylocaine, bactβriostatic agents such as silver nitrate; antibacterial agents of which preferred agents include silver sulphadiazine, chlorhexidine salts, PVP-I, and biguanides antibiotics; topical steroids, enzyme stimulants, coagulants and anticoagulants and antifungal agents. Advantageously water soluble medicaments such as chlorhexidine and its salts may be dissolved in water which is used to hydrate the cross-linked polyurethane. It is found that chlorhexidine is unaffected during the hydrating process and the resulting adhesive provides effective release of chlorhexidine when placed onto a surface. The invention will now be illustrated but in no way limited with reference to the following examples. Raw Materials Example 1 673g Emkarox VG680W (0.280 moles OH from H2O and OH values), 175g Desmodur N3200 (NCO/OH ratio = 3.5) and 0.2% w/w Metatin 812ES catalyst were mixed in a 1 litre flange flask on a water bath at 80° for 2 hours. The percentage isocyanate in the resulting prepolymer was determined in the standard way and was found to be 2.97% w/w NCO in this case. Other prepolymers were synthesised which were formulated to give different residual isocyanate concentrations. This would be expected to affect the degree of cross-linking in the gel adhesive. The residual isocyanate functionalities in the prepolymer were reactecj, for example, with hydroxyethylacrylate in order the synthesise the acrylated prepolymer. The isocyanate/hydroxyethylacrylate reaction was performed at a 1 :1 NCO/OH mole ratio. The two components were stirred at room temperature for approx 6 hours and the disappearance of isocyanate was monitored by infra-red spectroscopy. Infra-red spectra of isocyanate terminated prepolymers contain a strong isocyanate peak at 2270cm -' ' . The Michael addition was performed by mixing equimolar ratios of acrylate groups to amine (or thiol) functionalities. This reaction generally proceeds more quickly at room temperature than at elevated temperatures. Catalysts were added, where applicable, dropwise to the two component mixture. Example 2 Preparation of Prepolymer Emkarox VG680W, polyisocyanate and Metatin 812ES catalyst were weighed into a flange flask fitted with a stirrer, nitrogen inlet and bubbler. This was stirred at 80°C for 2 hours under nitrogen and then allowed to cool to room temperature. The oligomer was then mixed, at room temperature, stoichiometrically with hydroxyacrylate to cap-off the remaining isocyanate groups. The reaction mix was then analysed periodically by infra-red spectroscopy to monitor the disappearance of the isocyanate peak at 2250cm "1 . The prepolymer stored at room temperature after synthesis in a sealed container. The polyol: isocyanate ratio was such to give a suitable number of acrylate groups which could be effectively crosslinked to give a tacky gel. The isocyanate content of the prepolymer varied between 0.64% and 2.5% and was dependant on the isocyanate and end-capping acrylate (see Table 1). Table 1 Example 3 Crosslinking of Prepolymer A sample of acrylate terminated prepolymer was mixed in a 1 : 1 vinyl:NH (or NH 2 , depending on the sample) ratio with the crosslinker and poured into a tray and left to gel via the Michael Addition reaction. 3a) Crosslinking of Prepolymer PC0896039 Hydroxyethylacrylate capped Desmodur N3200 - derived prepolymer (PC0896039) was crosslinked with a range of amines of different molecular weight and functionality. These took between V 2 hour and 5 days to give a tacky clear (some bubbles present from mixing), gel. The lower molecular weight amines crosslinked first (1 ,3-diaminopropane) and higher molecular weight last (Jeffamine D2000). All of these gels when placed in water dissolved in 13 - 48 hours. Only Versalink P650 did not gel the prepolymer successfully. When polysulphide was used as a crosslinker this gave a gel in 3 days and did not dissolve in water, but gave a 71% water uptake. 3b) Crosslinking of Prepolymer PC0896173 Hydroxyethylacrylate capped Suprasec 5005 - derived prepolymer (PC0896173) was crosslinked with Jeffamine D2000 and N.N-dimethylethylenediamine and gave a tacky clear gel in less than three days. Both of these gels when placed in water dissolved in five days. 3c Crosslinking of Prepolymer PC1196045 Hydroxypropylacrylate capped Desmodur prepolymer (PC1196045) was crosslinked with Jeffamine D2000 to give a tacky gel which dissolved in water in several days. Once the sample had gelled it was subjectively assessed for its appearance and then a sample was placed in distilled water to assess its hydrophilicity.

Claims: CLAIMS 1. A.cross-linked polyurethane wherein the polyurethane comprises an acrylated isocyanate cross-linked with polyamine or disulphide group. 2. A cross-linked polyurethane according to claim 1 wherein the acrylate moiety is a hydroxylated alkyl acrylate. 3. A cross-linked polyurethane according to claim 2 wherein the alkyl moiety is a C to C 10 group. 4. A cross-linked polyurethane according to claim 3 wherein the alkyl moiety is a C^ to C 6 group. 5. A cross-linked polyurethane according to claim 4 wherein the alkyl moiety is an ethyl group. 6. A cross-linked polyurethane according to any preceding claim wherein the polyamine is a diamine. 7. A cross-linked polyurethane according to claim 6 wherein the diamine is an alkyl diamine. 8. A cross-linked polyurethane according to claim 7 wherein the alkyl diamine is a C 1 to C 10 diamine. 9. A cross-linked polyurethane according to claim 8 wherein the C 1 to C 10 diamine is ethylene diamine. 10. A cross-linked polyurethane according to claim 6 wherein the diamine is a polyoxyalkene diamine. 11. A cross-linked polyurethane according to claim 6 wherein the diamine is a polyoxylkene diamine with a urea coupling. 12. A cross-linked polyurethane according to any of claims 1 to 5 wherein the disulphide groups is a polysulphide with the general formula HS(C 2 H 4 OCH 2 OC 2 H 4 S x ) n C 2 H 4 OCH 2 OC 2 H 4 SH wherein x is an integer and n is an integer from 1 to 30. 13. A ' pressure sensitive adhesive comprising a cross-linked polyurethane wherein the polyurethane comprises an acrylated isocyanate which isocyanate is cross-linked with polyamine or disulphide group. 14. A process for the preparation of a pressure sensitive adhesive which comprises reacting an isocyanate with hydroxylated acrylate to produce a prepolymer and reacting the prepolymer with a polyamine or disulphide group to produce a cross-linked polyurethane and, hydrating the cross-linked polyurethane with from 5 to 95% w/w of water.

Inventors: ANSELL CHRISTOPHER, WEST PETER JOHN, ANSELL, CHRISTOPHER, WEST, PETER, JOHN
Applicants: ANSELL CHRISTOPHER, SMITH & NEPHEW, WEST PETER JOHN, ANSELL, CHRISTOPHER, SMITH & NEPHEW, PLC, WEST, PETER, JOHN
Application year: 1997
Main classification: C08G18
IPC codes: C08G18, C09J175