Polysulphone polymer solution
I United States Patent 1 1 1111 3,875,103  
 Leslie Apr. 1, 1975 [54] POLYSULPHONE POLYMER SOLUTION 3,647,751 3/1972 Darsow 260/302 3,657,177 4/1972 Adesko 1 260/304 R Jeff&#34;? 3,673,162 6/1972 Buckley et al. 260/302 England 3,723.389 3/1973 Khattah 260/49 7 z 3 773,720 11/1973 Vogel 1 260/302 1 3] Asslgnee gzggf gggfi&#39; 3.819.582 6/1974 Feasey 260/326 R [221 Filed: 1973 Primary E.\&#39;aminerAllan Lieberman 2 APPL 425,277 Attorney, Agent, or FirmCushman, Darby &amp;  
 Cushman {30] Foreign Application Priority Data [57] ABSTRACT Jan. 26, 1973 United Kingdom 4125/73 1 Jam 26, United Kingdom H 26/73 A solution for coating is provided coinpnslng at least one thermoplastic amorphous aromatic polysulphone {52] CL 260/30 8 Ds 06,311 260/30 2 dissolved in a solvent mixture comprising 70 to EE 266/326 R 5 by volume of at least one cyclic aliphatic ketone and [5H Int CL Cnsg 51/34, &#39;cosg 51/44 CO8g 51/46 at least one low boiling highly polar nert liquid. the [58] Field of Search 260/30 8 R 30 DS 32 8 R cyclic aliphatic ketone to low bo1l1ng highly polar inert 6 1 liquid volume ratio being 70:30 to :5 and 30 to l5% by volume of at least one high volatility aliphatic ke- I56] References Cited tone, the concentration of the polysulphone being 5 to UNITED STATES PATENTS 25 g in cm&#34; of solvent mixture. 3 41s.277 12/1968 260/49 10 Claims, 2 Drawing Figures POLYSULPI-IONE POLYMER SOLUTION This invention relates to polymer solutions and in particular to a solution for coating.  
  Thermoplastic amorphous aromatic polysulphones have high melting points and are therefore useful as coatings and adhesives to be used in environments where high temperatures are likely to arise. Coatings, adhesives and films are often prepared using solutions of polymers.  
  Solutions of thermoplastic amorphous aromatic polysulphones have hitherto suffered from instability leading to solutions having a short shelf-life. Such solvents are chlorinated hydrocarbons such as methylene chloride, chloroform, 1,1,2-trichloroethane, and dichloroethane. Alternatively, solvents which give solutions of the polysulphones having long shelf life have high boiling points, and are therefore difficult to remove. Other solvents such as ketones are low stress cracking agents for polysulphones and can attack polysulphones to form highly viscous solutions, for example methyl ethyl ketone swells polysulphones to give only very concentrated solutions.  
  According to the present invention a solution for coating is provided comprising at least one thermoplastic amorphous aromatic polysulphone dissolved in a solvent mixture comprising 70 to 85% by volume of at least one cyclic aliphatic ketone and at least one low boiling highly polar inert liquid, the cyclic aliphatic ketone to low boiling highly polar inert liquid volume ratio being 70:30 to 95:5 and 30 to 15% by volume of at least one high volatility aliphatic ketone, the concentration of the polysulphone being 5 to g in 100 cm of solvent mixture.  
  Thermoplastic amorphous aromatic polysulphones and methods for making them, are described in British Patent Specifications Nos. 1,016,245; 1,060,546; 1,078,234; 1,109,842; 1,122,192; 1,124,200; 1,133,561; 1,153,035; 1,153,528; 1,160,666; 1,177,183; 1,234,301; 1,255,588; 1,265,144;  
 1,295,584; 1,296,383; 1,298,821 and 1,303,252; Belgian Specification No. 741,965; Canadian Specification No. 847,963; US. Pat. No. 3,432,468; Netherlands Specifications No. 69, 03070; German Specification No. 1,938,806 and Swiss Specification No. 491,981, the disclosures of which are incorporated herein by reference.  
  The thermoplastic amorphous aromatic polysulphones described in the above mentioned specifications comprise repeating units of the formula in which Ar is a bivalent aromatic radical which may vary from unit to unit in the polymer chain (so as to form copolymers of various kinds). Thermoplastic amorphous aromatic polysulphones generally have at least some units of the structure in which Y is oxygen or sulphur or the residue of an aromatic diol such as 4,4&#39;-bisphenol. One example of such a polymer which is commercially available (Imperial Chemical lndustries Limited) has repeating units of another has repeating units of the formula and others (which are also commercially available) are said to have repeating units of the formula OH 3 s afl o -0 (Union Carbide Corporation) or copolymerised units in various proportions of the formulae ro am 0 0- (Minnesota Mining and Manufacturing Company). Another group of such polymers has repeating units of the formula (where Y is oxygen or sulphur) which may be copolymerised with units of other formulae given above. Preferred such polymers have a reduced viscosity of at least 0.3 (as measured at 25C on a solution of the polymer in dimethyl formamide containing 1 g of polymer in cm of solution).  
  By the term cyclic aliphatic ketone&#34; is meant a cyclic ketone having a ring containing 5, 6 or 7 carbon atoms and a boiling point of less than 200C at atmospheric pressure. Suitable cyclic aliphatic ketones include cyclopentanone, cyclohexanone, cycloheptanone and their alkyl, alkoxy derivatives provided that their boiling points is less than 200C. Preferred cyclic aliphatic ketones are cyclopentanone and cyclohexanone.  
  By the term low boiling highly polar inert liquid&#34; is meant a liquid boiling at a temperature less than 210C at atmospheric pressure and containing an SO (sulphoxicle) or -SO, (sulphone) or ides and sulphones such as for example dimethyl sulphoxide, l,l-dioxothiolan; substituted amides such as for example N,N-dimethyl formamide, N,N-diethyl form amide and N-methyl pyrrolidone; amines such as aniline and pyridine and piperidine.  
  By the term high volatility aliphatic ketone&#34; is meant a dialkyl ketone having boiling point less than 150C at atmospheric pressure and not including a cyclic aliphatic ketone. Suitable ketones have the formula R.CO.R&#39; where R and R&#39; are alkyl radicals which may be substituted with inert groups provided that the boiling point is less than 150C. Preferred such ketones are acetone and methyl ethyl ketone.  
  The composition range of solvent mixture according to the invention is defined by the area enclosed ABCD of the accompanying drawing FIG. 1.  
  A particularly preferred solvent mixture for optimum shelf life of the coating solution consists of cyclohexanone (15 to 20 parts by volume preferably about 18 parts), methyl ethyl ketone (4 to 7 parts preferably parts) and dimethyl sulphoxide l to 3 parts preferably 2 parts).  
  By the term amorphous is meant amorphous to X- rays.  
  Polymer concentration in solvent mixture is within the range 5 to 20 g of polymer in 100 cm of solution, preferably 10 to g of polymer; the lower the concentration of polymer the lower is the viscosity and the longer is the shelflife of the solution. The polymer may be dissolved in the solvent mixture merely by addition of polymer to the mixture but a preferred method is to dissolve polymer in a mixture ofcyclic aliphatic ketone and low boiling highly polar inert liquid in the desired ratio at 70 to 95C, preferably 75 to 85C, and then after cooling to about 50C to add the high volatility aliphatic ketone to that solution. The temperature of the polymer/cyclic ketone/inert liquid solution before addition of high volatility aliphatic ketone is not important but should for convenience be at least C below the boiling point of the ketone.  
  The solutions of the invention may be used for casting films, impregnating, coating wire and other solid objects for insulation or protection and lacquering.  
  The solvents are removed by evaporation conveniently in an air circulating oven. A suitable procedure is to heat the coated article immediately after coating in an oven at 70 to 90C for up to 2 hours and then raising the temperature to 160 to 200C for 2 hours. However the exact conditions will depend on the thickness of the coating and the solvents used. It is preferred that the solvent evaporation stage is carried out in a dry atmospherev The invention is illustrated by the following example.  
  Thermoplastic amorphous aromatic polysulphone having repeating units of the formula was made by the method of Example 3 of British Patent Specification No. 1,153,035. The polymer had a reduced viscosity of 0.45 as measured at C on a solution of the polymer in dimethyl formamide containing 1 g of polymer in 100 cm of solution. The polymer was divided into two portions (a) and (b). Portion (a) had reactive end-groups removed by reaction with methyl chloride. Portion (b) contained hydroxyl end-groups to give a polymer particularly useful as an adhesive as described in Dutch Patent Application No. 71 08260 lie.  
 a polymer whose number average molecular weight is sufficiently high to give a reduced viscosity of at least 0.3 (measured at 25C on a solution in dimethyl formamide containing 1 g of polymer in 100 cm of solution) and which contains at least 0.2 aromatically bound hydroxyl groups per 100 polymer repeat units].  
  Solutions of the above polymers were prepared at C in a mixture of cyclohexanone and dimethyl sulphoxide (ratio :10 by volume). The solutions contained 10 g polymer in 100 cm solution (i.e. 10% w/v). The solutions were cooled to 50C, and divided into 1 1 portions of 100 cm each. To 10 portions of each solution, was added methyl ethyl ketone in amounts varying by 5 cm from 5 cm to 50 cm. The resulting solutions were cooled to 20C and shelf life recorded. Shelf life was estimated as the time (days) taken for the solution to show first signs of cloudiness, followed shortly by formation of a flocculent precipitate. The results of shelflife determination is shown in accompanying FIG. 2 in which the shelf life in days (ordinate) is plotted against volume (cm&#34;) of methyl ethyl ketone in 10% w/v polymer in 100 cm of cyclohexanone/dimethyl sulphoxide (90:10 by volume) (abscissa). The graph shows that for both polymers, concentration of 17.5 to 43 parts of methyl ethyl ketone in 100 parts of polymer/cyclohexanone/dimethyl sulphoxide is most effective at increasing shelf life. 0n the graph, methyl ethyl ketone concentration in the solvent mixture is also expressed as a percentage (7c In these terms the most effective methyl ethyl ketone concentration is 15 to 30% by volume. Also the results show that the shelf life of a solution of polymer (b) having hydroxyl endgroups was longer than that of a solution of polymer (21) having reactive end-groups removed by methyl chloride.  
 1 claim:  
  1. A solution for coating which comprises at least one thermoplastic amorphous aromatic polysulphone dissolved in a solvent mixture comprising (a) 70 to 85% by volume of a mixture of (i) at least one cyclic aliphatic ketone having a ring containing 5 to 7 carbon atoms and having a boiling point, at atmospheric pressure, of less than 200C and (ii) at least one inert liquid compound containing a polar group selected from SO, SO-,,  
 groups and having a boiling point, at atmospheric pressure, of less than 210C, the cyclic aliphatic ketone to inert liquid compound volume ratio being 70:30 to :5, and (b) 30 to 15% by volume of at least one dialkyl ketone having a boiling point, at atmospheric pressure, of less than 150C, the concentration of the polysulphone being 5 to 25 g in cm of solvent mixture.  
  2. A solution according to claim 1 in which the cyclic aliphatic ketone is selected from cyclopentanone and cyclohexanone.  
  3. A solution according to claim 1 in which the low inert liquid compound is selected from dimethyl sulphoxide and l l -dioxothiolan.  
  4. A solution according to claim 1 in which the dialkyl ketone is selected from acetone and methyl ethyl ketone.  
  5. A solution for coating which comprises at least one thermoplastic amorphous aromatic polysulphone dissolved in a solvent mixture comprising cyclohexanone 0 c so where Y is oxygen or sulphur or the residue of an aromatic diol.  
  8. A solution according to claim 7 in which the thermoplastic aromatic polysulphone has repeating units of the formula 9. A solution according to claim 1 in which the thermoplastic aromatic polysulphone has a number average molecular weight sufficiently high to give a reduced viscosity of at least 0.3 (measured at 25C on a solution in dimethyl formamide containing 1 g of polymer in l00 cm of solution) and contains at least 0.2 aromatically bound hydroxyl groups per 100 polymer repeat UllllS.  
  10. A method of making a solution as claimed in claim 1 comprises dissolving the thermoplastic amorphous aromatic polysulphone in a mixture of the cyclic aliphatic ketone and the inert liquid compound in the desired ratio at C to C, cooling that solution to about 50C and adding the dialkyl ketone to that cooled solution.