Application of sulfone containing polyalkyl ethers to medical materials

Abstract: A polyalkyl ether/polyaryl ether sulfone or ketone copolymer and a specific polyether ester copolymer are useful for producing a medical material to be used to contact the blood; and methods for producing the medical material comprising said polyalkyl ether/polyaryl ether sulfone or ketone copolymer or a specific polyether ester copolymer.

Description: Detailed Description of the Invention This invention relates to the application of sulfone containing polyalkyl ether units to medical materials. More specifically, it relates to the application of these compounds to medical materials, making use of their excellent blood compatibility. In recent years, synthetic polymer materials have been widely used in medical materials such as artificial organs and catheters. Typical synthetic polymer materials for use in medical materials include hydrophobic polymers such as polyester, polyvinyl chloride, polystyrene, silicone resin, polymethacrylate and fluorine-containing resin; and hydrophilic polymers such as polyvinyl alcohol, polyether urethane (segmented polyurethane, SPU), poly(methacrylic acid-2-hydroxyethyl) and polyacrylamide. Most of these conventional materials have been used mainly from the viewpoint of their physical and mechanical properties, while SPU is known for its relatively excellent antithrombogenic property. Particularly, attempts have been made to apply Biomer®, Cardiothane® and the like to an artificial heart. However, satisfactory effects have been not yet obtained (B. Nylas, R.C. Reinbach, J.B. Caulfield, N.H. Buckley, W.G. Austen: J. Biomed, Mater. Res. Symp., 3,129 (1972); and L.P. Joyce, M.C. Devries, W.S. Hastings, D.B. Olsen, R.K. Jarvik, W.J. Kolff: Trans. ASAIO, 29,81 (1983)). Polyethylene glycol which is a polyether having oxyethylene units covalently bonded in a chain form has high hydrophilic nature and low antigen properties and has been so far used as a nonionic surfactant, plasticizer or pharmaceutical base. Since polyethylene glycol has a hydroxyl group at both terminals of a polymer chain, hydrogel having a hydrophilic surface can be prepared by graft polymerizing it to a polymethacrylic acid (Y. Mori et al., Trans. Am. Soc. Artif. Intern. Organs, 28, 459 (1982)). Further, segmented polyurethane has been prepared by using polyethylene glycol as the hydrophilic phase of polyether urethane which is a bifunctional copolymer. It has been reported that these polymers can suppress the adhesion of platelets to the surface thereof (E.W. Merril, V. Sa Da Costa, E.W. Salzman, D. Brier-Russell, L. Kirchner, D.F. Wangh, G. Trudel, S. Stopper, V. Vitale: Adv. Chem. Ser., 199, 95 (1982)). Meanwhile, along with progress in medical technology, there have been more and more chances for materials to contact with bio tissues or blood and the affinity of materials for living bodies has been becoming a big issue. Particularly, adhesion to the surface of a material and denaturation of bio components such as protein and blood corpuscles cause not only adverse effects on living bodies which are not observed normally, such as thrombus formation and inflammation reaction, but also degradation of the material. Therefore, these are the serious and radial problems of medical materials which must be solved immediately. For the prevention of blood coagulation on the surface of a material, a blood anti-coagulant typified by heparin has been continuously administered. However, in recent years, the effects of long-time administration of heparin (side effects such as liver troubles, e.g., lipid metabolism abnormality, prolonged bleeding time and an allergy reaction) have been called in question. Particularly, as for hemodialysis method for chronic renal failure patients who undergo blood purification such as hemodialysis or blood filtration, the development of a blood contacting material which does not need an anti-coagulant has been strongly desired. At present, more than 100,000 patients undergo a blood purification in Japan. The principle of blood purification is to allow blood to contact with a dialysis solution through a membrane, disperse waste matters and metabolic products contained in the blood in the dialysis solution to remove them and further remove excess water by making use of pressure difference. A blood purifier is used for blood purification. This apparatus comprises a blood circuit consisting of a bundle of hollow yarns stored in a housing. The blood flows inside the hollow yarn and the dialysis solution flows outside the hollow yarn. As the material of a dialysis membrane for this blood purifier, a regenerated cellulose membrane, particularly regenerated cellulose membrane prepared by a copper ammonium method, has been widely used and greatly contributed to the prolongation of the life and the rehabilitation of a renal failure patient along with progress in a dialysis apparatus and dialytic technology. This is due to nothing but the fact that the regenerated cellulose membrane has excellent dialysis performance and mechanical strength and high safety supported by the results of actual long-time use. On the other hand, in spite of progress made in hemodialysis treatment, various problems arisen in dialysis are yet to be solved in fact. One of the main problems is a temporary reduction in the number of leukocytes due to the activation of complements contained in the blood by a cellulose polymer. Another one is various side effects which are considered to be caused by long-term administration of a large quantity of an anti-coagulant. As described above, for hemodialysis, a blood anti-coagulant typified by heparin has been continuously administered to suppress a blood coagulation reaction in a blood purifier. However, under the current circumstances where the solute removal performance of the blood purifier has been improved and the prolongation of life to 20 years is now possible, problems caused by the use of heparin have been reported one after another. Particularly, it has been revealed that the long-term administration of heparin causes side effects such as liver troubles, e.g., lipid metabolism abnormality, prolonged bleeding time and an allergy reaction. From this point of view, the development of a blood purifier which can reduce the amount of an anti-coagulant for blood purification treatment or which does not cause blood coagulation without using an anti-coagulant, that is, has antithrombogenic property has been ardently desired. Further, the antithrombogenic blood purifier makes it possible to hand-carry a whole apparatus, promote the rehabilitation of a patient which is confined to the hospital a few days a week for 5 hours and enhance his/her quality of life. There have been proposed several methods for suppressing the activation of complements or improving antithrombogenic property without impairing other excellent properties of a regenerated cellulose membrane. For example, as for the suppression of the activation of complements, a method for fixing a polymer having a tertiary amino group to the surface, a method for grafting a hydrophilic polymer such as polyethylene oxide chain to the surface of the membrane by covalent bonding and the like have been reported and a certain measure of its effect of suppressing the activation of complements has been confirmed. However, it is still unsatisfactory in terms of the suppression of blood coagulation (antithrombogenic property). There have been reported several methods for improving antithrombogenic property, such as one for affixing heparin to the surface of a membrane (Japanese Laid-open Patent Application No. 51-194), one for providing antithrombogenic property by the modification of the surface of a membrane by means of a prostaglandin E1-cellulose derivative adsorption layer (Japanese Laid-open Patent Application No. 54-77497), one for graft polymerizing 2-methacryloyloxyethylphosphocholine (MPC) which is excellent antithrombogenic polymer and fixing it to the surface (BIO INDUSTRY, 8 (6), 412420 (1991)), one for fixing a chemically modified MPC graft cellulose derivative to hollow yarn (Japanese Laid-open Patent Applications Nos. 5-220218 and 5-345802) and the like. However, they are not sufficiently effective to solve such problems as the low stability of a physiologically active material, and still have many problems in high costs due to a complicated fixing method and difficulty of acquiring a homogeneous fixing surface layer, and have not been put to practical use yet. All of the above hydrophobic polymer materials such as polyvinyl chloride and polymethacrylate and hydrophilic polymer materials such as polyvinyl alcohol and poly(methacrylic acid-2-hydroxyethyl) are not satisfactory in terms of mechanical strength, bio compatibility and the like. On the other hand, polyethylene glycol itself is water-soluble and hence, cannot be processed as a medical material. It has been verified by in vitro experiments that a methacrylic acid copolymer prepared by grafting a polyethylene glycol chain as a free terminal chain has the property of significantly damaging a cell membrane and causes a reduction in cell function due to the high mobility of polyethylene glycol or a free hydroxyl group which strongly interacts with a polar group contained in vivo though it relatively suppresses the adhesion of platelets (Masaki Miyamoto, Shigeru Sasagawa, Yoshizo Terada, Shoji Nagaoka, Yuichi Mori, Polym, Prepr., Jpn., 33, 2143 (1984)). Therefore, the above material is not suitable for use in a medical material which must be safe. Further, in segmented polyurethane such as Biomer® or Cardiothane®, the adhesion of platelets is suppressed by a micro-phase separation structure between a hard aromatic urethane bonding site and a soft polyether bonding site, but its effect is not always satisfactory. Particularly, since a partial structure of hydrogen bonding, such as urethane bonding and urea bonding has strong interaction between the polar groups of a main chain though it contributes to improvement in the hardness of a molecular chain, the hydration of water molecules capable of lightening hydrophobic interaction is checked. Therefore, it has been reported that the structure induces the denaturation of protein when the protein contained in the blood is adsorbed, and promotes the adhesion of platelets. Generally speaking, polar sites such as a hydroxyl group and amino group induce the activation of complements (second route) at the time when contacting the blood and causes thrombus formation due to the promotion of fibrin formation. A cellulose triacetate membrane which is a semisynthetic polymer has both merits of cellulose and a synthetic polymer and exhibits higher ability to suppress the activation of complements over regenerated cellulose, and its water permeability and material permeability are well balanced. In addition, since it has sufficient mechanical strength, it rarely suffers from the production of pin holes. Therefore, its research and development is now under way as a dialysis membrane material substituting regenerated cellulose and its sufficient performance has been confirmed by therapeutical and clinical results. However, this cellulose triacetate membrane is still unsatisfactory in terms of antithrombogenic property, and the development of a novel antithrombogenic membrane which can reduce the use of an anti-coagulant is desired. Japanese Laid-open Patent Application No. 5-36065 discloses an antithrombogenic medical material which is composed of a polyester-based copolymer containing 80 to 50 mol% of terephthalic acid, 20 to 50 mol% of an acid other than terephthalic acid and 5 to 40 % by weight of polyalkylene glycol consisting of glycol having a molecular weight of 250 or less and polyalkylene glycol having a number average molecular weight of about 3,000 to 60,000. Japanese Patent Publication No. 58-47182 discloses a blood transport tube or blood container which is composed of a polyester-polyether block copolymer containing 5 to 85 % by weight of poly(alkyleneoxide)glycol units having a number average molecular weight of 800 to 6,000 and a carbon atom/oxygen atom ratio of 2.5 to 4.3. Japanese Laid-open Patent Application No. 58-183171 teaches a blood transport tube or a blood handling tool which comprises a polyester-polyether block copolymer and a polyvinyl chloride resin dispersed uniformly in a micro-phase dispersion state. Japanese Patent Publication No. 4-75052 discloses selective permeable hollow yarn for hemodialysis which is prepared by melt-spinning a block copolymer comprising condensed hydrophobic polymer components having a water absorption of 1.0 % or less and polyoxyalkylene, and orienting the yarn in a lengthwise direction of the yarn by drafting or drawing. The above prior art teaches a polysulfone as one of the condensed hydrophobic polymer components but fails to disclose specific examples of the polysulfone. Japanese Patent Publication No. 6-11789 discloses a process for providing hydrophilic nature to an aromatic polysulfone, which comprises reacting an aromatic polysulfone having (1) a benzene ring containing a halogen group which is activated by a sulfonyl group present at a p-position of a molecular terminal and eliminated by a nucleophilic substitution and (2) recurring units represented the following formula: - (-M-R a -M b -O) c -M-SO 2 -M-O- or -M-SO 2 -M-SO 2 -M-O- wherein M is the same or different and an aromatic group, R is a divalent organic group, and a, b and c are each 0 or 1, with a polyol under alkaline conditions to bond the polyol to the molecular terminus of the aromatic polysulfone via an ether bond. An object of the present invention is to provide a novel polyalkyl ether/polyaryl ether sulfone copolymer. Another object of the present invention is to provide the use of the above novel copolymer as a starting material for a medical material or a coating material thereof. Still another object of the present invention is to provide a medical material which is composed of a composition comprising, as part of the material, the above novel copolymer of the present invention. A further object of the present invention is to provide the above novel composition constituting the above medical material of the present invention. A still further object of the present invention is to provide an industrially advantageous method for producing the medical material of the present invention. The above and other objects and advantages of the present invention will become apparent from the following description. According to the present invention, firstly, the above objects and advantages of the present invention can be attained by a polyalkyl ether/polyaryl ether sulfone copolymer which has a reduced viscosity, measured at 35°C in a mixed solvent having a phenol/1,1,2,2-tetrachloroethane weight ratio of 6/4, of at least 0.5 dl/g and which essentially consists of recurring units represented by the following formula (1): -[-O-Ar 1 -Z-Ar 2 -O-Ar 3 -]- wherein Ar 1 , Ar 2 and Ar 3 are the same or different and each is a divalent aromatic hydrocarbon group which may be substituted and Z is or >SO 2 , and recurring units represented by the following formula (2): -[-(OR) n -O-Ar 3 -]- wherein R is an alkylene group having 2 or 3 carbon atoms or a combination of an alkylene group having 2 or 3 carbon atoms and an alkylene group having 4 carbon atoms, Ar 3 is defined the same as above, and n is a numeral which ensures that the molecular weight of a unit represented by -(OR) n - is in the range of 400 to 20,000, at least two on the average of the recurring unit represented by the above formula (2) being present in the molecule and the proportion of the unit represented by -(OR) n - in the above formula (2) being 10 to 90 % by weight based on the total weight of the recurring units (1) and (2). Brief Description of the Drawings Fig. 1 is an NMR chart of a polyalkyl ether/polyaryl ether sulfone copolymer obtained in Example 2; Fig. 2 shows an SEM photo for evaluating the amount of protein adsorbed and the number of platelets adhered in Example 8; Figs. 3a, 3b and 3c show respectively SEM photos for evaluating the amount of protein adsorbed and the number of platelets adhered in Examples 13 and 16 and Comparative Example 1; The polyalkyl ether/polyaryl ether sulfone copolymer of the present invention essentially consist of the recurring units represented by the above formulas (1) and (2). Ar 1 , Ar 2 and Ar 3 in the formula (1) are the same or different and each a divalent aromatic hydrocarbon group which may be substituted. In the case of the polyalkyl ether/polyaryl ether sulfone copolymer, the aromatic hydrocarbon group is selected from the group consisting of p-phenylene, m-phenylene, 2,6-naphthylene, 2,7-naphthylene, 1,4-naphthylene, 1,5-naphthylene, 4,4'-biphenylene, 2,2'-biphenylene, 4,4'-oxylenediphenylene, 4,4'-isopropylidenediphenylene, 4,4'-isopropylidene-2,2',6,6'-tetramethyldiphenylene, 4,4'-sulfonyldiphenylene and the like. Out of these, Ar 1 and Ar 2 are preferably p-phenylene and Ar 3 is preferably 4,4'-isopropylidenediphenylene, 4,4'-oxylenediphenylene, 4,4'-isopropylidene-2,2',6,6'-tetramethyldiphenylene, 4,4'-sulfonyldiphenylene or the like. In this case, when Ar 3 in the formula (1) contains a sulfone bond(-SO 2 -), it is preferable that Ar 3 is not identical with the group of -Ar 1 -SO 2 -Ar 2 -. In the formula (2), R is an alkylene group having 2 or 3 carbon atoms or a combination of an alkylene group having 2 or 3 carbon atoms and an alkylene group having 4 carbon atoms. Illustrative examples of the alkylene group having 2 or 3 carbon atoms include ethylene, propylene and trimethylene. R is particularly preferably ethylene. Illustrative examples of the alkylene group having 4 carbon atoms are tetramethylene or the like. R may be one or a combination of two or more of these. In the case of a combination of an alkylene group having 2 or 3 carbon atoms and an alkylene group having 4 carbon atoms, the proportion of the alkylene group having 4 carbon atoms is preferably up to 80 mol%, more preferably up to 60 mol%. n is a numeral which ensures that the molecular weight of a polyoxyalkylene structure unit represented by -(RO) n - is in the range of 400 to 20,000. The molecular weight of the polyoxyalkylene structure unit is preferably 600 to 15,000, more preferably 800 to 10,000, particularly preferably 1,000 to 6,000. The copolymer of the present invention comprises at least two on the average of the recurring unit represented by the above formula (2) in the molecule. The copolymer of the present invention which consists of the smallest numbers of the recurring units is a copolymer consisting of one recurring unit of the formula (1) and two recurring units of the formula (2). Further, the copolymer of the present invention contains the structural unit -(RO) n - in the formula (2) in a proportion of 10 to 90 % by weight based on the total weight of the recurring units of the formulas (1) and (2). If the proportion is less than 10 % by weight, the resulting copolymer will have too high hydrophobic nature and unsatisfactory wetability when it is formed into a dry film. If the proportion is more than 90 % by weight, the resulting copolymer will have too high hydrophilic nature and may dissolve in water, significantly swell or have insufficient mechanical strength. The structural unit -(RO) n - is preferably contained in a proportion of 30 to 80 % by weight, more preferably 40 to 70 % by weight based on the same standard. Further, the copolymer of the present invention has a reduced viscosity, measured at 35°C and at a concentration of 1.2 g/dl in a mixed solvent having a phenol/1,1,2,2-tetrachloroethane weight ratio of 6/4, of at least 0.5 dl/g. If the viscosity is less than 0.5 dl/g, the resulting copolymer will have insufficient mechanical strength. The reduced viscosity is preferably at least 1.0 dl/g, more preferably 1.0 to 3.0 dl/g. The copolymer of the present invention can be produced in the following manner, for example. Bis(haloaryl)sulfone or ketone represented by the following formula (3): X-Ar 1 -Z-Ar 2 -X wherein Ar 1 , Ar 2 and Z are defined the same as above and X is a halogen atom, α,ω-bis(haloalkoxy)polyoxyalkylene represented by the following formula (4): X-R-(OR) n-1 -X wherein R, n and X are defined the same as above, and a dihydroxyaryl compound represented by the following formula (5): HO-Ar 3 -OH wherein Ar 3 is defined the same as above, are heated in the presence of an alkali to allow them to react with each other. In the formula (3), X is selected from fluorine, chlorine, bromine and iodine. X is preferably chlorine. Illustrative examples of the bis(haloaryl)sulfone represented by the formula (3) include bis(4-fluorophenyl)sulfone, bis(4-chlorophenyl)sulfone, bis(3-fluorophenyl)sulfone, bis(3-chlorophenyl)sulfone, 3-fluorophenyl-4'-fluorophenylsulfone, 3-chlorophenyl-4'-chlorophenylsulfone and the like. Before giving illustrative examples of α,ω-bis(haloalkoxy)polyoxyalkylene represented by the formula (4), there are exemplified specific examples of the dihydroxyaryl compound represented by the above formula (5), which include bis(4-hydroxyphenyl)methane, hydroquinone, bis(4-hydroxyphenyl)ether, 4,4'-dihydroxybiphenyl, 1,5-dihydroxynaphthalene, 2,3-dihydroxynaphthalene, 2,7-dihydroxynaphthalene and the like. In the formula (4), X is exemplified the same as those in the formula (3). Preferred examples of the α,ω-bis(haloalkoxy)polyoxyalkylene represented by the formula (4) include α,ω-bis(2-bromoethoxy)polyoxyethylene, α,ω-bis(2-chloroethoxy)polyxoyethylene, α,ω-bis(2-bromo-1-methylethoxy)polyoxyisopropylene, α,ω-bis(2-chloro-1-methylethoxy)polyoxyisopropylene and α,ω-bisbromo and/or chloro product of a polyoxyethylene-polyoxyisopropylene block copolymer. The α,ω-bis(2-haloalkoxy)polyoxyalkylene used in the present invention can be synthesized by various methods. Typical methods are as follows: (i) one in which polyoxyalkylene glycol and phosphorus halide are reacted with each other in the presence of a base; and (ii) one in which polyoxyalkylene glycol and thionyl halide are reacted with each other in the presence of a base. In the above method (i), phosphorus halide is added dropwise to corresponding polyoxyalkylene glycol and a base in the presence of an arbitrary solvent and the resulting mixture is heated and stirred to produce the α,ω-bis(2-haloalkoxy)polyoxy-alkylene. When the number of moles of the polyoxyalkylene glycol is taken as (A) and the number of moles of the phosphorus halide is taken as (B), they must satisfy the following formula (6). 0.75 ≦ (B)/(A) ≦ 2 When the value of (B)/(A) is too large, the quantity of the phosphorus halide is excessive and of waste. When the value is too small, an end material cannot be obtained at a high yield. It is preferable from a view point of reactivity that the phosphorus halide used in this method is phosphorus tribromide. Any solvent is acceptable if it can dissolve and mix these reactive components and does not contain a functional group which reacts with the phosphorus halide, such as hydroxyl group, primary or secondary amino group or the like, and may be selected, for example, from methylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, tetrahydrofuran, carbon disulfide and the like. From a viewpoint of solubility and simplicity of reaction operation, methylene chloride and chloroform are preferred. The amount of the solvent is preferably 1.0 to 10.0 times, more preferably 2.0 to 5.0 times, the total weight of reaction substrates. When the amount of the solvent is below the above range, the reaction substrates will separate out, whereas when the amount of the solvent is above the above range, the purification operation of the product will become complicated or reaction efficiency may deteriorate. As the base, there may be used known organic bases such as pyridine, triethylamine, N,N'-tetramethylethylenediamine, HMPA (hexamethyltriamide phosphate), DBU (1,8-diazabicyclo[5.4.0]undecene-7) and the like, out of which pyridine is preferred. Although the base is used in an amount of 1.5 to 3.0 equivalents of phosphorus halide, the optimal amount thereof differs depending on type of the base and reaction conditions such as the value of (B)/(A) in the above formula (6). For example, when pyridine is used as the base, methylene chloride is used as the solvent and (B)/(A) is 0.75, pyridine is preferably used in an amount of about 3.0 equivalents of the phosphorus halide. The reaction temperature may be equal to or lower than room temperature if raw material components are not crystallized from the solvent. When a solvent having a boiling point of 100°C or less is used, a reaction may be carried out at a solvent reflux temperature. However, when phosphorus halide is added dropwise to a mixture solvent of a base and polyoxyalkylene glycol in an early stage of a reaction, there may be such risks as abrupt heat generation and bumping during operation. Therefore, the temperature is preferably maintained at 0 to 5°C by cooling with ice during dropping. When the reaction temperature exceeds 100°C, a side reaction occurs and the yield of an end substance decreases, whereas when the reaction temperature is too low, the reaction rate lowers. When phosphorus tribromide is used as the phosphorus halide, the reaction temperature is preferably 30 to 50°C. In the above method (ii), thionyl halide of a first stage is added dropwise to and mixed with corresponding polyoxyalkylene glycol and a base in the presence of an arbitrary solvent to cause reaction, and the same amount of thionyl halide of a second stage is added to the reaction product, heated and stirred to synthesize the end substance. The first-stage and second-stage reactions are shown by the following formulas (7) and (8). m[HO-(-RO-) n -OH] + mSOX 2 → -[-O-(RO-) n -OS(O)] m - +2mHX -[O-(RO-) n -OS(O)] m - + mSOX 2 → m[X-(-RO-) n -X] + 2SO 2 Therefore, when the number of moles of polyoxyalkylene glycol is taken as (A), the numbers of moles of thionyl halide are taken as B1 (the number of moles in the first stage) and B2 (the number of moles in the second stage), the reaction conditions are set to satisfy the following formulas (9) and (10). (B1)/(A) = 1 (B2)/(A) = 1 In other words, thionyl chloride may be used in an amount of double the molar equivalent of polyoxyalkylene glycol. In this respect, when the value of (B1 or B2)/(A) is too large, the quantity of the thionyl halide is in excess and of waste. When the value is too small, an end material cannot be obtained at a high yield. The thionyl halide used in this method is preferably thionyl chloride from a view point of reactivity. As in the above method (i), any solvent is acceptable if it can dissolve and mix these reactive components and does not contain a functional group which reacts with the thionyl halide, such as hydroxyl group, primary or secondary amino group or the like, and may be selected, for example, from methylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, tetrahydrofuran, carbon disulfide and the like. From a viewpoint of solubility and simplicity of reaction operation, methylene chloride is preferred. The quantity of the solvent and the reaction temperature are the same as in the above method (i). The type of the base used is also pursuant to those in the above method (i), and pyridine is preferably used. The base is used in an amount of 2.0 equivalents or slightly more (e.g., 2.1 equivalents) of thionyl halide which has been added in the first-stage reaction, but it is not necessary to add the base in the second-stage reaction. The optimal amount of the base added in the first-stage reaction, which differs depending on type of the base, may be a theoretical value which can neutralize hydrochloric acid by-produced. For example, when pyridine is used as the base and polyoxyalkylene glycol is chlorinated with thionyl chloride, pyridine is preferably used in an amount of 2.0 equivalents of thionyl halide added in the first stage. The reaction is carried out as follows. Bis(halo-aryl)sulfone and α,ω-bis(haloalkoxy)polyoxyalkylene represented by the above formulas (3) and (4) are charged and mixed with the dihydroxyaryl compound represented by the above formula (5) such that the total number of moles of the first two substances becomes almost equal to the number of moles of the latter compound, and caused to react with an alkali in the presence of an appropriate solvent. Various copolymers having different compositions and a polyoxyalkylene structure unit content of 10 to 90 % by weight based on the resulting copolymer can be obtained by changing the amount charged of the bis(haloaryl)sulfone and α,ω-bis(haloalkoxy)polyoxyalkylene. The reaction temperature is preferably 120 to 400°C, more preferably 160 to 350°C. When the reaction temperature is higher than 400°C, a side reaction or the decomposition of the starting materials is liable to occur, whereas when the reaction temperature is lower than 120°C, the reaction becomes slow. As the alkali used in the reaction, an alkali metal carbonate or hydroxide is preferred, and examples thereof include lithium carbonate, potassium carbonate, sodium carbonate, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate and the like. Of these, carbonates, especially potassium carbonate is preferred. The amount of the alkali must be such that it can substantially neutralize hydrogen halide produced during the reaction. Practically, even if the amount is 5 % larger or smaller than the theoretical value, the reaction can be carried out. An appropriate plasticizer or solvent may be used in the reaction. Examples of the appropriate solvent include diphenyl sulfone, N-methyl pyrrolidone, N,N-dimethylacetoamide, dimethylsulfoxide and the like, out of which N,N-dimethylacetoamide and diphenylsufone are preferred. An additive may be added to promote the reaction. Examples of such additive are metals or salts thereof, clathrate compounds, chelating agents, organic metal compounds and the like. The thus obtained copolymer of the present invention has an extremely small amount of protein adsorbed, measured by a Micro-BCA method, when contacting human blood plasma at 37°C for 1 hour, that is, 0.7 µg/cm 2 or less. Therefore, the copolymer has an excellent adsorption suppression effect against the adhesion of protein and platelets contained in the blood when contacting a blood plasma solution. The amount of protein adsorbed is desirably as small as possible, while if it is in the range of 0.3 to 0.7 µg/cm 2 , the copolymer exhibits actually sufficient effect. The above copolymer of the present invention not only can be advantageously used as a protein filtration membrane, support film for a permeable membrane, medical hemodialysis membrane and agent for imparting antithrombogenic property to medical polymer but also is useful as an ultrafiltration membrane, precision filtration membrane and the like. Therefore, the present invention has made it clear that the above polyalkyl ether/polyaryl ether sulfone copolymer of the present invention are advantageously used to produce a medical material to be used to contact the blood. According to the present invention, there is provided the use of the above copolymers of the present invention to produce a medical material to be used to contact the blood. This use include not only use of the copolymer of the present invention as a starting material of a medical material but also use of the copolymer as a coating material for coating a medical material prepared from other materials. Illustrative examples of the other materials for preparing a medical material include polysulfone, polyaryl ether sulfone, cellulose, cellulose triacetate, polyurethane, polycarbonate, aromatic polyester such as polyethylene terephthalate, polyethylene, polypropylene, polyvinyl chloride, polystyrene, silicone resin, polymethacrylates such as polymethyl methacrylate, fluororesin, polyvinyl alcohol, poly(methacrylic acid-2-hydroxyethyl), polyacrylamide and the like. Of these, polysulfone, polyaryl ether sulfone, cellulose triacetate, polypropylene, polyurethane and polycarbonate are preferred in the present invention. According to a first preferred aspect of the present invention, there is provided the use of the above polyalkyl ether/polyaryl ether sulfone copolymer (A) of the present invention for coating the blood-contacting surface of a medical material to be used to contact the blood, which is formed from at least one polymer (B) selected from the group consisting of polysulfone, polyaryl ether sulfone, cellulose triacetate, polypropylene, polyurethane and polycarbonate. According to a second preferred aspect of the present invention, there is provided the use of a polymer composition comprising 1 to 99 parts by weight of the above polyalkyl ether/polyaryl ether sulfone copolymer (A) of the present invention and 1 to 99 parts by weight of the above polymer (B) as a starting material for producing a medical material to be used to contact the blood. In the above polymer composition, the total weight of the copolymer (A) and the polymer (B) is 100 parts by weight. The polymer composition comprising 1 to 99 parts by weight of the above copolymer (A) and 1 to 99 parts by weight of the above polymer (B) is novel by itself and is an object claimed by the present invention.. A description is first given of the first preferred aspect of the present invention. The polymer (B) which is a starting material constituting a medical material is preferably polysulfone, polyaryl ether sulfone, cellulose triacetate, polyvinylchloride, polypropylene, polyurethane or polycarbonate as described above. They may used alone or in combination of two or more. As the polysulfone and polyaryl ether sulfone may be preferably used a homopolymer or copolymer of an aromatic polysulfone which is composed of recurring units represented by the following formula (11): wherein Ar 4 , Ar 5 and Ar 6 are the same or different and each a divalent aromatic hydrocarbon group which may be substituted. Preferably, this polymer has a reduced viscosity, measured at 35°C and at a concentration of 1.2 g/dl in a phenol/1,1,2,2-tetrachloroethane mixed solvent (weight ratio of 6/4), of 0.5 to 3.0. In the above formula (11), illustrative examples of the aromatic hydrocarbon group represented by Ar 4 , Ar 5 and Ar 6 are the same as those for Ar 1 , Ar 2 and Ar 3 in the formula (1). Of the examples, aromatic polysulfone of a medical grade such as (a) aromatic polysulfone (specific gravity of 1.24 and glass transition point of 190°C) having a number average molecular weight of 20,000 to 30,000 and obtained by heat-condensing 2,2'-bis(4-hydroxyphenyl)propane and 4,4'-dichlorodiphenylsulfone or (b) polyaryl ether sulfone (specific gravity of 1.37 to 1.60 and glass transition point of 220°C) having a number average molecular weight of 20,000 to 30,000 and obtained by heat-condensing 4,4'-dihydroxydiphenylsulfone and 4,4'-dichlorodiphenylsulfone are preferred. Preferably, the cellulose triacetate has a number average molecular weight of 30,000 to 300,000 and an acetylation degree of 2.8 or more. As the polypropylene may be used a low-molecular-weight polymer of medical grade, which may be either a homopolymer or a random or block copolymer copolymerized with other olefin such as ethylene or the like, from the purpose of affording processability and flexibility, as far as it has a number average molecular weight of 100,000 or more and is free from elution of impurities. Preferably, the polyurethane has a number average molecular weight of 20,000 to 30,000 and is obtained by polyaddition of methylenediphenyl-4,4'-diisocyanate and ethylene glycol. Preferably, the polycarbonate is obtained by polycondensing a bisphenol derivative such as 4,4'-isopropylidenediphenol and phosgene or diphenylcarbonate, and particularly preferably has a number average molecular weight of 20,000 to 50,000. Coating of the blood contacting surface of a medical material can be effected by dissolving the above copolymer (A) of the present invention in an organic solvent capable of dissolving the copolymer, immersing the medical material formed from the above material in the resulting polymer solution and drying to remove the organic solvent. The polymer solution may be applied to the medical material by brushing in place of immersion. The polymer solution preferably has a polymer concentration of 0.1 to 10 % by weight, more preferably 0.5 to 2 % by weight. When the polymer concentration is lower than 0.1 % by weight, it is difficult to coat the surface completely and the surface is likely to have partially non-uniform coating. When the polymer concentration is higher than 10 % by weight, the viscosity of the solution is too high to make coating smoothly, with the result that the thickness of the coating film is apt to become non-uniform. Illustrative examples of the organic solvent include cyclic ether-based solvents such as tetrahydrofuran, 1,3-dioxolane and 1,4-dioxane; amide-based organic solvents such as N,N'-dimethylformamide (DMF), N,N'-dimethylacetoamide (DMAc) and N-methyl-2-pyrrolidone (NMP); and halogen-based organic solvents such as chloroform and methylene chloride. The organic solvent contained in the polymer solution applied to the medical material is removed by drying at ordinary temperatures under ordinary pressures or at 40 to 50°C under a reduced pressure, or by extracting the solvent in a poor solvent for both of the above polymers, such as ethanol, whereby a coating film layer of the above copolymer is formed on the medical material. Examples of the medical material include hollow yarn for artificial kidney, hollow yarn for artificial lung, catheter, artificial blood vessel, blood-collecting tube, tube for blood circuit, blood container, hemodialysis membrane, plasma skimming membrane and medical suture. At least the blood contacting surface of the medical material is covered with the thin film of the above copolymer of the present invention. The "blood contacting portion" denotes the surface of the material, which contacts the blood, and a neighboring portion thereof. For instance, when the medical material is used as a dialysis membrane for an artificial kidney, at least the interior of the membrane which the blood runs through may be formed from the above copolymer. The coating film formed on the medical material preferably has a thickness of 10 nm to 10 µm, more preferably 100 nm to 1 µm. A description is subsequently given of the second preferred aspect of the present invention. The polymer composition comprises 1 to 99 parts by weight of the above copolymer (A) of the present invention and 1 to 99 parts by weight of the polymer (B). The total weight of the copolymer (A) and the polymer (B) is 100 parts by weight. The polymer (B) is the same as in the first preferred aspect of the present invention. When the amount of the copolymer (A) is less than 1 part by weight, the amount of the copolymer (A) present on the surface of a medical material is too small and hence, a satisfactory antithrombogenic effect cannot be obtained. When the amount of the copolymer (A) is more than 99 parts by weight, disadvantageously, the inherent physical properties and use conditions of the copolymer (A) greatly change depending on type of the polymer (B). Preferably, the polymer composition comprises 1 to 50 parts by weight of the above copolymer (A) and 50 to 99 parts by weight of the polymer (B) (the total weight of both materials is 100 parts by weight), more preferably 10 to 30 parts by weight of the above copolymer (A) and 70 to 90 parts by weight of the polymer (B). The polymer composition can be prepared, for example, by dissolving the copolymer (A) and the polymer (B) in an organic solvent in the above predetermined ratio and then, removing the organic solvent, or by melt-mixing the copolymer (A) and the polymer (B) in the above predetermined ratio. As the organic solvent may be used the same organic solvent as used in the first aspect of the present invention. In the above polymer composition, the copolymer (A) and the polymer (B) form separate phases without being mixed uniformly in a molecular level, and are present as separate phases. According to the present invention, by making use of the above properties of the polymer composition, there is provided a medical material to be used to contact the blood, which is characterized in that at least a portion thereof having a surface used to contact the blood is formed from a polymer composition comprising the polyalkyl ether/polyaryl ether sulfone copolymer (A) and the polymer (B) and that the concentration of the copolymer (A) in the vicinity of the surface of the portion is higher than the concentration of the above copolymer (A) contained in the whole polymer composition forming the portion. In this medical material, the polymer composition preferably comprises 5 to 20 parts by weight of the copolymer (A) and 80 to 95 parts by weight of the polymer (B) (the total weight of both materials is 100 parts by weight) and the proportion of the copolymer (A) in the vicinity of the surface is 50 to 90 parts by weight based on the same standard. The proportion of the copolymer (A) in the vicinity of the surface is higher than the proportion (concentration) of the copolymer (A) contained in the whole polymer composition when a medical material is produced from an organic solvent solution of the polymer composition. In other words, as the organic solvent is scattered from the solution, phase separation occurs and a medical material having a high concentration of the copolymer (A) in the vicinity of the surface is obtained. in the end. The "vicinity of the surface" as used herein means an area down to a depth of about 100 Å from the surface. According to the present invention, a medical material having a thin portion to be used to contact the blood is advantageously produced by the following method in particular. That is, according to the present invention, there is further provided a method for producing a medical material, which comprises the steps of: preparing a dope comprising the polyalkyl ether/polyaryl ether sulfone copolymer (A), the polymer (B) and an aprotic polar organic solvent (C) capable of dissolving these, the total concentration of the above components (A) and (B) being 1 to 30 % by weight; forming this dope into a thin film; and subjecting the thin film to a wet or dry molding method to produce a medical material having a 1 mm or less thick portion to be used to contact the blood. As the aprotic polar organic solvent are advantageously used tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethylformamide, dimethylacetoamide, N-methyl-2-pyrrolidone, dimethylsufoxide, methylene chloride and chloroform. The dope can be formed into a thin film, for example, by casting it on a substrate or spinning it into hollow yarn. The total concentration of the components (A) and (B) contained in the dope is preferably 5 to 20 % by weight, more preferably 10 to 15 % by weight in the case of casting and preferably 5 to 30 % by weight, more preferably 10 to 20 % by weight, particularly preferably 13 to 14 % by weight in the case of spinning into hollow yarn. After the dope is formed into a thin film, the aprotic polar organic solvent is removed from the dope by a wet or dry method to provide a medical material as an independent molded article. The wet method is a method comprising removing the aprotic organic solvent contained in the dope by treating the thin film of the dope in water/aprotic organic solvent and then water. The dry method is a method comprising removing the aprotic organic solvent contained in the dope by treating the thin film of the dope at ordinary temperatures under ordinary pressures or at 40 to 50°C under a reduced pressure of 1 to 30 mmHg. The thin film which is the blood contacting portion of the thus obtained medical material preferably has a thickness of 1 µm to 1 mm. In the case of hollow yarn, in particular, it is advantageous that it should have a film thickness of 10 to 50 µm. When all of the medical materials of the present invention described above are allowed to contact to a phosphoric acid buffer solution of human platelet poor plasma (PPP) having a concentration of 5 % by weight, at 37°C for 1 hour, the amount of protein adsorbed to the surfaces thereof is preferably 0.8 µg/cm 2 or less, more preferably 0.6 µg/cm 2 or less (in terms of albumin according to a Micro-BCA method). When the amount of protein adsorbed at contacting the blood is larger than 0.8 µg/cm 2 , the adhesion and activation of platelets which occur subsequently cannot be suppressed completely and hence, thrombus formation is liable to proceed. Although it is desirable that the amount of protein adsorbed be as small as possible, the medical materials are actually fully effective, if it is in the range of 0.3 to 0.7 µg/cm 2 . The reason why the polyalkyl ether/polyaryl ether sulfone and a blend polymer containing the same in the present invention exhibit excellent blood compatibility is assumed to be as follows. The above copolymer has a hard component which is a hard site and a hydrophilic polyoxyalkylene glycol chain fixed in the main chain of the polymer. Both the hydrophilic segment and hydrophobic segment are characterized by the molecular structure in which phases are separated from one another thermodynamically and microscopically. Since such a polymer has no hydrogen bond-providing group in most part of the main chain, the interaction between main chains is weak and its contact with molecules of water, which can reduce hydrophobic interaction easily occurs. Therefore, in the presence of water (blood), a hydrated hydrogel layer is formed on the interface at which the polymer contacts with water. Owing to this, the protein adsorption and blood corpuscles adhesion are low and the denaturation of protein adsorbed as well as the adhesion and activation of contacted platelets can be suppressed. Further, it is assumed-that the activation of complements and damage to a cell membrane can be avoided because the number of polyoxyalkylene free terminal chains and the number of free hydroxyl group terminals greatly reduce. The polymer composition comprising the above copolymer is microscopically separated in phase from the other polymer which is a medical polymer material and the other polymer component to be blended. In the preparation of the blend polymer, for example, in the removal of the solvent in the case of wet blending, the polyoxyalkylene units of the copolymer are orientated in the interface between the blend polymer and bulk (such as air/blend polymer interface or water/blend polymer interface) rather than the interior of the blend polymer to stabilize interface free energy in the blend polymer. Therefore, the copolymer is orientated in most part of its water contacting interface in the presence of water (blood) and the hydrogel layer of the hydrated copolymer is formed. Owing to this, the adsorption of protein and the adhesion of blood corpuscles is small and the denaturation of protein adsorbed and the adhesion and activation of contacted platelets can be suppressed. Further, it is assumed that the activation of complements and damage to a cell membrane can be avoided because the number of polyoxyalkylene free terminal chains and the number of free hydroxyl group terminals greatly reduce. To further illustrate the present invention, and not by way of limitation, the following examples and comparative examples are given. "Parts" in the following examples means "parts by weight" unless otherwise specified. The reduced viscosity (η sp /c) of the polyalkyl ether/polyaryl ether sulfone copolymer was measured as follows. 120 mg of the copolymer was dissolved in 10 ml of a phenol/1,1,2,2-tetrachloroethane mixed solvent (weight ratio of 6/4) and measured for its reduced viscosity at 35°C. The number average molecular weight was measured by a GPC (developing solvent: chloroform, in terms of polystyrene). The 1 H-NMR spectrum was measured in a mixed solvent (CF 3 COOD/CHCl 3 = 1/1) using the JNM-A600 of Japan Electron Optical Laboratory (JEOL). The quantitative evaluation of protein adsorbed was determined by a Micro-BCA method. This method is a protein quantitative determination method using a Micro-BCA kit (Micro BCA Assay Reagent Kit manufactured by Pierce Co., Ltd.) which employs copper ions and a BCA protein detection reagent shown by the following chemical structure. Since only copper ions reduced to a valence of 1 by protein present in a sample are allowed to cause a chelating reaction with the reagent thereby to develop a color (570 nm), the concentration of protein (in terms of albumin) can be determined by measuring the absorbance of a sample. Micro reagent A contains sodium carbonate, sodium bicarbonate and sodium tartarate in 0.2N NaOH. Micro reagent B contains 4% BCA in water. Micro reagent C contains 4% cupric sulfate, pentahydrate in water. For the measurement of a surface composition by ESCA, a film was cut to form a 1 cm-diameter disk as a measurement sample. ESCALAB-200 of VG Co. Ltd. was used as the measurement instrument, and an MgKα-ray was irradiated onto the sample at an incident angle of 45° and scanning was effected. The measurement was made on a surface (front side) which was in contact with an air interface at the time of casting. An SEM photo was taken by cutting out a 5 x 5 mm piece of a gold-deposited sample prepared by gold spattering and fixing it on a copper sample plate to make an observation sample. The top surface of this sample was observed by SEM (scanning electron microscopy) using S-510 of Hitachi, Ltd. Synthesis Example 1 (synthesis of α,ω-bis(2-chloroethoxy)polyoxyethylene) 30 parts of polyoxyethylene glycol (#2000), 3.2 parts of pyridine and 150 parts of dehydrated chloroform were charged into a three necked round bottom flask and stirred to prepare an uniform solution. To this was added a mixed solution containing 2.4 parts of thionyl chloride and 15 parts of dehydrated chloroform dropwise over 30 minutes while cooling it with ice. After the ice was removed and the liquid temperature rose to room temperature, stirring was further continued for another 8 hours. The chloroform was distilled off under reduced pressure and then, 15 parts of new thionyl chloride was further added, and dried by distillation under heating for 24 hours. Thereafter, excess thionyl chloride was distilled off under reduced pressure, and the residue was dissolved in 300 parts of new chloroform, washed with 200 parts of a saturated NaCl solution three times and then with 200 parts of pure water once to dispense a chloroform layer, and dried over anhydrous sodium sulfate for one night. An oily liquid obtained by removing chloroform solidified immediately at room temperature. The oily liquid was heated to be dissolved into 40 parts of acetone and reprecipitated with 200 parts of diethyl ether to obtain 28.8 parts of white powdery crystals. The product had a melting point of 50.5 to 53.5°C. It was confirmed from an IR (infrared spectroscopy) chart that this compound was α,ω-bis(2-chloroethoxy)polyoxyethylene (number average molecular weight of 2,000). Examples 1 to 6 (Preparation of polyalkyl ether/polyaryl ether sulfone copolymer) 12-64 parts of 4,4'-isopropylidenebisphenol, 12.74 parts of bis(4-chlorophenyl)sulfone, 22.11 parts of α,ω-bis(2-chloroethoxy)polyoxyethylene (number average molecular weight of 2,000), 20 parts of toluene and 8.63 parts of potassium carbonate were charged into a three-necked flask having nitrogen introducing and discharging ports, which was then guided to a Dean-Starks trap, substituted with nitrogen and heated at 110°C under reflux for 6 hours to cause a reaction. After completion of effluent of water caused by this reaction, toluene was distilled off and 20 parts of N,N-dimethylacetoamide was newly added. The inside of the flask was substituted with nitrogen and the content was further heated at 160°C for 15 hours under stirring to cause a reaction. The thus obtained polymer was extracted with chloroform, reprecipitated with methanol, washed with boiling water and dried. The finally obtained polymer was measured for its reduced viscosity and number average molecular weight. The results are shown in Table 1. Further, the same operation as described above was repeated to produce various polyalkyl ether/polyaryl ether sulfone copolymers and measure their reduced viscosities and number average molecular weights. The structures of the obtained polymers were confirmed by NMR, IR or the like. As an example, an NMR chart of the polyalkyl ether/polyaryl ether sulfone copolymer (PEO2000 (30)-co-PS(70)) obtained in Example 2 is shown in Fig. 1. In the above Table, the abbreviations of the polymers stand for the following structural formulas and the figures in the parentheses indicate composition ratios (% by weight). The structures and abbreviations of polymers other than those used in Examples and Comparative Examples are shown below. Cellulose triacetate: (TAC) Polypropylene: (PP) Polyurethane: (PU) Tecoflex 60 (a product of Terumo Electron Co., Ltd.) Polyvinyl chloride: (PVC) Polyethyleneterephthalate: (PET) Silicone resin: A vulcanized, crosslinked product of the following formula and a reinforcing filler therefor. Examples 7 to 10 (Evaluation of antithrombogenic properties of polyalkyl ether/polyaryl ether sulfone copolymers) (1) Preparation of samples for evaluation The polyalkyl ether/polyaryl ether sulfone copolymers produced in the above examples were each dissolved in chloroform to prepare dope solutions having a concentration of 1.0 % by weight. A sterilized polyethylene terephthalate (PET) disk (diameter of 15 mm and thickness of 0.5 mm) was immersed in 10 ml of each of the dope solutions. After 1 minute, the PET disk was taken out and left in a solvent atmosphere for one night to allow the solvent to volatilize. Thus, samples of PET coated with the copolymer were prepared. (2) Evaluation of amount of protein adsorbed When the sample prepared in the above (1) was brought into contact with a human platelet poor plasma (PPP) solution, the amount of protein adsorbed to the copolymer was determined spectroscopically. For evaluation, a phosphoric acid buffer solution containing PPP in a predetermined concentration (a 5 wt.% phosphoric acid buffer solution) was brought into contact with the above sample for 1 hour and the protein adsorbed was extracted with 1 % by weight of an aqueous solution of dodecyl sodium sulfate. Thereafter, the amount of protein adsorbed was estimated by a Micro-BCA method. The number of samples was 4 for each Example. (3) Evaluation of amount of platelets adhered by SEM observation Generally speaking, it is known that type of protein adsorbed to the surface of a material and the orientation of the protein on the surface take great part in the adhesion and aggregation of platelets which are the prestages of serious thrombus formation. The activation of platelets adhered such as deformation and release of particles has an influence on their aggregation, thrombus formation in platelets and the promotion of a reaction of coagulation factors, that follow the activation. Therefore, the degree of compatibility of a material with blood can be roughly estimated by observing the state of platelets adhered to the surface of the material after the material is brought into contact with the blood (total blood or component blood). In the present case, the state of platelets adhered to the surface of a polymer which had been brought into contact with human platelet rich plasma (PRP) was observed by SEM. As the PRP was used a supernatant liquid obtained by adding 1/9 part by volume of an aqueous solution containing 3.5 % by weight of trisodium citrate to fresh blood collected from the vein of an upper part of a human arm and centrifuging at 1,000 rpm for 10 minutes. The sample coated with the above copolymer was brought into contact with 0.7 ml of PRP in a culture Petri dish (Falcon, 24 wells) at 37°C for 3 hours. This sample was then washed well with distilled water and fixed in an aqueous solution containing 2.5 % by weight of glutaraldehyde at room temperature over 2 hours, freeze dried and subjected to gold spattering to prepare a sample to be observed. Using this sample, the number of platelets adsorbed to the surface was counted by SEM. The number of samples was 2 for each Example. Table 2 shows the amount of protein adsorbed and the number of platelets adhered. Fig. 2 shows SEM photos of Example 8. It has been obvious from the above results that the polyalkyl ether/polyaryl ether sulfone copolymers of the present invention exhibit excellent antithrombogenic property with a trace amount of protein adsorbed and a small number of platelets adhered. Examples 11 to 17 and Comparative Examples 1 to 3 [Evaluation (1) of antithrombogenic properties of polymer compositions] (1) Surface analysis by ESCA The polyalkyl ether/polyaryl ether sulfone copolymers produced in the above examples and the polymers shown in Table 3 below were dissolved under heating in N-methyl-2-pyrrolidone (NMP) in predetermined blend ratios to produce various dope solutions (concentration of 10 % by weight). Each of these solutions was cast on a Teflon mold and the solvent was extracted with water to obtain a film (thickness of about 0.5 mm) of a polymer composition. The concentration of the above copolymer in the vicinity of the surface of this film was analyzed by ESCA. (2) Evaluation of antithrombogenic properties The amount of protein adsorbed and the number of platelets adhered were obtained in the same manner as in Examples 7 to 10. Table 3 shows the results of (1) and (2) and Fig. 3 shows SEM photos of Examples 13 and 16 and Comparative Example 1. Examples 18 to 20 [Evaluation (2) of antithrombogenic properties of polymer compositions] A film formed from each of polymer compositions ((PEO3000(70)-co-PPES (30))/polyurethane (PU) = 10/90 (composition ratio), (PEO3000 (50)-co-PES (50))/PU = 10/90 and (PEO3000 (50)-co-PES (50))/PMMA = 10/90) was prepared in the same manner as in the above Examples 16 to 22 and measured for the amount of protein adsorbed and the number of platelets adhered. Both amounts were found to be small. It has been obvious from the above results that in the polymer compositions containing the polyalkyl ether/polyaryl ether sulfone or ketone copolymer of the present invention, the copolymer is present on the surface in a high concentration and the polymer compositions are excellent in ability to suppress the adsorption of protein and also suppress the adhesion of platelets significantly. Examples 21 to 22 and Comparative Example 4 (Evaluation of antithrombogenic property of polypropylene having coated surface) (1) Preparation of sample for evaluation A chloroform solution containing 1.0 % by weight of each of the copolymers produced in the above Examples was prepared and a polypropylene film (diameter of 15 mm and thickness of 0.1 mm) was immersed in the solution. After 1 minute, the film was taken out and left in a solvent atmosphere for one night to allow the solvent to volatilize. Thus, samples of polypropylene coated with a film (thickness of 500 µm) of the copolymer were prepared. (2) Evaluation of antithrombogenic property The amount of protein adsorbed and the number of platelets adhered were obtained in the same manner as in the above Examples 7 to 10. Table 4 shows the results of (2). Examples 23 to 25 and Comparative Example 5 (Preparation and evaluation of hollow fiber membrane produced by wet spinning from dope solution of polymer composition comprising polyalkyl ether/polyaryl ether sulfone copolymer and cellulose triacetate) (1) preparation of hollow fiber membrane Each of the polyalkyl ether/polyaryl ether sulfone copolymers prepared in the above Examples and cellulose triacetate (manufactured by Daicel Chemical, number average molecular weight (in terms of polystyrene) of 250,000) was dissolved under heating in N-methyl-2-pyrrolidone (NMP) to prepare a dope solution of a cellulose triacetate composition (concentration of 13 % by weight). This solution was injected into hot water from a nozzle to carry out a wet spinning to obtain an uniform porous membrane. (2) evaluation of hollow fiber membrane This porous membrane was measured for its water-permeability (UFR), dialyzability (DA10000) and sieving coefficient (Sc70000). Water permeability (UFR), dextran 10,000 dialyzability (DA10000) and dextran 70,000 sieving coefficient (SC70000) were evaluated as the dialyzing properties of the hollow fiber. A dialyzer having an effective membrane area of 1.5 m 2 was used for the evaluations. Measurement conditions are as follows. (a) Water-permeability (UFR) A time necessary to permeate 20 ml of pure water through a sheath portion of a hollow fiber at a temperature of 35°C under a differential pressure of 300 mmHg (39,996 Pa) applied between the inside surface and the outside surface of the hollow fiber, was measured. The UFR in ml/m 2 /hr/mmHg of the hollow fiber bundle was calculated from the amount of the water, the permeating surface area of the hollow fibers, the permeating time and the differential pressure. (b) Dextran 10,000 dialyzability (Dextran 10,000 DA) An aqueous solution of 0.02 % by weight of dextran 10,000 was flowed through the hollow spaces of the hollow fibers in the module, at a temperature of 37°C at a flow rate of 200 ml/min, while allowing a portion of dextran 10,000 in the aqueous solution to be dialyzed through the hollow fibers, and the difference in concentration of dextran 10,000 between the supplied dextran 10,000 solution into an end of the module and the delivered dextran 10,000 solution from the opposite end of the module was measured. The dextran 10,000 dialyzability of the hollow fiber bundle was calculated from the concentration difference. (c) Dextran 70,000 sieving coefficient (Dextran 70,000 Sc) An aqueous solution of 0.01 % by weight of dextran 70,000 was subjected as an original solution to a permeation through the sheath portions of hollow fibers under a pressure of 10 mmHg (1,333.2 Pa). The concentrate of dextran 70,000 in the resultant permeated solution was measured. The dextran 70,000 Sc was calculated from the measured data. The test results are shown in Table 5. A hollow fiber membrane prepared from any of cellulose triacetate compositions exhibited almost the same excellent dialyzability as that of cellulose triacetate. It has been obvious from this results that there can be provided a medical membrane material having excellent blood compatibility while retaining excellent membrane characteristics of cellulose triacetate by wet-spinning the cellulose triacetate composition of the present invention.

Claims: A polyalkyl ether/polyaryl ether sulfone copolymer which has a reduced viscosity, measured at 35°C in a mixed solvent of phenol and 1,1,2,2-tetrachloroethane in a weight ratio of 6/4, of at least 0.5 dl/g and which essentially consists of recurring units represented by the following formula (1): - [O-Ar 1 -Z-Ar 2 -O-Ar 3 -]- wherein Ar 1 , Ar 2 and Ar 3 are the same or different and each is a divalent aromatic hydrocarbon group which may be substituted and Z is >SO 2 , and recurring units represented by the following formula (2): -[-(OR) n -O-Ar 3 -]- wherein R is an alkylene group having 2 or 3 carbon atoms or a combination of an alkylene group having 2 or 3 carbon atoms and an alkylene group having 4 carbon atoms, Ar 3 is defined the same as above and n is a numeral which ensures that the molecular weight of a unit represented by -(OR) n - is in the range of 400.to 20,000, the recurring units represented by the above formula (2) being present at least two on an average in one molecule, and the proportion of the unit represented by -(RO) n - in the above formula (2) being 10 to 90 % by weight based on the total weight of the recurring units of the above formulas (1) and (2). The copolymer of claim 1, wherein the proportion of the unit represented by -(OR) n - in the above formula (2) is 30 to 80 % by weight. The copolymer of claim 1 which has a reduced viscosity of at least 1.0 dl/g. The copolymer of claim 1, which is a polyalkyl ether/polyaryl ether sulfone copolymer represented by the formula (1), in which Ar 3 is a divalent aromatic hydrocarbon group which may be substituted and differs from the group of -Ar 1 -SO 2 -Ar 2 -. Use of the polyalkyl ether/polyaryl ether sulfone copolymer (A) as defined in claim 1 for producing a medical material to be used to contact the blood. Use of the polyalkyl ether/polyaryl ether sulfone copolymer (A) as defined in claim 1 for coating the blood-contacting surface of a medical material which is to be used to contact the blood, said medical material being formed from at least one polymer (B) selected from the group consisting of polysulfone, polyaryl ether sulfone, cellulose triacetate, polyvinylchloride, polypropylene, polyurethane and polycarbonate. Use of a polymer composition comprising 1 to 99 parts by weight of the polyalkyl ether/polyaryl ether sulfone copolymer (A) as defined in claim 1 and 1 to 99 parts by weight of the polymer (B) selected from the group consisting of polysulfone, polyaryl ether sulfone, cellulose triacetate, polyvinyl chloride, polypropylene, polyurethane and polycarbonate, as a starting material for producing a medical material to be used to contact the blood, the total weight of the copolymer (A) and the polymer (B) being 100 parts by weight. A polymer composition comprising 1 to 99 parts by weight of the polyalkyl ether/polyaryl ether sulfone copolymer (A) as defined in claim 1 and 1 to 99 parts by weight of the polymer (B), selected from the group consisting of polysulfone, polyaryl ether sulfone, cellulose triacetate, polyvinyl chloride, polypropylene, polyurethane and polycarbonate, the total weight of the copolymer (A) and the polymer (B) being 100 parts by weight. A medical material to be used to contact the blood wherein a portion having at least a surface to be used to contact the blood is formed from a polymer composition comprising the polyalkyl ether/polyaryl ether sulfone copolymer (A) as defined in claim 1 and the polymer (B), selected from the group consisting of polysulfone, polyaryl ether sulfone, cellulose triacetate, polyvinyl chloride, polypropylene, polyurethane and polycarbonate, and the concentration of the copolymer (A) in a depth of about 100 Å from the surface of the portion is higher than the concentration of the copolymer (A) contained in the whole polymer composition forming the portion. The medical material of claim 9, wherein the polymer composition comprises 5 to 20 parts by weight of the copolymer (A) and 80 to 95 parts by weight of the polymer (B), the total weight of both materials being 100 parts by weight, and the proportion of the copolymer (A) in the vicinity of the surface is 50 to 90 parts by weight based on the same standard. The medical material of claim 9 which is hollow yarn for artificial kidney, hollow yarn for artificial lung, catheter, artificial blood vessel, blood-collecting tube, tube for blood circuit, blood container, hemodialysis membrane, blood plasma separation membrane or medical suture. A method for producing a medical material which comprises the steps of: preparing a dope comprising the polyalkyl ether/polyaryl ether sulfone copolymer (A) as defined in claim 1, the polymer (B) selected from the group consisting of polysulfone, polyaryl ether sulfone, cellulose triacetate, polyvinylchloride, polypropylene, polyurethane and polycarbonate and an aprotic polar organic solvent (C) capable of dissolving these, the total concentration of the components (A) and (B) being 1 to 30 % by weight; forming the dope into a thin film; and subjecting the thin film to a wet or dry molding method to produce a medical material having a 1 mm or less thick portion to be used to contact the blood. The method of claim 12, wherein the aprotic polar organic solvent is at least one selected from the group consisting of tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, dimethylformamide, dimethylacetoamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, methylene chloride and chloroform.

Inventors: KAWAGUCHI TAKEYUKI, KUWAHARA HIROAKI, MATSUMURA SHUNICHI, OHMORI SATORU, KAWAGUCHI, TAKEYUKI, KUWAHARA, HIROAKI, MATSUMURA, SHUNICHI, OHMORI, SATORU
Applicants: TEIJIN LTD, TEIJIN LIMITED
Application year: 1996
Main classification: C08G75
IPC codes: C08L81, B01D71, C08L71, C08G75, C08G65, B01D67, C08L67