Patent Publication Number: US-2018028726-A1

Title: Antithrombotic block copolymer

Description:
TECHNICAL FIELD 
     The present invention relates to an antithrombotic block copolymer. 
     BACKGROUND ART 
     Polymers, ceramics, glasses, metals, and like materials having excellent mechanical properties (high strength, high elasticity or flexibility) and moldability have been used for medical devices. Among these, medical devices used in contact with blood, such as artificial kidney membranes, plasma-separating membranes, artificial lung membranes, catheters, stents, and artificial blood vessels, are required to have antithrombogenicity. 
     However, most of the above materials do not have antithrombogenicity. When these materials are used, they must be used with an anticoagulant agent, such as heparin. 
     However, heparin is known to have adverse effects on blood, such as a reduction in the number of platelets. Therefore, there is a time constraint on the continuous usage of heparin. Further, since a raw material for producing heparin is generally obtained from bovine or porcine intestinal mucosa, infection risk has been cited. 
     To solve such problems, a method comprising coating the surface in contact with blood with a heparin-containing material and immobilizing the heparin has been used to achieve antithrombogenicity while making use of the characteristics of various materials. However, even this method has a problematic reduction in antithrombogenicity due to the elution of heparin. Thus, there is a need to develop a heparin-free coating agent having excellent antithrombogenicity. 
     On the other hand, biocompatible polymers having antithrombogenicity are known to have water, called intermediate water, which is weakly bound to polymer chains by interactions with the polymer chains. The antithrombogenicity due to the presence of this intermediate water is presumed to be achieved based on the following mechanism. Biological components (e.g., blood cells, platelets, plasma, and like blood-derived proteins) form a hydration shell and are thereby stabilized in blood. However, when unfreezable water on a material surface is contacted with the hydration shell and disrupts the hydration shell, adsorption of biological components on the material surface occurs. The presence of the intermediate water between the hydration shell of a biological component and unfreezable water on the material surface prevents direct contact between the hydration shell and unfreezable water, thereby exhibiting antithrombogenicity. 
     For example, a homopolymer of 2-methacryloyloxyethyl phosphorylcholine (hereinafter referred to as “MPC”) and a homopolymer of 2-methoxyethyl acrylate (hereinafter referred to as “MEA”) are known as biocompatible polymers having antithrombogenicity. 
     However, because the homopolymer of MPC is soluble in water and readily dissolves upon contact with a body fluid, such as blood, the homopolymer of MPC cannot be used as a medical material. On the other hand, the homopolymer of MBA is in a rubber state at room temperature, and thus has poor morphological stability. 
     Accordingly, Patent Literature (PTL) 1 proposes a medical device comprising a base material whose surface is coated with a random copolymer of MPC and a hydrophobic monomer. 
     Patent Literature (PTL) 2 proposes a medical polymer material comprising a base material whose surface is coated with a material obtained by crosslinking a random copolymer of MPC and an epoxy-containing monomer with a compound having two or more amino groups and/or two or more carboxyl groups. 
     Patent Literature (PTL) 3 proposes a medical instrument comprising a base material whose surface is coated with a block copolymer comprising MEA and a (meth)acrylamide or a derivative thereof. 
     The technique disclosed in PTL 1 incurs few problems if the contact time with blood is short. However, since the adhesion of the coating layer (coating) of a random copolymer to the base material is weak, long-term use may result in gradual elution of the copolymer coating into blood or omission of the copolymer from the base material surface, thus leading to a problem such that blood compatibility does not last long. 
     The technique disclosed in PTL 2, in which a copolymer is immobilized by a covalent bond, requires a pretreatment on the base material surface and involves many steps, and is therefore complicated. 
     The technique disclosed in PTL 3 has insufficient adhesion to the base material because of the use of N,N-substituted (meth)acrylamide, which is more hydrophilic than MEA. Therefore, long-term excellent antithrombogenicity is difficult to obtain. 
     Thus, there is a need to develop a block copolymer that is satisfactory in terms of both adhesion to a base material and antithrombogenicity. 
     CITATION LIST 
     PTL 
     PTL 1: JPH3-039309A 
     PTL 2: JPH7-184989A 
     PTL 3: JP2013-056146A 
     SUMMARY OF INVENTION 
     Technical Problem 
     An object of the present invention is to provide a block copolymer that has excellent adhesion to a base material, and that imparts excellent antithrombogenicity to the base material surface. Another object of the present invention is to provide a medical device comprising the block copolymer. 
     Solution to Problem 
     The present inventors conducted extensive research to achieve the above object. As a result, the inventors found that excellent antithrombogenicity can be imparted to the surface of a base material, and that enhanced adhesion of a block copolymer to the base material can also be achieved by using a block copolymer comprising a specific structural unit capable of containing intermediate water. The present inventors have accomplished the present invention through further research based on the above findings. 
     Specifically, the present invention provides the following block copolymers and medical devices comprising the block copolymers. 
     Item 1. 
     A block copolymer comprising an A block and a B block, the A block being being more hydrophobic than the A block. 
     Item 2. 
     The block copolymer according to Item 1, wherein the A block is a polymer block comprising a vinyl monomer-derived structural unit capable of containing intermediate water. 
     Item 3. 
     The block copolymer according to Item 1 or 2, wherein the B block is a polymer block comprising a vinyl monomer-derived structural unit. 
     Item 4. 
     The block copolymer according to any one of Items 1 to 3, wherein the A block and the B block are present at a molar ratio (A:B) of 90:10 to 10:90. 
     Item 5. 
     The block copolymer according to any one of Items 1 to 4, wherein the block copolymer has a weight average molecular weight W of 10,000 to 1,000,000. 
     Item 6. 
     The block copolymer according to any one of Items 1 to 5, wherein the block copolymer has a molecular weight distribution (Mw/Mn) of 3.0 or less. 
     Item 7. 
     The block copolymer according to any one of Items 1 to 6, wherein the block copolymer is a living radical polymerization reaction product. 
     Item 8. 
     A block copolymer composition comprising intermediate water and the block copolymer according to any one of Items 1 to 7. 
     Item 9 
     An antithrombotic coating agent comprising the block copolymer according to any one of claims  1  to  7 . 
     Item 10. 
     A medical device comprising a base material coated with the antithrombotic coating agent according to Item 9. 
     Item 11. 
     A method for producing the block copolymer according to any one of Items 1 to 7, 
     the method using a living radical polymerization, 
     the method comprising: 
     polymerizing either A block-forming monomer (s) or B block-forming monomer(s) to form a first block polymer; and 
     thereafter polymerizing the other of the A block-forming monomer (s) or B block-forming monomer (s) to form a second block polymer. 
     Item 12. 
     The method according to Item 11, wherein an organic tellurium compound is used in the living radical polymerization. 
     Advantageous Effects of Invention 
     According to the present invention, a block copolymer that has excellent adhesion to a base material and that imparts excellent antithrombogenicity to a base material surface can be provided. Further, a medical device that has excellent adhesion to a base material and excellent antithrombogenicity can be provided by using the block copolymer. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  shows the peaks in the differential scanning calorimetry (DSC) profile of the block copolymer obtained in Example 1. 
         FIG. 2  shows the peaks in the differential scanning calorimetry (DSC) profile of the block copolymer obtained in Comparative Example 4. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A preferred embodiment of the present invention is described below. The following descriptions of the embodiment are given by way of illustration, and not of limitation. 
     1. Block Copolymer 
     The block copolymer of the present, invention comprises an A block and a B block. The A block is capable of containing intermediate water. The B block is more hydrophobic than the A block. 
     The A block can also be paraphrased as “A segment.” The B block can also be paraphrased as “B segment.” 
     Each constituent etc. of the block copolymer of the present invention are explained below. 
     1-1. A Block 
     The A block is a polymer block comprising a vinyl monomer-derived structural unit capable of containing intermediate water. 
     The “vinyl monomer-derived structural unit capable of containing intermediate water” refers to a structural unit that is foamed by radical polymerization of a vinyl monomer, and that can contain intermediate water. Specifically, the “vinyl monomer-derived structural unit” refers to a structural unit obtained by conversion of a radically polymerizable carbon-carbon double bond in a vinyl monomer to a carbon-carbon single bond. 
     In the present invention, intermediate water refers to water in a state in which an exothermic peak based on a low-temperature crystallization of water is observed at or below 0° C. in an elevated temperature process from −100° C. in measurement using a differential scanning calorimeter (DSC). The differential scanning calorimeter is not particularly limited. For example, a DSC-7000 instrument (produced by Seiko Instruments Inc.) can be used. 
     The calorific value of the exothermic peak is not particularly limited. For example, in view of the presence of a sufficient amount of intermediate water, the calorific value is preferably 1 J/g or more, more preferably 1 to 120 J/g, and still more preferably 3 to 100 J/g. 
     The vinyl monomer used as a starting material for the A block is not particularly limited, as long as a polymer block comprising a vinyl monomer-derived structural unit capable of containing intermediate water can be obtained. Examples include vinyl monomers represented by the following formulas (1) to (7): 
     
       
         
         
             
             
         
       
     
     (wherein R 1  is a hydrogen atom or methyl.
 
R 2  is alkylene having 2 or 3 carbon atoms,
 
R 3  is methyl or ethyl,
 
n is an integer of 1 to 10);
 
     
       
         
         
             
             
         
       
     
     (R 4  is a hydrogen atom or methyl,
 
R is alkylene having 2 or 3 carbon atoms, and
 
m is an integer of 2 to 13);
 
     
       
         
         
             
             
         
       
     
     (wherein R 7  is a hydrogen atom or methyl); 
     
       
         
         
             
             
         
       
     
     (R 8  is a hydrogen atom or methyl,
 
R 9  and R 12  are independently alkylene having 1 to 6 carbon atoms,
 
R 10  and R 11  are independently alkyl having 1 to 4 carbon atoms, and
 
Q is carboxylate-anion (COO − ) or sulfo-anion (SO − );
 
     
       
         
         
             
             
         
       
     
     (R 13  is a hydrogen atom or methyl,
 
R 14  and R 15  are independently alkylene having 1 to 6 carbon atoms, and
 
R 16 , R 17 , and R 18  are independently alkyl having 1 to 4 carbon atoms);
 
     
       
         
         
             
             
         
       
     
     (wherein R 19  is a hydrogen atom or methyl, and
 
R 20  is alkylene having 2 or 3 carbon atoms); and
 
     
       
         
         
             
             
         
       
     
     (wherein o is an integer of 1 to 3). 
     The block copolymers of the present invention produced by using vinyl monomers represented by formulas (1) to (7) contain, as the A block, structural units represented by the following formulas (1′) to (7′): 
     
       
         
         
             
             
         
       
     
     (wherein R 1 , R 2 , R 3 , and n are as defined above, and each * represents a bond); 
     
       
         
         
             
             
         
       
     
     (wherein R 4 , R 5 , and m are as defined above, and each * represents a bond); 
     
       
         
         
             
             
         
       
     
     (wherein R 7  is as defined above, and each * represents a bond); 
     
       
         
         
             
             
         
       
     
     (wherein R 8 , R 9 , R 10 , R 11 , R 12 , and Q are as defined above, and each * represents a bond); 
     
       
         
         
             
             
         
       
     
     (wherein R 13 , R 14 , R 15 , R 16 , R 17 , and R 18  are as defined above, and each. * represents a bond); 
     
       
         
         
             
             
         
       
     
     (wherein R 19  and R 20  are as defined above, and each * represents a bond); and 
     
       
         
         
             
             
         
       
     
     (wherein o is as defined above, and each * represents a bond). 
     Examples of compounds represented by Formula (1) include a wide variety of known compounds that fall within the scope of compounds of Formula (1). Among these compounds, 2-methoxyethyl acrylate, 2-ethoxyethyl acrylate, 2-(2-ethoxyethoxy)ethyl acrylate, polyethylene glycol monomethyl acrylate, polypropylene glycol monomethyl acrylate, polyethylene glycol monomethyl methacrylate, and polypropylene glycol monomethyl methacrylate are preferable. 
     Examples of compounds represented by Formula (2) include a wide variety of known compounds that fall within the scope of compounds of Formula (2). Among these compounds, polyethylene glycol monoacrylate, polypropylene glycol monoacrylate, polyethylene glycol monomethacrylate, and polypropylene glycol monomethacrylate are preferable. 
     Examples of compounds represented by Formula (3) include a wide variety of known compounds that fall within the scope of compounds of Formula (3). Among these compounds, tetrahydrofurfuryl acrylate is preferable. 
     Examples of compounds represented by Formula (4) include a wide variety of known compounds that fall within the scope of compounds of Formula (4). Among these compounds, N-methacryloiloxyethyl-N,N-dimethylammonium-α-N-methylcarboxybetaine and N-(3-sulfopropyl)-N-(meth)acryloyloxyethyl-N,N-dimethylammonium betaine are preferable. 
     Examples of compounds represented by Formula (5) include a wide variety of known compounds that fall within the scope of compounds of Formula (5) Among these, 2-methacryloiloxyethyl phosphorylcholine is preferable. 
     Examples of compounds represented by Formula (6) include a wide variety of known compounds that fall within the scope of compounds of Formula (6). Among these, 2-hydroxyethyl methacrylate is preferable. 
     Examples of compounds represented by Formula. (7) include a wide variety of known compounds that fall within the scope of Formula (7). Among these, 1-vinyl-2-pyrrolidone is preferable. 
     The vinyl monomers used to prepare the A block may be used singly, or in a combination of two or more. For example, the A block may comprise a copolymer of a structural unit comprising an a1 block and a structural unit comprising an a2 block. 
     The A block may consist of only a vinyl monomer-derived structural unit as described above, or may further comprise one or more other structural units, as long as the A block has intermediate water when the obtained block copolymer contains water. When the A block contains other structural units, the amount of the other structural units in the A block is preferably 20 mol % or less. Each structural unit of the A block may be contained in any form, such as a random copolymer or a block copolymer. In terms of uniformity, each structural unit is preferably contained in the form of a random copolymer. 
     1-2. B Block 
     The B block is a polymer block that is more hydrophobic than the A block, and that comprises a vinyl monomer-derived structural unit. 
     The vinyl monomer used to prepare the B block is not particularly limited, as long as the B block is more hydrophobic than the A block, and can be selected from known vinyl monomers. 
     The term “hydrophobic” refers to a property of exhibiting a weak interaction with water, and having low affinity with water. Accordingly, the ratio miscible with water, i.e., solubility, serves as a hydrophobic index. 
     The vinyl monomer for obtaining the B block that is more hydrophobic than the A block usually has a solubility in 20° C. water of less than 50 mass %, preferably less than 40 mass %, and more preferably less than 30 mass %. 
     Specifically, examples of vinyl monomers used in the B block include (meth)acrylic acid esters, such as (meth) acrylic acid alkyl esters, alicyclic alkyl esters of (meth)acrylic acid, (meth)acrylic acid aryl esters, and N,N-disubstituted aminoalkyl (meth)acrylate; aromatic vinyl monomers; heterocyclic ring-containing unsaturated monomers; and the like. 
     In the present invention, “(meth)acrylic” means “at least one of acrylic and methacrylic.” For example, “(meth)acrylic acid” means “at least one of acrylic acid and methacrylic acid.” 
     In this specification, “n-” means normal, “s-” means secondary (sec-), and “t-” means tertiary (tert-). 
     The (meth)acrylic acid alkyl ester is not particularly limited. Examples include (meth)acrylic acid alkyl esters, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, s-butyl (meth)acrylate, t-butyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, n-dodecyl (meth)acrylate, n-stearyl (meth)acrylate, and the like. 
     The alicyclic alkyl ester of (meth)acrylic acid is riot particularly limited. Examples include cyclohexyl (meth)acrylate, cyclohexylmethyl (meth)acrylate, cyclododecyl (meth)acrylate, bornyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and the like. 
     The (meth)acrylic acid aryl ester is not particularly limited. Examples include benzyl (meth)acrylate, phenyl (meth)acrylate, phenoxyethyl (meth)acrylate, and the like. 
     Examples of N,N-disubstituted aminoalkyl (meth)acrylates include N,N-dimethylaminopropyl (meth)acrylate, N,N-dimethylaminobutyl (meth)acrylate, N,N-diethylaminoethyl (meta)acrylate, N,N-diethylaminopropyl (meth)acrylate, N,N-diethylaminobutyl (meth)acrylate, N,N-dipropylaminoethyl (meth)acrylate, N,N-dibutylaminoethyl (meth)acrylate, diethylaminopropyl (meth)acrylate, N,N-dibutylaminobutyl (meth)acrylate, N,N-dihexylaminoethyl (meth)acrylate, N,N-dioctylaminoethyl (meth acrylate, and the like. 
     The aromatic vinyl monomer is not particularly limited. Examples include styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-methoxystyrene, 3-methoxystyrene, 4-methoxystyrene, 2-hydroxymethylstyrene, 1-vinylnaphthalene, and the like. 
     The heterocyclic ring-containing unsaturated monomer is not particularly limited. Examples include 2-vinylpyridine, 3-vinylpyridine, 4-vinylpyridine, and the like. 
     The vinyl monomers used to prepare the B block may be used singly, or in a combination of two or more. For example, the B block may comprise a copolymer of a structural unit comprising a b1 block and a structural unit comprising a b2 block. 
     The B block may consist of only a vinyl monomer-derived structural unit as described above, or may further comprise one or more other structural units, as long as the B block is more hydrophobic than the A block. When the B block comprises other structural units, the amount of the other structural units in the B block is preferably 5 mol % or less. Each structural unit of the B block may be contained in any form, such as a random copolymer or a block copolymer. In terms of uniformity, each structural unit is preferably contained in the form of a random copolymer. 
     1-3. Block Copolymer 
     The block copolymer of the present invention comprises an A block capable of containing intermediate water, and a B block that is more hydrophobic than the A block, and has intermediate water when the block copolymer contains water. The block copolymer is considered to phase-separate on the surface of a base material in such a manner that the B block is in contact with the base material, and the A block is positioned on the contact surface with the blood and has intermediate water. As a result, excellent antithrombogenicity can be exhibited over a long period of time. 
     In the block copolymer of the present invention, the molar ratio (A:B) of the A block to the B block is not particularly limited, and is preferably 90:10 to 10:90, and more preferably 85:15 to 40:60. 
     The weight average molecular weight (Mw) of the block copolymer is not particularly limited, and is usually in the range of 10,000 or more, preferably 10,000 to 1,000,000, more preferably 20,000 to 500,000, and still more preferably 30,000 to 100,000. 
     The molecular weight distribution (PDI) of the block copolymer is preferably 3.0 or less, and more preferably 2.0 or less. In the present invention, the molecular weight distribution (PDI) is determined by the following formula: 
       (Weight average molecular weight of block copolymer (Mw))/(Number average molecular weight of block copolymer (Mn)). 
     A smaller PDI indicates a copolymer with a narrow molecular weight distribution and a more uniform molecular weight. When the value is 1, the molecular weight distribution is the narrowest. Conversely, a larger PDI indicates the presence of many copolymers with a molecular weight smaller than that of the intended copolymer, and elution of low-molecular-weight copolymers is feared. 
     The arrangement of polymer (A) and polymer (B) in the block copolymer of the present invention is not particularly limited, as long as the block copolymer has the various properties described above. For example, a diblock type copolymer (A-B), triblock type copolymers (A-B-A and B-A-B), and like block copolymers are preferably used. When an A-B-A type triblock copolymer is formed, the two A blocks at both ends may be the same or different. When a B-A-B type triblock copolymer is formed, the two B blocks at both ends may be the same or different. 
     The water content of the block copolymer of the present invention is usually 1 to 50 mass %, preferably 2 to 40 mass %, and more preferably 3 to 35 mass %. 
     When a base material is coated with the block copolymer of the present invention to obtain a medical device, the elution rate is usually in the range of 0 to 2 mass %, and preferably 0 to 1 mass %. 
       2 . Method for Producing the Block Copolymer 
     The method for producing the block copolymer of the present invention is not particularly limited. Examples include block polymerization methods, such as living radical polymerization methods. The block copolymer of the present invention is obtained by sequentially subjecting monomers to a polymerization reaction by such a block polymerization method. 
     The method for producing the block copolymer of the present invention may comprise first producing an A block (an A segment) by a polymerization reaction of monomer(s), and then polymerizing B block (B segment) monomer(s) onto the A block; first producing a B block and then polymerizing A block monomer(s) onto the B block; or separately producing an A block and a B block by polymerization reactions of monomers, and then coupling the A block and the B block. For example, the method for producing the block copolymer of the present invention is a method using a living radical polymerization, and comprises the steps of polymerizing either A block-forming monomer(s) or B block-forming monomer(s) to form a first block polymer, and thereafter polymerizing the other of the A block-forming monomer(s) or B block-forming monomer(s) to form a second block polymer. 
     The arrangement of the A block and B block in the block copolymer of the present invention is not necessarily limited as long as the resulting block copolymer has the various properties described above. For example, a diblock type polymer (A-B), triblock type polymers (A-B-A and B-A-B), or like block polymers are preferably used. 
     When conventional radical polymerization methods are used, not only an initiation reaction and a growth reaction, but also a termination reaction and a chain transfer reaction occur. The termination reaction or the chain transfer reaction causes deactivation of the growth terminal, and tends to form a mixture of polymers having various molecular weights and a non-uniform composition. The living radical polymerization method is preferable because this method allows, while maintaining the convenience and general versatility of radical polymerization, the growth terminal to grow without deactivation, due to decreased likelihood of a termination reaction and a chain transfer reaction; accordingly, precise control of the molecular structure and production of a polymer having a uniform composition are easy. The living radical polymerization method includes the following methods that are different in terms of the method for stabilizing the polymerization growth terminal: a method using a transition metal catalyst (the atom transfer radical polymerization (ATRP) method); a method using a sulfur-based reversible chain transfer agent (the reversible addition-fragmentation chain transfer (RAFT) method); a method using an organic tellurium compound (the organotellurium-mediated living radical polymerization (TERP) method); and like methods. Among these methods, the TRAP method is preferable in view of monomer diversity, molecular weight control in the polymer range, uniform composition, and coloring. 
     The TERP method is a method for polymerizing a radical polymerizable compound using an organic tellurium compound as a polymerization initiator. Examples include the methods disclosed in WO2004/14848 and WO2004/14962. 
     Specific examples include polymerization methods using the following (a) to (d). 
     (a) an organic tellurium compound represented by Formula (8) shown below,
 
(b) a mixture of an organic tellurium compound represented by Formula (8) and an azo polymerization initiator,
 
(c) a mixture of an organic tellurium compound represented by Formula (8) and an organic ditellurium compound represented by Formula (9) shown below, or
 
(d) a mixture of an organic tellurium compound represented by Formula (8), an azo polymerization initiator, and an organic ditellurium compound represented by Formula (9),
 
     
       
         
         
             
             
         
       
     
     (wherein R 21  is alkyl having 1 to 8 carbon atoms, aryl, or heteroaryl, R 22  and R 23  are each a hydrogen atom or alkyl having 1 to 8 carbon atoms, R 24  is alkyl having 1 to 8 carbon atoms, aryl, heteroaryl, acyl, amide, oxycarbonyl, or cyano), 
       (R 21 Te) 2    (9)
 
     (wherein R 21  is as defined above). 
     Specific examples of organic tellurium compounds represented by Formula (8) include (methyltellanylmethyl)benzene, (methyltellanylmethyl)naphthalene, ethyl-2-methyl-2-methyltellanyl-propionate, ethyl-2-methyl-2-n-butyltellanyl-propionate, (2-trimethylsiloxyethyl)-2-methyl-2-methyltellanyl-propionate, (2-hydroxyethyl)-2-methyl-2-methyltellanyl-propionate, and (3-trimethylsilylpropargyl)-2-methyl-2-methyltellanyl-propionate, and the like. 
     Specific examples of organic ditellurium compounds represented by Formula (9) include dimethyl ditelluride, diethyl ditelluride, di-n-propyl ditelluride, diisopropyl ditelluride, dichloropropyl di-n-butyl ditelluride, di-s-butyl ditelluride, di-t-butyl ditelluride, dichlorobutyl ditelluride, diphenyl ditelluride, bis-(p-methoxypheny) ditelluride, bis-(p-aminophenyl) ditelluride, bis-(p-nitrophenyl) ditelluride, bis-(p-cyanophenyl) ditelluride, bis-(p-sulfonylphenyl) ditelluride, dinaphthyl ditelluride, dipyridyl ditelluride, and the like. 
     Any azo polymer nation initiators that are used in usual radical polymerization can be used as the azo polymerization initiator. Example include 2,2′-azobis(isobutyronitrile) (AIBN), 2,2′-azobis(2-methylbutyronitrile) (AMBN), 2,2′-azobis(2,4-dimethylvaleronitrile) (ADVN), 1,1′-azobis(1-cyclohexanecarbonitrile) (ACHN), dimethyl-2,2′-azobisisobutyrate (MAIB), 4,4′-azobis(4-cyanovaleric acid) (ACVA), 1,1′-azobis(1-acetoxy-1-phenylethane), 2,2′-azobis(2-methylbutylamide), 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70), 2,2′-azobis(2-methylamidinopropane) dihydrochloride, 2,2′-azobis[2-(2-imidazolin-2-yl)propane], 2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], 2,2′-azobis(2,4,4-trimethylpentane), 2-cyano-2-propylazoformamide, 2,2′-azobis(N-butyl-2-methylpropionamide), 2,2′-azobis(N-cyclohexyl-2-methylpropionamide), and the like. 
     The amount of the compound of Formula (8) in each of (a), (b), (c), and (d) described above can be appropriately adjusted according to the physical properties of the desired block copolymer. The compound of Formula (8) can be typically used in an amount of 0.05 to 50 mmol per mole of the starting monomer. 
     When the compound of Formula (8) is used with an azo polymerization initiator as described in (b), the amount of the azo polymerization initiator can be typically 0.01 to 10 moles per mole of the compound of Formula (8). 
     When the compound of Formula (8) is used with the compound of Formula (9) as described in (c), the amount of the compound of Formula (9) can be typically 0.01 to 100 moles per mole of the compound of Formula (8). 
     When the compound of Formula (8) is used with the compound of Formula (9) and an azo polymerization initiator as described in (d), the amount of the azo polymerization initiator can be typically 0.01 to 100 moles per mole of the total amount of the compound of Formula (8) and the compound of Formula (9). 
     The polymerization reaction in the production method of the present invention is performed using a solvent commonly used in radical polymerization (an organic solvent or an aqueous solvent) and stirring the mixture, although the polymerization reaction can also be performed in the absence of a solvent. 
     Usable organic solvents are not particularly limited. Examples include benzene, toluene, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetone, 2-butanone (methyl ethyl ketone), dioxane, hexafluoroisopropanol, chloroform, carbon tetrachloride, tetrahydrofuran (THF), ethyl acetate, trifluoromethylbenzene, and the like. 
     Examples of aqueous solvents include water, methanol, ethanol, isopropanol, n-butanol, ethyl cellosolve, butyl cellosolve, 1-methoxy-2-propanol, diacetone alcohol, and the like. 
     The amount of the solvent can be appropriately adjusted. For example, the amount of the solvent is typically in the range of 0.01 to 50 ml, preferably 0.05 to 10 ml, and more preferably 0.1 to 1 ml, per gram of the starting monomer. 
     The reaction temperature and the reaction time can be appropriately adjusted according to the molecular weight or molecular weight distribution of the obtained copolymer. The mixture is typically stirred at 0 to 150° C. for 1 minute to 100 hours. The TERP method can achieve a high yield and precise molecular weight distribution even at a low polymerization temperature and in a short polymerization time period. 
     After completion of the polymerization reaction, the desired copolymer can be isolated from the obtained reaction mixture by usual separation and purification means. 
     3. Block Copolymer Composition 
     The block copolymer composition of the present invention is a composition comprising intermediate water and a block copolymer of the present invention. 
     Water is present inside or on the surface of the block copolymer in the block copolymer composition of the present invention. The following three forms of water are considered to be present: 
     (1) free water that has a weak interaction with the A block polymer capable of containing intermediate water, and melts at 0° C.;
 
(2) unfreezable water that has a strong interaction with the A block polymer capable of containing intermediate water, and that does not freeze even at −100° C.; and
 
(3) intermediate water that has an intermediate level of interaction, i.e., an interaction stronger than the interaction of free water and weaker than the interaction of unfreezable water, and that freezes at a temperature of less than 0° C.
 
     Biological components, such as hemocytes or like cell proteins, form a hydration shell and are thereby stabilized in blood. 
     However, conventional polymer materials, which have only an unfreezable water layer on the material surface, are known to destroy the hydration shell of cell proteins, such as hemocytes, thus resulting in adsorption of biological components on the material surface as a thrombus (JP2004-161954A). 
     In contrast, the block copolymer of the present invention has intermediate water inside or on the surface of the copolymer. Due to the presence of the intermediate water, the block copolymer of the present invention is considered to exhibit antithrombogenicity without destroying the hydration shell of cell proteins, such as hemocytes. 
     Unfreezable water may be present between the block copolymer of the present invention and intermediate water. Intermediate water is considered to be present between unfreezable water and the hydration shell of a biological component. 
     The ratio (mass ratio) of intermediate water and the block copolymer of the present invention in the block copolymer composition of the present invention is not particularly limited. The ratio of intermediate water to the block copolymer is usually in the range of 1:99 to 30:70, preferably 1.5:98.5 to 25:75, and more preferably 2:98 to 20:80. 
     The method of producing the block copolymer composition of the present invention can form the block copolymer composition by bringing the block copolymer of the present invention into contact with a water-containing solution (e.g., water or a biological component such as blood) to allow the block copolymer to contain water upon which water molecules are hydrogen-bonded to polar groups of polymer side chains. 
     4. Antithrombotic Coating Agent 
     The block copolymer of the present invention can be used as an antithrombotic coating agent. The antithrombotic coating agent of the present invention is characterized by containing the block copolymer of the present invention. The antithrombotic coating agent can be mixed, dispersed, or dissolved in a solvent, if necessary, and then used. 
     Examples of usable solvents include water, organic solvents, or mixed solvents thereof. The type and concentration of the solvent used vary depending on, for example, the composition and molecular weight of the obtained block copolymer, and the type, and surface texture of the base material to be coated, and can be suitably selected. 
     In the present invention, as a base material (for a medical device) subjected to antithrombotic coating, various materials can be used. Examples include polyvinyl chloride, polycarbonate, polyethylene terephthalate, polyethylene, polypropylene, polymethylpentene, thermoplastic polyurethane, thermosetting polyurethane, silicone rubber such as polydimethylsiloxane having a crosslinked portion, polymethylmethacrylate, poly vinylidene fluoride, tetrafluoropolyethylene, polysulfone, polyethersulfone, polyacetal, polystyrene, ABS, and like resins and mixtures of these resins; metals such as stainless steel, titanium, and aluminum; glass; ceramics; and the like. 
     The base material may be in any shape or form, such as plates, sheets, straw, pipes, fabrics, globular shape, nonwoven fabrics, and porous forms. 
     The coating agent of the present invention can form a uniform coating film on the base material. 
     The method for coating the base material of a medical device etc. with the coating agent is not particularly limited. 
     Specific examples of coating methods include an immersion method comprising immersing a base material in the composition for a long period of time; a spraying method comprising spraying over a base material; a method of application using a brush, a flocked brush, etc.; a method comprising bringing a base material into contact with a solution of the coating agent; and like methods. Among these methods, a method comprising bringing a base material into contact with a solution of the coating agent is preferable in view of ease of control of a coating layer etc. To coat a base material with the coating agent, one type of such coating methods may be performed several times, or two or more types of such coating methods may be performed several times. 
     5. Medical Device 
     The medical device of the present invention is obtained by coating a base material with the antithrombotic coating agent of the present invention. The medical device of the present invention can be provided with greatly enhanced antithrombogenicity, and the entire medical device surface or a selected portion thereof is coated with the antithrombotic coating agent of the present invention. The medical device of the present invention can be used as is after being coated or after being further subjected to a priming treatment with physiological saline or the like. 
     The medical device of the present invention is not particularly limited, as long as it is used in direct contact with the blood. Examples include catheters (e.g., catheters, balloons of balloon catheters, and guide wires), artificial blood vessels, blood vessel bypass tubes, artificial valves, blood filters, plasma separation devices, artificial internal organs (e.g., artificial lungs, artificial livers, and artificial hearts), blood transfusion tools, extracorporeal circulation blood circuits, blood bags, adhesion preventing films, wound dressings, and the like. 
     EXAMPLES 
     The present invention is described below in detail with reference to Examples. However, the present invention is not limited to the Examples. In the Examples and Comparative Examples below, various physical properties were measured using the following instruments. 
     Monomer-to-Polymer Conversion 
       1 H-NMR was measured using a 500-MHz NMR instrument (AVANCE500, produced by Bruker BioSpin). The monomer-to-polymer conversion was calculated from the integration ratio of vinyl groups of the starting monomers to polymer peaks. 
     Composition Ratio 
     H-NMR was measured using a 500-MHz NMR instrument (AVANCE500, produced by Bruker BioSpin). The composition ratio was calculated from the integration ratio of each polymer peak. 
     Weight Average Molecular Weight (Mw) and Molecular Weight Distribution (PDI) 
     A calibration curve was prepared using a GPC system (HLC-8320GPC, produced by Tosoh Corporation), two TSKgel SuperMultipore HZ-H columns (φ4.6×150, produced by Tosoh Corporation, Tokyo, Japan), tetrahydrofuran as a mobile phase, and polystyrene (Tosoh-TSK Standard) as a standard substance to determine the weight average molecular weight (Mw)) and the number average molecular weight (Mn) of each sample. The molecular weight distribution (PDI) was calculated from these measurement values. 
     Example 1 
     Poly(2-methoxyethyl acrylate)-polystyrene-poly(2-methoxyethyl acrylate) 
     In a nitrogen-purged glove box, a mixture of 2.05 g (15.8 mmol) of 2-methoxyethyl acrylate (hereinafter referred to as “MEA”), 22.9 μl (0.10 mmol) of ethyl-2-methyl-2-n-butyltellanyl-propionate (hereinafter referred to as “BTEE”), 4.9 mg (0.020 mmol) of 1,1′-azobis(1-cyclohexanecarbonitrile) (hereinafter referred to as “ACHN”), and 2.05 g of propylene glycol monomethyl ether acetate (hereinafter referred to as “PMA”) was prepared. The resulting mixture was allowed to react at 90° C. for 21 hours. The monomer-to-polymer conversion was 100%, Mw was 27,370, and PDI was 1.27. 
     After 0.90 g (8.64 mmol) of styrene (hereinafter referred to as “St”), 12.2 mg (0.050 mmol) of ACHN, and 0.9 g of PMA were added to the obtained solution, the resulting mixture was allowed to react at 90° C. for 46 hours. The monomer-to-polymer conversion was 91%, Mw was 37,320, and PDI was 2.0. 
     After 2.05 g (15.8 mmol) of MEA, 4.9 mg (0.020 mmol) of ACHN, and 2.05 g of PMA were added to the obtained solution. The resulting mixture was allowed to react at 90° C. for 26 hours. The monomer-to-polymer conversion was 99%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 4.06 g of poly(2-methoxyethyl acrymate)-polystyrene-poly(2-methoxyethyl acrylate). Mw was 52,190, PDI was 1.89, and the composition ratio of poly(2-methoxyethyl acrylate)/polystyrene was 81/19. 
     Example 2 
     Poly(2-methoxyethyl acrylate)-polystyrene-poly(2-methoxyethylacrylate) 
     In a nitrogen-purged glove box, a mixture of 1.35 g (10.4 mmol) of MEA, 22.9 μl (0.10 mmol) of BTEE, 4.9 mg (0.020 mmol) of ACHN, and 1.35 g of PMA was allowed to react at 90° C. for 21 hours. The monomer-to-polymer conversion was 100%, Mw was 18,850, and PDI was 1.22. 
     After 2.30 g (22.1 mmol) of St, 12.2 mg (0.050 mmol) of ACHN, and 2.30 g of PMA were added to the obtained solution, the resulting mixture was allowed to react at 90° C. for 46 hours. The monomer-polymer conversion was 89%, Mw was47,500, and PDI was 1.76. 
     After 1.35 g (10.4 mmol) of MEA, 4.9 mg (0.020 mmol) of ACHN, and 1.35 g of PMA were added to the obtained solution, the resulting mixture was allowed to react at 90° C. for 26 hours. After 3.3 mg (0.020 mmol) of 2,2′-azobis(isobutyronitrile) (hereinafter referred to as “AIBN”) was added, the resulting mixture was allowed to react at 60° C. for 68 hours. The monomer-to-polymer conversion was 98%. 
     After the completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 4.53 g of poly(2-methoxyethyl acrylate)-polystyrene-poly(2-methoxyethyl acrylate). Mw was 59,830, PDI was 1.75, and the composition ratio of poly(2-methoxyethyl acrylate)/polystyrene was 49/51. 
     Example 3 
     Poly(2-methoxyethyl acrylate)-polystyrene 
     In a nitrogen-purged glove box, a mixture of 3.90 g (30.0 mmol) of PEA, 22.9 μl (0.10 mmol) of BTEE, 7.3 mg (0.030 mmol) of ACHN, and 3.90 g of PMA was allowed to react at 90° C. for 20 hours. The monomer-to-polymer conversion was 100%, Mw was 51,510, and PDI was 1.39. 
     After 1.10 g (10.6 mmol) of St, 24.4 mg (0.10 mmol) of ACHN, and 1.10 g of PMA were added to the obtained solution, the resulting mixture was allowed to react at 90° C. for 22 hours. The monomer-to-polymer conversion was 77%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain. 4.07 g of poly(2-methoxyethyl acrylate)-polystyrene. Mw was 54,990, PCI was 2.0, and the composition ratio of poly(2-methoxyethyl acrylate)/polystyrene was 81/19. 
     Example 4 
     Poly(2-methoxyethyl acrylate)-polystyrene nitrogen 
     In a nitrogen-purged glove box, a mixture of 2.50 g (19.2 mmol) of MEA, 22.9 μl (0.10 mmol) of BTEE, 4.9 mg (0.020 mmol) of ACHN, and 2.50 g of PMA was allowed to react at 90° C. for 21 hours. The monomer-to-polymer conversion was 100%, Mw was 32,720, and PDI was 1.27. 
     After 2.50 g (24.0 mmol) of St, 12.2 mg (0.05 mmol) of ACHN, and 2.50 g of PMA were added to the obtained solution, the resulting mixture was reacted at 90° C. for 22 hours. After 12.2 mg (0.05 mmol) ACHN was added to the mixed solution, the resulting mixture was allowed to react at 90° C. for 24 hours. The monomer-to-polymer conversion was 84%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 4.07 g of poly(2-methoxyethyl acrylate)-polystyrene. Mw was 57,520, PDI was 1.65, and the composition ratio of poly(2-methoxyethyl acrylate)/polystyrene was 49/51. 
     Example 5 
     Poly[2-(2-ethoxyethoxy)ethyl acrylate]-polystyrene 
     In a nitrogen-purged glove box, a mixture of 5.32 g (28.3 mmol) of 2-(2-ethoxyethoxy)ethyl acrylate (hereinafter referred to as “EERA”), 33.1 μl (0.14 nmol) of BTEE, 4.7 mg (0.029 mmol) of AIBN, and 5.0 g of propylene glycol monomethyl ether (hereinafter referred to as “MP”) was allowed to react at 60° C. for 48 hours. The monomer-to-polymer conversion was 99%, Mw was 28,620, and PEI was 1.78. 
     After 1.90 g (18.2 mmol) of St, 17.6 mg (0.07 mmol) of ACHN, and 2.30 g of PMA were added to the obtained solution, the resulting mixture was allowed to react at 90° C. for 24 hours. After 17.6 mg (0. 07 mmol) of ACHN was added, the resulting mixture was allowed to react at 90° C. for 56 hours. The monomer-to-polymer conversion was 91%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 5.62 g of poly[2-(2-ethoxyethoxy)ethyl acrylate]-polystyrene. Mw was 32,990, PDI was 1.84, and the composition ratio of poly[2-(2-ethoxyethoxy)ethyl acrylate)/polystyrene was 65/35. 
     Example 6 
     Polyethylene Glycol Monomethyl Acrylate-polystyrene 
     In a nitrogen-purged glove box, a mixture of 4.20 g (8.7 mmol) of polyethylene glycol monomethyl acrylate (produced by NOF Corporation, Blemmer AME-400, hereinafter referred to “M9EGA”), 23.8 μl (0.10 mmol) of BTEE, 5.1 mg (0.021 mmol) of ACHN, and 4.0 q of MP was allowed to react at 90° C. for 24 hours. The monomer-to-polymer conversion was 96%, MW was 16,680, and PCI was 1.46. 
     After 1.50 g (9.6 mmol) of St, 12.7 mg (0.05 mmol) of ACHN, and 2.0 g of PMA were added to the obtained solution, the resulting mixture was allowed to react at 90° C. for 29 hours. After 8.5 mg (0.05 mmol) of AIBN was added, the resulting mixture was allowed to react at 60° C. for 62 hours. The monomer-to-polymer conversion was 89%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 4.60 g of polyethylene glycol monomethyl acrylate-polystyrene. Mw was 31,170, PDI was 1.79, and the composition ratio of polyethylene glycol monomethyl acrylate/polystyrene was 40/60. 
     Example 7 
     Poly(tetrahydrofurfuryl acrylate)-polystyrene 
     In a nitrogen-purged glove box, a mixture of 5.51 g (35.3 mmol) of tetrahydrofurfuryl acrylate (hereinafter referred to as “THFA”), 37.9 μl (0.17 mmol) of BTEE, 5.4 mg (0.033 mmol) of AIBN, and 5.10 g of anisole was reacted at 60° C. for 64 hours. The monomer-to-polymer conversion was 100%, Mw was 45,500, and PDI was 1.49. 
     After 2.76 g (26.5 mmol) of St, 12.1 mg (0.05 mmol) of ACHN, and 3.50 g of anisole were added to the obtained solution, the resulting mixture was allowed to react at 90° C. for 25 hours. After 12.1 mg (0.05 mmol) of ACHN was added, the resulting mixture was allowed to react at 90° C. for 48 hours. The monomer-to-polymer conversion was 88%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 7.00 g of poly(tetrahydrofurfuryl acrylate) polystyrene. Mw was 72,540, PDI was 2.76, and the composition ratio of polytetrahydrofurfuryl acrylate/polystyrene was 65/35. 
     Example 8 
     Poly(1-vinyl 2-pyrrolidone)-polystyrene 
     In a nitrogen-purged glove box, a mixture of 4.70 g (42.3 mmol) of 1-vinyl-2-pyrrolidone (hereinafter referred to as “VP”), 41.2 μl (0.18 mmol) of BTEE, 5.9 mac (0.036 mmol) of AIBN, and 4.50 g of anisole was allowed to react at 60° C. for 64 hours. The monomer-to-polymer conversion was 100%, Mw was 30,490, and PDI was 1.36. 
     After 4.30 g (41.3 mmol) of St, 13.2 mg (0.05 mmol) of ACHN, and 5.50 g of anisole were added to the obtained solution, the resulting mixture was reacted at 90° C. for 24 hours. After 13.2 mg (0.05 mmol) of ACHN was added, the resulting mixture was allowed to react at 90° C. for 24 hours. The monomer-to-polymer conversion was 89%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptanes and then dried to obtain 8.45 g poly(1-vinyl 2-pyrrolidone)-polystyrene. Mw was 75,340, PDI was 2.38, and the composition ratio of poly(1-vinyl 2-pyrrolidone)/polystyrene was 53/47. 
     Comparative Example 1 
     Poly(2-methoxyethyl acrylate) 
     In a nitrogen-purged glove box, 5.0 g (38.4 mmol) of MEA, a mixture of 14.3 μl (0.063 mmol) of BTEE, 4.6 mg (0.020 mmol) of ACHN, and 5.0 g of PMA was allowed to react at 90° C. for 23 hours. The monomer-to-polymer conversion was 100%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 4.49 g of poly(2-methoxyethyl acrylate). Mw was 84,800 and PDI was 1.96. 
     Comparative Example 2 
     Polystyrene 
     In a nitrogen-purged glove box, a mixture of 6.0 g (57.6 mmol) of St, 3.9 μl (0.017 nmol) of BTEE, and 2.1 mg (0.009 mmol) of ACHN was allowed. to react at 90° C. for 22 hours. The monomer-to-polymer conversion was 69%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 3.52 g of polystyrene. Mw was 176,000 and PDI was 1.57. 
     Comparative Example 3 
     Poly(2-methoxyethyl acrylate)-poly(N,N-dimethylacrylamide)-poly(2-methoxyethyl acrylate) 
     In a nitrogen-purged glove box, a mixture of 0.794 g (6.10 mmol) of MEA, 5.61 μl (0.0245 mmol) of BTEE, 0.8 mg (0.0049 mmol) of AIBN, and 0.80 g of PMA was allowed to react at 60° C. for 24 hours. The monomer-to-polymer conversion was 95%. 
     After 3.63 g (36.59 mmol) of N,N-dimethylacrylamide (DMAAm), 0.8 mg (0.0049 mmol) of AIBN, and 8.0 g of PMA were added to the obtained solution, the resulting mixture was allowed to react at 60° C. for 23 hours. The monomer-to-polymer conversion was 100%. 
     After 0.794 q (6.10 mmol) of MEA, 0.8 mg (0.0049 mmol) of AIBN, and 2.0 g of PEA were added to the obtained solution, the resulting mixture was allowed to react at 60° C. for 23 hours. After 0.8 mg (0.0049 mmol) of AIBN was added to this mixed solution, the resulting mixture was allowed to react at 60° C. for 16 hours. The monomer-to-polymer conversion was 96%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 4.71 g of poly(2-methoxyethyl acrylate)-poly(N,N-dimethylacrylamide)-poly(2-methoxyethyl acrylate). The composition ratio of poly(2-methoxyethyl acrylate)/poly(N,N-dimethylacrylamide) was 27/73. 
     Comparative Example 4 
     Poly(2-methoxyethyl acrylate-styrene) 
     In a nitrogen-purged glove box, a mixture of 4.10 g (31.5 mmol) of PEA, 0.90 g (8.64 mmol) of St, 22.9 μl (0.10 mmol) of BTEE, 12.2 mg (0.050 mmol) of ACHN, and 5.0 g of PMA was allowed to react at 90° C. for 23 hours. After 4.9 mg (0.02 mmol) of ACHN was added, the resulting mixture was allowed to react at 90° C. for 24 hours. The monomer-to-polymer conversion was 100%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 4.25 g of poly(2-methoxyethyl acrylate-styrene). Mw was 59,530, PDI was 1.41, and the composition ratio of poly(2-methoxyethyl acrylate)/polystyrene was 77/23. 
     Comparative Example 5 
     (Poly(2-methoxyethyl acrylate-styrene) 
     In a nitrogen-purged glove box, a mixture of 2.80 g (21.5 mmol) of MEA, 2.20 g (21.1 mmol) of St, 22.9 μl (0.10 mmol) of BTEE, 12.2 mg (0.050 mmol) of ACHN, and 5.0 g of PMA was allowed to react at 90° C. for 23 hours. After 4.9 mg (0.02 mmol) of ACHN was added to the mixed solution, the resulting mixture was allowed to react at 90° C. for 47 hours. The conversion of St was 100%, and the conversion of PEA was 89%. 
     After completion of the reaction, the reaction product was subjected to a reprecipitation treatment with heptane, and then dried to obtain 4.0 g of poly(2-methoxyetyl acrylate-styrene). Mw was 61,450, PDI was 1.58, and the composition ratio of poly(2-methoxyethyl acrylate)/polystyrene was 47/53. 
     Test Example 1 
     Calorific Value Measurement of Exothermic Peak Based on Low-Temperature Crystallization 
     The polymers obtained in the Examples and the Comparative Examples were immersed in water so that the polymers contained water. A prescribed amount of each sample after containing water was weighed out and thinly spread over the bottom of an aluminum pan whose weight had been measured beforehand. The sample was cooled from room temperature to −100° C., then maintained for 10 minutes, and heated from −100° C. to 50° C. at a temperature-rise rate of 5.0° C./min, during which the endothermic and exothermic amounts were measured using a differential scanning calorimeter (DSC-7000, produced by Seiko Instruments Inc.). Table 1 below shows the calorific value of the exothermic peak based on low-temperature crystallization at 0° C. or less. 
     Test Example 2 
     Measurement of Water Content 
     The water content of each sample used in the calorific value measurement of the exothermic peak based on low-temperature crystallization was measured in the following manner. A prescribed amount of each sample after containing water was weighed out and thinly spread over the bottom of an aluminium oxide pan whose weight had been weighed beforehand. After DSC measurement, pinholes were formed in the aluminum pan, and each sample was vacuum-dried. The water content was determined by measuring the weight before and after the drying. The water content (WC) of each sample was calculated according to the following formula (I): 
       WC=( W   1   −W   0 )/ W   1 )×100
 
     (wherein WC is water content (mass %), W 0  is dry weight (g) of a sample, and W 1  is wet weight (g) of a sample)
 
Table 1 shows the water content of each sample.
 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                   
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
               
               
                   
               
               
                 Calorific value 
                 7.23 
                 5.62 
                 7.64 
                 5.92 
               
               
                 of the 
               
               
                 exothermic peak 
               
               
                 based on low- 
               
               
                 temperature 
               
               
                 crystallization 
               
               
                 (J/g) 
               
               
                 Water content 
                 11.34 
                 9.05 
                 10.99 
                 6.27 
               
               
                 (mass %) 
               
               
                   
               
               
                   
                 Example 5 
                 Example 6 
                 Example 7 
                 Example 8 
               
               
                   
               
               
                 Calorific value 
                 7.35 
                 25.3 
                 4.67 
                 17.7 
               
               
                 of the 
               
               
                 exothermic peak 
               
               
                 based on low- 
               
               
                 temperature 
               
               
                 crystallization 
               
               
                 (J/g) 
               
               
                 Water content 
                 4.20 
                 26.97 
                 4.20 
                 31.12 
               
               
                 (mass %) 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Comparative 
                 Comparative 
                 Comparative 
               
               
                   
                 Example 1 
                 Example 4 
                 Example 5 
               
               
                   
               
               
                 Calorific value 
                 13.4 
                 — 
                 — 
               
               
                 of the 
               
               
                 exothermic peak 
               
               
                 based on low- 
               
               
                 temperature 
               
               
                 crystallization 
               
               
                 (J/g) 
               
               
                 Water content 
                 9.78 
                 16.59 
                 7.64 
               
               
                 (mass %) 
               
               
                   
               
            
           
         
       
     
     Test Example 3 
     Platelet Adhesion Test 
     The substrates (base material: polyethylene terephthalate) that were spin-coated with the polymers obtained in the Examples and Comparative Examples were cut into 8 mm×8 mm squares, and fixed to the specimen stage of a scanning electron microscope (SU8000, produced by Hitachi High-Technologies Corporation). 
     Human blood was centrifuged at 1500 rpm for 5 minutes, and the supernatant was recovered as platelet-rich plasma (PRP). The rest of the blood was further centrifuged at 4000 rpm for 10 minutes, and the supernatant was recovered as platelet-poor plasma (PPP). The PPP was diluted 800 times with a phosphate-buffered saline (PBS) solution. While the platelet count was confirmed under a microscope, the PRP was further diluted to prepare a platelet solution with a platelet concentration of 4×10 7  cells/mL. This platelet solution was added dropwise to each substrate in an amount of 200 μL, and the substrate was allowed to stand at 37° C. for 1 hour. 
     Each substrate was then washed twice with a PBS solution, immersed in a 1% glutaraldehyde solution, and allowed to stand at 37° C. for 2 hours to fix platelets. The platelet-fixed sample was washed by immersion in a PBS solution for 10 minutes, then in PBS:water=1:1 for 8 minutes, thereafter in water for 8 minutes, and again in water for 8 minutes. Each sample was air-dried at room temperature. The number of adhered platelets was counted using SEM. 
     The number of platelets adhered to polyethylene terephthalate (PET) was defined as 100. Table 2 shows the measurement results. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                   
                 Comparative 
                 Comparative 
                   
               
               
                   
                 Example 2 
                 Example 1 
                 Example 2 
                 PET 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 Platelet 
                 22.41 
                 4.95 
                 134.29 
                 100 
               
               
                   
                 count 
               
               
                   
                   
               
            
           
         
       
     
     Test Example 4 
     Adhesion Test (Coating Evaluation) 
     Test Example 4-1 
     Base Material: Soda Glass 
     5 cm×5 cm soda glass (0.7 mm in thickness) was spin-coated with each of the dilute solutions of the polymers obtained in the Examples and the Comparative Examples, and then dried in a heated-air oven at 90° C. for 30 minutes to obtain a coated base material. The obtained coated base material was observed with the naked eye, and under a light microscope and an atomic force microscope. When the surface has a uniform coating, it was evaluated as A. When floating of the coating layer on the coated base material (i.e., poor adhesion) was observed, it was evaluated as B. Table 3 shows the results. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
               
                   
                   
                 Comparative 
                 Comparative 
                 Comparative 
               
               
                   
                 Example 2 
                 Example 1 
                 Example 3 
                 Example 5 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Base material: 
                 A 
                 B 
                 B 
                 B 
               
               
                 soda glass 
               
               
                   
               
            
           
         
       
     
     Test Example 4-2 
     Base material: Polypropylene (PP) 
     Evaluation was performed in the same manner as in Test Example 4-1, except that polypropylene (PP) resin plates were used as the base material. Table 4 shows the results, 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
             
            
               
                   
                 Example 2 
                 Example 4 
                 Example 5 
                 Example 6 
                 Example 7 
               
               
                   
               
               
                 Base 
                 A 
                 A 
                 A 
                 A 
                 A 
               
               
                 material: 
               
               
                 PP 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                   
                 Comparative 
                 Comparative 
                 Comparative 
               
               
                   
                 Example 8 
                 Example 1 
                 Example 3 
                 Example 5 
               
               
                   
               
               
                 Base 
                 A 
                 B 
                 B 
                 B 
               
               
                 material: PP 
               
               
                   
               
            
           
         
       
     
     Test Example 4-3. Substrate: Polyethylene Terephthalate (PET) 
     Evaluation was performed in the same manner as in Test Example 4-1, except that polyethylene terephthalate (PET) resin plates were used as the base material. Table 5 shows the results. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
             
            
               
                   
                 Example 2 
                 Example 4 
                 Example 5 
                 Example 6 
               
               
                   
               
               
                 Base material: 
                 A 
                 A 
                 A 
                 A 
               
               
                 PET 
               
               
                   
               
               
                   
                   
                   
                 Comparative 
                 Comparative 
               
               
                   
                 Example 7 
                 Example 8 
                 Example 1 
                 Example 5 
               
               
                   
               
               
                 Base material: 
                 A 
                 A 
                 B 
                 B 
               
               
                 PET 
               
               
                   
               
            
           
         
       
     
     Test Example 4-4 
     Base Material: Polymethyl methacrylate (PMMA) 
     Evaluation was performed in the same manner as in Test Example 4-1, except that poles ethyl methacrylate (PMMA) resin plates were used as the base material. Table 6 shows the results. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 6 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 Comparative 
               
               
                   
                 Example 2 
                 Example 4 
                 Example 5 
                 Example 6 
                 Example 7 
                 Example 8 
                 Example 1 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Base 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 B 
               
               
                 material: PMMA 
               
               
                   
               
            
           
         
       
     
     Test Example 4-5 
     Base Material: Polyvinyl Chloride (PVC) 
     Evaluation was performed in the same manner as in Test Example 4-1, except that polyvinyl chloride (PVC) resin plates were used as the substrate. Table 7 shows the results. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 Comparative 
               
               
                   
                 Example 2 
                 Example 4 
                 Example 5 
                 Example 6 
                 Example 7 
                 Example 8 
                 Example 1 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Base 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 B 
               
               
                 material: PVC 
               
               
                   
               
            
           
         
       
     
     Test Example 4-6 
     Base Material: Polycarbonate (PC) 
     Evaluation was performed in the same manner as in Test Example 4-1, except that polycarbonate (PC) resin plates were used as the base material. Table 8 shows the results. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 8 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 Comparative 
               
               
                   
                 Example 2 
                 Example 4 
                 Example 5 
                 Example 6 
                 Example 7 
                 Example 8 
                 Example 1 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Base 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 B 
               
               
                 material: PC 
               
               
                   
               
            
           
         
       
     
     Test Example 4-7 
     Substrate: Stainless Steel (SUS) 
     Evaluation was performed in the same manner as in Test Example 4-1, except that stainless steel (SOS) plates were used as the base material. Table 9 shows the results. 
     
       
         
           
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 9 
               
               
                   
                   
               
               
                   
                   
                   
                   
                   
                   
                   
                 Comparative 
               
               
                   
                 Example 2 
                 Example 4 
                 Example 5 
                 Example 6 
                 Example 7 
                 Example 8 
                 Example 1 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 Base 
                 A 
                 A 
                 A 
                 A 
                 A 
                 A 
                 B 
               
               
                 material: SUS 
               
               
                   
               
            
           
         
       
     
     Test Example 5 
     Elution Test of Bulk Polymer 
     Each of the polymers obtained in the Examples and the Comparative Examples was placed into a 15-ml centrifuge tube. After 10 ml of water was added to the tube, shaking was performed using a shaker at room temperature for 24 hours. The resulting mixture was then centrifuged (at 10,000 rpm for 10 minutes) to precipitate each polymer. The supernatant other than the precipitate was removed by decantation to measure the weight change of the polymer. The weight reduction percentage was defined as the elution rate. Table 10 below shows the results. 
     Test Example 6 
     Elution Test of Coating Film 
     5 cm×12.5 cm soda glass (0.7 mm in thickness) was coated with each of the solutions of the polymers obtained in the Examples and the Comparative Examples (to a wet film thickness of 50 μm) using a bar coater, and then dried in a heated-air oven at 90° C. for 1 hour to obtain a coated base material. The obtained coated base material was immersed in 500 ml of water, and allowed to stand at room temperature for 20 hours. After the coated base material was removed from the water and dried, the weight change was measured. The weight reduction percentage was defined as the elution rate. Table 10 below shows the results. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 10 
               
               
                   
                   
               
               
                   
                   
                 Comparative 
                 Comparative 
               
               
                   
                 Example 2 
                 Example 1 
                 Example 3 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 Elution 
                 Bulk 
                 0 
                 1 
                 40 
               
               
                 rate (%) 
                 Coating film 
                 1 
                 3 
                 97 
               
               
                   
               
            
           
         
       
     
     The results show the following. Since the copolymer of Comparative Example 5, which is a random copolymer of several types of monomers, had no intermediate water as shown in Table 1, antithrombogenicity was not imparted and the copolymer also had insufficient adhesion as shown in Table 3. In contrast, the block copolymers of the present invention obtained in Examples 1 to 8 had intermediate water, and further had excellent adhesion. The polymer obtained in Comparative Example 1 had intermediate water as shown in Table 1, and short-term antithrombogenicity was imparted as shown in Table 2. However due to its poor adhesion as shown in Table 3, the polymer of Comparative Example 1 fails to solve the problem such that antithrombogenicity does not last for a long period of time.