Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L29/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical; Compositions of hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Compositions of derivatives of such polymers
  • C08L29/02—Homopolymers or copolymers of unsaturated alcohols
  • C08L29/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F218/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an acyloxy radical of a saturated carboxylic acid, of carbonic acid or of a haloformic acid
  • C08F218/02—Esters of monocarboxylic acids
  • C08F218/04—Vinyl esters
  • C08F218/08—Vinyl acetate
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F218/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an acyloxy radical of a saturated carboxylic acid, of carbonic acid or of a haloformic acid
  • C08F218/20—Esters containing halogen
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F293/00—Macromolecular compounds obtained by polymerisation on to a macromolecule having groups capable of inducing the formation of new polymer chains bound exclusively at one or both ends of the starting macromolecule
  • C08F293/005—Macromolecular compounds obtained by polymerisation on to a macromolecule having groups capable of inducing the formation of new polymer chains bound exclusively at one or both ends of the starting macromolecule using free radical "living" or "controlled" polymerisation, e.g. using a complexing agent
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F2438/00—Living radical polymerisation
  • C08F2438/03—Use of a di- or tri-thiocarbonylthio compound, e.g. di- or tri-thioester, di- or tri-thiocarbamate, or a xanthate as chain transfer agent, e.g . Reversible Addition Fragmentation chain Transfer [RAFT] or Macromolecular Design via Interchange of Xanthates [MADIX]
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
  • C08F8/00—Chemical modification by after-treatment
  • C08F8/12—Hydrolysis

Definitions

• the present invention relates to polyvinyl alcohol polymers (partially saponified polyvinyl alcohol polymers), etc.
• Polyvinyl alcohol polymers are polymers obtained by saponifying polymers (polyvinyl esters, etc.) that have vinyl esters as their polymerization component. Taking advantage of their properties, such as water solubility and film properties (strength, oil resistance, film-forming properties, gas barrier properties, etc.), they are used in a variety of applications, such as emulsifiers, suspending agents, surfactants, fiber processing agents, various binders, paper processing agents, adhesives, and films.
• PVAs have a specific degree of saponification, polymerization, etc., depending on the application and desired properties.
• a block copolymer may exhibit different physical properties from its random copolymer.
• Patent Document 1 discloses a modified vinyl alcohol polymer (A) having a sulfonic acid group or a salt thereof in the side chain, a modification amount of the sulfonic acid group or the salt thereof being 0.01 mol % or more and 10 mol % or less, and a block character of the remaining vinyl ester unit being 0.55 or more and 1 or less.
• the object of the present invention is to provide a polyvinyl alcohol polymer (PVA) and the like.
• PVA partially saponified polyvinyl alcohol (based polymer)
• Vinyl alcohol units are hydrophilic, while vinyl ester units are generally hydrophobic, so in this respect PVA can be said to be a polymer that has both hydrophilic and hydrophobic units.
• the block character in PVA is an index showing the distribution of vinyl ester units [residual vinyl ester units (units derived from vinyl ester that remain unsaponified), -CH 2 -CH(OCOR)-] in the PVA [partially saponified polyvinyl alcohol (based polymer)] and takes a value from 0 to 2.
• this blocking can be adjusted to some extent by adjusting the reaction conditions during saponification (for example, when a basic catalyst such as sodium hydroxide is used as the saponification catalyst, the distribution of the remaining vinyl ester groups tends to be blocked, and when an acidic catalyst such as sulfuric acid is used, the distribution of the remaining vinyl ester groups tends to be random).
• a basic catalyst such as sodium hydroxide
• an acidic catalyst such as sulfuric acid
• a polyvinyl alcohol polymer (partially saponified polyvinyl alcohol polymer) having a block character [block character of vinyl ester units (residual vinyl ester units), block character of units derived from vinyl ester] of 0.4 or less.
• a polyvinyl alcohol-based polymer having a hydrodynamic radius in water (25° C.) (hydrodynamic radius of an aggregate formed in water) of 8 nm or more.
• a polyvinyl alcohol-based polymer having a block character of 0.4 or less and a hydrodynamic radius in water (25° C.) of 8 nm or more.
• [4] The polyvinyl alcohol-based polymer according to any one of [1] to [3], having a block character of 0.37 or less (e.g., 0.35 or less).
• [5] The polyvinyl alcohol-based polymer according to any one of [1] to [4], wherein the vinyl ester units (residual vinyl ester units) contain two or more types of vinyl ester units.
• [6] The polyvinyl alcohol-based polymer according to any one of [1] to [5], wherein the vinyl ester units (residual vinyl ester units) contain vinyl acetate units and vinyl ester units other than vinyl acetate units.
• Mw/Mn molecular weight distribution
• a block copolymer e.g., a diblock copolymer, a triblock copolymer
• the polyvinyl alcohol-based polymer according to any one of [1] to [13] having a degree of polymerization of 50 or more.
• the block character is 0.37 or less (e.g., 0.35 or less), The hydrodynamic radius in water (25° C.) is 10 nm or more; The degree of polymerization is 50 to 1000, The degree of saponification is 40 to 96 mol %, A polyvinyl alcohol-based polymer satisfying at least one of the following (1), (2) and (3): (1) The molecular weight distribution (Mw/Mn) when completely saponified is 2 or less; (2) The YI of a 1% by mass DMSO solution is 30 or less; (3) The chlorine (chlorine atom) content is 100 ppm or less [17] An aqueous liquid containing the polyvinyl alcohol-based polymer according to any one of [1] to [16] ⁇ for example, an aqueous liquid containing an association (micelle) of the polyvinyl alcohol-based polymer according to any one of [1] to [16] [the polyvinyl alcohol-based polymer according to any one of [1] to [16] in the
• Step 2 A step of synthesizing a block copolymer by subjecting a second vinyl ester different from the first vinyl ester to living radical polymerization in the presence of the macro chain transfer agent obtained in step 1.
• Step 3 A step of partially saponifying the block copolymer obtained through at least step 2.
• RAFT polymerization reversible addition-fragmentation chain transfer polymerization
• a micelle (association, preparation) comprising the polyvinyl alcohol-based polymer according to any one of [1] to [16] and an ingredient [an ingredient encapsulated in the polyvinyl alcohol-based polymer, such as a drug or a hydrophobic component (e.g., a component having a solubility (20°C) of 500 mg or less in 100 mL (100 g) of water (solubility at 20°C of 500 mg/100 g H 2 O))].
• a hydrophobic component e.g., a component having a solubility in 100 mL of water (20°C) of 500 mg or less.
• An aqueous liquid comprising the micelle (association, preparation) according to [24] or [25].
• the present invention can provide PVA [new or specific PVA, partially saponified polyvinyl alcohol (based polymer)].
• the PVA of the present invention in one aspect, has a particular small block character (0.4 or less, 0.35 or less, etc.).
• Such PVA has such a high blocking property that it can be called a block copolymer (high-level block copolymer), and it is expected that the physical properties thereof will be significantly different from those of conventional PVA (e.g., PVA with a large block character).
• amphiphilic polymer due to its high blocking ability, it can function efficiently as an amphiphilic (excellent amphiphilic) polymer, and as such an amphiphilic polymer it can be efficiently applied to various applications (e.g., medical materials such as drug delivery systems, etc.).
• applications e.g., medical materials such as drug delivery systems, etc.
• such functions are preferable because they can be realized while retaining the physical properties and functions of PVA.
• the PVA of the present invention in one aspect, has a relatively large hydrodynamic radius in water.
• Such PVA is believed to be easily capable of efficiently forming aggregates (large aggregates) in water, and by utilizing such a function, it can be efficiently applied to various applications (e.g., medical materials such as drug delivery systems, etc.)
• Such a function is preferable because it can be realized while maintaining the physical properties and functions of PVA, as described above.
• the PVA of the present invention can have a specific hue (coloring property) while satisfying the specific small block character (0.4 or less, 0.35 or less, etc.) and a relatively large hydrodynamic radius in water as described above. Therefore, it is possible to simultaneously achieve the above-mentioned functions and properties (e.g., function as an amphiphilic polymer, efficient formation of aggregates, etc.) and suppression of coloring.
• a method for producing PVA can be provided. With this method, the PVA described above can be easily and efficiently obtained.
• the present invention can provide a specific polyvinyl alcohol-based polymer (hereinafter, sometimes referred to as a PVA-based polymer, PVA, etc.).
• a PVA-based polymer PVA, etc.
• Such a PVA may be a partially saponified product of a polymer having a vinyl ester as a polymerization component.
• the block character of the PVA may be small (i.e., high blocking as a PVA), for example, 0.42 or less (e.g., 0.4 or less, 0.38 or less), preferably 0.37 or less (e.g., 0.36 or less), more preferably 0.35 or less (e.g., 0.34 or less, 0.33 or less, 0.32 or less, 0.31 or less), particularly 0.3 or less (e.g., 0.29 or less, 0.28 or less, 0.27 or less, 0.26 or less, 0.25 or less), or 0.24 or less (e.g., 0.23 or less, 0.22 or less, 0.21 or less, 0.2 or less, 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less), etc.
• 0.42 or less e.g., 0.4 or less, 0.38 or less
• preferably 0.37 or less e.g., 0.36 or less
• more preferably 0.35 or less e.g., 0.34 or less, 0.33 or less
• the lower limit of the PVA block character is not particularly limited, but may be, for example, 0 or more, 0.01 or more, 0.03 or more, 0.05 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.1 or more, etc.
• PVA block characters include, for example, 0.01-0.35, 0.05-0.30, and 0.07-0.25.
• the block character ( ⁇ ) is expressed by the following formula (1).
• (OH, OCOR) represents the proportion of two-unit chain structures (OH, OCOR) in which an OH group and an OCOR group are adjacent to each other, (OH) represents the proportion of vinyl alcohol, and (OCOR) represents the proportion of remaining vinyl ester groups. Each is represented by a mole fraction.
• This block character takes a value between 0 and 2; the closer to 0, the higher the blockiness of the vinyl ester group distribution; the closer to 1, the higher the randomness; and the closer to 2, the higher the alternation.
• the measurement method for this block character is described in detail in Macromolecules, 10, 532 (1977).
• PVA with small block characters as described above can be obtained efficiently by, for example, selecting the vinyl ester in the polymer containing the vinyl ester as a polymerization component, selecting the polymerization method, selecting the saponification conditions, etc., as described below.
• block copolymers those with low block character as described above can be called block copolymers.
• PVA is usually a partially saponified polymer that uses vinyl ester as a polymerization component.
• PVA polymer that uses vinyl ester as a polymerization component into a block copolymer.
• block form is not particularly limited and can be appropriately selected depending on the desired performance, etc., and may be a diblock copolymer, a block copolymer consisting of three or more blocks (e.g., a triblock polymer, a tetrablock polymer, etc.), etc., but from the viewpoint of efficient ease of production, etc., a diblock copolymer, a triblock copolymer, etc. may also be used.
• the PVA may be dissolved (or dispersed) in water or a medium containing water (aqueous medium), and may form (be capable of forming) aggregates (micelles) in water or a medium containing water (in water or a medium containing water).
• the hydrodynamic radius of such PVA in water (e.g., at 25°C (e.g., in water containing PVA at a concentration of 1 g/L)) (hydrodynamic radius of the aggregate formed in water) may be relatively large, for example, 7 nm or more (e.g., 7.5 nm or more), preferably 8 nm or more (e.g., 9 nm or more), and more preferably 10 nm or more (e.g., 11 nm or more), and may be 12 nm or more (e.g., 13 nm or more).
• 14 nm or more 14 nm or more, 15 nm or more, 16 nm or more, 17 nm or more, 18 nm or more, 19 nm or more, 20 nm or more, 21 nm or more, 22 nm or more, 23 nm or more, 24 nm or more, 25 nm or more, 26 nm or more, 27 nm or more, 28 nm or more, 29 nm or more, 30 nm or more, 31 nm or more, 32 nm or more, 33 nm or more, 35 nm or more, 38 nm or more, 40 nm or more, 45 nm or more, 48 nm or more, 50 nm or more, etc.
• the upper limit of the hydrodynamic radius of PVA in water (hydrodynamic radius of the aggregate formed in water) at 25°C is not particularly limited, but may be, for example, 200 nm or less, 180 nm or less, 150 nm or less, 120 nm or less, 100 nm or less, 80 nm or less, 70 nm or less, 60 nm or less, etc.
• hydrodynamic radius of PVA in water examples include 10 to 200 nm, for example, at 25°C (for example, in water containing PVA at a concentration of 1 g/L).
• the hydrodynamic radius can be measured, for example, using dynamic light scattering (DLS) (DLS analyzer).
• DLS dynamic light scattering
• the hydrodynamic radius as described above is thought to be an indicator of the ease and degree (ability) of forming an aggregate (for example, an aggregate having a shell made up of segments (hydrophilic segments) that contain (abundantly) vinyl alcohol units and a core made up of segments (hydrophobic segments) that contain (abundantly) vinyl ester units), and is also thought to be due to the degree of blockiness as described above.
• PVA with the above hydrodynamic radius can be obtained efficiently by, for example, selecting the vinyl ester in the polymer having the vinyl ester as a polymerization component, selecting the degree of saponification (and further the degree of polymerization), selecting the polymerization method, selecting the saponification conditions, etc., as described below.
• the YI (yellowness index) of a 1% by mass solution of PVA in dimethyl sulfoxide (DMSO) may be selected from a range of, for example, about 80 or less (e.g., 70 or less), preferably 65 or less (e.g., less than 65, 60 or less), and more preferably 55 or less (e.g., 50 or less, 45 or less, 35 or less, 30 or less, 28 or less, 25 or less, 22 or less, 20 or less, 18 or less, 15 or less, 12 or less, 10 or less, 8 or less), etc.
• the YI of a 1% by weight solution of PVA in DMSO can be calculated from the data obtained by measuring the UV-Vis spectrum of a 1% by weight solution of PVA in DMSO at 20°C (for example, a quartz cell with a path length of 10 mm) using an ultraviolet-visible spectrophotometer.
• Such a YI reflects the coloring, and such a YI has excellent hue (coloring is suppressed).
• the YI can be efficiently obtained within the above range by selecting the raw material of the PVA (for example, not using chlorine-containing vinyl ester as the vinyl ester or reducing the proportion of chlorine-containing vinyl ester used), reducing (removing) the content of unreacted vinyl ester after the polymerization step, neutralizing the remaining alkali catalyst after the saponification step, and not setting the drying temperature after neutralization too high.
• PVA has vinyl alcohol units [units (-CH 2 -CH(OH)-) obtained by saponifying (hydrolyzing) units derived from vinyl esters] and vinyl ester units [units derived from vinyl esters, -CH 2 -CH(OCOR)-].
• vinyl alcohol units units (-CH 2 -CH(OH)-) obtained by saponifying (hydrolyzing) units derived from vinyl esters]
• vinyl ester units units derived from vinyl esters, -CH 2 -CH(OCOR)-.
• PVA is a saponified product of a polymer of polymerization components containing vinyl esters.
• the saponification degree of the PVA (corresponding to [x/(x+y+z) ⁇ 100% (mol%)] described below) may be selected, for example, from a range of about 99 mol% (or 99%) or less, and from the viewpoint of the desired functionality (e.g., water solubility, ease of forming aggregates, etc.), block character, and ease of obtaining the aforementioned hydrodynamic radius (and also ease of efficiently achieving both), it may be about 98 mol% or less (e.g., 97 mol% or less), preferably 96 mol% or less (e.g., 95 mol% or less), and more preferably 94 mol% or less (e.g., 93.5 mol% or less), and may be about 93 mol% or less (e.g., 92 mol% or less, 91 mol% or less, 90 mol% or less, less than 90 mol%, 89.5 mol% or less, 89 mol%, 88 mol% or less, 87
• the degree of saponification of PVA can be selected according to the desired properties (e.g., water solubility, ease of forming aggregates, etc.), and may be selected, for example, from a range of about 10 mol% (or 10%) or more, 12 mol% or more (e.g., 15 mol% or more), preferably 20 mol% or more (e.g., 25 mol% or more), and more preferably 30 mol% or more (e.g., 35 mol% or more, 38 mol% or more), or 40 mol% or more (e.g., more than 40 mol%, 41 mol% or more, 42 mol% or more, 43 mol% or more, 44 mol% or more, 45 mol% or more, 46 mol% or more, 47 mol% or more, 48 mol% or more, 49 mol% or more, 50 mol% or more, more than 50 mol%, 51 mol
• % or more 55 mol% or more, 56 mol% or more, 57 mol% or more, 58 mol% or more, 59 mol% or more, 60 mol% or more, more than 60 mol%, 61 mol% or more, 62 mol% or more, 63 mol% or more, 64 mol% or more, 65 mol% or more, 66 mol% or more, 67 mol% or more, 68 mol% or more, 69 mol% or more, 70 mol% or more, more than 70 mol%, 71 mol% or more, 72 mol% or more, 73 mol% or more , 74 mol% or more, 75 mol% or more, 76 mol% or more, 77 mol% or more, 78 mol% or more, 79 mol% or more, 80 mol% or more, more than 80 mol%, 81 mol% or more, 82 mol% or more, 83 mol% or more, 84 mol%
• saponification degree of PVA (or [x/(x+y+z) ⁇ 100% (mol %)] described below) include 40 to 96 mol%, 50 to 94 mol%, and 60 to 92 mol%, etc.
• the degree of saponification (or [x/(x+y+z) ⁇ 100% (mol%)] described below) can be determined, for example, by NMR (a combination of the degree of polymerization and composition analysis by NMR), the method for measuring the degree of saponification of PVA specified in JIS K 6726, or calculations based on other analytical methods.
• the degree of polymerization (average degree of polymerization) of PVA may be selected from a range of about 20 or more (e.g., 30 or more), and from the viewpoint of the desired function (good amphiphilicity, etc.), block character, and ease of obtaining the aforementioned hydrodynamic radius (and also ease of efficiently achieving both), it may be, for example, about 35 or more, preferably 40 or more, and more preferably about 50 or more (e.g., 55 or more), or may be 60 or more (e.g., 65 or more, 70 or more, 75 or more, 80 or more, 85 or more, 90 or more, 95 or more, 100 or more, 105 or more, 110 or more, 120 or more, 130 or more, 140 or more, 150 or more), etc.
• the upper limit of the degree of polymerization (average degree of polymerization) of PVA is not particularly limited, but may be, for example, 10,000, 8,000, 7,000, 6,000, 5,000, 4,000, 3,000, 2,000, 1,500, 1,200, 1,000, 900, 800, 700, 600, 500, 450, 400, 350, 300, less than 300, 290, 280, 270, 260, 250, 240, 230, 220, 210, 200, etc.
• the degree of polymerization is not too high (for example, 1000 or less), it is easier to control the polymerization.
• degree of polymerization (average degree of polymerization) of PVA total number/amount of units derived from monomers, or total number/amount of vinyl alcohol units and vinyl ester units (x+y+z described below)] include 40-1000, 50-1000, 60-700, 70-500, etc.
• the total number/amount of vinyl alcohol units may be selected from a range of about 10 or more (e.g., 15 or more), and from the viewpoint of the desired functionality (good amphiphilicity, etc.), ease of obtaining block character and the aforementioned hydrodynamic radius (and ease of efficiently achieving both), etc., it may be, for example, about 20 or more, preferably 30 or more, and more preferably about 40 or more (e.g., 45 or more), or may be 50 or more (e.g., 55 or more, 60 or more, 65 or more, 70 or more, 80 or more, 85 or more, 90 or more, 95 or more, 100 or more, 120 or more, 150 or more), etc.
• the upper limit of the total number/amount of vinyl alcohol units is not particularly limited, but may be, for example, 5000, 4000, 3000, 2000, 1500, 1200, 1000, 900, 800, 700, 600, 500, 450, 400, 350, 300, less than 300, 290, 280, 270, 260, 250, 240, 230, 220, 210, 200, 180, 150, 120, 100, etc.
• Specific examples of the total number/amount of vinyl alcohol units in PVA (x, described below) include 30 to 1000, 40 to 1000, 40 to 700, and 50 to 400.
• the total number/amount of vinyl ester units may be selected from a range of about 2 or more (e.g., 3 or more), and from the viewpoint of the desired functionality (good amphiphilicity, etc.), block character, and ease of obtaining the aforementioned hydrodynamic radius (and also ease of efficiently achieving both), it may be, for example, about 3.5 or more, preferably 4 or more, and more preferably 4.5 or more (e.g., 5 or more), or it may be 6 or more (e.g., 6.5 or more, 7 or more, 7.5 or more, 8 or more, 8.5 or more, 9 or more, 9.5 or more, 10 or more, 10.5 or more, 11 or more), etc.
• the upper limit of the total number/amount of vinyl ester units is not particularly limited, but may be, for example, 3000, 2000, 1500, 1200, 1000, 900, 800, 700, 600, 500, 450, 400, 350, 300, less than 300, 290, 280, 270, 260, 250, 240, 230, 220, 210, 200, 180, 150, 120, 100, 80, 70, 60, 50, 40, 30, 20, 18, 15, 12, etc.
• Specific examples of the total number/amount of vinyl ester units in PVA include 4 to 500, 6 to 300, and 8 to 200.
• the degree of polymerization, the total number and amount of vinyl alcohol units and vinyl ester units, etc. can be determined, for example, by NMR, GPC [e.g., calculation based on the value of a completely saponified product, calculation based on a re-esterified product (e.g., acetylation)], the method specified in JIS K 6726, calculation based on other analytical extraction methods, or a combination of these methods.
• the molecular weight distribution [mass (weight) average molecular weight (Mw)/number average molecular weight (Mn)] of the PVA when fully saponified (when the degree of saponification is 100%) may be about 5 or less (e.g., 4 or less, 3.5 or less), for example, 3 or less (e.g., 2.8 or less), preferably 2.5 or less (e.g., 2.4 or less, less than 2.4, 2.3 or less), more preferably 2.2 or less (e.g., 2.1 or less, 2 or less, 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less, 1.5 or less, etc.), or 1 or more (e.g., 1.01 or more, 1.02 or more, 1.05 or more, 1.07 or more, 1.1 or more, 1.15 or more, 1.2 or more, 1.3 or more, etc.).
• Specific molecular weight distributions include, for example, 1 to 2.2, 1.05 to 2, 1.2 to 2, 1.07 to 1.9, and 1.1 to 1.8.
• the molecular weight distribution is thought to be related to the presence (or absence) of chain transfer and the formation (or absence) of branched structures. Therefore, depending on the desired physical properties of the PVA (e.g., good amphiphilicity, ease of association), a narrow (small) molecular weight distribution is thought to be preferable.
• the number average molecular weight (Mn) of the PVA when fully saponified may be, for example, 300 or more (e.g., 500 or more, 800 or more), preferably 1000 or more (e.g., 1500 or more), and more preferably 2000 or more (e.g., 2500 or more, 3000 or more, 3500 or more, 4000 or more, 4500 or more, 5000 or more, 5500 or more, 6000 or more, 6500 or more, 7000 or more, 8000 or more, 9000 or more, etc.).
• the number average molecular weight (Mn) of the PVA when fully saponified (with a degree of saponification of 100%) may be, for example, 1,000,000 or less (e.g., 500,000 or less), preferably 300,000 or less (e.g., 200,000 or less), and more preferably about 100,000 or less (e.g., 80,000 or less), or may be 50,000 or less (e.g., 40,000 or less, 30,000 or less, 20,000 or less, 15,000 or less, 12,000 or less, etc.).
• Mn, Mw, and Mw/Mn can be determined, for example, by GPC (e.g., GPC using polyethylene glycol as the standard substance).
• the chlorine (chlorine atom) content of the PVA may be selected from a range of about 10,000 ppm (ppm by mass) or less (e.g., 9,000 ppm or less, 8,000 ppm or less, 7,000 ppm or less, 6,000 ppm or less), and may be, for example, 5,000 ppm or less (e.g., 4,000 ppm or less), preferably 3,000 ppm or less (e.g., 2,000 ppm or less), more preferably 1,000 ppm or less (e.g., 800 ppm or less), and particularly 500 ppm or less (e.g., 300 ppm or less, 200 ppm or less, 100 ppm or less, 80 ppm or less, 60 ppm or less, 50 ppm or less, 40 ppm or less, 30 ppm or less).
• Examples of the form of chlorine contained in PVA include the case where it is contained as a substituent (e.g., a chlorine atom in a monochlorovinyl acetate unit described below) and the case where it is contained as an impurity (e.g., a chloride ion in sodium chloride).
• Chlorine content varies depending on its origin. For example, when chlorine is derived from a vinyl ester, it is considered to be related to the content of vinyl ester units (residues), the presence or absence (or the amount) of chain transfer, and the formation (or the amount) of a branched structure. Thus, depending on the desired physical properties of the PVA (for example, good amphiphilicity, ease of association), a PVA with a low chlorine content is considered to be preferable.
• Chlorine also appears to be a factor in discoloring PVA, so it is thought that PVA with less discoloration can be obtained more efficiently when the chlorine content is low.
• the chlorine content may be measured, for example, on combusted PVA, specifically by the method described below.
• PVA has vinyl alcohol units and vinyl ester units.
• examples of the vinyl ester include vinyl esters that do not have a chlorine atom (particularly a halogen atom other than a fluorine atom) (e.g., fatty acid vinyl esters that may have a fluorine atom, such as vinyl formate, vinyl acetate, vinyl propionate, vinyl caprylate, vinyl pivalate, vinyl versatate, and vinyl trifluoroacetate; aromatic vinyl esters that may have a fluorine atom, such as vinyl benzoate), vinyl esters that have a halogen atom other than a fluorine atom (e.g., a chlorine atom) [e.g., a fatty acid ester in which one or more halogen atoms other than a fluorine atom (e.g., a chlorine atom) are substituted for the fatty acid vinyl ester, such as vinyl monochloroacetate], and the like.
• a halogen atom other than a fluorine atom e.g., a
• the vinyl ester unit may have one or more types of vinyl ester units.
• the PVA when the polymer before saponification has two or more types of vinyl ester units as described below, the PVA often has two or more types of vinyl ester units corresponding to these two or more types of vinyl ester units (two or more types of vinyl ester units that remain without being saponified), although this depends on the saponification conditions, etc.
• the vinyl ester units preferably contain at least vinyl acetate units (units derived from vinyl acetate), and typically may contain vinyl acetate units and vinyl ester units other than vinyl acetate units.
• the vinyl ester units do not contain vinyl ester units (e.g., vinyl monochloroacetate units) having halogen atoms other than fluorine atoms (e.g., chlorine atoms), or if they do contain such units, their proportion in the total vinyl ester units is small (e.g., 30 mol % or less, 20 mol % or less, 15 mol % or less, 10 mol % or less, 5 mol % or less, 1 mol % or less).
• vinyl ester units e.g., vinyl monochloroacetate units having halogen atoms other than fluorine atoms (e.g., chlorine atoms)
• their proportion in the total vinyl ester units is small (e.g., 30 mol % or less, 20 mol % or less, 15 mol % or less, 10 mol % or less, 5 mol % or less, 1 mol % or less).
• the vinyl ester units other than vinyl acetate units may be any units other than vinyl acetate units, but in many cases they differ (significantly differ) from vinyl acetate units in ease of saponification (hydrolysis) (easily or difficultly saponified).
• the vinyl ester units other than the vinyl acetate units may be one or two or more types of vinyl ester units, and from the viewpoint of easy synthesis, etc., it is preferable that the number of units is not too large (for example, one or two types, particularly one type).
• vinyl ester units other than vinyl acetate units include vinyl ester units containing at least one unit (e.g., at least a vinyl pivalate unit) selected from vinyl pivalate units, vinyl versatate units, and vinyl trifluoroacetate units.
• the ratio or proportion of a certain type of vinyl ester unit (e.g., vinyl acetate unit) to other vinyl ester units (e.g., vinyl ester units other than vinyl acetate units) [vinyl ester unit (e.g., vinyl acetate unit)/other vinyl ester units (e.g., vinyl ester units other than vinyl acetate units), y/z or z/y described below, etc.] is not particularly limited, and may be, for example, 0.0001 to 10,000, 0.001 to 1000, 0.01 to 100, 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, less than 1, 0.5 or less, 0.3 or less, 0.25 or less, 0.2 or less, etc.
• the PVA has vinyl alcohol units and vinyl ester units, it may also have units that do not fall into these categories [for example, units derived from monomers (non-vinyl ester monomers, monomers that are not vinyl esters)].
• Such monomers are not particularly limited, but examples thereof include ⁇ -olefins (e.g., ethylene, propylene, n-butene, isobutylene, etc.), (meth)acrylic acid and its salts, (meth)acrylic acid esters [e.g., (meth)acrylic acid alkyl esters (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, i-propyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, etc.
• ⁇ -olefins e.g., ethylene, propylene, n-buten
• vinyl ethers for example, methyl
• alkyl vinyl ether, etc. 1, 20 alkyl vinyl ether, etc.), nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl halides (e.g., vinyl chloride, vinyl fluoride, etc.), vinylidene halides (e.g., vinylidene chloride, vinylidene fluoride, etc.), allyl compounds (e.g., allyl acetate, allyl chloride, sodium allylsulfonate, etc.), unsaturated dicarboxylic acids (e.g., maleic acid, itaconic acid, fumaric acid, etc.) and salts or esters thereof, vinyl silyl compounds (e.g., vinyltrimethoxysilane, etc.), fatty acid alkenyl esters (e.g., isopropenyl acetate, etc.), and the like.
• vinyl halides e.g., vinyl chloride, vinyl fluoride,
• These monomers can be used alone or in combination of two or more.
• the ratio of the units derived from the other monomers when the total amount of vinyl alcohol units and vinyl ester units is 100 moles (or 100 parts by mass), may be, for example, 20 moles or less (or 20 parts by mass or less) [e.g., 0.1 to 20 moles (or 0.1 to 20 parts by mass)], 10 moles or less (or 15 parts by mass or less), 5 moles or less (or 5 parts by mass or less), 3 moles or less (or 3 parts by mass or less), etc.
• PVA has (at least has) vinyl alcohol units and vinyl ester units
• a PVA may be, for example, a PVA (PVA, polymer) having a unit represented by the following formula (1) (vinyl alcohol unit) and at least one unit (vinyl ester unit) selected from a unit represented by the following formula (2) and a unit represented by the following formula (3).
• R1 and R2 are residues derived from different vinyl esters, and x, y, and z are the total number/amount of each unit, respectively.
• the unit (structure) shown in the above formula (1) is a vinyl alcohol unit, and is usually a structure obtained by saponifying a vinyl ester unit.
• the unit (structure) represented by the above formula (2) or (3) is a vinyl ester unit, and as described above, R1 and R2 are both residues derived from a vinyl ester and are different from each other.
• Such structures can usually be obtained by using the corresponding vinyl esters in the polymerization process.
• the residues derived from vinyl esters include residues derived from the vinyl esters mentioned above, such as hydrogen atoms (residues derived from vinyl formate), aliphatic hydrocarbon groups (e.g., hydrocarbon groups having 1 to 10 carbon atoms) that do not have chlorine atoms (particularly halogen atoms other than fluorine atoms) and aromatic hydrocarbon groups [e.g., methyl groups (residues derived from vinyl acetate), t-butyl groups (residues derived from vinyl pivalate), trifluoromethyl groups (residues derived from vinyl trifluoroacetate), ethyl groups, n-propyl groups, isopropyl groups, n-butyl groups, sec-butyl groups, isobutyl groups, n-heptyl groups, aliphatic hydrocarbon groups (e.g., alkyl groups) or aromatic hydrocarbon groups that may have fluorine atoms, such
• the vinyl ester units do not contain vinyl ester units (e.g., vinyl monochloroacetate units) having halogen atoms other than fluorine atoms (e.g., chlorine atoms), or if they do contain such units, their proportion in the total vinyl ester units is small (e.g., 30 mol % or less, 20 mol % or less, 15 mol % or less, 10 mol % or less, 5 mol % or less, 1 mol % or less).
• vinyl ester units e.g., vinyl monochloroacetate units having halogen atoms other than fluorine atoms (e.g., chlorine atoms)
• their proportion in the total vinyl ester units is small (e.g., 30 mol % or less, 20 mol % or less, 15 mol % or less, 10 mol % or less, 5 mol % or less, 1 mol % or less).
• neither R1 nor R2 contains a residue (e.g., monochloromethyl group) derived from a vinyl ester having a halogen atom other than a fluorine atom (e.g., a chlorine atom), or even if it does contain one, the proportion of this residue in the total of R1 and R2 (y+z) is small (e.g., 30 mol % or less, 20 mol % or less, 15 mol % or less, 10 mol % or less, 5 mol % or less, 1 mol % or less).
• a residue e.g., monochloromethyl group
• R1 and R2 are different, and examples thereof include a combination of a methyl group (for example, when R1 is a methyl group) and a group other than a methyl group (for example, when R1 is a group other than a methyl group, such as t-butyl).
• R 1 is usually one type of group (residue), and R 2 may be one type or two or more different types of groups (residues).
• R 1 or R 2 is a methyl group or a tert-butyl group, and it is more preferable that R 1 is a methyl group and R 2 is a tert-butyl group.
• x is the total number/amount of units (structures) represented by formula (1) (the total number/amount of units (structures) represented by formula (1) in the polymer or PVA) (i.e., it does not indicate that x units represented by formula (1) are continuously bonded).
• x is as described above, and may be selected from a range of, for example, about 10 or more (e.g., 15 or more), and from the viewpoint of the ease of obtaining the desired function (good amphiphilicity, etc.), block character, and the aforementioned hydrodynamic radius (and also the ease of efficiently achieving both), may be, for example, about 20 or more, preferably 30 or more, and more preferably about 40 or more (e.g., 45 or more), or may be 50 or more (e.g., 55 or more, 60 or more, 65 or more, 70 or more, 80 or more, 85 or more, 90 or more, 95 or more, 100 or more, 120 or more, 150 or more), etc.
• the upper limit of x is not particularly limited, but may be, for example, 5000, 4000, 3000, 2000, 1500, 1200, 1000, 900, 800, 700, 600, 500, 450, 400, 350, 300, less than 300, 290, 280, 270, 260, 250, 240, 230, 220, 210, 200, 180, 150, 120, 100, etc.
• x is not too high (e.g., 1000 or less), polymerization is easier to control.
• x examples include 30 to 1000, 40 to 1000, 40 to 700, and 50 to 400.
• y and z are the total number/amount of units (structures) represented by formula (2) and units (structures) represented by formula (3), respectively (the total number/amount of units (structures) represented by formula (2) in the polymer or PVA, and the total number/amount of units (structures) represented by formula (2) in the polymer or PVA) (i.e., it does not indicate that y units represented by formula (2) are continuously bonded together, or that z units represented by formula (3) are continuously bonded together).
• y and z are each 0 or greater than 0 (finite values). However, y and z cannot be 0 at the same time.
• y+z is as described above and may be selected from the range of about 2 or more (e.g., 3 or more), and from the viewpoint of the desired function (good amphiphilicity, etc.), block character, and ease of obtaining the aforementioned hydrodynamic radius (and ease of efficiently achieving both), may be, for example, about 3.5 or more, preferably 4 or more, and more preferably 4.5 or more (e.g., 5 or more), or may be 6 or more (e.g., 6.5 or more, 7 or more, 7.5 or more, 8 or more, 8.5 or more, 9 or more, 9.5 or more, 10 or more, 10.5 or more, 11 or more), etc.
• the upper limit of y+z is not particularly limited, but may be, for example, 3000, 2000, 1500, 1200, 1000, 900, 800, 700, 600, 500, 450, 400, 350, 300, less than 300, 290, 280, 270, 260, 250, 240, 230, 220, 210, 200, 180, 150, 120, 100, 80, 70, 60, 50, 40, 30, 20, 18, 15, 12, etc.
• y+z is not too high (e.g., 500 or less), it is easier to control the polymerization.
• y+z examples include 4 to 500, 6 to 300, and 8 to 200.
• y/z is as described above and is not particularly limited, but may be, for example, about 0.0001 to 10,000, 0.001 to 1,000, or 0.01 to 100.
• x+y+z is as described above and may be selected from the range of about 20 or more (e.g., 30 or more), and from the viewpoint of the desired function (good amphiphilicity, etc.), block character, and ease of obtaining the aforementioned hydrodynamic radius (and also ease of efficiently achieving both), may be, for example, about 35 or more, preferably 40 or more, and more preferably about 50 or more (e.g., 55 or more), or may be 60 or more (e.g., 65 or more, 70 or more, 75 or more, 80 or more, 85 or more, 90 or more, 95 or more, 100 or more, 105 or more, 110 or more, 120 or more, 130 or more, 140 or more, 150 or more), etc.
• the upper limit of x+y+z is not particularly limited, but may be, for example, 10,000, 8,000, 7,000, 6,000, 5,000, 4,000, 3,000, 2,000, 1,500, 1,200, 1,000, 900, 800, 700, 600, 500, 450, 400, 350, 300, less than 300, 290, 280, 270, 260, 250, 240, 230, 220, 210, 200, etc.
• x + y + z is not too high (e.g., 1000 or less), polymerization is easier to control.
• x+y+z examples include 40 to 1000, 50 to 1000, 60 to 700, and 70 to 500.
• x/(x+y+z) ⁇ 100% (mol%) is as described above, and may be selected, for example, from a range of about 99 mol% (or 99%) or less. From the viewpoint of the desired function (e.g., water solubility, ease of forming aggregates, etc.), block character, and ease of obtaining the aforementioned hydrodynamic radius (and also ease of efficiently achieving both), it may be about 98% or less (e.g., 97 mol% or less), preferably 96 mol% or less (e.g., 95 mol% or less), and more preferably 94 mol% or less (e.g., 93.5 mol% or less), and may be about 93 mol% or less (e.g., 92 mol% or less, 91 mol% or less, 90 mol% or less, less than 90 mol%, 89.5 mol% or less, 89 mol%, 88 mol% or less, 87 mol% or less, 86 mol% or
• 84 mol% or less 83 mol% or less, 82 mol% or less, 81 mol% or less, 80 mol% or less, less than 80 mol%, 79 mol% or less, 78 mol% or less, 77 mol% or less, 76 mol% or less, 75 mol% or less, 74 mol% or less, 73 mol% or less, 72 mol% or less, 71 mol% or less, 70 mol% or less, less than 70 mol%, 69 mol% or less, 68 mol% or less, 67 mol% or less, 66 mol% or less, 65 mol% or less, 64 mol% or less, 63 mol% or less, 62 mol% or less, 61 mol% or less, 60 mol% or less, less than 60 mol%, 59 mol% or less, 58 mol% or less, 57 mol% or less, 56 mol% or less, 55 mol% or less, 54
• x/(x+y+z) ⁇ 100% (mol%) is as described above and can be selected depending on the desired properties (e.g., water solubility, ease of forming aggregates, etc.), and may be selected, for example, from a range of about 10 mol% (or 10%) or more, 12 mol% or more (e.g., 15 mol% or more), preferably 20 mol% or more (e.g., 25 mol% or more), and more preferably 30 mol% or more (e.g., 35 mol% or more, 38 mol% or more), and may be 40 mol% or more (e.g., more than 40 mol%, 41 mol% or more, 42 mol% or more, 43 mol% or more, 44 mol% or more, 45 mol% or more, 46 mol% or more, 47 mol% or more, 48 mol% or more, 49 mol% or more, 50 mol% or more, more than 50 mol%, 51 mol% or more, 52
• x/(x+y+z) ⁇ 100% include 40 to 96 mol%, 50 to 94 mol%, and 60 to 92 mol%, etc.
• the PVA when the PVA has a unit represented by the formula (1) and at least one unit selected from the unit represented by the formula (2) and the unit represented by the formula (3), it may further have other units (units not belonging to any of the categories represented by the formulas (1) to (3)). Such units include the units derived from other monomers mentioned above.
• the ratio of the units derived from other monomers when the total amount of the units represented by formula (1) and at least one unit selected from the units represented by formula (2) and the units represented by formula (3) is 100 mol (or 100 parts by mass), may be, for example, 20 mol or less (or 20 parts by mass or less) [e.g., 0.1 to 20 mol (or 0.1 to 20 parts by mass)], 10 mol or less (or 15 parts by mass or less), 5 mol or less (or 5 parts by mass or less), 3 mol or less (or 3 parts by mass or less), etc.
• the method for producing PVA is not particularly limited, but for example, it can be produced through a process including at least the following steps 1, 2, and 3.
• Step 1 A step of synthesizing a macro chain transfer agent by subjecting a first vinyl ester to living radical polymerization.
• Step 2 A step of synthesizing a block copolymer by subjecting a second vinyl ester different from the first vinyl ester to living radical polymerization in the presence of the macro chain transfer agent obtained in step 1.
• Step 3 A step of partially saponifying the block copolymer obtained through at least step 2.
• RAFT polymerization reversible addition-fragmentation chain-transfer polymerization
• RAFT polymerization is a type of living radical polymerization that uses a thiocarbonyl compound (RAFT agent) as a chain transfer agent, and can synthesize polymers with narrow molecular weight distribution while controlling the molecular weight.
• RAFT agent thiocarbonyl compound
• vinyl ester (vinyl ester monomer) used in step 1 examples include those exemplified above (monomers corresponding to vinyl ester units), such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl caprylate, vinyl versatate (product names: VeoVa9, VeoVa10, manufactured by HEXION, etc.), vinyl pivalate (pivalic acid), vinyl trifluoroacetate, and other fatty acid vinyl esters, and vinyl benzoate, and other aromatic vinyl esters.
• vinyl acetate or vinyl pivalate is preferably used.
• vinyl monochloroacetate and the like may cause coloring or may make it difficult to increase the degree of polymerization due to chain transfer (e.g., chain transfer due to a chloromethyl group), and therefore it is preferable not to use them or to use them in a small amount even if they are used.
• chain transfer e.g., chain transfer due to a chloromethyl group
• Polymerization methods include known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among them, bulk polymerization, which is performed without a solvent, or solution polymerization, which is performed in various organic solvents, are usually used. Bulk polymerization is preferred because it can achieve a high polymerization rate and there is no risk of the solvent causing chain transfer or reaction with the RAFT agent. Solution polymerization is preferred because it is possible to control the viscosity of the polymerization reaction solution and the polymerization rate by adding an organic solvent.
• organic solvents used in solution polymerization include esters such as methyl acetate and ethyl acetate; aromatic hydrocarbons such as benzene and toluene; lower alcohols such as methanol and ethanol; and ethers such as diethyl ether and tetrahydrofuran (THF).
• the amount of solvent used may be determined in accordance with the number average molecular weight and reaction yield of the target polymer, taking into consideration the viscosity of the reaction solution.
• the mass ratio (solvent/monomer) is selected from the range of 0.01 to 10.
• the mass ratio (solvent/monomer) is preferably 0.1 or more and preferably 5 or less.
• dithiocarbamate type RAFT agents cyanomethyl methyl(phenyl)carbamodithioate and cyanomethyl diphenylcarbamodithioate are preferably used.
• a xanthate-type RAFT agent ethyl 2-[(ethoxycarbonothioyl)thio]propionate can be preferably used.
• RAFT polymerization produces one polyvinyl ester chain from one molecule of added RAFT agent.
• the amount of RAFT agent added is determined taking into account the desired number average molecular weight and polymerization rate, and it is usually preferable to use 0.01 to 2 moles of RAFT agent per 100 moles of vinyl ester monomer.
• the radical initiator used in step 1 is appropriately selected from conventionally known azo initiators, peroxide initiators, redox initiators, photopolymerization initiators, etc.
• azo initiators include 2,2'-azobisisobutyronitrile (AIBN), 2,2'-azobis(2,4-dimethylvaleronitrile) (ADVN), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile) ("V-70")
• examples of peroxide initiators include percarbonate compounds such as di-n-propyl peroxydicarbonate, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate, ⁇ -cumyl peroxyneodecanate, and t-butyl peroxyneodecanate; acetyl
• the number of moles of radical initiator used is preferably 0.1 to 5 times the number of moles of the RAFT agent, and is determined taking into consideration the type of radical initiator used (initiator efficiency and half-life temperature) and the polymerization temperature. If the number of moles of radical initiator is small, it is difficult to obtain a sufficient reaction rate, and an induction period may occur. If the number of moles of radical initiator is too large, and the number of moles of radicals generated is greater than the number of moles of the RAFT agent, the proportion of uncontrolled radical polymerization increases, making it difficult to obtain a block copolymer in step 2.
• the polymerization temperature is preferably, for example, 0°C to 80°C. If the polymerization temperature is below 0°C, the polymerization rate will be insufficient, resulting in reduced productivity. From this point of view, it is more preferable that the polymerization temperature be 10°C or higher, and even more preferable that it be 20°C or higher. On the other hand, if the polymerization temperature exceeds 80°C, it becomes difficult to control the RAFT polymerization. From this point of view, it is more preferable that the polymerization temperature be 70°C or lower, and even more preferable that it be 60°C or lower.
• the polymerization reaction may be stopped by cooling or the like, and the unreacted vinyl ester may be removed.
• Methods for removing the unreacted vinyl ester include dropping the reaction liquid into a poor solvent such as hexane to precipitate and recover the resulting polymer, or distilling off the unreacted vinyl ester by drying under reduced pressure. Note that by making the polymerization rate 100%, all of the vinyl ester may be consumed by polymerization. In this case, a solution polymerization method in which an organic solvent is added is preferred.
• the polyvinyl ester polymer thus obtained is used as a chain transfer agent (macro RAFT agent) in the next step 2.
• Step 2 Step of synthesizing polyvinyl ester block copolymer>
• the polyvinyl ester polymer obtained in step 1 is used as a chain transfer agent (macro RAFT agent) to carry out RAFT polymerization of a vinyl ester monomer different from that in step 1, thereby synthesizing, for example, an A-B type block copolymer consisting of two types of polyvinyl esters.
• the second vinyl ester (vinyl ester monomer) used in step 2, as in step 1, may include fatty acid vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl caprylate, vinyl versatate (product names: VeoVa9, VeoVa10, manufactured by HEXION), vinyl pivalate (pivalic acid), vinyl trifluoroacetate, and aromatic vinyl esters such as vinyl benzoate, but a vinyl ester different from the first vinyl ester used in step 1 is used. As mentioned above, it is preferable not to use vinyl chloroacetate, or to use as little as possible.
• the hydrolysis resistance of the ester group of the first vinyl ester and the second vinyl ester is significantly different.
• the ester group with low hydrolysis resistance is selectively saponified, thereby making it possible to obtain a PVA (partially saponified polyvinyl alcohol) with high blocking properties.
• the hydrolysis resistance of an ester group depends on the structure (steric factors, electronic factors) of the vinyl ester group. From this viewpoint, the first vinyl ester and the second vinyl ester are preferably a combination of vinyl acetate and vinyl pivalate, which have significantly different steric structures.
• the vinyl ester polymerization method in step 2 includes known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization.
• bulk polymerization which is performed without a solvent, or solution polymerization, which is performed in various organic solvents, is usually used.
• Bulk polymerization is preferred because it provides a high polymerization rate and there is no risk of the solvent causing chain transfer or reaction with the RAFT agent.
• Solution polymerization is preferred because it is possible to control the viscosity of the polymerization reaction solution and the polymerization rate by adding an organic solvent.
• organic solvents used in solution polymerization include esters such as methyl acetate and ethyl acetate; aromatic hydrocarbons such as benzene and toluene; lower alcohols such as methanol and ethanol; and ethers such as diethyl ether and tetrahydrofuran (THF).
• the amount of solvent used may be determined in accordance with the number average molecular weight and reaction yield of the target polymer, taking into consideration the viscosity of the reaction solution.
• the mass ratio (solvent/monomer) is selected from the range of 0.01 to 10.
• the mass ratio (solvent/monomer) is preferably 0.1 or more and preferably 5 or less.
• the RAFT agent used in step 2 is the polyvinyl ester polymer obtained in step 1, which is used as a chain transfer agent (macro RAFT agent) to carry out RAFT polymerization of the second vinyl ester to synthesize an A-B type block copolymer.
• the amount of RAFT agent added is determined taking into consideration the desired number average molecular weight and polymerization rate, and it is usually preferable to use 0.1 to 10 moles of RAFT agent per 100 moles of vinyl ester monomer.
• the radical initiator used in step 2 may be appropriately selected from conventionally known azo initiators, peroxide initiators, redox initiators, photopolymerization initiators, etc., but the initiator used in step 1 may be used as is.
• the number of moles of radical initiator used is preferably 0.1 to 5 times the number of moles of the RAFT agent, and is determined taking into consideration the type of radical initiator used (initiator efficiency and half-life temperature) and the polymerization temperature. If the number of moles of radical initiator is small, it is difficult to obtain a sufficient reaction rate, and an induction period may occur. If the number of moles of radical initiator is too large, and the number of moles of radicals generated becomes greater than the number of moles of the RAFT agent, the proportion of uncontrolled radical polymerization increases, which may cause the production of a second vinyl ester homopolymer.
• the polymerization temperature is preferably, for example, 0°C to 80°C. If the polymerization temperature is below 0°C, the polymerization rate will be insufficient, resulting in reduced productivity. From this point of view, it is more preferable that the polymerization temperature be 10°C or higher, and even more preferable that it be 20°C or higher. On the other hand, if the polymerization temperature exceeds 80°C, it becomes difficult to control the RAFT polymerization. From this point of view, it is more preferable that the polymerization temperature be 70°C or lower, and even more preferable that it be 60°C or lower.
• the polymerization reaction can be stopped by cooling or adding a polymerization inhibitor, and the unreacted vinyl ester can be removed.
• Methods for removing the unreacted vinyl ester include dropping the reaction liquid into a poor solvent such as hexane as in step 1 to precipitate and recover the resulting polymer, or distilling off the unreacted vinyl ester by drying under reduced pressure. In this way, an A-B type diblock copolymer consisting of two polyvinyl ester segments can be obtained.
• step 2 it is also possible to use the diblock polymer obtained in step 2 as a chain transfer agent (macro RAFT agent) to carry out RAFT polymerization of a vinyl ester (a third vinyl ester) different from that in step 2, to synthesize an A-B-C type or A-B-A type triblock copolymer.
• a chain transfer agent macro RAFT agent
• fatty acid vinyl esters such as vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl caproate, vinyl caprylate, vinyl versatate, vinyl pivalate (pivalic acid), and vinyl trifluoroacetate, and aromatic vinyl esters such as vinyl benzoate can be mentioned, but a vinyl ester different from the second vinyl ester used in step 2 is used. As mentioned above, it is preferable not to use vinyl chloroacetate or to use a small amount of it.
• an A-B-A type triblock copolymer can be synthesized, and if a vinyl ester not used in step 1 is used, an A-B-C type triblock copolymer can be synthesized.
• the synthesis method of the triblock copolymer is the same as that of the diblock copolymer described above. Additionally, the process can be repeated using quaternary or more vinyl esters. If necessary, other monomers may be polymerized (for example, copolymerized with the first, second and/or third vinyl esters) before or after (particularly before) step 3.
• Step 3 Step of partially saponifying the polyvinyl ester block copolymer>
• a block copolymer having a plurality of polyvinyl ester segments (polyvinyl ester block copolymer) obtained through at least step 2 is partially saponified.
• the vinyl ester units constituting the polyvinyl ester have different hydrolysis resistance of the ester group, it is possible to make the degree of hydrolysis different for each segment by setting appropriate saponification conditions.
• polyvinyl ester segment having relatively high hydrolysis resistance e.g., polyvinyl pivalate segment
• polyvinyl ester segment having relatively low hydrolysis resistance e.g., polyvinyl acetate segment
• the method of saponification of the polyvinyl ester block copolymer is not particularly limited and may follow a conventionally known method.
• alcoholysis or hydrolysis using a conventionally known basic catalyst such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium methoxide, or an acidic catalyst such as sulfuric acid or p-toluenesulfonic acid can be applied.
• Solvents used in the saponification reaction include water, as well as alcohols such as methanol and ethanol; esters such as methyl acetate and ethyl acetate; ketones such as acetone and methyl ethyl ketone; aromatic hydrocarbons such as benzene and toluene, and the like.
• the saponification reaction can be controlled by adjusting the saponification temperature, saponification time, type of catalyst, amount of catalyst used, concentration of the polyvinyl ester block copolymer, water content, and the like.
• the saponification temperature can be selected from the range of usually 20°C to 70°C, preferably from 30°C to 60°C.
• the saponification time can be selected from the range of usually 5 minutes to 5 hours, preferably from 10 minutes to 1 hour.
• the amount of catalyst used can be selected from the range of usually 0.2 to 10 mol%, preferably from 0.4 to 5 mol%, based on the vinyl ester unit of the polyvinyl ester block copolymer.
• the concentration of the polyvinyl ester block copolymer can be selected from the range of usually 5 to 70 mass%, preferably from 10 to 60%.
• the water content can be selected from the range of usually 0 to 5 mass%, preferably from 0.2 to 2 mass%.
• saponification conditions are too severe, not only vinyl ester groups with low hydrolysis resistance but also vinyl ester groups with high hydrolysis resistance may be saponified, and in this case, the block character of the resulting PVA tends to be reduced. Conversely, if the saponification conditions are too mild, vinyl ester groups with low hydrolysis resistance may not be sufficiently saponified, and in this case, the block character of the resulting PVA tends to be reduced.
• the PVA may be dissolved (or dispersed) in water or an aqueous medium containing water. Therefore, the present invention also includes an aqueous liquid containing PVA [for example, an aqueous solution, an aqueous dispersion, or a liquid dissolved or dispersed in an aqueous medium (for example, a mixed solvent of water and an organic solvent (a hydrophilic solvent such as alcohol))].
• an aqueous liquid containing PVA for example, an aqueous solution, an aqueous dispersion, or a liquid dissolved or dispersed in an aqueous medium (for example, a mixed solvent of water and an organic solvent (a hydrophilic solvent such as alcohol)
• the proportion of PVA (or aggregate) is not particularly limited, but may be selected from a range of, for example, about 0.00001% by mass or more (e.g., 0.00005% by mass or more), may be 0.0001% by mass or more (e.g., 0.0005% by mass or more), preferably 0.001% by mass or more (e.g., 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, 0.5% by mass or more), etc., or may be 90% by mass or less (e.g., 80% by mass or less, 50% by mass or less, 30% by mass or less, 20% by mass or less, 10% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.5% by mass or less, etc.).
• the PVA may form aggregates (micelles).
• the present invention also includes such aggregates (micelles).
• the size (hydrodynamic radius) of the aggregate may be in the same range as described above (eg, 10 to 200 nm, etc.).
• the aggregate (micelle) may contain (encapsulate) an ingredient (a drug (e.g., a hydrophobic drug), a hydrophobic component, a hydrophilic component, etc.).
• a drug e.g., a hydrophobic drug
• a hydrophobic component e.g., a hydrophobic component
• hydrophilic component e.g., etc.
• the present invention also includes such aggregates (micelles, preparations).
• the contents may be a hydrophobic component.
• hydrophobic components include components (substances) whose solubility (20°C) in 100 mL (100 g) of water (solubility at 20°C) is 500 mg (500 mg/100 g H2O ) or less, 300 mg or less, 200 mg or less, 100 mg or less, 50 mg or less (e.g., 30 mg or less, 20 mg or less, 10 mg or less, 5 mg or less, 3 mg or less, 2 mg or less, 1.5 mg or less, 1.2 mg or less, 1 mg or less, 0.8 mg or less, 0.5 mg or less, 0.3 mg or less, 0.2 mg or less), etc.
• solubility (20°C) in 100 mL (100 g) of water (solubility at 20°C) is 500 mg (500 mg/100 g H2O ) or less, 300 mg or less, 200 mg or less, 100 mg or less, 50 mg or less (e.g., 30 mg or less, 20 mg or less, 10 mg or less, 5 mg or less, 3 mg or
• the ratio of the contents may be selected from a range of, for example, about 0.0001 parts by mass or more (e.g., 0.001 parts by mass or more) relative to 100 parts by mass of PVA, and may be 0.01 parts by mass or more (e.g., 0.05 parts by mass or more), preferably 0.1 parts by mass or more (e.g., 0.5 parts by mass or more, 1 part by mass or more, 3 parts by mass or more, 5 parts by mass or more, 10 parts by mass or more), etc., or may be 1000 parts by mass or less (e.g., 500 parts by mass or less, 300 parts by mass or less, 200 parts by mass or less, 100 parts by mass or less, 80 parts by mass or less, 50 parts by mass or less, 40 parts by mass or less, 30 parts by mass or less, 20 parts by mass or less, 10 parts by mass or less, etc.).
• 0.0001 parts by mass or more e.g., 0.001 parts by mass or more
• the ratio of the contents hydrophobic components, etc
• Theoretical degree of polymerization (molar amount of vinyl ester (VE1) charged/molar amount of RAFT agent charged) ⁇ reaction rate of vinyl ester (VE1)
• the theoretical degree of polymerization of the PVE2 component of the polyvinyl ester block copolymer (PVE1-b-PVE2) can be calculated in the same manner as above using the reaction rate of VE2.
• Theoretical number average molecular weight: Mn (theoretical) molecular weight of RAFT agent + molecular weight of vinyl ester (VE1) x theoretical degree of polymerization
• Method of determining the composition of partially saponified polyvinyl alcohol As an example, a method for calculating the content (x, y, z) of each unit of a partially saponified polyvinyl alcohol obtained by partially saponifying a block copolymer obtained by using vinyl acetate as VE1 and vinyl pivalate as VE2 as in Example C1 will be described below.
• the degree of polymerization P may be the theoretical degree of polymerization described above or a degree of polymerization calculated based on the molecular weight (number average molecular weight Mn, weight average molecular weight Mw, etc.) of a fully saponified polyvinyl alcohol or the molecular weight (number average molecular weight Mn, weight average molecular weight Mw, etc.) of a polyvinyl ester obtained by re-esterification (acetylation, etc.) (calculated as molecular weight/molecular weight of vinyl alcohol unit or molecular weight/molecular weight of vinyl ester unit) (theoretical degree of polymerization was used in this embodiment).
• the block character ( ⁇ ) was calculated using the integral value obtained above according to the following formula.
• Block character ( ⁇ ) (OH, OCOR) / [2(OH)(OCOR)]
• (OH, OH) and (OCOR, OCOR) are as follows.
• the resulting partially saponified polyvinyl alcohol was dissolved in water, and the size of the aggregates (micelles) formed was determined by DLS (Dynamic Light Scattering) measurement.
• DLS Dynamic Light Scattering
• the partially saponified polyvinyl alcohol obtained was dissolved in water at a concentration of 1 g/L and filtered through a membrane filter having a pore size of 1 ⁇ m.
• the hydrodynamic radius of this sample solution was measured at 25° C. using a Malvern Zetasizer NanoZS (He-Ne laser, 4 mW at 632.8 nm).
• the chlorine content in the sample was measured using a sample combustion device AQF-2100H manufactured by Nitto Seiko Analytech Co., Ltd. and an ion chromatograph manufactured by Thermo Fisher Scientific.
• the polymerization solution after the reaction was measured by NMR, and as a result, the reaction rate of vinyl pivalate was found to be 50%.
• THF and unreacted vinyl pivalate were distilled off under reduced pressure at 120°C.
• the analytical results of the obtained polyvinyl acetate-polyvinyl pivalate block copolymer (PVE1-PVE2) are shown in Table 2.
• the degree of polymerization (theoretical) in Table 2 indicates the degree of polymerization of the PVE2 component.
• the fully saponified polyvinyl alcohol for GPC measurement was synthesized as follows: an aqueous solution of sodium hydroxide was added to partially saponified polyvinyl alcohol dissolved or dispersed in methanol, and the mixture was allowed to react at 55° C.
• Examples C2 to C13 Partially saponified polyvinyl alcohol was synthesized in the same manner as in Example C1, except that the types of block copolymer and saponification catalyst used and the amount added thereof were changed as shown in Table 4. The analysis results are shown in Table 5.
• the partially saponified polyvinyl alcohol obtained in Example C12 had a higher YI value, a higher chlorine content, and a higher Mw/Mn of the fully saponified PVA than the partially saponified polyvinyl alcohols obtained in Examples C1 to C11.
• anthracene was used as the hydrophobic substance, and the solubility of anthracene dissolved in water was estimated by UV absorbance.
• the solubility of anthracene in 100 mL (100 g) of water (20°C) is approximately 0.13 mg (0.13 mg/100 g water). The specific method is shown below.
• Example D1 50 mg of the partially saponified polyvinyl alcohol obtained in Example C1 and 5 mg of anthracene were dissolved in 950 mg of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). Anthracene was saturated and some of the anthracene was left undissolved. The solution was dialyzed against water for 24 hours using a cellulose tube for dialysis (dialysis membrane 36/32, pore size 5 nm, manufactured by Sekisui Material Solutions Co., Ltd.) to prepare an anthracene saturated aqueous solution.
• HFIP 1,1,1,3,3,3-hexafluoro-2-propanol
• Undissolved anthracene was filtered through a membrane filter with a pore size of 0.45 ⁇ m.
• the sample liquid was diluted with water to a concentration of 0.5 mass percent of partially saponified polyvinyl alcohol.
• the UV-Vis spectrum (quartz cell with an optical path length of 10 mm) was measured at 20° C. using an ultraviolet-visible spectrophotometer (V-730, manufactured by JASCO Corporation).
• the UV-Vis spectrum of a 0.5 mass percent aqueous solution of partially saponified polyvinyl alcohol was also measured as a blank.
• the absorbance of anthracene dissolved in the aqueous solution of partially saponified polyvinyl alcohol was calculated by subtracting the absorbance of the blank at 254 nm from the absorbance of the sample solution at 254 nm.
• Example D2 The absorbance of anthracene dissolved in the aqueous solution of partially saponified polyvinyl alcohol was determined in the same manner as in Example D1, except that the partially saponified polyvinyl alcohol used was changed to that obtained in Example C12.
• Comparative Example D1 The absorbance of anthracene dissolved in an aqueous solution of a partially saponified polyvinyl acetate having a degree of polymerization of 300 obtained in Comparative Example C1 (saponification degree 88 mol%, block character 0.45) was determined in the same manner as in Example D1, except that the partially saponified polyvinyl alcohol used was changed to the partially saponified polyvinyl acetate having a degree of polymerization of 300 obtained in Comparative Example C1.
• Example D2 The absorbance of anthracene dissolved in water was determined in the same manner as in Example D1, except that partially saponified polyvinyl alcohol was not added. Water was used as a blank.
• Example D1 and D2 Compared to Comparative Example D1, Examples D1 and D2 had a higher absorbance due to anthracene, and in particular, Example D1 had an absorbance of more than 80 times that of Example D1. This shows that the partially saponified polyvinyl alcohol obtained in Examples C1 and C12 (particularly Example C1) can significantly improve the solubility of anthracene by encapsulating anthracene in the hydrophobic core of the micelle.
• Examples E1, E2, Comparative Examples E1, E2 In Examples D1 and D2 and Comparative Examples D1 and D2, the anthracene was changed to ethenzamide [a component having a solubility in 100 mL (100 g) of water (20° C.) of approximately 100 mg (100 mg/100 g water)], and the partially saponified polyvinyl alcohol was changed from 0.5 mass percent to 0.2 mass%, but the absorbance was determined in the same manner. The results showed similar trends to those of Examples D1 and D2 and Comparative Examples D1 and D2.
• the present invention provides specific polyvinyl alcohol-based polymers. Such polymers can be used for various applications, such as medical materials for drug delivery systems.

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