Classifications

• • 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
  • C08F18/00—Homopolymers and 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
  • C08F18/02—Esters of monocarboxylic acids
  • C08F18/04—Vinyl esters
  • C08F18/08—Vinyl acetate
• • D—TEXTILES; PAPER
  • D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
  • D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
  • D01F6/00—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
  • D01F6/02—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
  • D01F6/16—Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polymers of unsaturated carboxylic acids or unsaturated organic esters, e.g. polyacrylic esters, polyvinyl acetate
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P31/00—Antiinfectives, i.e. antibiotics, antiseptics, chemotherapeutics
  • A61P31/04—Antibacterial agents
  • A61P31/06—Antibacterial agents for tuberculosis
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P35/00—Antineoplastic agents
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61P—SPECIFIC THERAPEUTIC ACTIVITY OF CHEMICAL COMPOUNDS OR MEDICINAL PREPARATIONS
  • A61P9/00—Drugs for disorders of the cardiovascular system
• • 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
  • C08F18/00—Homopolymers and 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
  • C08F18/02—Esters of monocarboxylic acids
  • C08F18/04—Vinyl esters
  • C08F18/10—Vinyl esters of monocarboxylic acids containing three or more carbon atoms
• • 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 a method of preparing poly(vinyl pivalate) by low temperature suspension polymerization of vinyl pivalate, and poly(vinyl pivalate) and poly(vinyl alcohol) prepared using the same, and more particularly, to a method of preparing high molecular weight poly(vinyl pivalate) having a particulate or microspherical structure for a precursor of poly(vinyl alcohol) with a high molecular weight and excellent syndiotacticity at a high conversion rate using only a chemical initiator without initiation by ultraviolet rays, through the low temperature suspension polymerization of vinyl pivalate monomer, a method of preparing poly(vinyl pivalate) microspheres, and a method of preparing poly(vinyI alcohol) in the form of precipitate, fiber, and microspherical particulate through the saponification of poly (vinyl pivalate).
• PVA Poly(vinyl alcohol)
• German Patent No. 450,286, 1924 is a linear semicrystalline hydroxy group-containing polymer prepared through the saponification of vinylester- based polymers such as poly(vinyl acetate).
• PVA is widely used in plastics, textiles, industrial fibers, and films with respect to the molecular weight thereof.
• the synthesized PVA should bear a high degree of saponification, a high molecular weight, and an excellent syndiotacticity.
• Monomers for synthesizing precursors of, an atactic PVA and a syndiotactic PVA are widely known.
• vinyl pivalate is known to elucidate the best syndiotacticity due to a steric hindrance of tertiary butyl groups thereof, but it cannot be easily saponified.
• the present inventor established a method of saponifying poly(vinyl pivalate) (see U.S. Patent No. 6,124,033).
• vinyl trifluoroacetate has been extensively used for monomers for obtaining syndiotactic PVA.
• polymers from such monomers can be saponified in a relatively easy manner compared to that from a vinyl pivalate monomer, the use thereof involves shortcomings of high material cost and poor syndiotacticity.
• Embolotherapy is a medical treatment technology wherein the blood flow in blood supply vessels for lesions at surgically untreatable sites is blocked through injecting a special material into the blood vessels, thereby treating the lesions, relieving symptoms due to an excessive blood flow, and preventing hemorrhaging during surgical operations.
• Embolotherapy is used to treat hypervascular tumors with high vascularity, vascular diseases such as arteriovenous malformation (AVM), and traumatic or inflammatory hemorrhaging as with tuberculosis.
• AVM arteriovenous malformation
• Markowitz first established the concept of treating diseases by embolotherapy in 1952. He suggested a technique of treating hepatic tumors through blocking arterial blood flow, based on the fact that the liver is supplied with blood via both the hepatic portal vein and the hepatic artery, while the primary and metastatic hepatic tumor cells are mainly supplied via the hepatic artery (See J. Markowitz, Surg. Gynecol. Obstet., 395, 644, 1952). For selective embolization, it is necessary to confirm whether the hepatic tumor cells are supplied with blood via the hepatic portal vein or the hepatic artery.
• embolic materials there are various materials that are used as embolic materials. Such materials include metallic coils, liquid tissue adhesives, barium impregnated silastic balls, methacrylates, stainless steels, and particulate materials. Since the 1970s, PVA has been widely used as an embolic material.
• an ideal embolic material should be made of a substance that exhibits excellent biocompatibility due to the interaction with tissues surrounding the site to be treated. Second, it should effectively get to the target site of lesions to achieve an excellent therapeutic effect and to predict therapeutic effects. Third, the ideal embolic material should be easily handled and injected for general clinical use. Fourth, the ideal embolic material should exhibit permanent embolic effects while bearing a uniform distribution of particle sizes. Finally, it should form a homogeneous suspension in a nonionic vehicle. In consideration of such requirements, it can be easily understood that the ideal embolic material should bear a uniform size distribution of particles with a microspherical shape.
• PVA has been highlighted as an embolic material because of its biocompatibility, technical ease, and capability of fluent adjustment in particle size.
• PVA is used as an embolic material for malignant hepatic tumors, hepatic AVMs, cerebral AVMs, and vascular tumors in many sites, etc.
• PVA is the most widely used among currently existing embolic materials, extensive studies related thereto are in progress.
• the commercial PVA embolic material "Contour®” has a very rough and sharp surface while being significantly differentiated from spherical particles with a uniform size distribution.
• many researchers have made attempts to prepare spherical particles from various polymers other than PVA, such as porous cellulose, gelatin, collagen and collagen-coated acryl polymer.
• polymers other than PVA such as porous cellulose, gelatin, collagen and collagen-coated acryl polymer.
• natural polymeric materials such as gelatin are obtained directly from nature, it is impossible to control the molecular parameters (e.g. molecular weight, molecular weight distribution, and degree of branching) and physical dimensions (particle size and shape) of the natural polymeric materials.
• the permanent embolic effects of such embolic materials have not yet been confirmed.
• a uniform particle size distribution is necessary for the embolic materials to be fed to the target area through a catheter during a surgical operation as well as to enhance the therapeutic effects of embolotherapy through selective occluding of blood vessels.
• the polymeric particles prepared by suspension polymerization are generally retained in spherical forms, their sizes are very different with respect to the conditions of polymerization. Furthermore, it is very difficult to separate them into individual uniform sized particles because they associate due to static attractive forces between the suspending agents used during polymerization and the polymeric particles.
• poly(vinyl pivalate) is prepared by means of suspension polymerization of vinyl pivalate.
• poly(vinyl pivalate) is saponified to PVA, the PVA particles are retained in spherical forms but their sizes are non-uniform. With the associated particles, it becomes difficult to inject them into the required position and to facilitate high selectivity occluding of the blood vessels around injuries. Therefore, in order to prepare PVA particles as an excellent high quality embolic material, it is necessary to separate poly(vinyl pivalate) microspheres for a precursor.
• the PVA embolic materials are prepared through saponifying poly(vinyl pivalate).
• the saponification of poly(vinyl pivalate) is achieved by completely dissolving poly(vinyl pivalate) in an organic solvent such as tetrahydrofuran, acetone and methyl ethyl ketone, and adding the alkali solution in a dropwise manner.
• the resulting PVA materials have a very irregular surface, various shapes ranging from a precipitation phase to a fibrous phase, and a very wide size distribution. Accordingly, in order to produce embolic particulate materials with excellent embolic ability, a new saponification method that can prohibit the association of particles while maintaining the particle shape in a stable manner is needed.
• poly(vinyl pivalate) is prepared through suspension polymerization of vinyl pivalate where a suspension including vinyl pivalate, azobisdimethylvaleronitrile as an initiator, a suspending agent and water is
• suspension has a composition of per 1 mol of the vinyl pivalate 1x10 "5 mol to 5x10 "3 mol of the initiator, 1x10 "6 mol to 1x10 ⁇ 4 mol of the suspending agent, and 1.0 mol to 50 mol of water.
• syndiotactic poly(vinyl pivalate) is obtained with the characteristics of a conversion rate from monomer to polymer of 50% or more, a number-average degree of polymerization of 300 to 50,000, a syndiotactic diad content of 54 to 65%, and a degree of branching of 0.2 to 6.0 with respect to the pivalate group.
• PVA in the form of precipitate, fiber, or microsphere with high syndiotacticity, a high molecular weight, and a number-average degree of polymerization of 200 to 20,000 can be obtained using the poly(vinyl pivalate).
• poly(vinyl pivalate) microspheres are prepared through adding inorganic salt as a dispersing and antistatic agent to poly(vinyl pivalate) microspheres, milling the associated poly(vinyl pivalate) microspheres, and separating the poly(vinyl pivalate) microspheres using standard sieves to obtain the uniform sized poly(vinyl pivalate) microspheres.
• the resultant microspherical poly(vinyl pivalate) microspheres have uniform particle
• embolic particles having a dual structure of an outer PVA skin and an inner poly(vinyl pivalate) core are prepared through suspending microspherical poly(vinyl pivalate) microspheres in an aqueous alkali solution including at least one salt selected from the group consisting of sulfates, sulfites, and mixtures thereof; hydroxides; alcohols for an inflating agent; and water, such that the surface of the po!y(vinyl pivalate) microspheres is saponified.
• the embolic particles have a degree of saponification of 1 to 99.9%, and a polydispersity index of particle diameter of 1.00 to 1.20.
• Fig. 1 is a scanning electronic microscopic (SEM) photograph of
• Fig. 2 is a SEM photograph of PVA prepared by conventional homogeneous saponification of poly(vinyl pivalate) according to Comparative Example.
• the process of preparing high molecular weight syndiotactic poly(vinyl pivalate) according to the present invention differs largely from the conventional poly(vinyl pivalate) preparation process.
• the conventional poly(vinyl pivalate) preparation process involves the use of ultraviolet rays or gamma rays because the monomers are initiated at low temperatures. This process involves complicated processing steps while requiring high-cost polymerization equipment.
• poly(vinyl pivalate) is synthesized using azobisisobutylonitrile or benzoyl
• the temperature range of initiation in usual addition polymerization As the polymerization is performed at relatively high temperatures, the molecular weight of the resulting poly(vinyl pivalate) becomes lowered compared to that of poly(vinyl pivalate) prepared by the usual light illumination polymerization at low temperatures.
• the polymerization rate is elevated due to the high polymerization temperatures so that it becomes difficult to obtain a high molecular weight, while the conversion rate is lowered. In the case of bulk polymerization, it is difficult to obtain a conversion rate of 80% or more when low temperature polymerization is undertaken to obtain high molecular weight poly(vinyl pivalate) with high syndiotacticity.
• Emulsion polymerization also involves problems related to bulk polymerization.
• the conversion rate can be highly elevated through increasing the amount of polymerizing solvent, but this seriously effects a chain transfer reaction to the solvent, resulting in a lowered molecular weight of the poly(vinyl pivalate).
• poly(vinyl pivalate) microspheres having a high number-average degree of polymerization, various particle sizes, and uniform size distributions are prepared at a high conversion rate through
• the amount of azobisdimethylvaleronitrile initiator is established to be 1x10 "5 mol to 5x10 "3 mol
• the amount of suspending agent is established to be 1x10 "5 mol to 5x10 "3 mol
• the amount of water is established to be 0.1 mol to 50 mol per 1 mol of vinyl pivalate.
• suspension polymerization an initiator and a suspending agent capable of being dissolved in monomers are used, and this makes it easy to separate microspherical polymer particles from the polymerization reaction system. Furthermore, as the polymerization mechanism for the respective suspended particles is basically the same as in the case of bulk polymerization, high molecular weight poly(vinyl pivalate) exhibiting excellent linearity for preparing high molecular weight PVA can be prepared in an effective manner. That is, ultrahigh molecular weight poly(vinyl pivalate) exhibiting excellent linearity for preparing high molecular weight PVA can be prepared in an effective manner. That is, ultrahigh molecular weight poly(vinyl pivalate) exhibiting excellent linearity for preparing high molecular weight PVA can be prepared in an effective manner. That is, ultrahigh molecular weight poly(vinyl
• Suspension polymerization is performed through mixing and stirring water and a suspending agent in a mixer equipped with a thermometer, a
• Nitrogen which passes a trap of pyrogallol-alkali solution and a trap of CaCI 2 to remove its oxygen and moisture content, is forcefully passed through the mixture to thereby remove the oxygen and moisture content from the mixture.
• Vinyl pivalate monomer and azobisdimethylvaleronitrile initiator are added to the mixture,
• the azobisdimethylvaleronitrile initiator may induce the
• polymerization initiators such as azobisisobutylonitrile and benzoyl peroxide.
• the suspending agent may be at least one selected from PVA,
• arabic gum hydroxyethyl cellulose, methyl cellulose, starch, sodium
• polyacrylate sodium polymethacrylate, gelatine, or styrene-maleic anhydride copolymer neutralized with sodium hydroxide or aqueous ammonia, but it is not limited thereto. It is most preferable to use partially or completely saponified PVA as the suspending agent.
• high molecular weight poly(vinyl pivalate) microspheres with various particle sizes and a uniform size distribution can be prepared through controlling the amount of initiator, suspending agent, and water while regulating the polymerization temperature and the stirring speed.
• the bottommost values of the polymerization conditions are the minimal values of occurrence of polymerization. For instance, the bottommost value of concentration in the initiator is established to be 1 x10 "5 mol per 1 mol of vinyl pivalate. In the case the concentration of the initiator is lower than the value, polymerization at the relevant temperature does not occur.
• the molecular weight of poly(vinyl pivalate) is controlled through varying the concentration of the initiator and the polymerization temperature. The greater the stirring speed is, the more particle shapes become uniform, and the molecular weight and the conversion rate are increased.
• the poly(vinyl pivalate) prepared using the method according to the first preferred embodiment invention bears a conversion rate from monomer to polymer of 50% or more, a number-average degree of polymerization of 300 to 50,000, a syndiotactic diad content of 54 to 65%, and a degree of branching of 0.2 to 6.0 with respect to the pivalate group.
• the poly(vinyl pivalate) may have various sizes of microspherical particles ranged from 1 ⁇ m to 3000 ⁇ m, for instance, 1 ⁇ m, 5 ⁇ m, 10 ⁇ m, 50
• microspheres prepared during one process can be controlled to be uniformly distributed.
• high molecular weight PVA in the form of precipitate, fibrous or microspherical shapes with a high syndiotacticity and a number- average degree of polymerization of 200 to 20000 can be prepared using the poly(vinyl pivalate) prepared through the method according to the first preferred embodiment.
• poly(vinyl pivalate) may be used as a precursor for preparing microspherical PVA embolic particles.
• PVA is prepared through the saponification of poly(vinyl pivalate).
• the process of separating poly(vinyl pivalate) microspheres is a critical factor in obtaining PVA with a uniform particle size distribution.
• the associations occur because of the electrostatic attraction between the suspending agents and the particles, and because of the electrostatic attraction among the particles themselves.
• the associated particles are separated through milling, the particles are re- associated due to the electrostatic charge of the particles. Therefore, it is very difficult to separate the particles to a uniform size.
• the electrostatic charge makes it difficult to perform the subsequent saponification process in a precise and stable manner while arising many problems such as adhesion of the particles to the reactor wall.
• the poly(vinyl pivalate) microspheres with uniform size distributions are separated from the various sized poly(vinyl pivalate) microspheres using inorganic salt as a dispersing and antistatic agent during the milling process, thereby preventing the breakage of the microspheres due to the milling and removing the electrostatic charge of the microspherical particles while making the subsequent processing steps easier and blocking re-association of the microspherical particles.
• inorganic salt is added to the poly(vinyl pivalate) microspheres prepared through the suspension polymerization as a dispersing and antistatic agent, and the associated poly(vinyl pivalate) microspheres are milled and separated using standard sieves.
• the resulting poly(vinyl pivalate) microspheres have
• uniform particle diameters ranging from 1 ⁇ m to 3000 ⁇ m, where a
• the inorganic salt for the dispersing and antistatic agent is preferably at least one selected from alkali metal salts, alkali earth metal salts, or mixtures thereof.
• alkali metal salts preferably at least one selected from alkali metal salts, alkali earth metal salts, or mixtures thereof.
• sodium sulfate (Na 2 SO 4 ), sodium sulfite (Na 2 S0 3 ), sodium chloride (NaCI), calcium sulfate (CaSO ), or magnesium sulfate (MgS0 4 ) may be used for these purposes.
• the inorganic salt for the dispersing and antistatic agent is added to the poly(vinyl pivalate) microspheres in the amount of 0.1 g to 100 g per 1 g of the poly(vinyl pivalate) microspheres.
• the amount of inorganic salt is less than 0.1 g, the desired antistatic effect cannot be obtained.
• the amount of inorganic salt exceeds 100 g, the desired milling process cannot be achieved.
• the inorganic salt for the dispersing and antistatic agent prevents association of particles within the reaction solution during the subsequent saponification process, and it is ultimately removed through washing. Therefore, it does not cause any problems to the PVA particles for embolic materials, while being differentiated from the conventional organic dispersing agent.
• the particle In the preparation of poly(vinyl pivalate) microspheres using the method according to the second preferred embodiment, the particle
• diameters range from 1 ⁇ m to 3000 ⁇ m, where a difference between upper
• the poly(vinyl pivalate) microspheres have similar particle sizes and size distributions of 1 -5 ⁇ m, 5-10 ⁇ m, 10-30 ⁇ m, 30-50 ⁇ m,
• the poly(vinyl pivalate) microspheres prepared using the method according to the second preferred embodiment are saponified such that the particles are maintained in their spherical shapes without deformation while having a dual structure of a PVA skin and a poly(vinyl pivalate) core where only the surface of the poly(vinyl pivalate) is saponified.
• the embolic particles have an outer PVA skin and an inner poly(vinyl pivalate) core while bearing sizes available for use in embolotherapy, with a uniform size distribution.
• the new method of preparing such embolic particles has several specific characteristics.
• the conversion of the poly(vinyl pivalate) into PVA is carried out through dissolving poly(vinyl pivalate) in an organic solvent such as tetrahydrofuran, acetone, or methyl ethyl ketone while using a high concentration of aqueous alkali solution as a catalyst.
• the resulting PVA particles however, have irregular sizes and rough surfaces so that, upon use as embolic materials, the desired high selectivity occlusions of the blood vessels cannot be achieved, and they cause inflammation to the vascular wall.
• the poly(vinyl pivalate) microspheres prepared through suspension polymerization are suspended in an aqueous alkali solution so as to induce the inhomogeneous surface saponification, thereby maintaining a completely spherical shape and smooth surface of the microspheres.
• the aqueous alkali solution includes at least one salt selected from the group consisting of sulfates, sulfites, and mixtures thereof; hydroxides; alcohols for an inflating agent; and water.
• sodium sulfate may be used for the sulfate salt
• sodium sulfite may be used for the sulfite salt
• Alkali metal hydroxides may be used for the hydroxide, and among them, sodium hydroxide and potassium hydroxide are preferably used for that purpose.
• Methanol and ethanol or mixtures thereof may be preferably used for the alcohols for an inflating agent.
• the respective amount of the salts, and the hydroxides is preferably established to be 0.1 to 100 g per 1 g of the poly (vinyl pivalate) microspheres.
• the amount of alcohols for an inflating agent is established to be 0.1 to 100 g per 1 g of the poly(vinyl pivalate) microspheres.
• the amount of the aqueous alkali solution is established to be 10 to 1000 ml per 1 g of the poly(vinyl pivalate) microspheres.
• the inhomogeneous surface saponification reaction of the poly(vinyl pivalate) microspheres is performed at 0 to 150 ° C .
• the poly(vinyl pivalate) microspheres are prepared as the particulate embolic material with an inner poly(vinyl pivalate) core and an outer PVA skin through the surface saponification.
• the polydispersity index of particle diameter is established to be 1.00 to 1.20
• the saponification degree of the poly(vinyl pivalate) is established to be 1 to 99.9%. It is preferable that the ratio of the outer diameter of PVA to the inner diameter of the poly(vinyl pivalate) microspheres is established to be 1 :0.01 to 0.99.
• the particle diameters uniformly range
• embolic particles have nearly similar particle sizes and size distributions of
• Example 1 In a 200 ml four-neck flask equipped with a thermometer, a nitrogen inlet, a cooling column, and an anchor-type stirrer, 60 ml (3.3 mol) of distilled water and 0.9 g of PVA (7.09x10 "6 mol, degree of saponification of 88%, and number-average molecular weight of 127,000) for a suspending
• Nitrogen which passed a trap of pyrogallol-alkali solution and a trap of CaCI 2 to remove its oxygen and moisture content, was forcefully passed through the mixture for two hours to thereby remove the oxygen and moisture content from the mixture.
• 44.1 ml (0.3 mol) of vinyl pivalate monomer and 0.0166 g (2x10 "4 mol/mol of monomer) of azobisdimethylvaleronitrile initiator were added to the mixture, and the oxygen and moisture content were removed from the mixture for one hour.
• the temperature in the flask was elevated to 50 ° C , and the vinyl pivalate
• Example 3 Other conditions were established to be the same as those related to Example 1 except that the amount of azobisdimethylvaleronitrile initiator was 0.0083 g (1x10 ⁇ 4 mol/mol of monomer).
• Example 4 Other conditions were established to be the same as those related to Example 1 except that the amount of azobisdimethylvaleronitrile initiator was 0.0017 g (2x10 "5 mol/mol of monomer).
• Example 1 Example 1 except that the polymerization was performed at 40 ° C for 36 hours.
• Example 2 Example 2 except that the polymerization was performed at 30 ° C for 52
• Example 10 Other conditions were established to be the same as those related to Example 9 except that the amount of azobisdimethylvaleronitrile initiator was 0.0083 g (1 x10 "4 ol/mol of monomer).
• Example 12 Example 12 except that the amount of azobisdimethylvaleronitrile initiator was 0.0025 g (3x10 "5 mol/mol of monomer).
• Example 12 Example 12 except that the amount of azobisdimethylvaleronitrile initiator was 0.0008 g (1x10 "5 mol/mol of monomer).
• Example 15 Example 15 except that the amount of azobisdimethylvaleronitrile initiator was 0.0025 g (3x10 "5 mol/mol of monomer).
• Example 9 Example 9 except that the amount of PVA for the suspending agent was 2.7 g (2.13x10 "5 mol, degree of saponification of 88%, and number-average
• Example 19 Other conditions were established to be the same as those related to Example 17 except that the amount of azobisdimethylvaleronitrile initiator was 0.0025 g (3x10 "5 mol/mol of monomer).
• Example 20 Other conditions were established to be the same as those related to Example 1 except that the amount of PVA for the suspending agent was 0.3 g (2.36x10 "6 mol, degree of saponification of 88%, and number-average molecular weight of 127,000).
• the amount of PVA for the suspending agent was 0.3 g (2.36x10 "6 mol, degree of saponification of 88%, and number-average molecular weight of 127,000).
• Example 21 Other conditions were established to be the same as those related to Example 19 except that the amount of azobisdimethylvaleronitrile initiator was 0.0008 g (1x10 "5 mol/mol of monomer).
• Example 1 1 Other conditions were established to be the same as those related to Example 1 1 except that the polymerization was performed while stirring at 100 rpm.
• Example 1 1 Example 1 1 except that the polymerization was performed while stirring
• Example 1 1 Example 1 1 except that the polymerization was performed while stirring
• Example 29 Other conditions were established to be the same as those related to Example 11 except that the polymerization was performed while stirring at 2000 rpm.
• Example 30 Other conditions were established to be the same as those related to Example 11 except that the polymerization was performed while stirring at 3000 rpm.
• Example 11 Example 11 except that the polymerization was performed at 25 ° C for
• microspheres were stirred with a magnetic stirrer in a 250 ml beaker,
• microspheres had size distributions of 1 -5 ⁇ m, 5-10 ⁇ m, 10-30 ⁇ m,
• ⁇ m 800-900 ⁇ m, 900-1000 ⁇ m, 1000-1200 ⁇ m, 1200-1500 ⁇ m, 1500-1800 ⁇ m,
• the "polydispersity index of particle diameter” is defined as the
• polydispersity index of the particle diameter is in the range of 1 .0 to 1 .2, it is known that these microspheres may be referred to as monodisperse or
• Example 3 prepared by suspension polymerization as in Example 3 were milled with a mortar and pestle using magnesium sulfate as a dispersing and antistatic agent in an amount of 0.5 g per 1.0 g of the poly(vinyl pivalate) microspheres, and separated using standard sieves. The separated microspheres were stirred with a magnetic stirrer in a 250 ml beaker, washed with 100 ml of distilled water for 4 hours, and filtered with a glass
• microspheres had size distributions of 1 -5 ⁇ m, 5-10 ⁇ m, 10-30 ⁇ m,
• ⁇ m 800-900 ⁇ m, 900-1000 ⁇ m, 1000-1200 ⁇ m, 1200-1500 ⁇ m, 1500-1800 ⁇ m,
• microspheres had size distributions of 1 -5 ⁇ m, 5-10 ⁇ m, 10-30 ⁇ m,
• ⁇ m 800-900 ⁇ m, 900-1000 ⁇ m, 1000-1200 ⁇ m, 1200-1500 ⁇ m, 1500-1800 ⁇ m,
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• Example 42 In a 250 ml two-neck flask equipped with a thermometer and a cooling column, 100 ml of aqueous alkali solution where 8.75 g of potassium hydroxide, 8.75 g of sodium sulfate and 8 g of methanol are added to medium water. 0.5 g of poly(vinyl pivalate) microspheres
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly (vinyl pivalate) (core) microspheres had a degree of
• Example 43 In a 250 ml two-neck flask equipped with a thermometer and a cooling column, 100 ml of aqueous alkali solution where 8.75 g of potassium hydroxide, 8.75 g of sodium sulfate and 8 g of methanol are added to medium water. 0.5g of poly(vinyl pivalate) microspheres (particle
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• Example 38 average degree of polymerization of 33,000 prepared using sodium sulfite for the dispersing and antistatic agent as in Example 38 were suspended in
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• Example 38 average degree of polymerization of 24,000 prepared using sodium sulfite for the dispersing and antistatic agent as in Example 38 were suspended in the aqueous alkali solution, and saponified at 40 ° C for 4 hours while being
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• Example 38 average degree of polymerization of 24,000 prepared using sodium sulfite for the dispersing and antistatic agent as in Example 38 were suspended in
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• Example 49 In a 250 ml two-neck flask equipped with a thermometer and a cooling column, 100 ml of aqueous alkali solution where 8.75 g of potassium hydroxide, 8.75 g of sodium sulfite and 8 g of methanol are added to medium water. 0.5 g of poly(vinyl pivalate) microspheres
• Example 38 average degree of polymerization of 24,000 prepared using sodium sulfite for the dispersing and antistatic agent as in Example 38 were suspended in
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• Example 50 In a 250 ml two-neck flask equipped with a thermometer and a cooling column, 100 ml of aqueous alkali solution where 8.75 g of potassium hydroxide, 8.75 g of sodium sulfite and 8 g of methanol are added to medium water. 0.5 g of poly(vinyl pivalate) microspheres
• Example 38 average degree of polymerization of 24,000 prepared using sodium sulfite for the dispersing and antistatic agent as in Example 38 were suspended in
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• Example 51 In a 250 ml two-neck flask equipped with a thermometer and a
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• Example 52 In a 250 ml two-neck flask equipped with a thermometer and a
• poly(vinyl pivalate) microspheres particles size of 210 to 230 ⁇ m, polydispersity index of 1.01 , and number-
• Example 38 average degree of polymerization of 24,000 prepared using sodium sulfite for the dispersing and antistatic agent as in Example 38 were suspended in
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of
• the PVA (skin)/poly(vinyI pivalate) (core) microspheres had a degree of saponification of 23.4%, a particle diameter of 87 to 95 ⁇ m, and a
• Example 56 In a 250 ml two-neck flask equipped with a thermometer and a cooling column, 100 ml of aqueous alkali solution where 8.75 g of sodium hydroxide, 8.75 g of sodium sulfate and 8 g of methanol are added to medium water. 0.5 g of poly(vinyl pivalate) microspheres (particle size of
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of saponification of 12.4%, a
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of saponification of 9.6%, a
• polymerization of 43,000) prepared using sodium sulfate for the dispersing and antistatic agent as in Example 37 were suspended in the aqueous alkali solution, and saponified at 40 ° C for 4 hours while being stirred with
• poly(vinyl pivalate) microspheres where only the surface thereof was saponified to PVA.
• the PVA (skin)/poly(vinyl pivalate) (core) microspheres had a degree of saponification of 19.2%, a
• azobisdimethylvaleronitrile initiator was added to the mixture.
• the vinyl pivalate monomer was solution-polymerized for 11 hours under the nitrogen stream, and precipitated in methanol.
• the polymerized material was dissolved in benzene, and precipitated in methanol. After this process was repeated several times while removing the remaining monomers, the
• the temperature in the flask was elevated to 30 ° C , and then, 0.0033g
• Embolic particles with an outer PVA skin and an inner poly(vinyl pivalate) core prepared through the inhomogeneous surface saponification of the poly(vinyl pivalate) microspheres were photographed by way of SEM.
• SEM photograph of the PVA embolic particles prepared according to Example 46 is shown in Fig. 1.
• a SEM photograph of the PVA prepared by general homogeneous saponification of poly(vinyl pivalate) according to Comparative Example 2 is shown in Fig. 2. It can be confirmed from Fig. 1 that the PVA particles of Example 46 have a completely spherical shape while having a uniform size distribution. On the contrary, the PVA of Fig. 2 has a very rough and sharp surface while having a non-uniform size distribution.
• vinyl pivalate is suspension-polymerized at 20
• poly(vinyl pivalate) microspheres involve a high conversion rate of 50% or
• microspheres are separated using a dispersing and antistatic agent to
• particle sizes are uniformly distributed in the range of 1 to 3000 ⁇ m, the
• the separated poly(vinyl pivalate) microspheres are surface-saponified using an aqueous alkali solution to thereby obtain spherical embolic particles with a dual structure of an outer PVA skin and an inner poly(vinyl pivalate) core where the shape
• the spherical embolic particles have a polydispersity index
• the spherical embolic particles involve a smooth surface and a
• embolotherapy the blood flow in blood
• the embolotherapy based on the embolic material of the present invention may be used for treatment for hypervascular tumors with high vascularity, vascular diseases such as arteriovenous malformation (AVM), and traumatic or inflammatory hemorrhaging as with tuberculosis.
• AVM arteriovenous malformation

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