Radical polymerization control agent, composition for radical polymerization, and method for producing polymer

Abstract

This radical polymerization control agent comprises an organic compound (A) represented by formula (I). The radical polymerization control agent has high molecular weight controllability even at a relatively high polymerization temperature. By performing polymerization at a relatively high temperature, it becomes possible to reduce the concentration of radicals required for the polymerization reaction and increase the heat removal efficiency. Therefore, the radical polymerization control agent is suitable for use in industrial production of polymers such as polyvinyl alcohol. [In formula (I), R1 represents an alkoxy group having 1-4 carbon atoms, an alkyl group having 1-4 carbon atoms, or a hydroxyl group. n represents 2-5.]

Description

Radical polymerization controller, composition for radical polymerization, and method for producing polymer

[0001] The present invention relates to a radical polymerization controller used in a polymerization process for polymerizing a polymerizable monomer by controlled radical polymerization, and also to a composition for radical polymerization and a method for producing a polymer using such a radical polymerization controller.

[0002] Polyvinyl alcohol resin is a crystalline, water-soluble polymer material. Taking advantage of its excellent water solubility and film-forming properties (strength, oil resistance, film-forming ability, oxygen gas barrier properties, etc.), it is widely used in emulsifiers, suspending agents, surfactants, fiber processing agents, various binders, paper processing agents, adhesives, films, etc. Conventional polyvinyl alcohols with different degrees of saponification and polymerization have been used depending on the application. Various modified polyvinyl alcohols have also been proposed, in which special functions are imparted by introducing functional groups into polyvinyl alcohol.

[0003] Polyvinyl alcohol is industrially produced by saponifying polyvinyl acetate obtained by radical polymerization of vinyl acetate. In the radical polymerization of vinyl acetate, various side reactions such as chain transfer reactions and recombination termination reactions occur concomitantly, making it generally difficult to precisely control the molecular arrangement and terminal structure of the resulting polyvinyl acetate (and polyvinyl alcohol).

[0004] In recent years, advances in so-called living radical polymerization technology have led to the development of several methods for controlling the radical polymerization of vinyl acetate. For example, a method has been proposed for obtaining polyvinyl acetate with a precisely controlled structure by conducting the radical polymerization of vinyl acetate in the presence of a radical polymerization initiator and a specific control agent. In this polymerization reaction, the growing radical end of the polyvinyl acetate molecular chain covalently bonds with the control agent to form a dormant species, and the polymerization proceeds while an equilibrium is formed between the dormant species and the radical species generated by its dissociation. This type of polymerization reaction is called controlled radical polymerization.

[0005] However, it has been difficult to obtain high-molecular-weight polyvinyl acetate using conventional controlled radical polymerization methods. This is thought to be because the radicals generated at the terminals of head-to-head bonds (bonds between adjacent acetyl groups in vinyl acetate), which are generated with a certain probability during polymerization, are extremely thermally unstable, causing the equilibrium to shift significantly toward the dormant species, preventing further polymerization reaction progress. On the other hand, if the polymerization temperature is increased to promote thermal dissociation of the dormant species, the reaction proceeds, but controllability deteriorates. Therefore, it has been extremely difficult to obtain high-molecular-weight polyvinyl acetate while maintaining controllability.

[0006] To address these issues, a method has been proposed for synthesizing high-molecular-weight polyvinyl acetate with a controlled structure by controlled radical polymerization using an organic cobalt complex as a control agent. In this polymerization reaction, the growing radical end of the polyvinyl acetate molecular chain covalently bonds with the cobalt atom of the organic cobalt complex to form a dormant species, and polymerization proceeds while an equilibrium is formed between the dormant species and the radical species generated by its dissociation. For example, Non-Patent Document 1 reports the synthesis of polyvinyl acetate with a number-average molecular weight (Mn) of 99,000 and a molecular weight distribution (Mw / Mn) of 1.33 by polymerizing vinyl acetate in the presence of cobalt(II) acetylacetonate.

[0007] Patent Document 1 describes that polyvinyl alcohol obtained by controlled radical polymerization has a problem of being significantly colored, but that polyvinyl alcohol with reduced coloration can be obtained by contacting a polyvinyl acetate solution obtained by controlled radical polymerization using an organic cobalt complex as a control agent with an aqueous solution containing a water-soluble ligand, extracting and removing the cobalt complex, and then saponifying the resulting solution.

[0008] However, such polymerization methods using metal complexes have the drawback that it is not easy to completely remove the used complex from the resulting polymer. Many transition metals are highly toxic, and the toxicity of the transition metals remaining in molded articles using the resulting polymers can pose environmental problems, making it difficult to use molded articles containing transition metals in food packaging, biomedical materials, and the like. The toxicity of unnecessary complexes or complexes removed from the polymer after the reaction can also pose environmental problems. Furthermore, complex removal requires the use of a large amount of extraction liquid, which complicates the process and increases costs. Furthermore, metal complexes are typically expensive and require complex synthesis.

[0009] Living radical polymerization methods that do not require the use of metal complexes are also known. For example, methods using nitroxyl-, iodine-, or dithioester-based compounds are known. However, these methods require the introduction of special protecting groups into the growing polymer chain, which are very expensive. Another drawback is that the polymerization reaction must be carried out at extremely high temperatures (e.g., 110°C or higher). Another drawback is that the controllability of vinyl ester polymerization is insufficient, making it difficult to obtain high-molecular-weight polymers. Another drawback is that the resulting polymers tend to have undesirable properties, such as coloration or odor. Furthermore, it is difficult to completely remove the compounds used from the product, and residual organic halogen compounds, organic sulfur compounds, etc. may cause health and environmental problems.

[0010] Non-Patent Document 2 describes that 2,2'-(1,2-Phenylenebis(azanediyl))bis(cyclohepta-2,4,6-trien-1-one) (tralen) and tropone, which are organic compounds containing only C, H, O, and N atoms, can control the radical polymerization of vinyl acetate, N-vinylpyrrolidone, and acrylonitrile. However, in this method, the polymerization rate is low even when a radical generator is added in large excess relative to the control agent, and it is easily conceivable that adding more radical generator to increase the polymerization rate would result in a deterioration in molecular weight controllability due to side reactions, etc., and this poses industrial problems in terms of safety and cost.

[0011] Furthermore, when polymers such as polyvinyl alcohol are produced industrially, various problems may arise if the polymerization temperature is too low. In conventional controlled radical polymerization methods, molecular weight controllability is high when the polymerization temperature is low, but increasing the polymerization temperature may result in a decrease in molecular weight controllability.

[0012] WO2017 / 170974 publication

[0013] Highly Efficient Cobalt-Mediated Radical Polymerization of Vinyl Acetate, Angewandte Chemie International Edition, 2005, vol.44, p1101-1104Reversible-deactivation radical polymerization of vinyl acetate mediated by tralen, an organomediator, Polymer chemistry, 2021, vol. 12, p5159-5167

[0014] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an organic radical polymerization inhibitor that has high molecular weight controllability even at relatively high polymerization temperatures and can be suitably used for industrial polymer production. Another object of the present invention is to provide a radical polymerization composition and a polymer production method that use such a radical polymerization inhibitor.

[0015] As a result of extensive research, the present inventors have found that a radical polymerization inhibitor comprising an organic compound (A) having a predetermined conjugated polyene structure has high molecular weight controllability even at relatively high polymerization temperatures, and have thus completed the present invention.

[0016] That is, the present invention includes the following inventions: [1] A radical polymerization inhibitor comprising an organic compound (A) represented by the following formula (I):

[0017] [In formula (I), R １ is an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a hydroxyl group; and n is 2 or more and 5 or less.

[0018] [2] A composition for radical polymerization comprising an organic compound (A) represented by the following formula (I) and a radical generator (B), wherein the molar ratio (B / A) of the radical generator (B) to the organic compound (A) is 0.5 to 20:

[0019] [In formula (I), R １ is an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a hydroxyl group; and n is 2 or more and 5 or less.

[0020] [3] The composition for radical polymerization according to [2], further comprising a monomer (Y), wherein the molar ratio (Y / A) of the monomer (Y) to the organic compound (A) is 300 to 30000. [4] A method for producing a polymer, comprising a polymerization step of obtaining a polymer by controlled radical polymerization of the monomer (Y) in the presence of an organic compound (A) represented by the following formula (I) and a radical generator (B):

[0021] [In formula (I), R １ is an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a hydroxyl group; and n is 2 or more and 5 or less.

[0022] [5] The method for producing a polymer according to [4], wherein the monomer (Y) comprises an olefin, a vinyl ester, acrylic acid, an acrylic acid ester, an acrylamide monomer, a styrene monomer, an N-vinylamide monomer, or a dicarboxylic acid monomer. [6] The method for producing a polymer according to [5], wherein the monomer (Y) comprises a vinyl ester or an N-vinylamide monomer. [7] The method for producing a polymer according to [6], wherein the method comprises a polymerization step of sequentially carrying out controlled radical polymerization of a vinyl ester and controlled radical polymerization of a vinyl ester and a monomer other than the vinyl ester in the presence of an organic compound (A) and a radical generator (B) to obtain a vinyl ester block copolymer. [8] The method for producing a polymer according to [6], wherein the method comprises a polymerization step of sequentially carrying out controlled radical polymerization of a vinylamide monomer and controlled radical polymerization of an N-vinylamide monomer and a monomer other than the N-vinylamide monomer in the presence of an organic compound (A) and a radical generator (B) to obtain an N-vinylamide block copolymer. [9] The method for producing a polymer according to [6], which comprises a polymerization step of performing controlled radical polymerization of a vinyl ester in the presence of an organic compound (A) and a radical generator (B) to obtain a vinyl ester polymer, and a saponification step of saponifying the obtained vinyl ester polymer to obtain a vinyl alcohol polymer.

[10] The method for producing a polymer according to [9], wherein the polymerization step involves controlled radical polymerization of a vinyl ester and a monomer other than the vinyl ester.

[0023] The radical polymerization inhibitor of the present invention has high molecular weight controllability even at relatively high polymerization temperatures. By carrying out polymerization at relatively high temperatures, the radical concentration required for the polymerization reaction can be reduced and heat removal efficiency can be increased. Therefore, the radical polymerization inhibitor is suitable for industrial production of polymers such as polyvinyl alcohol.

[0024] 1 is a diagram in which number average molecular weight (Mn) is plotted against the conversion rate of vinyl acetate in Example 1.

[0025] The radical polymerization inhibitor of the present invention comprises an organic compound (A) represented by the following formula (I). Such a radical polymerization inhibitor has high molecular weight controllability even at relatively high polymerization temperatures. By carrying out polymerization at a relatively high temperature, the radical concentration required for the polymerization reaction can be reduced. As a result, side reactions are suppressed and safety is improved. Furthermore, by carrying out polymerization at a relatively high temperature, heat removal efficiency can also be increased. The radical polymerization inhibitor makes it possible to produce polymers having desired molecular weight distributions and molecular arrangements with good productivity under such industrially suitable relatively high temperature conditions. Moreover, the radical polymerization inhibitor is also used as a food additive and is low in toxicity.

[0026] [In formula (I), R １ is an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a hydroxyl group; and n is 2 or more and 5 or less.

[0027] In formula (I), n is 2 or more and 5 or less. n is preferably 4 or less, more preferably 3 or less, and particularly preferably 2.

[0028] In formula (I), R １ is an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a hydroxyl group, and is preferably an alkoxy group having 1 to 4 carbon atoms or a hydroxyl group.

[0029] In formula (I), R １The alkoxy group used as the alkoxy group has 1 to 4 carbon atoms. The number of carbon atoms is preferably 3 or less, more preferably 2 or less, and particularly preferably 1. Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a sec-butoxy group, and a tert-butoxy group. Among these, a methoxy group is preferred. The alkoxy group may have a substituent, as long as the effects of the present invention are not impaired. Examples of such a substituent include an alkoxy group, an amino group (including a monoalkylamino group and a dialkylamino group), a carboxyl group, an ester group, a silyl group, a sulfanyl group, a cyano group, a nitro group, a sulfo group, a formyl group, an aryl group, a halogen atom (such as a chlorine atom, a fluorine atom, a bromine atom, or an iodine atom), a hydroxyl group, an ether group, and an alkenyl group. From the viewpoints of extremely low toxicity and superior environmental and safety aspects, it is preferable that the alkoxy group has no substituent.

[0030] R １ The number of carbon atoms in the alkyl group used as R is 1 to 4. The number of carbon atoms is preferably 3 or less, more preferably 2 or less, and particularly preferably 1. Examples of the alkyl group include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group. Of these, a methyl group is preferred. The alkyl group may have a substituent, as long as it does not impair the effects of the present invention. Examples of such a substituent include R １ Examples of the substituent of the alkoxy group used as the alkyl group include those mentioned above. From the viewpoint of extremely low toxicity and superior environmental and safety aspects, it is preferable that the alkyl group does not have a substituent.

[0031] Specific examples of the organic compound (A) represented by the above formula (I) include sorbic acid, methyl sorbate, 2,4,6-octatrienoic acid, 2,4,6,8-decatetraenoic acid, and 2,4,6,8,10-dodecapentaenoic acid, with sorbic acid and methyl sorbate being preferred.

[0032] The method for producing a polymer of the present invention includes a polymerization step of obtaining a polymer by performing controlled radical polymerization of a monomer (Y) in the presence of an organic compound (A) represented by the following formula (I) and a radical generator (B):

[0033] [In formula (I), R １ is an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a hydroxyl group; and n is 2 or more and 5 or less.

[0034] As the organic compound (A) used in the production method, the organic compound (A) described above as a radical polymerization inhibitor is used.

[0035] The radical generator (B) used in the polymerization step may be appropriately selected from conventionally known azo radical generators, peroxide radical generators, redox radical generators, etc. Examples of azo radical generators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile), etc. Examples of peroxide radical generators include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanate, α-cumyl peroxyneodecanate, and t-butyl peroxyneodecanate; acetylcyclohexylsulfonyl peroxide; diisobutyryl peroxide; and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. Furthermore, the radical generators can be prepared by combining the above-mentioned radical generators with peroxides such as potassium persulfate, ammonium persulfate, and hydrogen peroxide. Redox radical generators include those obtained by combining the above-mentioned peroxides with reducing agents such as sodium hydrogen sulfite, sodium hydrogen carbonate, tartaric acid, L-ascorbic acid, and Rongalit.

[0036] In the polymerization step, controlled radical polymerization of the monomer (Y) may be carried out in the presence of an organic compound (A), a radical generator (B), and a co-catalyst. Examples of the co-catalyst include Lewis bases such as water, N,N-dimethylformamide, dimethyl sulfoxide, pyridine, and triethylamine, and Lewis acids such as aluminum trichloride, tetraisopropyl orthotitanate, boron trifluoride, boron trichloride, and boron trifluoride diethyl ether. From an environmental perspective, it is preferable that the organic compound (A) does not form a metal salt.

[0037] Examples of polymerization methods include well-known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization. Among these, bulk polymerization, which involves polymerization without a solvent, and solution polymerization, which involves polymerization in various organic solvents, are commonly used. Bulk polymerization, which does not use a solvent or a dispersion medium, is preferred from the viewpoint of suppressing the decrease in propagating radical ends due to chain transfer reactions to the solvent or dispersion medium. On the other hand, solution polymerization may be preferable from the viewpoint of adjusting the viscosity of the reaction solution and controlling the polymerization rate. Examples of organic solvents used as solvents during 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 carbonates such as dimethyl carbonate and diethyl carbonate. Of these, esters, aromatic hydrocarbons, and dimethyl carbonate are preferred to prevent chain transfer. Furthermore, when the monomer (Y) contains vinyl acetate, alkali treatment in methanol is often performed after polymerization. Therefore, methanol is also preferably used as a polymerization solvent in consideration of processability. The amount of solvent used can be determined taking into account the number-average molecular weight of the target polymer and the viscosity of the reaction solution. For example, the mass ratio [solvent / monomer (Y)] is selected from the range of 0.01 to 10.

[0038] In the controlled radical polymerization used in the present invention, radicals generated by decomposition of the radical generator (B) first combine with a small number of monomers (Y) to produce short-chain polymers. The resulting radicals at the growing ends of the polymers then combine with the organic compound (A), forming dormant species in which the organic compound (A) is covalently bonded to the polymer ends. For a certain period after the start of the reaction, short-chain polymers are produced and converted to dormant species, and polymerization does not substantially proceed. This period is called the induction period. After the organic compound (A) is consumed, the reaction enters a growth period in which polymerization proceeds, and the molecular weights of most molecular chains in the reaction system increase at the same rate in proportion to the polymerization time. The time required for the polymerization of the monomer (Y), including the induction period and growth period, is usually 0.5 to 30 hours.

[0039] The reason why the radical polymerization inhibitor of the present invention has high molecular weight controllability even at relatively high temperatures is thought to be as follows. During the induction period, when dormant species in which the polymerization inhibitor is covalently bonded to the polymer terminal are generated, the higher the radical scavenging ability of the polymerization inhibitor, the more the propagation reaction of the previously generated dormant species is suppressed, and the timing of the initiation of propagation is synchronized, thereby improving molecular weight controllability. Under conditions where the radical generation rate is low during the induction period, it takes time for the generation of dormant species to be completed, and at high polymerization temperatures, radicals are difficult to scavenge. Therefore, it is presumed that if the radical scavenging ability of the inhibitor is low, the timing of the initiation of propagation is likely to be shifted, resulting in reduced molecular weight controllability. Compared to, for example, cinnamic acids having an aryl group, the organic compound (A) represented by the above formula (I), which is a conjugated polyene compound, is less likely to be conjugated and stabilized, and the equilibrium between the active species and the dormant species is more biased toward the dormant species, resulting in high radical scavenging ability. This is thought to result in high molecular weight controllability in the early stages of polymerization, even at high polymerization temperatures.

[0040] As described above, in the controlled radical polymerization of the present invention, theoretically, one polymer chain is produced from one molecule of the added organic compound (A). Therefore, the amount of organic compound (A) added to the reaction solution is determined taking into consideration the target number average molecular weight and conversion rate. From the viewpoint of obtaining a high molecular weight polymer, the molar ratio (Y / A) of the organic compound (A) to the monomer (Y) in the polymerization step is preferably 300 or more, more preferably 1000 or more, even more preferably 2000 or more, even more preferably 4000 or more, and particularly preferably 6000 or more. On the other hand, from the viewpoint of improving the activity rate of the propagating radical terminal, the molar ratio (Y / A) is preferably 30,000 or less, more preferably 25,000 or less, and even more preferably 20,000 or less. When the organic compound (A) or the monomer (Y) is added in multiple portions, the molar ratio (Y / A) is calculated using the total amount of each portion.

[0041] In the polymerization step, the molar ratio (B / A) of the radical generator (B) to the organic compound (A) is 0.5 to 20. If the number of moles of radicals generated is not greater than the number of moles of the organic compound (A), the polymerization reaction proceeds solely by the mechanism of thermal dissociation of the organic compound (A) from the dormant species, resulting in extremely slow polymerization rates depending on the reaction temperature. Therefore, considering that the radical generator (B) generates two radicals, both the radical generator (B) and the organic compound (A) must be added to the reaction solution in the polymerization step so that the molar ratio (B / A) of the radical generator (B) to the organic compound (A) is 0.5 or greater. Generally, the amount of active radicals supplied from the radical generator depends on the efficiency (initiator efficiency) of the radical generator, so in reality, some radical generator is deactivated without being used to form dormant. Therefore, the molar ratio (B / A) of the radical generator (B) to the organic compound (A) is preferably 0.6 or greater, more preferably 0.8 or greater. On the other hand, if the number of moles of radicals generated is too much greater than the number of moles of organic compound (A), the proportion of uncontrolled radical polymerization increases, and polymerization controllability decreases. The molar ratio of (B) to (A) (B / A) is preferably 15 or less, more preferably 10 or less, and even more preferably 5 or less. When the organic compound (A) or the radical generator (B) is added in multiple portions, the molar ratio (B / A) is calculated using the total amount of each portion.

[0042] The monomer contained in the monomer (Y) used in the polymerization step is not particularly limited as long as it is radically polymerizable, and examples thereof include olefins such as ethylene, propylene, and isobutylene; halogenated olefins such as vinyl chloride, vinyl fluoride, vinylidene chloride, and vinylidene fluoride; vinyl esters such as vinyl formate, vinyl acetate, vinyl trifluoroacetate, vinyl propionate, vinyl valerate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl benzoate, and vinyl versatate; vinylidene cyanide; acrylic acid; methacrylic acid; acrylic acid esters such as methyl acrylate, ethyl acrylate, N-propyl acrylate, i-propyl acrylate, N-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, and octadecyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, and 2-hydroxyethyl methacrylate; dimethylaminoethyl acrylate , dimethylaminoethyl methacrylate and quaternized products thereof; acrylamide-based monomers such as acrylamide, N-methylolacrylamide, N,N-dimethylacrylamide, acrylamido-2-methylpropanesulfonic acid and its sodium salt; methacrylamide-based monomers such as methacrylamide, N,N-dimethylmethacrylamide, trimethyl[3-(methacryloylamino)propyl]aminium chloride; styrene-based monomers such as styrene, α-methylstyrene, p-styrenesulfonic acid and its sodium salt and potassium salt; N N-vinylamide monomers such as vinylacetamide, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinylmethylacetamide, N-vinylformamide, N-vinylcarbazole, N-vinylimidazole, N-vinylphthalimide, N-vinyl-2,3-naphthalimide, and N-vinylindole; allyl monomers such as allyl acetate, allyl chloride, 3,4-diacetoxy-1-butene, 2-methylene-1,3-propanediol, 2-methylene-1,3-propanediol diacetate, allyl alcohol, and dimethylallyl alcohol;Preferred are vinyl cyanide monomers such as acrylonitrile and methacrylonitrile; vinyl ether monomers such as alkyl (C1 to C18) vinyl ether, hydroxyalkyl vinyl ether, and alkoxyalkyl vinyl ether; and dicarboxylic acid monomers such as maleic acid, monomethyl maleate, dimethyl maleate, maleic anhydride, itaconic acid, monomethyl itaconate, dimethyl itaconate, and itaconic anhydride. Olefins, vinyl esters, acrylic acid, acrylic acid esters, acrylamide monomers, styrene monomers, N-vinylamide monomers, and dicarboxylic acid monomers are more preferred, vinyl esters or N-vinylamide monomers are even more preferred, vinyl esters or N-vinylpyrrolidone are particularly preferred, and vinyl esters are most preferred. Monomer (Y) may contain one of these monomers or two or more of them. It is preferred that monomer (Y) contains one of these monomers as the main component. Here, the main component means the monomer contained in the monomer (Y) with the largest content. The content of the main component monomer in the monomer (Y) is preferably 30 mol % or more, more preferably 50 mol % or more, even more preferably 70 mol % or more, and particularly preferably 80 mol % or more.

[0043] The vinyl ester is preferably vinyl acetate from an economical viewpoint, and the acrylic ester is preferably methyl acrylate from an economical viewpoint.

[0044] In the production method of the present invention, a homopolymer may be obtained by using one type of monomer as the monomer (Y), or a copolymer may be obtained by using two or more types of monomers. The copolymer may be either a random copolymer or a block copolymer. Furthermore, the polymer obtained by the production method of the present invention may be either a branched or linear polymer, but is preferably a linear polymer in order to take advantage of the high polymerization controllability provided by the organic compound (A).

[0045] The method for mixing the organic compound (A), the radical generator (B), the monomer (Y), and, if necessary, the co-catalyst is not particularly limited, as long as it is a method that can generate dormant species and control the increase in molecular weight of the polymer. Examples of such methods include: adding the organic compound (A), the radical generator (B), and, if necessary, the co-catalyst to the monomer (Y); mixing the organic compound (A), the radical generator (B), and, if necessary, the co-catalyst, and then mixing the resulting mixture with the monomer (Y); mixing the organic compound (A), the radical generator (B), the monomer (Y), and, if necessary, the co-catalyst all at once; and mixing the organic compound (A), the co-catalyst, and the monomer (Y), and then mixing the resulting mixture with the radical generator (B). Alternatively, the organic compound (A), the radical generator (B), the monomer (Y), and the co-catalyst may be mixed in portions. For example, there may be mentioned a method in which the organic compound (A), the radical generator (B), and, if necessary, the co-catalyst, and a portion of the monomer (Y) are mixed to generate dormant species in which the organic compound (A) is covalently bonded to a short-chain polymer terminal, and then the dormant species is mixed with the remainder of the monomer (Y) to increase the molecular weight. Note that the dormant species may be isolated as a macroinitiator and then mixed with the remainder of the monomer (Y) to increase the molecular weight.

[0046] The polymerization temperature is preferably, for example, 0 to 80°C. If the polymerization temperature is below 0°C, the polymerization rate may be insufficient, which may result in a decrease in productivity. From this point of view, the polymerization temperature is more preferably 10°C or higher, and even more preferably 20°C or higher. On the other hand, if the polymerization temperature exceeds 80°C, the controllability of the radical polymerization may decrease. From this point of view, the polymerization temperature is more preferably 70°C or lower, and even more preferably 65°C or lower.

[0047] From the viewpoint of further improving polymerization controllability, when the conversion rate of the monomer (Y) is 5.0% by mass, the ratio (Mn / theoretical Mn) of the number average molecular weight (Mn) (measured value) to the theoretical number average molecular weight (theoretical Mn) of the polymer is preferably 10.0 or less, more preferably 8.0 or less, even more preferably 6.0 or less, even more preferably 5.0 or less, particularly preferably 4.0 or less, and most preferably 3.0 or less. On the other hand, from the viewpoint of productivity, when the conversion rate of the monomer (Y) is 5.0% by mass, the ratio (Mn / theoretical Mn) of the polymer is preferably 0.5 or more, more preferably 0.8 or more. The conversion rate of the monomer (Y) at the end of polymerization is not particularly limited and may be adjusted depending on the amounts of the organic compound (A) and the monomer (Y) added, the target number average molecular weight, etc., but is typically 3 to 50% by mass. The conversion rate is preferably 10% by mass or more, more preferably 20% by mass or more. The number average molecular weight (Mn) (measured value) of the polymer when the conversion rate is 5.0% by mass is determined as follows. GPC (gel permeation chromatography) measurement of the polymer is performed multiple times from the start of polymerization to the end of polymerization to determine the number average molecular weight (Mn) at multiple conversion rates. The number average molecular weight (Mn) is then plotted against the conversion rate, and the number average molecular weight (Mn) of the polymer when the conversion rate is 5.0% by mass is determined from a straight line passing through the point closest to 5.0% by mass where the conversion rate is 1.0% by mass or more and less than 5.0% by mass, and the point closest to 5.0% by mass where the conversion rate is more than 5.0% and 15% by mass or less. However, if the number average molecular weight (Mn) of the polymer when the conversion rate is 5.0% by mass is measured directly, the measured value is used as the number average molecular weight (Mn) of the polymer when the conversion rate is 5.0% by mass. Specifically, the method described in the Examples below is adopted. The theoretical number average molecular weight (theoretical Mn) of the polymer is determined by the following formula: Theoretical Mn = molar ratio of monomer (Y) to organic compound (A) (Y / A) × average molecular weight of monomer (Y) [g / mol] × (conversion rate [mass%] / 100)

[0048] In order to take advantage of the high polymerization controllability of the production method of the present invention, it is preferable to produce a block copolymer in the polymerization step. Specifically, in the polymerization step, it is preferable to sequentially carry out controlled polymerization of a monomer (Ya) and a monomer (Yb) other than the monomer (Ya) in the presence of an organic compound (A), a radical generator (B), and, if necessary, the co-catalyst, thereby obtaining a block copolymer containing a polymer block (a) containing a monomer (Ya) unit and a polymer block (b) containing a monomer (Yb) unit. It is more preferable to sequentially carry out controlled polymerization of a monomer (Ya) and a monomer (Ya) and a monomer (Yb) in the presence of an organic compound (A), a radical generator (B), and, if necessary, the co-catalyst, thereby obtaining a block copolymer containing a polymer block (a) containing a monomer (Ya) unit and a polymer block (ab) containing a monomer (Ya) unit and a monomer (Yb) unit. The polymerization step will be described below.

[0049] In the polymerization step, first, the monomer (Ya), if necessary, another monomer (Yc) other than the monomer (Ya) and the monomer (Yb), the organic compound (A), the radical generator (B), and, if necessary, the co-catalyst are mixed by the method described above to initiate polymerization of the monomer (Ya). Then, after the number average molecular weight of the polymer block (a) containing the monomer (Ya) reaches a target value, the monomer (Yb) is polymerized to synthesize the polymer block (b) containing the monomer (Yb) unit. At this time, the remaining monomer (Ya) may be removed, and then the monomer (Yb) is added to the reaction solution to polymerize the monomer (Yb), thereby synthesizing the polymer block (b) containing the monomer (Yb) unit. Alternatively, the monomer (Yb) may be added to the reaction solution without removing the monomer (Ya), and the remaining monomer (Ya) may be copolymerized with the monomer (Yb) to synthesize a copolymer block (ab) containing a monomer (Ya) unit and a monomer (Yb) unit. When the monomer (Yb) is added, an additional monomer (Ya) or another monomer (Yc) may be added as necessary.

[0050] Alternatively, polymer block (ab) may be synthesized by first mixing monomer (Ya), monomer (Yb), if necessary, another monomer (Yc), organic compound (A), radical generator (B), and if necessary, the co-catalyst, and after monomer (Yb) is completely consumed or the remaining monomer (Yb) is removed, polymerizing monomer (Ya) to synthesize polymer block (a).

[0051] In this way, a diblock copolymer may be obtained by synthesizing the polymer block (a) and the polymer block (b) or the copolymer block (ab), or a ternary or higher multiblock copolymer may be obtained by repeatedly polymerizing the monomer (Ya), the monomer (Yb), or another monomer (Yc). From the viewpoint of cost, the block copolymer is preferably a diblock copolymer, a triblock copolymer, or a tetrablock copolymer, more preferably a diblock copolymer or a triblock copolymer, and even more preferably a diblock copolymer. The bonding form of each block is preferably linear.

[0052] In order to easily obtain the performance derived from each block, the ratio of the number average molecular weight (Mn) of each block to the number average molecular weight (Mn) of the block copolymer (Mn of block / Mn of block copolymer) is preferably 0.01 to 0.99. The ratio (Mn of block / Mn of block copolymer) is more preferably 0.05 or more, and even more preferably 0.1 or more. On the other hand, the ratio (Mn of block / Mn of block copolymer) is more preferably 0.95 or less, and even more preferably 0.9 or less.

[0053] The content of the monomer (Ya) unit in the polymer block (a) is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more. The content of the monomer (Yb) unit in the polymer block (a) is preferably less than 10 mol%, more preferably less than 5 mol%, and even more preferably less than 1 mol%. The content of the monomer (Yb) unit in the polymer block (b) is preferably 50 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more. The content of the monomer (Ya) unit in the polymer block (b) is preferably less than 10 mol%, more preferably less than 5 mol%, and even more preferably less than 1 mol%. The content of the monomer (Ya) unit in the polymer block (ab) is preferably 1 to 99 mol%, more preferably 5 to 99 mol%, and even more preferably 10 to 90 mol%. The content of the monomer (Yb) unit in the polymer block (ab) is preferably from 1 to 99 mol %, more preferably from 5 to 99 mol %, and even more preferably from 10 to 90 mol %.

[0054] The monomer (Ya), the monomer (Yb), and the other monomer (Yc) are not particularly limited, and the monomers described above as the monomer (Y) can be used in appropriate combination. Among these, it is preferable to use the vinyl ester or N-vinyl amide monomer as one of the monomers (Ya) and (Yb). The other monomer used together with the vinyl ester is not particularly limited as long as it is a monomer other than a vinyl ester, but is preferably the acrylic ester, the olefin, or the acrylic acid. The other monomer used together with the N-vinyl amide monomer is not particularly limited as long as it is a monomer other than a vinyl ester, but is preferably the acrylic ester, the olefin, or the acrylic acid.

[0055] Among these, it is particularly preferred to obtain a vinyl ester-based block copolymer containing a vinyl ester polymer block and a polymer block containing vinyl ester units and units derived from a monomer other than the vinyl ester by sequentially carrying out controlled radical polymerization of a vinyl ester and controlled radical polymerization of a vinyl ester and a monomer other than the vinyl ester in the presence of an organic compound (A), a radical generator (B), and, if necessary, the co-catalyst in the polymerization step.It is also particularly preferred to obtain an N-vinylamide-based monomer block copolymer containing an N-vinylamide polymer block and a polymer block containing units derived from an N-vinylamide-based monomer and a monomer other than the N-vinylamide-based monomer by sequentially carrying out controlled radical polymerization of an N-vinylamide-based monomer and a monomer other than the N-vinylamide-based monomer in the polymerization step in the presence of an organic compound (A), a radical generator (B), and, if necessary, the co-catalyst.

[0056] In the polymerization step, it is preferable to carry out a termination step in which a polymerization terminator is added to terminate the polymerization reaction when the number average molecular weight of the polymer or the conversion rate of the monomer (Y) reaches a target value. Examples of the polymerization terminator include 1,1-diphenylethylene; hydroxy aromatic compounds such as p-methoxyphenol, hydroquinone, cresol, t-butylcatechol, and p-nitrosophenol; quinone compounds such as benzoquinone and naphthoquinone; conjugated carboxylic acids such as muconic acid and sorbic acid; thioethers such as phenothiazine, distearyl thiodipropionate, and dilauryl thiodipropionate; aromatic amines such as p-phenylenediamine and N-nitrosodiphenylamine; nitroxides such as 2,2,6,6-tetramethylpiperidine 1-oxyl and 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl; and transition metal salts such as copper acetate, copper dithiocarbamate, and manganese acetate. Of these, 1,1-diphenylethylene, sorbic acid and benzoquinone are preferred, and 1,1-diphenylethylene is more preferred.

[0057] The number of moles of the polymerization terminator to be added is preferably 1 to 100 moles per mole of the added organic compound (A). If the number of moles of the polymerization terminator is too small, radicals at the polymer terminals may not be sufficiently captured, and the color tone of the resulting polymer may deteriorate. On the other hand, if the number of moles of the polymerization terminator is too large, the production cost may increase.

[0058] The temperature of the reaction solution in the termination step may be any temperature at which the polymerization terminator can react with the terminal radicals of the polymer, and is preferably 0 to 80° C. The time required for the termination step is usually 1 minute to 5 hours.

[0059] After the polymerization step, a removal step may be carried out to remove the organic compound (A) and the like contained in the obtained polymer, but it is preferable not to carry out such a removal step from the viewpoint of a good balance between environmental aspects, safety, and cost. Since the organic compound (A) is highly safe, the safety of the obtained polymer is high even without carrying out the removal step.

[0060] As described above, it is preferable that the monomer (Y) used in the polymerization step contains a vinyl ester. That is, in the polymerization step, it is preferable to obtain a vinyl ester polymer by controlled radical polymerization of a vinyl ester in the presence of an organic compound (A), a radical generator (B), and, if necessary, the cocatalyst. In this case, a vinyl ester homopolymer may be obtained by using only a vinyl ester as a monomer. Alternatively, it is possible to obtain a random copolymer containing vinyl ester units and units derived from a monomer other than a vinyl ester, or a vinyl ester block copolymer containing a polymer block (a) containing vinyl ester units and a polymer block (b) containing units derived from a monomer other than a vinyl ester, by using a vinyl ester and a monomer other than a vinyl ester as monomers. The vinyl ester polymer thus obtained is suitable for various applications.

[0061] It is also preferable to carry out a saponification step in which the vinyl ester polymer is saponified to convert vinyl ester units into vinyl alcohol units, thereby obtaining a vinyl alcohol polymer.

[0062] In the saponification step, for example, the vinyl ester polymer can be saponified in a state where it is dissolved in alcohol to obtain a vinyl alcohol polymer. When the vinyl ester polymer contains acrylic ester units, the acrylic ester units can be converted to acrylic acid units by adjusting the saponification conditions. In addition, the acrylic ester units or acrylic acid units may form a lactone ring with adjacent vinyl alcohol units.

[0063] Examples of the alcohol used in the saponification reaction include lower alcohols such as methanol and ethanol, with methanol being particularly preferred. The alcohol may be a hydrous alcohol or a dehydrated alcohol. The alcohol used in the saponification reaction may contain a solvent such as acetone, an ester such as methyl acetate or ethyl acetate, or toluene. Examples of catalysts used in the saponification reaction include alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; alkali catalysts such as sodium methylate; and acid catalysts such as mineral acids. The temperature of the saponification reaction is preferably in the range of 20 to 80°C. If a gel-like product precipitates as the saponification reaction proceeds, the product can be pulverized at this point, washed, and dried to obtain a vinyl alcohol polymer.

[0064] The degree of saponification of the vinyl alcohol polymer may be adjusted depending on the application and is not particularly limited, but is usually 50 to 99.99 mol %. In the present invention, the degree of saponification refers to the ratio (mol %) of the total number of moles of vinyl alcohol units (including units derived from vinyl alcohol monomers forming lactone rings) to the total number of moles of vinyl ester units and vinyl alcohol units (including units derived from vinyl alcohol monomers forming lactone rings) in the vinyl alcohol polymer. The degree of saponification of the vinyl alcohol polymer １ It can be determined by H-NMR measurement.

[0065] The total amount of vinyl ester units and vinyl alcohol units in the vinyl alcohol polymer is preferably 50 mol % or more, more preferably 70 mol % or more, and even more preferably 80 mol % or more.

[0066] When the vinyl ester block copolymer containing a polymer block (a) containing vinyl ester units and a polymer block (b) containing units derived from a monomer other than vinyl ester is saponified, a vinyl alcohol block copolymer containing a polymer block (a') containing vinyl alcohol units and a polymer block (b') containing units derived from a monomer other than vinyl ester is obtained. Furthermore, when the vinyl ester block copolymer containing a polymer block (a) containing vinyl ester units and a copolymer block (ab) containing vinyl ester units and units derived from a monomer other than vinyl ester is saponified, a vinyl alcohol block copolymer containing a vinyl alcohol polymer block (a') and a copolymer block (ab') containing vinyl alcohol units and units derived from a monomer other than vinyl ester is obtained.

[0067] The number-average molecular weight (Mn) of the polymer obtained by the production method of the present invention is not particularly limited, but is preferably 1,000 or more. According to the production method of the present invention, it is possible to synthesize a high-molecular-weight polymer while precisely controlling the molecular arrangement, terminal structure, etc. Therefore, this production method is suitably used for producing a polymer with a high number-average molecular weight (Mn). The number-average molecular weight (Mn) of the polymer is more preferably 2,000 or more, even more preferably 4,000 or more, even more preferably 10,000 or more, particularly preferably 20,000 or more, and most preferably 40,000 or more. On the other hand, from the viewpoint of ease of handling, the number-average molecular weight (Mn) of the polymer is preferably 1,000,000 or less, more preferably 500,000 or less, and even more preferably 300,000 or less. The number-average molecular weight (Mn) and molecular weight distribution (Mw / Mn) are values ​​measured by GPC using polymethyl methacrylate as a standard substance. The column may be appropriately selected taking into consideration the solubility of the polymer in the solvent, etc., and a tetrahydrofuran-based column, an HFIP-based column, etc. are preferably used. Specific measurement methods are as described in the Examples.

[0068] The molecular weight distribution (Mw / Mn) of the polymer obtained by the production method of the present invention is not particularly limited, but is preferably 1.00 to 3.5. Polymerization by controlled radical polymerization can produce a polymer with a narrow molecular weight distribution. The molecular weight distribution (Mw / Mn) is more preferably 3.4 or less, even more preferably 3.3 or less, and particularly preferably 3.2 or less.

[0069] In the production method of the present invention, by using the organic compound (A), radical polymerization can be highly controlled even under relatively high temperature conditions suitable for industrial production of polymers, thereby enabling the production of high-molecular-weight polymers while precisely controlling the molecular arrangement, terminal structure, etc. By carrying out the polymerization at a relatively high temperature, the radical concentration required for the polymerization reaction can be reduced. As a result, side reactions are suppressed and safety is improved. Furthermore, by carrying out the polymerization at a relatively high temperature, heat removal efficiency can be improved. Therefore, the production method of the present invention produces high-performance polymers and is also cost-effective. The properties of the resulting polymers can be utilized to suitably use them in applications such as hygiene, daily necessities, construction and civil engineering, industrial, agricultural, medical, and food applications.

[0070] The composition for radical polymerization of the present invention contains an organic compound (A) represented by the following formula (I) and a radical generator (B), and the molar ratio (B / A) of the radical generator (B) to the organic compound (A) is 0.5 to 20:

[0071] [In formula (I), R １ is an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a hydroxyl group; and n is 2 or more and 5 or less.

[0072] By using the radical polymerization composition, radical polymerization of the monomer (Y) can be carried out at a high polymerization rate while precisely controlling the molecular arrangement, terminal structure, and the like, even under relatively high-temperature conditions suitable for industrial polymer production. By carrying out the polymerization at a relatively high temperature, the radical concentration required for the polymerization reaction can be reduced. As a result, side reactions are suppressed and safety is improved. Furthermore, carrying out the polymerization at a relatively high temperature can also increase heat removal efficiency. Furthermore, the radical polymerization composition is low-toxic. Therefore, it can be suitably used in the radical polymerization of various monomers, including the above-mentioned polymer production method. It is preferable that the radical polymerization composition further contains a monomer (Y). In this case, the molar ratio (Y / A) of the monomer (Y) to the organic compound (A) in the radical polymerization composition is preferably 300 to 30,000. It is also preferable that the radical polymerization composition further contains a co-catalyst. The organic compound (A) used in the radical polymerization composition is one of those described above as being used in polymerization controllers. The radical generator (B), the monomer (Y) and the co-catalyst may be those mentioned above as those used in the production method of the polymer.

[0073] The present invention will be explained in more detail below using examples.

[0074] [Organic Compound (A)] Sorbic acid Methyl sorbate Methyl cinnamate

[0075] [Radical generator (B)] Azobisisobutyronitrile (AIBN) [Monomer (Y)] Vinyl acetate (VAc) [Polymerization inhibitor] 1,1-diphenylethylene (1,1-DPEt)

[0076] [Number Average Molecular Weight (Mn)] The number average molecular weight (Mn) and molecular weight distribution (Mw / Mn) of the polymer were measured using a gel permeation chromatography (GPC) under any of the following conditions: <Condition 1> Apparatus: GPC manufactured by Shimadzu Corporation Column: Tetrahydrofuran-based column "KF-806M" manufactured by Showa Denko K.K. Standard sample: Polymethyl methacrylate Solvent and mobile phase: Tetrahydrofuran (THF) Flow rate: 1.0 mL / min Temperature: 40°C Sample solution concentration: 0.2% by mass (filtered through a filter with an opening diameter of 0.45 μm) Injection volume: 100 μL Detector: RI <Condition 2> Apparatus: GPC manufactured by Tosoh Corporation Column: Tetrahydrofuran-based column "KF-806M" manufactured by Showa Denko K.K. Standard sample: Polymethyl methacrylate Solvent and mobile phase: N,N-dimethylformamide (DMF) with 10 mM lithium bromide (LiBr) Flow rate: 1.0 mL / min Temperature: 40°C Sample solution concentration: 0.2% by mass (filtered through a filter with an opening diameter of 0.45 μm) Injection volume: 100 μL Detector: RI

[0077] [Theoretical Number Average Molecular Weight (Theoretical Mn)] The theoretical number average molecular weight (theoretical Mn) at a given conversion rate was calculated by the following formula: Theoretical Mn = Molar ratio of monomer (Y) to organic compound (A) (Y / A) × Average molecular weight of monomer (Y) [g / mol] × (Conversion rate [%] / 100)

[0078] [Polymerization controllability] When the conversion rate of the monomer (Y) is 5.0% by mass, the ratio (Mn / theoretical Mn) of the number average molecular weight (Mn) (measured) to the theoretical number average molecular weight (theoretical Mn) of the polymer is 5.0 or less, and when Mn increases with increasing conversion rate, the polymer was judged to have excellent controllability. The number average molecular weight (Mn) (measured) of the polymer when the conversion rate is 5.0% by mass was determined as follows. GPC (gel permeation chromatography) measurement of the polymer in the reaction solution was performed multiple times from the start of polymerization to the end of polymerization, and the number average molecular weight (Mn) at multiple conversion rates was determined. Figure 1 is a graph plotting the number average molecular weight (Mn) against the conversion rate in Example 1. 1, the number average molecular weight (Mn) (horizontal axis, linear scale) was plotted against the conversion (horizontal axis, linear scale), and the number average molecular weight (Mn) of the polymer when the conversion was 5.0% by mass was determined from a straight line passing through the point closest to 5.0% by mass where the conversion was 1.0% by mass or more and less than 5.0% by mass, and the point closest to 5.0% by mass where the conversion was more than 5.0% and 15% by mass or less. When the number average molecular weight (Mn) of the polymer when the conversion was 5.0% by mass was measured directly, the measured value was used as the number average molecular weight (Mn) of the polymer when the conversion was 5.0% by mass.

[0079] Example 1 Polymerization Step: 1,000 parts by mass of VAc as the monomer (Y), 0.16 parts by mass of sorbic acid as the organic compound (A), and 0.24 parts by mass of AIBN as the radical generator (B) were added to a reactor equipped with a stirrer, a reflux condenser, and an inlet for adding a radical generator. After dissolution, nitrogen was introduced to replace the atmosphere with an inert gas. The reactor was heated and stirred to an internal temperature of 65°C. Sampling was performed as needed, and the progress of polymerization was confirmed based on the solids concentration. When the VAc conversion rate reached 1.2% by mass, the number average molecular weight (Mn) was 68,000, the theoretical number average molecular weight (theoretical Mn) was 8,100, and the ratio (Mn / theoretical Mn) was 8.4. When the VAc conversion rate was 3.7% by mass, the number average molecular weight (Mn) was 96,600, the theoretical number average molecular weight (theoretical Mn) was 25,700, and the ratio (Mn / theoretical Mn) was 3.8. When the VAc conversion rate was 5.1% by mass, the number average molecular weight (Mn) was 109,900, the theoretical number average molecular weight (theoretical Mn) was 34,900, and the ratio (Mn / theoretical Mn) was 3.2. When the VAc conversion rate was 7.1% by mass, the number average molecular weight (Mn) was 129,800, the theoretical number average molecular weight (theoretical Mn) was 49,000, and the ratio (Mn / theoretical Mn) was 2.7. After 8.0 hours had elapsed since the start of heating, when the VAc conversion rate reached 12.3% by mass, 2.6 parts by mass of 1,1-DPEt was added as a polymerization terminator. The number average molecular weight (Mn) was 182,100, the theoretical number average molecular weight (theoretical Mn) was 84,300, the ratio (Mn / theoretical Mn) was 2.2, and the molecular weight distribution (Mw / Mn) was 2.35. Unreacted VAc was distilled off from the solution under reduced pressure to recover polyvinyl acetate, which was then dried in a vacuum dryer at 40°C for 24 hours to obtain polyvinyl acetate. Details of the above polymerization process are shown in Table 1. Figure 1 is a graph plotting the number average molecular weight (Mn) against the VAc conversion. The ratio (Mn / theoretical Mn) of the number average molecular weight (Mn) (measured) to the theoretical number average molecular weight (theoretical Mn) of the polymer, determined from Figure 1 when the VAc conversion was 5.0% by mass, was 3.2. [Example 2] <Polymerization Step> A polymerization reaction was carried out in the same manner as in Example 1 to obtain polyvinyl acetate, except that 0.18 parts by mass of methyl sorbate was added as the organic compound (A). Details are shown in Table 1.

[0080] <Saponification Step> Next, the concentration of the methanol solution was adjusted to 4,900 parts by weight of methanol per 100 parts by weight of polyvinyl acetate obtained in the polymerization step in the same reactor as above, and the water bath was heated and stirred until the internal temperature reached 40°C. 88 parts by weight of a methanol solution of sodium hydroxide (concentration 10.6% by weight, 9.3 parts by weight of sodium hydroxide) was added. The thus-prepared methanol solution containing polyvinyl acetate at a concentration of 2% by weight was subjected to a saponification reaction at 65°C for 1 hour. After dewatering, phenolphthalein solution was added to the washing liquid (methanol), and the mixture was washed with methanol until no alkaline reaction was observed, thereby removing the sodium hydroxide and sodium acetate. The solid obtained by centrifugal dehydration was dried in a vacuum dryer at 40°C for 24 hours to obtain white polyvinyl alcohol. The degree of saponification was 99.8%.

[0081] Comparative Example 1 Polymerization Step A polymerization reaction was carried out in the same manner as in Example 1, except that 0.24 parts by mass of methyl cinnamate was added instead of the organic compound (A), to obtain polyvinyl acetate. Details are shown in Table 1.

[0082] <Saponification Step> Next, a saponification reaction was carried out in the same manner as in Example 2 to obtain a white vinyl alcohol polymer. The details are shown in Table 1.

[0083]

[0084] In Examples 1 and 2, the ratio (Mn / theoretical Mn) at the beginning of polymerization was 5.0 or less, and Mn increased with increasing conversion, confirming high molecular weight controllability under high-temperature polymerization conditions. On the other hand, in Comparative Example 1, the ratio (Mn / theoretical Mn) at the beginning of polymerization was more than 5.0, confirming poor molecular weight controllability under high-temperature polymerization conditions.

Claims

1. A radical polymerization inhibitor comprising an organic compound (A) represented by the following formula (I): [In formula (I), R １ is an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a hydroxyl group; and n is 2 or more and 5 or less.

2. A composition for radical polymerization comprising an organic compound (A) represented by the following formula (I) and a radical generator (B), wherein the molar ratio (B / A) of the radical generator (B) to the organic compound (A) is 0.5 to 20: [In formula (I), R １ is an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a hydroxyl group; and n is 2 or more and 5 or less.

3. The composition for radical polymerization according to claim 2, further comprising a monomer (Y), wherein the molar ratio (Y / A) of the monomer (Y) to the organic compound (A) is 300 to 30,000.

4. A method for producing a polymer, comprising a polymerization step of obtaining a polymer by controlled radical polymerization of a monomer (Y) in the presence of an organic compound (A) represented by the following formula (I) and a radical generator (B): [In formula (I), R １ is an alkoxy group having 1 to 4 carbon atoms, an alkyl group having 1 to 4 carbon atoms, or a hydroxyl group; and n is 2 or more and 5 or less.

5. The method according to claim 4, wherein the monomer (Y) comprises an olefin, a vinyl ester, an acrylic acid, an acrylic acid ester, an acrylamide monomer, a styrene monomer, an N-vinylamide monomer, or a dicarboxylic acid monomer.

6. The method for producing a polymer according to claim 5, wherein the monomer (Y) comprises a vinyl ester or N-vinyl amide monomer.

7. A method for producing a polymer according to claim 6, comprising a polymerization step of sequentially carrying out controlled radical polymerization of a vinyl ester and controlled radical polymerization of a vinyl ester and a monomer other than a vinyl ester in the presence of an organic compound (A) and a radical generator (B) to obtain a vinyl ester-based block copolymer.

8. A method for producing a polymer according to claim 6, comprising a polymerization step of sequentially carrying out controlled radical polymerization of a vinylamide monomer and controlled radical polymerization of an N-vinylamide monomer and a monomer other than an N-vinylamide monomer in the presence of an organic compound (A) and a radical generator (B) to obtain an N-vinylamide block copolymer.

9. A method for producing a polymer according to claim 6, comprising: a polymerization step of obtaining a vinyl ester polymer by controlled radical polymerization of a vinyl ester in the presence of an organic compound (A) and a radical generator (B); and a saponification step of obtaining a vinyl alcohol polymer by saponifying the obtained vinyl ester polymer.

10. The method for producing a polymer according to claim 9, wherein the polymerization step involves controlled radical polymerization of a vinyl ester and a monomer other than a vinyl ester.

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