Method for producing vinyl ester copolymer

Abstract

A method for producing a vinyl ester copolymer includes the steps of: (i) polymerizing a composition containing a vinyl ester and (ii) a vinyl monomer having a boiling point of 100°C or higher, the vinyl ester having a lower boiling point than the vinyl monomer, to produce a copolymer paste (polymerization step); (removal step) removing the vinyl ester from the copolymer paste; (evaporation step) heating the copolymer paste in an evaporator at a pressure of less than 1 atmosphere to evaporate the vinyl monomer; and (ii) removing a copolymer paste having a viscosity of 8000 cP or higher from the evaporator. This method allows efficient recovery of unreacted vinyl monomer remaining in the copolymer paste.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a vinyl ester-based copolymer. [Background technology]

[0002] Ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as EVOH) has excellent transparency, gas barrier properties, flavor retention, solvent resistance, oil resistance, etc., and taking advantage of these properties, it is used in a wide range of applications, such as various packaging containers for food, pharmaceuticals, industrial chemicals, and agricultural chemicals.

[0003] EVOH can be produced by a process that includes a polymerization step in which different monomer units are reacted together to produce a vinyl ester-based copolymer paste. For example, ethylene, vinyl ester, and vinyl monomers are reacted together to form a vinyl ester copolymer, which is then saponified to produce the final EVOH product. This EVOH production process is described in detail in U.S. Pat. No. 9,663,592 B2 and U.S. Pat. No. 7,915,341 B2, which are incorporated by reference in their entireties. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] US9,663,592B2 [Patent Document 2] US7,915,341B2 Summary of the Invention [Problem to be solved by the invention]

[0005] During the polymerization process, not all of the monomer reactants are used up and incorporated into the polymer chain. The remaining unreacted monomer is essentially unused starting material and would be considered wasted if not recovered from the final polymer paste product. Furthermore, the unreacted monomer can have harmful effects if disposed of as waste in the environment. [Means for solving the problem]

[0006] According to some aspects of the present disclosure, a method for producing a vinyl ester-based copolymer includes polymerizing a composition including a vinyl ester and a vinyl monomer to produce a copolymer paste, removing the vinyl ester from the copolymer paste, and heating the copolymer paste at a low pressure and temperature configured to vaporize the vinyl monomer.

[0007] In one aspect, the present disclosure relates to a method for producing a vinyl ester-based copolymer, comprising the steps of: polymerizing a composition comprising (i) a vinyl ester and (ii) a vinyl monomer having a boiling point of 100° C. or greater, wherein the vinyl ester has a boiling point lower than that of the vinyl monomer, to produce a copolymer paste (polymerization step); removing the vinyl ester from the copolymer paste (removal step); heating the copolymer paste in an evaporator at a pressure less than 1 atmosphere to evaporate the vinyl monomer (evaporation step); and removing the copolymer paste having a viscosity of 8000 cP or greater from the evaporator.

[0008] In some embodiments, the vinyl ester comprises formula (I) shown below:

[0009] [ka]

[0010] In formula (I), R 5 is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. The most preferred vinyl ester is vinyl acetate.

[0011] In some embodiments, the vinyl monomer includes a compound having two or more groups selected from acyloxy groups or formyloxy groups having 1 to 10 carbon atoms. In other embodiments, the vinyl monomer includes a compound having 6 to 20 carbon atoms.

[0012] In some embodiments, the vinyl monomer comprises formula (II):

[0013] [ka]

[0014] In formula (II), R 8 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R 9 is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms, one of X and Y is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and the other of X and Y is a group containing the following formula (III).

[0015] [ka]

[0016] In formula (III), R 10 and R 11 are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R 12 is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms.

[0017] In some embodiments, the vinyl monomer comprises formula (IIa):

[0018] [ka]

[0019] In formula (IIa), R 9is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms, one of X and Y is a hydrogen atom, and the other of X and Y is a group containing the following formula (IIIa):

[0020] [ka]

[0021] In formula (IIIa), R 12 is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms.

[0022] In some embodiments, the vinyl monomer comprises formula (IIb):

[0023] [ka]

[0024] In formula (IIb), one of X and Y is a hydrogen atom, and the other of X and Y includes a group having formula (IIIb) shown below.

[0025] [ka]

[0026] In other embodiments, the vinyl monomer comprises formula (IV):

[0027] [ka]

[0028] In formula (IV), R 1 , R 2 , R 3 , and R 4 are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R 6 and R 7 are each independently a hydrogen atom or an alkyl group having 1 to 9 carbon atoms.

[0029] In some embodiments, the vinyl monomer comprises 2-methylene-1,3-propanediol diacetate (MPDAc). In other embodiments, the composition in the polymerizing step further comprises ethylene.

[0030] In some embodiments, the copolymer paste discharged from the evaporator has a viscosity of 10,000 cP or more and 2,000,000 cP or less. In some embodiments, the temperature of the copolymer paste discharged from the evaporator is 80°C or more, preferably 100 to 200°C.

[0031] In some embodiments, the method further comprises evaporating the solvent from the copolymer paste after the removing step and before the evaporating step. In some embodiments, the copolymer paste introduced into the evaporator has a viscosity of 5,000 cP or less, or a viscosity of 500 cP or more and 3,000 cP or less at 25°C. In some embodiments, the removing step occurs in a different location from the evaporating step. In other embodiments, the evaporating step occurs in a thin film evaporator. In some embodiments, the evaporating step occurs in a wiped film evaporator (WFE).

[0032] In some embodiments, the method further comprises recovering the vinyl monomer evaporated in the evaporation step and / or a second copolymerization of the vinyl ester and the vinyl monomer recovered in the evaporation step, hi some embodiments, at least 40% of the vinyl monomer not reacted in the polymerization step is recycled.

[0033] In some embodiments, the copolymer paste introduced into the evaporator contains an organic solvent having a boiling point of less than 100°C. Furthermore, a preferred organic solvent is methanol. In some embodiments, the method further comprises saponifying the copolymer paste removed from the evaporator. In some embodiments, the vinyl ester copolymer has a degree of saponification of at least 90 mol%. In some embodiments, the method further comprises concentrating vinyl monomers in a condensate obtained by evaporation in the evaporation step. In some embodiments, the method further comprises concentrating the vinyl monomers by fractional distillation.

[0034] These and other embodiments, features and advantages of the present invention will be more readily understood by those of ordinary skill in the art upon reading the following detailed description. [Effects of the Invention]

[0035] According to the method for producing a vinyl ester copolymer of the present invention, unreacted vinyl monomer remaining in the copolymer paste can be effectively recovered. DETAILED DESCRIPTION OF THE INVENTION

[0036] In the context of this description, all publications, patent applications, patents, and other references mentioned herein are expressly incorporated herein in their entirety for all purposes as if fully set forth, unless otherwise noted.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. In case of conflict, the present specification, including definitions, will control.

[0038] Trademarks are displayed in capital letters unless clearly stated otherwise.

[0039] Unless otherwise specified, all percentages, parts, ratios, etc. are by weight.

[0040] Unless otherwise specified, pressures expressed in psi are gauge pressures and pressures expressed in kPa are absolute pressures. However, pressure differences are expressed as absolute pressures (e.g., Pressure 1 is 25 psi higher than Pressure 2).

[0041] When an amount, concentration, or other value or parameter is provided as a range or as a list of upper and lower limits, it should be understood to specifically disclose all ranges formed from any pairing of any upper and lower range limits, regardless of whether the ranges are separately disclosed. When a range of numerical values ​​is recited herein, unless otherwise stated, the range is intended to include its endpoints, and all integers and fractions within the range. It is not intended that the scope of the present disclosure be limited to the specific values ​​recited when defining the range.

[0042] When the term "about" is used, it means that a particular effect or result will be obtained within a particular tolerance, and one of ordinary skill in the art knows how to achieve that tolerance. When the term "about" is used to describe a value or an endpoint of a range, the disclosure should be understood to include the specific value or endpoint referred to.

[0043] As used herein, "comprises," "comprising," "includes," "including," "has," "having," or other variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, article, or apparatus that includes a list of elements is not necessarily limited to only those elements and may include other elements that are not expressly listed or that are inherent in such process, method, article, or apparatus.

[0044] The transitional phrase "consisting of" closes a claim to the inclusion of materials other than those recited, except for impurities ordinarily associated therewith, and excludes any element, step, or ingredient not specified in the claim. When the phrase "consisting of" appears in a clause in the body of a claim rather than immediately following the preamble, it limits only the elements recited in that clause and does not exclude other elements from the claim as a whole.

[0045] The transitional phrase "consisting essentially of" limits the scope of a claim to the specified materials or steps and those that do not insignificantly affect the basic and novel characteristics of the claimed invention. A "consisting essentially of" claim occupies a middle ground between a closed claim written in the "consisting of" format and a fully open claim written in the "comprising" format. Optional additives and minor impurities, at appropriate levels as defined herein, are not excluded from the term "consisting essentially of."

[0046] Furthermore, unless expressly stated to the contrary, "or" and "and / or" refer to inclusiveness, not exclusion. For example, a condition "A or B," or "A and / or B," may be satisfied by any one of "A is true (or exists) and B is false (or does not exist)," "A is false (or does not exist) and B is true (or exists)," and "both A and B are true (or exist)."

[0047] The use of "a" or "an" to describe various elements and components herein is merely for convenience and to give a general sense of the disclosure. This description should be read to include one or at least one, and the singular also encompasses the plural unless it is clear that it is not meant to be plural.

[0048] As used herein, the terms "major portion" or "predominantly" mean greater than 50% of the referenced material, unless otherwise defined herein. Unless specified, the percentage is on a molar basis when referring to molecules (e.g., hydrogen and ethylene) and on a mass or weight basis in other cases (e.g., when referring to additive content).

[0049] As used herein, unless otherwise defined, the terms "substantial portion" or "substantially" mean all or nearly all or the majority as would be understood by one of ordinary skill in the art in the context in which it is used, allowing for some reasonable variation from 100% that would normally occur in an industrial or commercial scale situation.

[0050] The terms "depleted" or "reduced" are synonymous with less than what was originally present. For example, removing a significant portion of a material from a stream would result in a material-depleted stream that is substantially reduced in that material. Conversely, the terms "enriched" or "increased" are synonymous with more than what was originally present.

[0051] As used herein, the term "copolymer" refers to a polymer containing copolymerized units resulting from the copolymerization of two or more comonomers. In this context, a copolymer may be described herein in terms of its constituent comonomers or the amounts of its constituent comonomers, e.g., "a copolymer containing ethylene and 15 mol % comonomer," or similar descriptions. Such descriptions may be considered informal because they do not refer to the comonomers as copolymerized units; because they do not include conventional nomenclature for copolymers, such as the International Union of Pure and Applied Chemistry (IUPAC) nomenclature; because they do not use product-by-process terminology; or for other reasons. However, as used herein, a description of a copolymer based on its constituent comonomers or the amounts of its constituent comonomers means that the copolymer contains copolymerized units of the specified comonomers (in the specified amount, if specified). A corollary is that a copolymer is not the product of a reaction mixture containing a specified comonomer in a specified amount, unless expressly stated to be so within a limited range.

[0052] As used herein, the term "block copolymer" refers to a copolymer in which chemically distinct monomer units are grouped into discrete blocks along the polymer chain. Block copolymers can include two or more homopolymer subunits linked by covalent bonds.

[0053] For convenience, many elements of the invention may be discussed separately, lists of options may be provided, and numerical values ​​may be provided in ranges. However, for purposes of this disclosure, no limitation on the scope or support of this disclosure should be construed as to any claim of any such separate components, list items, or range combinations. Unless expressly stated otherwise, each and every combination possible in this disclosure should be considered to be expressly disclosed in all respects.

[0054] Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of this disclosure, suitable methods and materials are described herein. Therefore, the materials, methods, and examples herein are illustrative only and, unless specifically stated, are not limiting.

[0055] Production of vinyl ester copolymers Hereinafter, a method for producing a vinyl ester copolymer according to an embodiment of the present invention will be described.

[0056] In one embodiment, the method includes polymerizing a composition comprising (i) a vinyl ester and (ii) a vinyl monomer having a boiling point of 100°C or higher to produce a copolymer paste, wherein the vinyl ester has a lower boiling point than the vinyl monomer (polymerization step).

[0057] According to some embodiments, the method includes producing a copolymer in paste form by polymerization. The copolymer can include, for example, the vinyl ester and vinyl monomer described above. The boiling point of the vinyl monomer can be, for example, about 100, 110, 120, 150, or 200°C or higher and / or less than about 250, 300, 400, or 500°C. In some embodiments, the boiling point of the vinyl monomer is 100-500°C, 100-300°C, 150-300°C, 200-300°C, or 200-250°C. The boiling point of the vinyl ester in the copolymer is lower than the boiling point of the vinyl monomer. The boiling point of the vinyl ester is less than about 150, 140, 130, 120, 110, 100, 90, or 80°C and / or greater than about 50, 60, or 70°C.

[0058] In some embodiments, the vinyl ester included in the copolymer may include a monomer represented by formula (I) shown below:

[0059] [ka]

[0060] In formula (I), R 5 represents a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. The alkyl group preferably has 1 to 4 carbon atoms. Examples of vinyl esters represented by formula (I) include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl versatate, and vinyl caproate. In some embodiments, the vinyl ester includes vinyl acetate.

[0061] In some embodiments, the vinyl monomer comprises a compound having two or more groups selected from acyloxy groups or formyloxy groups having 2 to 10 carbon atoms. The acyloxy groups and formyloxy groups in the copolymer can be converted to hydroxy groups after the saponification process. Therefore, two or more hydroxy groups can be introduced into the structural units derived from the vinyl monomer. The saponified copolymer can then have good barrier properties. The number of carbon atoms in the acyloxy group is preferably 2 to 5, more preferably 2 to 3, and most preferably 2 (acetyloxy group).

[0062] In another embodiment, the vinyl monomer includes a compound having 6 to 20 carbon atoms. If the vinyl monomer has 6 to 20 carbon atoms, the vinyl monomer can be easily evaporated and separated from the vinyl ester and the solvent. The number of carbon atoms is preferably 7 or more. The number of carbon atoms is preferably 15 or less, more preferably 12 or less, and even more preferably 10 or less. The most preferred number of carbon atoms is 8.

[0063] In some embodiments, the vinyl monomer comprises formula (II) shown below:

[0064] [ka]

[0065] In formula (II), R 8 is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 8The number of carbon atoms in R is preferably 3 or less, more preferably 2 or less, and even more preferably 1 or less. 8 is a hydrogen atom. R 9 is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. 9 has preferably 1 to 3 carbon atoms, more preferably 1 or 2, and even more preferably 1 (methyl). One of X and Y is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and the other of X and Y is a group containing the formula (III) shown below. This means that, for example, when X is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, Y is a group containing the formula (III) shown below. The number of carbon atoms in the alkyl group is preferably 3 or less, more preferably 2 or less, and even more preferably 1 or less. The most preferred R 8 is a hydrogen atom.

[0066] [ka]

[0067] In formula (III), R 10 and R 11 are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 10 and R 11 are each preferably 3 or less, more preferably 2 or less, and even more preferably 1 or less. 10 and R 11 is a hydrogen atom. R 12 is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. 12 The number of carbon atoms in the group is preferably 1 to 3, more preferably 1 or 2, and even more preferably 1 (methyl).

[0068] In some embodiments, the vinyl monomer comprises formula (IIa) shown below:

[0069] [ka]

[0070] In formula (IIa), R 9 is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms, one of X and Y is a hydrogen atom, and the other of X and Y is a group containing the following formula (IIIa).

[0071] [ka]

[0072] In formula (IIIa), R 12 is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms.

[0073] In some embodiments, the vinyl monomer comprises formula (IIb) shown below:

[0074] [ka]

[0075] In formula (IIb), one of X and Y is a hydrogen atom, and the other of X and Y includes a group having formula (IIIb) shown below.

[0076] [ka]

[0077] When X contains a group containing formula (IIIb) and Y is a hydrogen atom, the vinyl monomer is 2-methylene-1,3-propanediol diacetate, which is used in the examples below. Because this vinyl monomer has eight carbon atoms, its boiling point is suitable for evaporation. Furthermore, this vinyl monomer contains two acetyloxy groups in the molecule. Therefore, two hydroxyl groups can be introduced into the saponified copolymer. The saponified copolymer then has excellent gas barrier properties and flexibility. These physical properties are well explained in U.S. Pat. No. 9,663,592 B2 (Patent Document 1).

[0078] On the other hand, when X is a hydrogen atom and Y contains a group having formula (IIIb), the vinyl monomer is 3,4-diacetoxy-1-butene. This vinyl monomer has the same molecular weight as 2-methylene-1,3-propanediol diacetate and contains two acetyloxy groups. Therefore, its boiling point is also suitable for evaporation. The saponified copolymer then has good gas barrier properties and flexibility. These physical properties are fully described in US Pat. No. 7,915,341 B2 (Patent Document 2).

[0079] In some embodiments, the vinyl monomer may include another vinyl ester or another vinyl acetate having a higher boiling point than the vinyl ester in the copolymer. Further, in some embodiments, the vinyl monomer may include a monomer represented by formula (IV) shown below:

[0080] [ka]

[0081] In formula (IV), R 1 , R 2 , R 3 , and R 4 R each independently represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms. 1 , R 2 , R 3 , and R 4 may be the same group or different groups. 1 , R 2 , R 3 , and R 4 may be a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

[0082] In formula (IV), R 6 and R 7each independently represents a hydrogen atom or an alkyl group having 1 to 9 carbon atoms. The alkyl group may have 1 to 4 carbon atoms. The unsaturated monomer represented by formula (IV) may include 2-methylene-1,3-propanediol diacetate, 2-methylene-1,3-propanediol dipropionate, 2-methylene-1,3-propanediol dibutyrate, etc. For example, from the viewpoint of ease of production, 2-methylene-1,3-propanediol diacetate can be used, and in this case, R 1 , R 2 , R 3 and R 4 is a hydrogen atom, and R 6 and R 7 is a methyl group. In some embodiments, 2-methylene-1,3-propanediol diacetate (MPDAc).

[0083] Furthermore, instead of the unsaturated monomer represented by the above formula (IV), an unsaturated monomer represented by the following formula (V) may be copolymerized.

[0084] [ka]

[0085] In formula (V), R 1 , R 2 , R 3 , and R 4 is the same as in formula (IV). The unsaturated monomer represented by formula (V) may include 2-methylene-1,3-propanediol, etc. For the same reason, the vinyl monomer may include 3,4-dihydroxy-1-butene, etc.

[0086] R 1 ~R 12The structure of the alkyl group in is not particularly limited, and may have a branched or cyclic structure in part. Furthermore, the alkyl group may contain a hydroxy group, an alkoxy group, or a halogen atom. An alkyl group containing only carbon atoms and hydrogen atoms is preferred, and an alkyl group having a linear structure is also preferred. Examples of the alkyl group include linear or branched alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, and pentyl.

[0087] The unsaturated monomers represented by formulas (II), (IV), and (V) used in some embodiments have high copolymerization reactivity with vinyl ester monomers, and therefore the copolymerization reaction proceeds easily. Therefore, it is easy to increase the degree of modification and polymerization of the resulting modified ethylene-vinyl ester copolymer. Furthermore, even if the polymerization reaction is terminated at a low conversion rate, the amount of unreacted unsaturated monomer remaining after polymerization is small, which is advantageous from an environmental and cost perspective. In this respect, the unsaturated monomers represented by formulas (II), (IV), and (V) are superior to other monomers, such as allyl glycidyl ether, which has a functional group at the allylic position and only one carbon atom at the allylic position. Here, the unsaturated monomers represented by formulas (II) and (IV) are more reactive than the unsaturated monomer represented by formula (V).

[0088] In some embodiments, the composition in the polymerization process can further include ethylene in addition to the vinyl ester and vinyl monomer to produce an ethylene-vinyl ester copolymer. The ethylene content of the copolymer can be 1, 5, 10, 15, 20 mol% or more, and 60, 50, 40 mol% or less.

[0089] In some embodiments, the polymerization method for producing a vinyl ester copolymer by copolymerizing a vinyl monomer represented by formula (I) with an unsaturated monomer represented by formula (II), (IV), or (V) can be any of batch polymerization, semi-batch polymerization, continuous polymerization, and semi-continuous polymerization. Furthermore, known methods such as bulk polymerization, solution polymerization, suspension polymerization, and emulsion polymerization can be used as the polymerization method. Typically, bulk polymerization or solution polymerization, in which polymerization proceeds without a solvent or in a solvent such as alcohol, is used. To obtain a modified ethylene-vinyl ester copolymer with a high degree of polymerization, emulsion polymerization is also an option. In the case of solution polymerization, the amount of solvent in the polymerization reaction solution can be selected taking into account the desired viscosity-average polymerization degree of the resulting polymer and chain transfer of the solvent. The weight ratio of the solvent to the total monomers contained in the reaction solution (solvent / total monomers) is selected from the range of 0.01 to 10, preferably from the range of 0.05 to 3.

[0090] The polymerization initiator used in copolymerization of the vinyl ester represented by formula (I) with the unsaturated monomer represented by formula (II), (IV), or (V) is selected from known polymerization initiators such as azo initiators, peroxide initiators, and redox initiators, depending on the polymerization method. Examples of azo initiators include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile). Examples of peroxide initiators include percarbonate compounds such as diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, and diethoxyethyl peroxydicarbonate; perester compounds such as t-butyl peroxyneodecanoate, α-cumyl peroxyneodecanoate, and acetyl peroxide; acetylcyclohexylsulfonyl peroxide; and 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate. Potassium persulfate, ammonium persulfate, hydrogen peroxide, and the like can also be used in combination with the above initiators. Redox initiators include polymerization initiators that combine the above peroxide initiators with reducing agents such as sodium bisulfite, sodium bicarbonate, tartaric acid, L-ascorbic acid, and Rongalit. The amount of polymerization initiator used varies depending on the polymerization catalyst and is not generally determined; it is adjusted according to the conversion rate. The amount of the polymerization initiator based on the vinyl ester monomer may be 0.01 to 0.2 mol %, or 0.02 to 0.15 mol %. The polymerization temperature is not particularly limited, but is suitably from room temperature to about 150°C, or above 40°C, and below the boiling point of the solvent used.

[0091] In copolymerizing the vinyl ester represented by formula (I) with the unsaturated monomer represented by formula (II), (IV), or (V), they can be copolymerized in the presence of a chain transfer agent, as long as the effects of the present invention are not impaired. Examples of chain transfer agents include aldehydes such as acetaldehyde and propionaldehyde; ketones such as acetone and methyl ethyl ketone; mercaptans such as 2-hydroxyethanethiol; and phosphinates such as sodium phosphinate monohydrate. Among these, aldehydes and ketones are preferred. The amount of chain transfer agent added to the polymerization reaction solution is determined according to the chain transfer constant of the chain transfer agent and the desired degree of polymerization of the modified ethylene-vinyl ester copolymer, but is typically 0.1 to 10 parts by mass per 100 parts by mass of vinyl ester monomer.

[0092] After the polymerization step, the unreacted vinyl ester is removed from the copolymer paste (removal step). The method for removing the vinyl ester is not particularly limited. In some embodiments, the removal step is performed in a different location from the evaporation step described below. For example, the removal step is performed in a different machine from the evaporation step or in a different compartment within the same evaporator. One preferred method for the removal step is to contact the copolymer paste with solvent vapor and then evaporate the vinyl ester vapor along with the solvent vapor. This method is suitable for large-scale continuous production, and the copolymer paste obtained after the removal step typically contains about 50% by weight of the solvent. In a preferred embodiment, vinyl acetate vapor is evaporated from the copolymer paste together with methanol vapor. The removed vinyl ester can then be recovered and reused, for example, by using it in a second polymerization to produce additional copolymer paste.

[0093] In some embodiments, the method further includes evaporating the solvent from the copolymer paste after the removing step and before the evaporating step. By evaporating a portion of the solvent, the viscosity of the copolymer paste entering the evaporator can be controlled within an appropriate range described below. Furthermore, it is not efficient to evaporate the vinyl monomer together with a large amount of solvent in the evaporation step.

[0094] As described above, the copolymer paste introduced into the evaporator contains a solvent. It may also contain a solvent used in solution polymerization. The solvent is not particularly limited, and alcohols, including lower alcohols such as methanol, ethanol, and propanol, or mixtures of different alcohols may be used. In some embodiments, the solvent includes methanol. The solvent may be an organic solvent having a boiling point greater than about 10, 30, 50, or 60°C and / or less than about 70, 80, 90, or 100°C. In some embodiments, the solvent may be an organic solvent having a boiling point between 10 and 100°C, between 50 and 90°C, or between 60 and 90°C. In some embodiments, the copolymer paste contains an organic solvent having a boiling point less than 100°C.

[0095] The copolymer paste resulting from the above removal step can be a viscous material. In some embodiments, the resulting copolymer paste has a viscosity of about 500, 600, 650, 700 cp or more and / or about 10,000, 9,000, 8,000, 7,000, 5,000, 3,000, 2,000, 1,000, 900 cp or less at room temperature (25° C.), for example, before being introduced into the evaporator.

[0096] The copolymer paste entering the evaporator in some embodiments may have a viscosity as described above. In some embodiments, the copolymer paste introduced into the evaporator may have a viscosity of 5,000 cP or less at room temperature (25° C.). In some embodiments, the copolymer paste introduced into the evaporator may have a viscosity of 4,000 cP or less at room temperature (25° C.). In some embodiments, the copolymer paste introduced into the evaporator has a viscosity of 500 cP or more and 3,000 cP or less at room temperature (25° C.).

[0097] In the evaporation step, the copolymer paste is heated in an evaporator at a pressure less than 1 atmosphere to evaporate the vinyl monomer. Any evaporator that operates under reduced pressure and high temperature can be used. In some embodiments, the evaporator is a thin film evaporator. Thin film evaporators are suitable for handling viscous pastes.

[0098] In some embodiments, the evaporator described herein is a wiped film evaporator (WFE), such as the Filmtruder manufactured by LCI (lcicorp.com / en-us / evaporation-equipment / high-viscosity-processor) or a similar device manufactured by Kobelco (kobelco-eco.co.jp / process_equipment / pdf / product / exeva.pdf). In some embodiments, the evaporation and removal described herein are performed in different locations within the evaporator.

[0099] The copolymer paste removed from the evaporator was approximately 8,000, 10,000, 11,000, 12,000, 15,000, 20,000, 30,000, 40,000, 45,000, 46,000, 50,000, 60,000, 70,000, 100,000, 200,000, 500,000, 1,000,000, and 1 The paste may have a viscosity of about 1,600,000, 1,700,000, 2,000,000, 10,000,000, 9,000,000, 8,000,000, 7,000,000, 6,000,000, 5,000,000, 4,000,000, or 3,000,000 cP or less. In some embodiments, the viscosity range for the pastes described herein is about 8,000 to about 25,000,000 cP. In some embodiments, the viscosity range for the pastes described herein is about 10,000 to about 2,000,000 cP. In some embodiments, the viscosity range for the pastes described herein is about 10,000 to about 16,000,000 cP. In some embodiments, the viscosity range of the pastes described herein is about 46,000 to about 16,000,000 cP. In some embodiments, the viscosity range of the pastes described herein is about 44,000 to about 20,000,000 cP. In some embodiments, the viscosity range of the pastes described herein is about 1,000,000 to about 10,000,000 cP. If the viscosity of the copolymer paste removed from the evaporator is too high, the removal operation may be difficult. On the other hand, if the viscosity of the copolymer paste removed from the evaporator is too low, the vinyl monomer may not be efficiently evaporated, resulting in a low recovery rate.

[0100] In some embodiments, removal of vinyl monomers having a boiling point higher than that of vinyl esters in the copolymer paste described herein is accomplished by applying heat to the copolymer paste. The heating can be performed in a reduced pressure environment to evaporate the vinyl monomers from the paste. For example, the copolymer removed from the evaporator is at a temperature of about 80, 90, 100, 110, 120, 130, or 140° C. or higher and / or less than 150, 170, 200, 250, 300, 350, 400, or 500° C. to evaporate the vinyl monomers. Additionally, reduced pressures, such as pressures greater than about 0.01 atmosphere (or about 7.6 torr), greater than about 0.05 atmosphere (or about 38 torr), greater than about 0.1 atmosphere (or about 76 torr), greater than about 0.2 atmosphere (or about 150 torr), and / or less than about 0.3 atmosphere (or about 230 torr), less than about 0.4 atmosphere (or about 300 torr), less than about 0.5 atmosphere (or about 380 torr), less than about 0.6 atmosphere (or about 460 torr), less than about 0.7 atmosphere (or about 530 torr), less than about 0.8 atmosphere (or about 610 torr), less than about 0.9 atmosphere (or about 680 torr), or less than about 1.0 atmosphere (or about 760 torr), can be applied to facilitate evaporation.

[0101] In some embodiments, unreacted vinyl esters and / or vinyl monomers can be recovered for reuse or recycling. Thus, some embodiments include removing vinyl esters from a copolymer paste produced by polymerization of a vinyl ester and a vinyl monomer. Such embodiments can also or alternatively include treating or heating the copolymer paste to remove the vinyl monomer from the paste.

[0102] Recovery and collection of vinyl monomer can be carried out in an evaporator described herein, such as a thin film evaporator or wiped film evaporator (WFE), such as the LCI Filmtruder (lcicorp.com / en-us / evaporation-equipment / high-viscosity-processor) or a similar device from Kobelco (kobelco-eco.co.jp / process_equipment / pdf / product / exeva.pdf). Recovery of vinyl monomer can be achieved at least about 1%, about 5%, about 10%, about 20%, about 30%, about 40%, about 50%, or about 60% of the unused vinyl monomer after the polymerization reaction. In some embodiments, at least 40% of the vinyl monomer unreacted in the polymerization process is recycled.

[0103] The recycling rate (%) disclosed herein can be calculated by the following equation: Recycled vinyl monomer / unreacted vinyl monomer after polymerization × 100; or (Flow rate of distillate from evaporator (e.g., WFE) × vinyl monomer concentration in distillate from evaporator) / (Feed rate of paste to evaporator × vinyl monomer concentration in feed to evaporator) × 100.

[0104] The recovered vinyl monomer can be recycled, for example, by being used in a second polymerization, which can produce additional copolymer paste. This can improve production efficiency, allowing for a larger amount of copolymer paste to be obtained from the same amount of starting material, compared to manufacturing methods that do not recover and collect the vinyl ester and vinyl monomer, and can also reduce the negative environmental impact of unreacted monomer that would otherwise be discarded as waste. In some embodiments, the vinyl monomer evaporated in the evaporation step is collected for later use or returned directly to the polymerization step described herein.

[0105] In some embodiments, the copolymer paste removed from the evaporator can be saponified. Known methods for saponifying vinyl ester copolymer pastes can be used. The saponification reaction is typically carried out in an alcohol or aqueous alcohol solution. The alcohol used can be a lower alcohol such as methanol, ethanol, or propanol. The alcohol or aqueous alcohol used in the saponification reaction may contain another solvent, such as acetone, methyl acetate, ethyl acetate, or benzene, in an amount of up to 40% by weight of the alcohol or aqueous alcohol. Catalysts used in saponification include, for example, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide; alkali metal alkoxides such as sodium methylate; and acid catalysts such as mineral acids. The temperature at which saponification is carried out is not limited, but can range from 20, 30, 40, 50, or 60°C to 60, 70, 80, 90, 100, 110, or 120°C. In some embodiments, the vinyl ester-based copolymers described herein can have a degree of saponification of at least 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99 mole percent.

[0106] Further, some embodiments may include concentrating the vinyl monomer in the condensate obtained by evaporation in the evaporation step and then saponifying it. Concentration of the vinyl monomer can be achieved by fractional distillation techniques. Fractional distillation techniques can be used to concentrate the vinyl monomer after evaporation and before its recycling polymerization. The distillate can be further condensed to remove solvents such as methanol to further concentrate the recovered vinyl monomer. [Example]

[0107] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0108] The vinyl monomers used were vinyl acetate, ethylene, and 2-methylene-1,3-propanediol diacetate. The vinyl monomer A, which has a boiling point of 100°C or higher, was 2-methylene-1,3-propanediol diacetate (MPDAc), and the solvent, which has a boiling point of less than 100°C, was methanol (MeOH). The boiling point of MPDAc is 225°C, and the boiling point of MeOH is 65°C.

[0109] 1. Polymerization process (1) 100 kg of vinyl acetate, 2.7 kg of MeOH, and 5.2 kg of 2-methylene-1,3-propanediol diacetate were added to a 200-liter pressurized reactor equipped with a jacket, a stirrer, a nitrogen inlet, an ethylene inlet, and an initiator addition port. The temperature was raised to 60°C, and then nitrogen was bubbled through for 30 minutes to replace the atmosphere inside the reactor. Ethylene was then introduced to a reactor pressure (ethylene pressure) of 5.3 MPa. After adjusting the temperature inside the reactor to 60°C, polymerization was initiated by adding 0.1 kg of a methanol solution of 2,2'-azobis(2,4-dimethylvaleronitrile) (Wako Pure Chemical Industries, Ltd., "V-65") as an initiator. During the polymerization, the ethylene pressure was maintained at 5.3 MPa, and the polymerization temperature was maintained at 60°C. After 6 hours, when the conversion of VAc reached 42%, the mixture was cooled to terminate the polymerization. The reaction vessel was opened, and the ethylene was removed. Nitrogen gas was then bubbled through to further remove the ethylene. Unreacted VAc was then removed under reduced pressure. MeOH was then added to the modified ethylene-vinyl acetate copolymer (hereinafter referred to as modified EVAc), and structural units derived from MPDAc were introduced by copolymerization to obtain a MeOH solution. This MeOH solution contained 29.7 wt.% modified EVAc and 0.94 wt.% MPDAc. The viscosity of this MeOH solution at 25°C was 700 cP. The method for measuring the viscosity of the MeOH solution is described below in "5. Viscosity Measurement Method."

[0110] 2. Content of each structural unit in modified EVAc Denaturing EVAc before saponification 1The ethylene content (a mol %), the content of structural units derived from vinyl acetate (b mol %), and the content of structural units derived from MPDAc (c mol %) in the modified EVAc were calculated by H-NMR measurement.

[0111] First, a small amount of the MeOH solution of modified EVAc obtained in polymerization step (1) was sampled, and the modified EVAc was precipitated in ion-exchanged water. The precipitate was collected and dried in vacuum at 60°C to obtain a dried product of modified EVAc. Next, the dried product of modified EVAc was dissolved in dimethyl sulfoxide (DMSO)-d6 containing tetramethylsilane as an internal standard and analyzed by a 500 MHz spectrometer. 1 Measurement was performed at 80°C using H-NMR (manufactured by JEOL Ltd.: "GX-500").

[0112] Denatured EVAc 1 The H-NMR spectrum was obtained in Example 1. The peaks in the spectrum are assigned as follows: 0.6 to 1.0 ppm: methylene protons (4H) in the terminal ethylene units. 1.0 to 1.85 ppm: methylene protons (4H) as ethylene units in the intermediate position, methylene protons (2H) in the main chain as structural units derived from MPDAc, and methylene protons (2H) as vinyl acetate units. 1.85 to 2.1 ppm: Methyl proton (6H) of the structural unit derived from MPDAc and methyl proton (3H) of the vinyl acetate unit. 3.7-4.1 ppm: Methylene protons (4H) at the side chain site of the structural unit derived from MPDAc 4.4-5.3 ppm: methine proton (1H) in vinyl acetate unit.

[0113] Based on the above assignments, assuming that the integral value from 0.6 to 1.0 ppm is x, the integral value from 1.0 to 1.85 ppm is y, the integral value from 3.7 to 4.1 ppm is z, and the integral value from 4.4 to 5.3 ppm is w, the content of ethylene units (a: mol %), the content of vinyl ester units (b: mol %), and the content of structural units derived from MPDAc (c: mol %) were calculated according to the following formulas. a=(2x+2y-z-4w) / (2x+2y+z+4w)×100 b=8w / (2x+2y+z+4w)×100 c=2z / (2x+2y+z+4w)×100

[0114] Using the above calculation method, the content of ethylene units (a) was 38.0 mol%, the content of vinyl ester units (b) was 59.5 mol%, and the content of structural units derived from MPDAc (c) was 2.5 mol%. The values ​​of a, b, and c in the modified EVAc are the same as the values ​​of a, b, and c in the modified EVOH after saponification.

[0115] 1 From the H-NMR analysis results, it was calculated that of the 5.2 kg of 2-methylene-1,3-propanediol diacetate introduced, 3.4 kg was converted to modified EVAc and consumed, and 1.8 kg remained unreacted in the methanol solution of modified EVAc. The composition of the MeOH solution of modified EVAc was EVAc / MeOH / vinyl monomer A = 30 / 69 / 1 (weight ratio).

[0116] 3. Vinyl Monomer A Evaporation Step (2) In the evaporation process of vinyl monomer A, 2-methylene-1,3-propanediol diacetate, a multi-stage inclined agitator (effective permeation area 0.2 m) manufactured by Kobelco Eco-Solutions Co., Ltd. was used. 2A thin-film evaporator equipped with a condenser was used. The modified EVAc MeOH solution prepared in polymerization step (1) was placed in a 50-liter storage tank equipped with a stirrer, and the modified EVAc MeOH solution was fed to the thin-film evaporator using a gear pump at the feed rate listed in Table 1. A slower feed rate results in a longer residence time in the evaporator and a higher recovery rate. MeOH and 2-methylene-1,3-propanediol diacetate were evaporated by maintaining the pressure inside the thin-film evaporator at the pressure listed in Table 1. The temperature of the heat transfer medium used to heat the evaporator is also listed in Table 1. The vapor evaporated from the thin-film evaporator was condensed in a cooler cooled to 2°C, and the weight of the condensate was measured. The modified EVAc paste concentrated in the thin-film evaporator was removed from the system via a gear pump from the bottom of the thin-film evaporator, and its weight, modified EVAc content, temperature, and viscosity were measured. The method for measuring the viscosity of the modified EVAc paste is described below in "5. Viscosity Measurement Method." The results are summarized in Table 1. The temperature of the copolymer paste taken out in Example 1 was higher than the temperature of the heat transfer medium due to shear heating.

[0117] [Table 1]

[0118] 4. Measurement of 2-methylene-1,3-propanediol diacetate concentration in the condensate obtained during the evaporation process (2) The concentration of 2-methylene-1,3-propanediol diacetate was measured using gas chromatography mass spectrometry (GC-MS) under the following conditions: GC: Shimadzu GC2014 GC column: Agilent J&W, DB-1701 (14%-cyanopropylphenyl)-methylpolysiloxane, low / medium polarity (50 m x 0.32 mm) Injection temperature: 250℃ Carrier: Helium Column temperature: 50°C for 5 minutes → 50 to 230°C (15°C / min) → 230°C for 30 minutes

[0119] As a result of the GC analysis, the concentration of 2-methylene-1,3-propanediol diacetate in the condensate is listed in Table 1. The recovery rate of 2-methylene-1,3-propanediol diacetate was calculated and listed in Table 1. The recovery rate was calculated according to "6. Calculation method for recovery rate" shown below.

[0120] 5.Viscosity measurement method 1) Fixation concentration greater than 40% Using a TA Instruments Japan rheometer, the shear rate was 10 seconds at the same temperature as the operating temperature. -1 The viscosity at 1000 kJ / min was measured.

[0121] 2) Fixation concentration less than 40% After heating the sample to the same temperature as the operating temperature, a 1 / 8 steel ball was dropped into the sample, and the time required for the ball to pass through a 5 cm measurement section was measured, and the viscosity was calculated using Stokes' equation. Vs=Dp 2 (ρp-ρf)g / 18η Vs: Terminal velocity; [m / s] Dp: diameter of the falling ball; [m] ρp: Density of the falling ball; [kg / m 3 ] ρf: Density of the denatured EVAc MeOH solution; [kg / m 3 ] g:Gravity acceleration; [m / s 2 ] η: Liquid viscosity: [Pa s] (1mPa s=1cP)

[0122] 6. Recovery rate calculation method Recovery rate = outflow rate of distillate × MPDAc concentration in distillate / supply rate of paste × MPDAc concentration in paste

[0123] In Examples 1 to 4, the solution viscosity of the modified EVAc paste removed from the evaporator was 10,000 cP or higher, allowing the vinyl monomer A, 2-methylene-1,3-propanediol diacetate, to evaporate and be separated and recovered from the modified EVAc. In Comparative Example 1, where the EVAc content was 63% and the solution viscosity was 3,800 cP, only a small amount of 2-methylene-1,3-propanediol diacetate was recovered.

[0124] 7. Reuse of vinyl monomer A contained in the condensate from the evaporation process (2) in the polymerization process (1) By concentrating the condensate obtained in the evaporation step (2) of Example 2, we succeeded in recovering 1.2 kg of 2-methylene-1,3-propanediol diacetate from the modified EVAc corresponding to the first polymerization step (1). Polymerization was carried out under the same conditions as in the polymerization step (1), except that 1.2 kg of the previously removed 2-methylene-1,3-propanediol diacetate and 4.0 kg of unused 2-methylene-1,3-propanediol diacetate were used. The polymerization proceeded without any problems, and the same modified EVAc as in the polymerization step (1) of Example 1 was obtained. Of the 1.8 kg of 2-methylene-1,3-propanediol diacetate remaining unreacted in the polymerization step (1), 1.2 kg was efficiently used. In other words, of the 5.2 kg introduced in the polymerization step (1), 3.4 kg was used in the modification reaction in the polymerization step (1), and 1.2 kg was recovered and reused in the polymerization. Its utilization rate is 88%.

[0125] 8. Saponification of Denatured EVAc A 10-liter reaction vessel equipped with a jacket, stirrer, nitrogen inlet, reflux condenser, and solution addition port was charged with 5 kg of a 20% by mass MeOH solution of the modified EVAc obtained in Examples 1 to 4. The solution was heated to 60°C while nitrogen was blown into it, and a 2 mol / L MeOH solution was added at a rate of 14.7 mL / min over 2 hours. After the addition of the sodium hydroxide MeOH solution was completed, the system temperature was maintained at 60°C while stirring for 2 hours to allow the saponification reaction to proceed. Then, 0.25 kg of acetic acid was added to terminate the saponification reaction. Next, while heating and stirring at 80°C, 3 L of ion-exchanged water was added to drain the MeOH from the reaction vessel, precipitating a modified ethylene-vinyl alcohol copolymer (hereinafter referred to as "modified EVOH"). The precipitated modified EVOH was recovered by decantation and pulverized in a mixer. The resulting modified EVOH powder was added to a 1 g / L aqueous acetic acid solution (bath ratio 20: 1 kg powder to 20 L of aqueous solution) and stirred for 2 hours to wash. After removing the liquid from this mixture, a 1 g / L aqueous acetic acid solution (bath ratio 20) was added and stirred for 2 hours for washing. The product remaining after removing the liquid was poured into ion-exchanged water (bath ratio 20), stirred for 2 hours for washing, and then the liquid was removed. This process was repeated three times for purification. The resulting product was immersed in 10 L of an aqueous solution containing 0.5 g / L acetic acid and 0.1 g / L sodium acetate and stirred for 4 hours, after which the liquid was removed. The remaining product was dried at 60°C for 16 hours to obtain 0.5 kg of dried crude modified EVOH. The degree of saponification of the modified EVOH was 99 mol%.

[0126] Comparative Example 2 The polymerization step (1) was carried out under the same conditions, and after the unreacted VAc was distilled off, the evaporation step of vinyl monomer A was not carried out. Of the 5.2 kg charged in the polymerization step (1), 3.4 kg was used in the modification reaction, and 1.8 kg remained unreacted and was not recovered or used, resulting in a utilization rate of 65%.

Claims

1. a step of polymerizing a composition containing (i) a vinyl ester and (ii) a vinyl monomer having a boiling point of 100°C or higher, wherein the vinyl ester has a boiling point lower than that of the vinyl monomer, to produce a copolymer paste (polymerization step); a step of removing the vinyl ester from the copolymer paste (removing step); a step of evaporating the vinyl monomer by heating the copolymer paste in an evaporator at a pressure of less than 1 atmosphere (evaporation step); and removing the copolymer paste having a viscosity of 8000 cP or more from the evaporator; A method for producing a vinyl ester copolymer, comprising:

2. 10. The method of claim 1, wherein the vinyl ester comprises formula (I): 【Chemistry 1】 [In the formula, R ５ is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms.

3. 3. The method of claim 1 or 2, wherein the vinyl ester comprises vinyl acetate.

4. The method according to any one of claims 1 to 3, wherein the vinyl monomer comprises a compound having two or more groups selected from acyloxy groups or formyloxy groups each having 1 to 10 carbon atoms.

5. The method according to any one of claims 1 to 4, wherein the vinyl monomer comprises a compound having 6 to 20 carbon atoms.

6. The method of any one of claims 1 to 5, wherein the vinyl monomer comprises formula (II): 【Chemistry 2】 [In the formula, R ８ is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ９ is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms, one of X and Y is a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and the other of X and Y is a group containing formula (III), 【Transformation 3】 R １０ and R １１ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R １２ is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms.

7. The method of claim 6 wherein the vinyl monomer comprises formula (IIa): 【Chemistry 4】 [In the formula, R ９ is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms, one of X and Y is a hydrogen atom, and the other of X and Y is a group containing the following formula (IIIa): 【Transformation 5】 R １２ is a hydrogen atom or an alkyl group having 1 to 9 carbon atoms.

8. The method of claim 7, wherein the vinyl monomer comprises formula (IIb): 【Transformation 6】 [In the formula, one of X and Y is a hydrogen atom, and the other of X and Y contains a group containing formula (IIIb)] 【Transformation 7】

9. The method of any one of claims 1 to 6, wherein the vinyl monomer comprises formula (IV): 【Transformation 8】 [In the formula, R １ , R ２ , R ３ , and R ４ are each independently a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and R ６ and R ７ are each independently a hydrogen atom or an alkyl group having 1 to 9 carbon atoms.

10. The method of claim 8 or 9, wherein the vinyl monomer comprises 2-methylene-1,3-propanediol diacetate (MPDAc).

11. The method of any one of claims 1 to 10, wherein the composition in the polymerization step further comprises ethylene.

12. 12. The method of any one of claims 1 to 11, wherein the copolymer paste removed from the evaporator has a viscosity of 10,000 cP or more and 2,000,000 cP or less.

13. The method according to any one of claims 1 to 12, wherein the temperature of the copolymer paste removed from the evaporator is 80°C or higher.

14. The method of any one of claims 1 to 13, further comprising evaporating the solvent from the copolymer paste after the removing step and before the evaporating step.

15. The method of any one of claims 1 to 14, wherein the copolymer paste introduced into the evaporator has a viscosity of 5,000 cP or less at 25°C.

16. 16. The method of claim 15, wherein the copolymer paste introduced into the evaporator has a viscosity of 500 cP or more and 3,000 cP or less at 25°C.

17. The method of any one of claims 1 to 16, wherein the removing step is performed at a different location than the evaporation step.

18. The method according to any one of claims 1 to 17, wherein the evaporation step is carried out in a thin film evaporator.

19. 20. The method of claim 18, wherein the evaporation step is carried out in a wiped film evaporator (WFE).

20. 20. The method of any one of claims 1 to 19, further comprising recovering the vinyl monomer evaporated in the evaporation step.

21. 20. The method of claim 19, further comprising a second copolymerization of a vinyl ester and the vinyl monomer recovered in the evaporation step.

22. 22. The method of any one of claims 1 to 21, wherein at least 40% of the vinyl monomer that did not react in the polymerization step is recycled.

23. The method according to any one of claims 1 to 22, wherein the copolymer paste introduced into the evaporator contains an organic solvent having a boiling point of less than 100°C.

24. 24. The method of claim 23, wherein the organic solvent comprises methanol.

25. The method of any one of claims 1 to 24, further comprising saponifying the copolymer paste removed from the evaporator.

26. 26. The method of claim 25, wherein the vinyl ester copolymer has a degree of saponification of at least 90 mole percent.

27. The method according to any one of claims 1 to 26, further comprising concentrating the vinyl monomer in a condensate obtained by evaporation in the evaporation step.

28. 28. The method of claim 27, further comprising concentrating the vinyl monomer by fractional distillation.

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