JP6746695B2 - Acrylic polymer and method for producing the same - Google Patents

Description

The present invention relates to a method for producing an acrylic polymer having no terminal vinyl group, which is characterized by performing a hydrogenation reaction after radical polymerization, and an acrylic polymer obtained thereby. Further, the present invention relates to a refrigerating machine lubricating oil using the acrylic polymer.

Acrylic polymers with low molecular weight are useful as plasticizers for molding materials such as vinyl chloride resin and ABS resin, and synthetic resins such as sealing materials, and for solvent-free and high-solidification of paints, adhesives and adhesives. is there.

As a method for producing such an acrylic polymer having a low molecular weight, a method of bulk polymerization at a high temperature of 200° C. or higher (Patent Document 1, Non-Patent Document 1) and a method of solution polymerization at a high temperature of 150° C. or higher (Patent Document 2, non-patent document 2), a method of thermally decomposing an acrylic polymer at a high temperature of 250° C. or higher (patent document 3) is known.

On the other hand, it is known that a low molecular weight acrylic polymer produced by high temperature polymerization or thermal decomposition inevitably has a terminal vinyl group (Non-Patent Document 1).
Further, it is described that a low molecular weight acrylic polymer can be obtained by anionic polymerization, is excellent in compatibility with a refrigerant, and is excellent in lubricating performance, and thus is suitable for a lubricating oil for a refrigerator. (Patent Document 5).

U.S. Pat. No. 4,414,370 JP 2004-18791 A JP, 11-240854, A International Publication No. 01/083619 JP-A-4-275397

Michihiro Kawai, "Synthesis of Macromonomers by High-Temperature Polymerization and Their Reactivity", Toa Synthetic Research Annual Report, 2002, No. 5, p. 2-10 Masatoshi Ohata, 2 others, “Effect of Polymerization Temperature on Properties of Low Molecular Weight Acrylic Resin”, Journal of Coloring Materials, 2006, Vol. 79, No. 7, p. 283-289

As described above, various methods for producing an acrylic polymer having a low molecular weight are known. However, low molecular weight acrylic polymers produced by high temperature polymerization or thermal decomposition have insufficient durability such as thermal stability, and have been required to improve heat resistance.

On the other hand, a mercapto compound or a phosphorus compound such as phosphoric acid (salt) as a chain transfer agent may be used, or those produced by anionic polymerization may show a certain level of durability such as thermal stability. However, in the former case, a large amount of a mercapto compound or a phosphorus compound needs to be added in order to improve thermal stability, and there are problems of odor and coloring, and there has been a demand for improvement. In the latter case, since a metal compound is used as a polymerization catalyst, the polymer contains a large amount of metal. In particular, in order to obtain a polymer having a low molecular weight, it is necessary to use a large amount of polymerization catalyst, and it is difficult to sufficiently remove the metal content even if the catalyst is removed. Therefore, there is a problem in application to applications such as electronic materials that require high insulation and corrosion resistance, and applications such as refrigerating machine lubricating oil that do not want to contain impurities, and there has been a demand for improvement.
Therefore, an object of the present invention is to provide a method for easily producing a low molecular weight acrylic polymer having excellent durability such as thermal stability, and an acrylic polymer produced by the method.
Another object of the present invention is to provide a low molecular weight acrylic polymer (composition) having excellent durability such as thermal stability and having a low content of a metal component and a low content of a sulfur component. ..

The present inventors have conducted extensive studies to solve the above problems, high temperature polymerization, in a low molecular weight acrylic polymer produced by thermal decomposition, the main factor impairing durability such as thermal stability is unavoidable. It was found that there is a terminal vinyl group present in the. Furthermore, it has been conceived that problems such as odor, coloring, and change in molecular weight can be solved by setting the sulfur content to less than 1000 ppm, the phosphorus content to less than 1000 ppm, and the metal content to less than 100 ppm. ..

Such a low molecular weight acrylic polymer having no terminal vinyl group, and further, a low molecular weight acrylic polymer having a sulfur content of less than 1000 ppm, a phosphorus content of less than 1000 ppm, and a metal content of less than 100 pm. In order to obtain the above, it is effective to carry out a hydrogenation reaction after radically polymerizing an acrylic monomer, and it was found that this production method is also an industrially suitable production method. The inventors have found that a low molecular weight acrylic polymer is suitable as a lubricating oil for refrigerators, and have conceived the present invention.

That is, the present invention provides a step of radically polymerizing a monomer component containing a (meth)acrylic acid ester at a polymerization temperature of 120° C. or higher (step I), and a step of hydrogenating the polymer obtained in the step I ( And a step II).

From another aspect of the present invention, an acrylic polymer (composition) is provided. That is, the present invention has a number average molecular weight of less than 3000, a weight average molecular weight of less than 4500, a terminal vinyl group content of 0 mass% or more and 1 mass% or less, and a sulfur content of less than 1000 ppm. It is also an acrylic polymer (composition) having a phosphorus content of less than 1000 ppm and a metal content of less than 100 ppm. Further, the present invention relates to a refrigerating machine lubricating oil comprising the above-mentioned acrylic polymer, and in particular, the refrigerating machine lubricating oil using a hydrogen-containing CFC as a refrigerant.

Since the acrylic polymer of the present invention has a low content of terminal vinyl groups, it is excellent in stability and has little change in molecular weight or change in color even when exposed to high temperature for a long time. Further, since it is possible to set the contents of sulfur, phosphorus and metals, which cause various stability deterioration, to be small, for example, applications requiring high durability such as lubricating oil for refrigerators. Can be suitably used.
The method for producing an acrylic polymer of the present invention does not require the use of a large amount of a metal-based catalyst, and an acrylic polymer having a low content of metal, sulfur, and phosphorus that causes various stability deteriorations can be obtained. It is possible to manufacture. In addition, since it is possible not to use a chain transfer agent as desired, it is possible to produce an acrylic polymer while avoiding the problems such as odor derived from the chain transfer agent.

1 is a 1H-NMR chart of the polymer (EA polymer) obtained in Example 1 before hydrogenation. 1 is a 1H-NMR chart of the polymer (EA polymer) obtained in Example 1 after hydrogenation.

[Method for producing acrylic polymer]
The production method of the present invention comprises a step of radically polymerizing a monomer component containing a (meth)acrylic acid ester at a polymerization temperature of 120° C. or higher (step I), and a step of hydrogenating the polymer obtained in the step I. And a step (II).
In the present invention, the “acrylic polymer” is a polymer containing a structural unit derived from a (meth)acrylic acid ester, and typically, a monomer component containing a (meth)acrylic acid ester is radical-polymerized. And a step of The structural unit derived from a (meth)acrylic acid ester is a structural unit having a structure in which a carbon-carbon double bond of a (meth)acrylic acid ester is replaced with a carbon-carbon single bond, and typically (meth)acrylic acid It is a structural unit formed by polymerizing an ester.
The acrylic polymer of the present invention may contain structural units derived from monomers other than (meth)acrylic acid ester, but all monomers ((meth)acrylic acid ester and other monomers) 80 mol% or more and 100 mol% or less of structural units derived from (meth)acrylic acid ester (total of two or more kinds of structural units) relative to 100 mol% of structural units derived from More preferably, it is contained in an amount of not less than 100 mol% and not more than 100 mol%, most preferably not more than 100 mol%.

In the present invention, the “(meth)acrylic acid ester” refers to either or both of a methacrylic acid ester and an acrylic acid ester. Examples of the (meth)acrylic acid ester include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, ( (Meth)acrylic acid alkyl esters such as n-octyl (meth)acrylate, dodecyl (meth)acrylate, and stearyl (meth)acrylate; (meth)acrylic acid aryl esters such as benzyl (meth)acrylate; Hydroxyalkyl esters of (meth)acrylic acid such as 2-hydroxyethyl (meth)acrylate and hydroxypropyl (meth)acrylate; methyl α-hydroxymethyl acrylate, ethyl α-hydroxymethyl acrylate, α-hydroxymethyl acrylic acid Butyl, α-hydroxyethyl methyl acrylate, α-hydroxyethyl ethyl acrylate, α-hydroxyalkyl acrylic acid alkyl esters such as α-hydroxyethyl butyl acrylate; methoxyethyl (meth)acrylate, (meth)acrylic acid (Meth)acrylic acid derivatives such as ethylene oxide adduct of (meth)acrylic acid trifluoromethylmethyl, (meth)acrylic acid 2-trifluoromethylethyl, (meth)acrylic acid 2-perfluoroethylethyl, ( (Meth)acrylic acid 2-perfluoroethyl-2-perfluorobutylethyl, (meth)acrylic acid 2-perfluoroethyl, (meth)acrylic acid perfluoromethyl, (meth)acrylic acid trifluoromethylmethyl, (meth) 2-trifluoromethylethyl acrylate, diperfluoromethylmethyl (meth)acrylate, 2-perfluoroethylethyl (meth)acrylate, 2-perfluoromethyl-2-perfluoroethylmethyl (meth)acrylate, Tripafluoromethylmethyl (meth)acrylate, 2-perfluoroethyl-2-perfluorobutylethyl (meth)acrylate, 2-perfluorohexylethyl (meth)acrylate, 2-perfluoro(meth)acrylate Perfluoroalkyl esters of (meth)acrylic acid such as decylethyl, 2-perfluorohexadecylethyl (meth)acrylic acid, and perfluoroethylene; silicon-containing (meth)acryl such as γ-(methacryloyloxypropyl)trimethoxysilane Examples thereof include acid ester monomers, and these may be used alone or in combination of two or more. May be used.
As the ester group in the (meth)acrylic acid ester, when the ester group is represented by -COOR, R is preferably a group having 1 to 18 carbon atoms, and more preferably a group having 1 to 8 carbon atoms. .. The above R may be a linear group, a branched group or a cyclic group, but is preferably a linear group. The R is preferably an alkyl group having a substituent or an alkyl group having no substituent, and more preferably an alkyl group having no substituent.

The acrylic polymer of the present invention is a polymer containing a structural unit derived from a (meth)acrylic acid ester, but is preferably a polymer containing a structural unit derived from an acrylic acid ester. A polymer containing a structural unit derived from an acrylate ester has favorable viscosity characteristics.
When the acrylic polymer of the present invention contains a structural unit derived from an acrylic acid ester, the ratio of the structural unit derived from an acrylic acid ester to 80 mol% of the structural unit derived from a (meth)acrylic acid ester is 80. It is preferably at least mol %. It is more preferably 90 mol% or more, and most preferably 100 mol%, that is, all the structural units derived from the (meth)acrylic acid ester of the acrylic polymer of the present invention are derived from the acrylic acid ester. Is to be.

The monomer component used in the above step I may contain a monomer other than (meth)acrylic acid ester (hereinafter, also referred to as “other monomer”). The other monomer is usually preferably a compound capable of radical polymerization. Two or more kinds of other monomers may be used. The above-mentioned monomer component is based on 100 mol% of all monomers ((meth)acrylic acid ester and other monomers), and (meth)acrylic acid ester (when two or more kinds are contained, the total thereof). The content is preferably 80 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less, and particularly preferably 100 mol%. Within the above range, the effect of the present invention tends to be more significantly exhibited.

The acrylic polymer of the present invention can be preferably produced by radical polymerization. Radical polymerization can be carried out in a relatively inexpensive device and is widely carried out industrially. The molecular weight of the acrylic polymer can be controlled by selecting the polymerization temperature in an appropriate range.
It is generally difficult to efficiently polymerize a (meth)acrylic monomer such as (meth)acrylic acid or its ester by anionic polymerization as described in Patent Document 5 described above. A lot remains. Although it is possible to reduce the residual monomer to some extent by purification or the like, it is difficult to sufficiently remove the residual monomer. On the other hand, by producing an acrylic polymer by radical polymerization, it is possible to obtain an acrylic polymer that has less residual monomers, is excellent in thermal stability, and is more suitable for use as a lubricating oil of a refrigerator.

The polymerization temperature is not particularly limited, but in order to obtain the acrylic polymer of the present invention, the polymerization is preferably performed at a temperature of 120° C. or higher, more preferably 150° C. or higher. Polymerization at 200° C. or higher and 350° C. or lower is more preferable, and polymerization at 240° C. or higher and 300° C. or lower is particularly preferable. When polymerizing at such a high temperature, it is preferable to use a reactor capable of sealing the reaction system.

There are no particular restrictions on the initiator used in Step I, but when the above-mentioned polymerization is carried out at 150 to 350°C, examples of the initiator include di(t-amyl)peroxide and di(t-butyl)peroxide. , T-amylperoxyacetate, t-butylperoxyacetate, t-butylperoxybenzoate, t-amylperoxybenzoate, methyl ethyl ketone peroxide, peroxides such as hydrogen peroxide; 2,2′-azobis(iso Butyronitrile), dimethyl 2,2-azobis(2-methylpropionate), 2,2′-azobis(2-methylbutyronitrile), 1,1′-azobis(cyclohexane-1-carbonitrile), An azo-based initiator such as dimethyl 1,1′-azobis(1-cyclohexanecarboxylate) or 2,2′-azobis(N-butyl-2-methylpropionamide) can be used.
The amount used is, for example, 0.5 to 10% by weight based on the monomer mixture. As the above-mentioned initiator, a compound having a 10-hour half-life temperature of 80 to 200°C is preferable, and a compound of 90 to 140°C is more preferable.

As the organic solvent used for polymerization, various types such as hydrocarbon type, ester type, ketone type, alcohol type and ether type can be used, but in consideration of the polymerization temperature, a solvent having a boiling point of 100° C. or higher. Is preferably used. In addition, these solvents can be used in combination of 2 or more types.
The amount of the solvent can be appropriately determined, but in the case of producing a binder contained in a high solid type coating material, it is preferably 25 to 65% by weight based on the monomer mixture.

For the above-mentioned polymerization reaction, the procedure of the acrylic polymerization method well known in the related art can be applied as it is or after being modified appropriately. For example, a method is used in which the monomer mixture and the initiator are added dropwise to a solvent heated to a predetermined polymerization temperature. After completion of the dropping, it is preferable to perform aging while maintaining the polymerization temperature. It is preferable that the polymerization reaction is usually performed for 1 to 9 hours.

The production method of the present invention includes a step of adding hydrogen to the polymer obtained in the above step I (step II). The hydrogenation reaction in step (II) is not particularly limited, but (1) a combination of an organic acid salt such as Ti, Co and Ni or an acetylacetone salt with an organic metal compound such as Li, Mg, Al and Sn. , A method using a so-called Ziegler-type homogeneous catalyst, (2) using a supported precious metal-based catalyst in which a precious metal such as palladium, platinum, ruthenium or rhodium is supported on a carrier such as carbon, alumina, silica-alumina or diatomaceous earth Known hydrogenation methods such as a method, (3) a method using a solid catalyst using a base metal such as nickel, (4) a method using a noble metal complex catalyst such as Rh or Ru, or a method obtained by appropriately modifying them. Can be used.

Preferred hydrogenation catalysts include titanocene compounds, reducing organometallic compounds, or mixtures of titanocene compounds and reducing organometallic compounds. The titanocene compound has at least one or more ligands having a (substituted) cyclopentadienyl skeleton, an indenyl skeleton, or a fluorenyl skeleton such as biscyclopentadienyl titanium dichloride and monopentamethylcyclopentadienyl titanium trichloride. Compounds. Examples of the reducing organic metal compound include organic alkali metal compounds such as organic lithium, organic magnesium compounds, organic aluminum compounds, organic boron compounds and organic zinc compounds.
In the present invention, the hydrogenation reaction is generally carried out in the temperature range of 0 to 200°C, more preferably 30 to 150°C.

The pressure of hydrogen used in the hydrogenation reaction is recommended to be 0.1 to 15 MPa, preferably 0.2 to 10 MPa, more preferably 0.3 to 5 MPa.
The hydrogenation reaction time is usually 3 minutes to 10 hours, preferably 10 minutes to 5 hours. The hydrogenation reaction can be performed by either a batch process, a continuous process, or a combination thereof.

The manufacturing method of the present invention may include any step other than the above step I and step II. For example, it may include a solvent removal step when a polymerization solvent or the like is used, a dilution step of diluting with an arbitrary solvent, a purification step, an extraction step, a filtration step and the like. The production method of the present invention preferably includes a solvent removal step, and the solvent removal step is more preferably performed under reduced pressure.

[Acrylic polymer]
The content of the terminal vinyl group in the acrylic polymer of the present invention is preferably 1.7% by mass or less, more preferably 0% by mass or more and 1% by mass or less. It is more preferably 0 mass% or more and 0.5 mass% or less, still more preferably 0 mass% or more and 0.3 mass% or less, and most preferably 0 mass%. Within the above range, the stability tends to be remarkably good, and for example, even when exposed to high temperature for a long time, the change in molecular weight and the change in color tone tend to be small.
The content of the terminal vinyl group can be calculated, for example, by evaluating the molar ratio of the terminal vinyl group to the monomer structure by 1HNMR and converting the content into a mass ratio.
The acrylic polymer of the present invention is preferably produced by the above-mentioned production method of the present invention.

The acrylic polymer of the present invention has a number average molecular weight determined by gel permeation chromatography (GPC) of preferably less than 5,000, more preferably less than 3,000, even more preferably less than 2,000, and particularly preferably less than 1,000. The weight average molecular weight determined by GPC is preferably less than 7500, more preferably less than 4500, further preferably less than 3000, and particularly preferably less than 1500. When the molecular weight is out of the above range, the viscosity becomes high, which may cause a problem in workability, and the compatibility with various materials may deteriorate.

Further, when the acrylic polymer is produced by the method for producing an acrylic polymer of the present invention, it is basically not necessary to produce it using a chain transfer agent, so that problems such as odor derived from the chain transfer agent are avoided. It is possible to use the above acrylic polymer, and further, it is possible to use an acrylic polymer having a small content of sulfur and phosphorus contained in the polymer that causes various stability deterioration.
For example, the content of sulfur in the acrylic polymer of the present invention means conversion to sulfur atom (calculated as a sulfur atom with respect to the mass of the polymer, for example, -SH group also means mass calculation as S). ) Is preferably 0 ppm or more and less than 1000 ppm, more preferably 0 ppm or more and less than 100 ppm, further preferably 0 ppm or more and less than 10 ppm, and particularly preferably 0 ppm or more and less than 2 ppm. In the acrylic polymer of the present invention, the content of the sulfur component bonded to the polymer molecule is preferably in the above range, and the content of the sulfur component contained in the main chain terminal is more preferably in the above range. ..
The content of phosphorus in the acrylic polymer of the present invention is equivalent to the mass of the polymer in terms of phosphorus atom (calculated as a phosphorus atom. For example, even if -OPO(OH) ₂ groups are used, the mass is calculated as P. It is preferably 0 ppm or more and less than 1000 ppm, more preferably 0 ppm or more and less than 100 ppm, further preferably 0 ppm or more and less than 10 ppm, particularly preferably 0 ppm or more and less than 2 ppm. .. In the acrylic polymer of the present invention, the content of phosphorus bound to the polymer molecule is preferably in the above range, and the content of phosphorus contained in the main chain terminal is more preferably in the above range. preferable.
The sulfur content and phosphorus content in the acrylic polymer of the present invention can be quantified by, for example, ICP emission spectrometry. In the acrylic polymer of the present invention, when a phosphorus-containing compound or a sulfur-containing compound is present as an impurity, the content of phosphorus or sulfur bound to the polymer molecule is determined by liquid chromatography or vacuum chromatography. Appropriate from the method of quantifying by sromatography and dividing from the measurement result of ICP emission spectrometry, the method of calculating from the measurement result of ICP emission spectrometry before and after purifying the acrylic polymer by a method such as reprecipitation or dialysis, etc. It is possible to calculate by selecting any method.

Further, since the acrylic polymer of the present invention does not need to be produced by using a large amount of a metal-based catalyst, it is possible to set the content of the metal component which causes various stability deterioration to be small. .. The content of the metal component contained in the polymer is preferably 0 ppm or more and less than 100 ppm in terms of metal atoms (calculated as metal atoms) with respect to the mass of the polymer. More preferably, it is 0 ppm or more and less than 20 ppm. Note that the metal atom refers to an atom of Group 1 to Group 12 of the periodic table. The metal content may or may not be bonded to the polymer molecule, but the content of the non-bonded metal content is more preferably within the above range.
That is, the above-mentioned “acrylic polymer” is used as a word that means an acrylic polymer molecule itself, and also as a word that means an acrylic polymer containing trace amounts of impurities (also referred to as an acrylic polymer composition). There are some cases.
The content of metal content can be quantified by ICP emission spectrometry.

Acrylic polymer of the present invention, the main chain terminal of the polymer, -CH (COOR) CH ₃ or _-CH 2 _CH 2 COOR (wherein, R is a is meanings given above), having a group represented by Is preferred. More preferably, the above group is formed by hydrogenating a terminal vinyl group.
In the acrylic polymer of the present invention, the content of the group represented by —CH(COOR)CH ₃ or —CH ₂ CH ₂ COOR at the terminal is calculated by the mass of the portion excluding the COOR of the terminal group. In this case, it is preferably 0.5% by mass or more and 10.0% by mass or less, and more preferably 1.0% by mass or more and 5.0% by mass or less. Within the above range, the effect of the present invention tends to be more significantly exhibited.

Further, the acrylic polymer of the present invention can be set to have a small content of residual monomer. From the viewpoint of durability such as thermal stability, the content of the (meth)acrylic acid ester contained in the polymer is, for example, 50,000 ppm or less, preferably 0 ppm or more and less than 20,000 ppm, relative to the mass of the polymer. .. More preferably, it is 0 ppm or more and less than 10000 ppm, further preferably 0 ppm or more and less than 5000 ppm, and even more preferably 0 ppm or more and less than 2000 ppm, since durability such as thermal stability tends to improve. And particularly preferably 0 ppm or more and less than 1000 ppm.
The content of the residual monomer can be measured by gas chromatography with the following equipment and conditions.
Device: SHIMADZU GC-2014
Column: Inert Cap 1 (length 30 m, inner diameter 0.25 mm, film thickness 0.25 μm)
Injection volume: 1.0 μL
Injection method: Split ratio 15.0
Inlet temperature: 300℃
Oven: 40°C (5min)-10°C/min-310°C (10min)-330°C (8min)
Carrier gas: He, linear velocity, 30.8 cm/s
Detector: FID, 350°C

The acrylic polymer of the present invention is excellent in stability and durability as its effects, and can be suitably used particularly for applications requiring high durability such as a lubricating oil for a refrigerator.

[Acrylic polymer composition]
The acrylic polymer composition of the present invention contains the acrylic polymer of the present invention. The acrylic polymer composition of the present invention preferably contains, for example, 35% by mass or more and 100% by mass or less of the acrylic polymer of the present invention with respect to 100% by mass of the entire acrylic polymer composition.

The acrylic polymer composition of the present invention may contain an organic solvent. Examples of the organic solvent include those exemplified as the organic solvent used for the polymerization in the method for producing an acrylic polymer of the present invention. The content of the organic solvent of the acrylic polymer composition of the present invention is preferably, for example, 0% by mass or more and 65% by mass or less based on 100% by mass of the entire acrylic polymer composition.

The acrylic polymer composition of the present invention can contain a low sulfur content by including the acrylic polymer of the present invention. The content of sulfur in the acrylic polymer composition of the present invention is preferably 0 ppm or more and less than 1000 ppm in terms of sulfur atom, and 0 ppm or more and less than 100 ppm with respect to the total mass of the acrylic polymer composition. Is more preferable, 0 ppm or more and less than 10 ppm is further preferable, and 0 ppm or more and less than 2 ppm is particularly preferable. Within the above range, it is possible to suppress odor and the like to a low level. In the present invention, the “sulfur content” refers to an ion, compound, group or the like containing a sulfur atom.

The content of the phosphorus component of the acrylic polymer composition of the present invention is preferably 0 ppm or more and less than 1000 ppm in terms of phosphorus atom, and is 0 ppm or more and less than 100 ppm with respect to the total mass of the acrylic polymer composition. Is more preferable, 0 ppm or more and less than 10 ppm is further preferable, and 0 ppm or more and less than 2 ppm is particularly preferable. Within the above range, coloring and the like can be suppressed low. In the present invention, the "phosphorus component" refers to an ion, compound, group or the like containing a phosphorus atom.

The acrylic polymer composition of the present invention can be set to have a low metal content. The metal content of the acrylic polymer composition of the present invention is preferably 0 ppm or more and less than 100 ppm in terms of metal atoms, and 0 ppm or more and less than 50 ppm with respect to the total mass of the acrylic polymer composition. Is more preferable. Within the above range, it is possible to suppress coloring during heating to a low level. In addition, in the present invention, the “metal component” refers to a metal ion, a compound containing a metal atom, a group, or the like.

Since the acrylic polymer composition of the present invention contains the acrylic polymer produced by the method for producing an acrylic polymer of the present invention, the content of the residual monomer can be set low. From the viewpoint of durability such as thermal stability and physical properties in various applications, the content of the (meth)acrylic acid ester contained in the polymer composition is, for example, 50,000 ppm or less based on the mass of the entire polymer composition. Is preferred. More preferably, it is 0 ppm or more and less than 20000 ppm, and further preferably, it is 0 ppm or more and less than 10000 ppm, and even more preferably 0 ppm or more and less than 5000 ppm, since durability such as thermal stability tends to improve. Yes, particularly preferably 0 ppm or more and less than 2000 ppm, and most preferably 0 ppm or more and less than 1000 ppm.

The acrylic polymer composition of the present invention may contain a compound obtained by hydrogenating a (meth)acrylic acid ester. From the viewpoint of durability such as thermal stability, the content of the compound obtained by hydrogenating the (meth)acrylic acid ester contained in the acrylic polymer composition of the present invention is, for example, 70,000 ppm with respect to the mass of the entire polymer composition. The following is preferable. More preferably, it is 0 ppm or more and less than 50,000 ppm, and even more preferably, it is 0 ppm or more and less than 10000 ppm, and even more preferably 0 ppm or more and less than 5000 ppm because the durability such as thermal stability tends to improve. Yes, particularly preferably 0 ppm or more and less than 2000 ppm, and most preferably 0 ppm or more and less than 1000 ppm. The compound obtained by hydrogenating the (meth)acrylic acid ester is a compound represented by CH ₃ CH ₂ COOR or CH ₃ CH(CH ₃ )COOR (where R is as described above).
The content of the compound obtained by hydrogenating the (meth)acrylic acid ester can be measured by gas chromatography under the same apparatus and conditions as those used for measuring the content of the residual monomer described above.

[Lubricant for refrigerator]
The refrigerating machine lubricating oil in the present invention refers to a lubricating oil used for a refrigerating machine and a lubricating oil for lubricating a compressor (compressor) for compressing a refrigerant in the refrigerating machine. Refrigerating machine lubricating oil circulates in the system in the state of always coexisting with a refrigerant, and is exposed to heat (high temperature) generated by compressing the refrigerant and heat (low temperature) taken by evaporation of the refrigerant. Also, the service life of refrigerators is usually very long, 10 to 20 years, and oil exchange is not premised on a sealed system. That is, it is necessary to maintain the quality of the refrigerator lubricating oil for a long period of time under the severe conditions as described above, and it is required to have high durability and reliability.

[Refrigerant]
Freon 12 has been often used as a refrigerant in a refrigerator, but the regulation of Freon 12 is becoming strict worldwide because it may cause environmental pollution such as destruction of the ozone layer. .. Therefore, a hydrogen-containing CFC compound represented by CFC134a is drawing attention as a new refrigerant. The hydrogen-containing chlorofluorocarbon compound is preferable because it is less likely to damage the ozone layer and can substitute for the chlorofluorocarbon 12 without substantially changing the structure of the conventional refrigerator.
INDUSTRIAL APPLICABILITY The lubricating oil for a refrigerator of the present invention can be suitably used for a refrigerator using a hydrogen-containing CFC compound as a refrigerant.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

(Method for determining metal content, sulfur content and phosphorus content)
It was quantified by ICP emission spectroscopy.

(Quantification method of terminal vinyl group)
From 1 H-NMR, the molar ratio of the vinyl group to the repeating unit was determined from the ratio of the peak derived from the terminal vinyl group at around 5.6 ppm and 6.2 ppm and the peak derived from the methylene chain near the oxygen of the acrylate ester at around 4 ppm. It was calculated and calculated by mass conversion.
Other terminal groups were similarly determined by 1H-NMR.

(Heat resistance evaluation, molecular weight measurement)
A 1 g sample was weighed into a 20 ml glass sample tube and heat-treated at 200° C. for 1 hour by a circulating hot air dryer. Then, the change in appearance (color) was visually observed, the molecular weight was measured by GPC (gel permeation chromatography), and the change in molecular weight before and after the heat treatment was measured.
The molecular weight measurement by GPC was performed with the following equipment and conditions.
Equipment: Tosoh HLC-8320
Column: guardcolumn superHL, TSKgel Super H2000
Column temperature: 40°C
Injection volume: 10 μL
Mobile phase: Tetrahydrofuran (Wako reagent special grade stabilizer included)
Flow rate: 0.6 mL/min
Detector: RI
Calibration curve: TSK standard POLYSTYRENE

(Example 1)
144 parts by mass of butyl acetate are added to a pressure-type stirred tank reactor having a capacity of 1000 ml and the reactor is hermetically closed, and pressure and decompression of nitrogen gas are repeated to replace the inside of the reactor with nitrogen. The temperature inside the reactor was raised to 240° C. with an electric heater, and then 144 parts by mass of butyl acetate and 3.6 parts by mass of methyl ethyl ketone peroxide (hereinafter referred to as MEKPO) were uniformly mixed to prepare an initiator solution and ethyl acrylate. 72 parts by mass (hereinafter referred to as EA) are continuously charged into the reactor simultaneously using a high-pressure metering pump over 2 hours. After that, the temperature inside the reactor was kept at 240° C. and kept for 10 minutes. At that time, the pressure in the reactor was 1.1 MPa.

Then, the mixture was cooled, and after confirming that the pressure inside the reactor was sufficiently lowered, the pressure was released and the contents were taken out to obtain a colorless transparent EA polymer solution.

Next, 75 parts by mass of the EA polymer solution thus obtained, 1.5 parts by mass of palladium carbon (manufactured by Degussa Japan Co., Ltd.) as a catalyst for hydrogenation reaction, a stir bar, and 300 ml of eggplant type The flask was charged. The eggplant-shaped flask was connected to a balloon filled with an aspirator and hydrogen gas with a three-way cock. After degassing the inside of the eggplant flask with an aspirator, a hydrogen gas atmosphere was created, and the reaction was carried out at 70° C. while rotating the stirring bar. After 3 hours, the palladium carbon was removed by filtration, and low-boiling components such as butyl acetate and residual EA were removed under reduced pressure.

Table 1 summarizes the physical properties of the EA polymer before and after the hydrogenation reaction. It is clear that hydrogenation improved the heat resistance stability of the EA polymer. 1 and 2 show 1H-NMR spectra of the EA polymer before and after hydrogenation, respectively. In the 1H-NMR spectrum, the peaks derived from the terminal vinyl group near 5.6 ppm and 6.2 ppm disappeared. Therefore, it was revealed that the hydrogenation reaction eliminated the absorption identified by the terminal vinyl group. No residual monomer was detected.
Further, the EA polymer after the hydrogenation reaction showed almost no change in the molecular weight even when heated at 200° C. for 1 hour, and the color tone remained colorless.

Claims (4)

A monomer component containing 90 mol% or more of (meth)acrylic acid ester with respect to 100 mol% of all monomers is used at a polymerization temperature of 120° C. or higher without using a chain transfer agent, and a transition metal complex is used as a polymerization catalyst. Polymer obtained by the step (step I) of radical polymerization without using, and a titanocene compound, a reducing organometallic compound, or a mixture of a titanocene compound and a reducing organometallic compound as a hydrogenation catalyst. And a step of adding hydrogen to the step (step II), the method for producing an acrylic polymer having a number average molecular weight of less than 1000 . A number average molecular weight of less than 1000, a weight average molecular weight of less than 4500,
The content of sulfur is less than 1000 ppm, the content of phosphorus is less than 1000 ppm, the content of metal is less than 100 ppm, and the content of (meth)acrylic acid ester contained in the polymer is a polymer. Is 50000 ppm or less with respect to the mass of
An acrylic polymer having a content of terminal vinyl groups of 0% by mass or more and 1% by mass or less. A number average molecular weight of less than 3000, a weight average molecular weight of less than 4500,
The content of sulfur is less than 1000 ppm, the content of phosphorus is less than 1000 ppm, the content of metal is less than 100 ppm, and the content of (meth)acrylic acid ester contained in the polymer is a polymer. Is 50000 ppm or less with respect to the mass of
A refrigerating machine lubricating oil comprising an acrylic polymer having a content of terminal vinyl groups of 0% by mass or more and 1% by mass or less. The lubricating oil for a refrigerator according to claim 3, wherein the refrigerant uses hydrogen-containing CFCs.

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