JP2007308693A - High-refractive-index linear polymer and its preparation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-refractive-index linear polymer which has a high refractive index, has no problem of discoloration and is excellent in moldability, processability, etc. <P>SOLUTION: The high-refractive-index linear polymer has a repeating unit represented by formula (1) (wherein A and B are each a bivalent organic group; X is an oxygen atom, -NH- or a sulfur atom, provided that the two X's in the formula may be identical or different from each other; and D is a 1-8C thioalkylene group, provided that the two D's in the formula may be identical or different from each other). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a high refractive index linear polymer and a method for producing the same. The present invention also relates to an optical material comprising such a high refractive index linear polymer.

  Conventionally, many optical components having a glass base have been used. For example, glass lenses have been used for various lenses. However, since the glass lens has a large specific gravity, it cannot sufficiently cope with the light weight and thinning currently required in various applications. Glass also has problems in formability and workability. For these reasons, resin lenses that are lightweight, have high mechanical strength, and are easy to mold and process are attracting attention.

  However, since the resin has a low refractive index, in order to mold a lens having desired optical characteristics, the thickness has to be increased, and it has been difficult to reduce the thickness of the lens. In addition, studies have been made to increase the refractive index of the resin itself, but it has been difficult to obtain a practical one with a refractive index (nD) of 1.6 or more. Therefore, the movement to obtain a material having a higher refractive index is increasing.

  Patent Document 1 discloses a method for producing a resin for a high refractive index plastic lens by a reaction between a dithiol compound and a polyvalent monomer.

  Patent Document 2 discloses a method for producing an optical resin by a reaction between a dithiol compound and divinylbenzene, and Patent Document 3 discloses a method for optical use by a reaction between a dithiol compound and a bifunctional monomer. A method of making a resin is disclosed.

Patent Document 4 discloses a wholly aromatic polyamide compound containing sulfur.
Japanese Patent Laid-Open No. 2-58001 JP-A-2-289622 JP-A-5-70524 JP-A-60-226527

  Since all of the high refractive index resins disclosed in Patent Documents 1 to 3 are three-dimensional cross-linked resins obtained by radical reaction, it has been difficult to mold them into a lens or the like in a subsequent process. In addition, it is difficult to perform injection molding by mixing with other resins and solvents or to prepare a coating composition.

  In addition, the resin disclosed in Patent Document 4 has a high glass transition temperature (Tg) (188 ° C. to 250 ° C .: Example), and therefore cannot be used as an optical material because it is difficult to mold and is colored. Met.

  An object of the present invention is to solve the above-mentioned drawbacks of the prior art, to provide a high refractive index linear polymer which has no problem of coloring, has a high refractive index, and is excellent in moldability, workability and the like. To do.

  As a result of intensive studies to achieve the above-mentioned problems, the inventors of the present invention have little coloration of a linear polymer having a specific structure, maintain a high refractive index, and Tg is not too high. The polymer was found to be excellent in properties and processability, and the present invention was reached based on such knowledge.

（式中、Ａ及びＢは２価の有機基を表し、
Ｘは酸素原子、−ＮＨ−、又は硫黄原子を示し、
Ｄは炭素数１〜８のチオアルキレン基を示す。
なお、一般式（１）中にそれぞれ２個あるＤ、Ｘは同一であっても異なるものであってもよい。） That is, the first gist of the present invention resides in a high refractive index linear polymer having a repeating unit represented by the following general formula (1).

(In the formula, A and B represent a divalent organic group,
X represents an oxygen atom, -NH-, or a sulfur atom;
D represents a thioalkylene group having 1 to 8 carbon atoms.
Note that two D and X in the general formula (1) may be the same or different. )

（式中、Ａ及びＢは２価の有機基を表し、
Ｘは酸素原子、−ＮＨ−、又は硫黄原子を示し、
Ｒは水素原子又はメチル基を表す。
なお、一般式（２）中にそれぞれ２個あるＲ、Ｘは同一であっても異なるものであってもよい。） The second gist of the present invention resides in a high refractive index linear polymer comprising a repeating unit represented by the following general formula (2).

(In the formula, A and B represent a divalent organic group,
X represents an oxygen atom, -NH-, or a sulfur atom;
R represents a hydrogen atom or a methyl group.
Note that two R and X in the general formula (2) may be the same or different. )

（式中Ｂ，Ｒ，Ｘは一般式（２）におけると同義である。） The third gist of the present invention is a method for producing the above high refractive index linear polymer in which a dithiol compound represented by the following general formula (3) and a divinyl compound represented by the following general formula (4) are reacted. , Exist.
HS-A-SH (3)
(In the formula, A has the same meaning as in formula (2).)

(In the formula, B, R and X have the same meanings as in the general formula (2).)

  The fourth gist of the present invention resides in an optical material formed by molding the above high refractive index linear polymer.

  In the present invention, the refractive index is a value measured at a temperature of 25 ° C. at a wavelength of sodium D line (wavelength 589.3 nm).

  According to the present invention, there is no coloring problem, the refractive index is high, the Tg is not too high, and the solvent solubility is excellent, so that the high refractive index linear weight excellent in moldability and workability is obtained. Coalescence is provided.

  This high refractive index linear polymer can be easily formed into an optical material such as a lens or other member by a general molding method such as injection molding or press molding. It is also possible to prepare a coating composition using a polymer.

  Therefore, according to the present invention, in the field of optical materials and the like, a conventional glass product can be replaced with a resin product to reduce its weight and thickness, and further, the use of a high refractive index resin can be expanded. be able to.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the description of the constituent elements described below is an example (representative example) of an embodiment of the present invention, and the present invention is not limited to the gist of the present invention. The content of is not limited.

  In the following, “(meth) acrylate” and “(meth) acryloyl” mean “acrylate or methacrylate” and “acryloyl or methacryloyl”, respectively.

（式中、Ａ及びＢは２価の有機基を表し、
Ｘは酸素原子、−ＮＨ−、又は硫黄原子を示し、
Ｄは炭素数１〜８のチオアルキレン基を示す。
なお、一般式（１）中にそれぞれ２個あるＤ、Ｘは同一であっても異なるものであってもよい。） [High refractive index linear polymer]
The high refractive index linear polymer of the present invention has a repeating unit represented by the following general formula (1).

(In the formula, A and B represent a divalent organic group,
X represents an oxygen atom, -NH-, or a sulfur atom;
D represents a thioalkylene group having 1 to 8 carbon atoms.
Note that two D and X in the general formula (1) may be the same or different. )

（式中、Ａ及びＢは２価の有機基を表し、
Ｘは酸素原子、−ＮＨ−、又は硫黄原子を示し、
Ｒは水素原子又はメチル基を表す。
なお、一般式（２）中にそれぞれ２個あるＲ、Ｘは同一であっても異なるものであってもよい。） A preferable embodiment of the high refractive index linear polymer of the present invention includes, for example, one having a repeating unit represented by the following general formula (2).

(In the formula, A and B represent a divalent organic group,
X represents an oxygen atom, -NH-, or a sulfur atom;
R represents a hydrogen atom or a methyl group.
Note that two R and X in the general formula (2) may be the same or different. )

In the general formulas (1) and (2), A represents a divalent organic group.
A is not particularly limited as long as it is a divalent organic group, but is preferably an aliphatic organic group having 2 to 12 carbon atoms or an organic group containing an aromatic group having 6 to 12 carbon atoms. The aliphatic organic group and the aromatic group-containing organic group may contain sulfur in the chemical form of -S- and / or oxygen in the chemical form of -O-. Specific examples of the aliphatic organic group having 2 to 12 carbon atoms which may contain sulfur in the chemical form of —S— and / or oxygen in the chemical form of —O— include the following groups.

—CH ₂ —CH ₂ —
—CH ₂ —CH ₂ —CH ₂ —
—CH ₂ —CH ₂ —S—CH ₂ —CH ₂ —
_{-CH 2 -CH 2 -O-CH 2} -CH 2 -O-CH 2 -CH 2 -

  The aliphatic organic group having 2 to 12 carbon atoms which may contain sulfur in the chemical form of —S— and / or oxygen in the chemical form of —O— may be a vinylene group substituted with the following cyano group: Good.

  The aromatic group in the organic group containing an aromatic group having 6 to 12 carbon atoms, which may contain sulfur in the chemical form of -S- and / or oxygen in the chemical form of -O-, is an aromatic hydrocarbon A group derived from a ring and a group derived from an aromatic heterocycle containing a nitrogen atom and / or a sulfur atom are preferred. Here, the aromatic heterocycle containing a nitrogen atom may be substituted with an aromatic amino group. Specific examples of the organic group containing 6 to 12 carbon atoms that may contain sulfur in the chemical form of -S- and / or oxygen in the chemical form of -O- include the following groups. .

  A is preferably a group containing a sulfur atom and / or an aromatic group. Particularly preferred is a group containing a sulfur atom and an aromatic group. A refractive index can be made high by containing a sulfur atom and an aromatic group.

In general formulas (1) and (2), B represents a divalent organic group. B is not particularly limited as long as it is a divalent organic group, but is preferably a group containing a sulfur atom and / or an aromatic group. Particularly preferred is a group containing a sulfur atom and an aromatic group. A refractive index can be made high by containing a sulfur atom and an aromatic group. B is preferably a group represented by the following general formula (1A).

In General Formula (1A), R ² represents a divalent hydrocarbon group having 1 to 12 carbon atoms, such a group has 1 to 12 carbon atoms, is composed of a carbon atom and a hydrogen atom, and has a bond. Although it will not specifically limit if it has two, Specifically, alkylene groups, such as a methylene group, ethylene group, a propylene group, a tetramethylene group, a hexamethylene group, an octamethylene group, a decamethylene group, are mentioned. Preferably it is a C1-C6 alkylene group, More preferably, it is a C2-C4 alkylene group.

Ar represents an arylene group having 6 to 30 carbon atoms which may be substituted with a halogen atom excluding fluorine, or an aralkylene group having 7 to 30 carbon atoms which may be substituted with a halogen atom excluding fluorine. Specific examples of the arylene group having 6 to 30 carbon atoms, preferably 6 to 12 carbon atoms, include a phenylene group and a naphthylene group. As the aralkylene group having 7 to 30 carbon atoms, preferably 7 to 14 carbon atoms, — (CH ₂ ) _x —Ar′—, —Ar ′ — (CH ₂ ) _x —, — (CH ₂ ) _x —Ar ′ — ( CH ₂ ) _y- . Here, Ar ′ represents an arylene group having 6 to 29 carbon atoms such as a phenylene group or a naphthylene group, x and y each represents an integer of 1 to 24, and the carbon number of the arylene group represented by x, y, and Ar ′. Is the sum of 7-30. These arylene groups and aralkylene groups may be substituted with halogen atoms other than 1 to 12, preferably 2 to 8, fluorine atoms. Here, the reason why the fluorine atom is excluded is that the fluorine atom has a function of lowering the refractive index.

  Q represents -O- or -S-.

Y represents —S— or —SO ₂ — when Q is —O—. Also, Y, if Q is _{-S-, -S -, - SO 2} -, - CO-, an alkylene group having 1 to 12 carbon atoms, an aralkylene group having 7 to 30 carbon atoms, or -Ar- ( Y-Ar) _p- represents an oligomer represented by the following general formula (1a) or the following general formula (1b). When Q is —S—, Y is preferably —S— or —SO ₂ —.

（式中、Ｒ^３は鎖中にエーテル結合を有していてもよい炭素数１〜１２のアルキレン基を示し、ｋは平均オリゴマー化度を表す１〜５の数である。）

(Wherein, R ³ represents an alkylene group having 1 to 12 carbon atoms which may have an ether bond in the chain, k is the number of 1 to 5 representing the average degree of oligomerization.)

（式中、ｌは平均オリゴマー化度を表す１〜５の数である。）

(In the formula, l is a number of 1 to 5 representing the average degree of oligomerization.)

Specific examples of the alkylene group having 1 to 12 carbon atoms of Y include a methylene group, an ethylene group, a propylene group, a tetramethylene group, a hexamethylene group, an octamethylene group, a decamethylene group, and a dodecamethylene group. . Preferably, it is a C1-C6 alkylene group. As the aralkylene group having 7 to 30 carbon atoms, preferably 7 to 14 carbon atoms, — (CH ₂ ) _x —Ar′—, —Ar ′ — (CH ₂ ) _x —, — (CH ₂ ) _x —Ar ′ — ( CH ₂ ) _y- . Here, Ar ′ represents an arylene group having 6 to 29 carbon atoms such as a phenylene group or a naphthylene group, x and y each represents an integer of 1 to 24, and carbon of the arylene group represented by x, y and Ar ′. The sum of the numbers is 7-30, preferably 7-14.

Further, as represented by R ^3, examples of an alkylene group having 1 to 12 carbon atoms which may have an ether bond in the chain, having 1 to 12 carbon atoms, preferably alkylene group having 1 to 6 carbon atoms The group which may have 1-5 -O- groups normally in arbitrary positions can be mentioned.

  In the general formula (1A), m and n each represent an integer of 1 to 5, preferably 1 to 3, and p represents a number of 0 to 10, preferably 0 to 5.

In the general formula (1A), a plurality of R ² , Ar, Q, and Y may be the same or different.

  Specific examples of A and B are shown below.

  In the general formula (1), D represents a thioalkylene group having 1 to 8 carbon atoms, that is, a group in which a sulfur atom is connected to the terminal of the alkylene group. Here, the part couple | bonded with A in D is a sulfur atom. The thioalkylene group may be a chain or a branch. Preferably it is a C1-C4 thioalkylene group.

  Moreover, in General formula (1), X represents an oxygen atom, -NH-, or a sulfur atom. Preferably it is an oxygen atom or -NH-, More preferably, it is -NH-.

  Note that two D and X in the general formula (1) and two X in the general formula (2) may be the same or different.

  In particular, in the high refractive index linear polymer of the present invention having a repeating unit represented by the general formula (2), in the general formula (2), A is represented by the following general formula, and X is an oxygen atom. It is preferable that B is represented by the following general formulas (B-1) to (B-3) in that a polymer having a higher refractive index can be obtained.

（式中、ｅ及びｆは、それぞれ独立して、１〜６の整数を表す。）

(In formula, e and f represent the integer of 1-6 each independently.)

（式中、ｇ，ｈ，ｉ及びｊは、それぞれ独立して、１〜６の整数を示す。）

(In the formula, g, h, i and j each independently represent an integer of 1 to 6.)

  Examples of more preferable polymers as the high refractive index linear polymer of the present invention include the following polymers.

  Such a high refractive index linear polymer of the present invention preferably has a refractive index of 1.55 or more, more preferably 1.6 or more, and particularly preferably 1.65 or more. Although the higher refractive index of the high refractive index linear polymer is preferable, the upper limit is usually 1.9 or less.

  The weight average molecular weight (Mw) of the high refractive index linear polymer of the present invention is preferably 1,000 or more, more preferably 5,000 or more, and particularly preferably 10,000 or more. The upper limit of the weight average molecular weight is preferably 10,000,000 or less, more preferably 1,000,000 or less, and particularly preferably 100,000 or less. If the weight average molecular weight (Mw) of the high refractive index linear polymer is too large, it will be difficult to dissolve in the solvent, and if it is too small, the refractive index will decrease.

  Further, the high refractive index linear polymer of the present invention has a solubility in a good solvent of 1% by weight or more, preferably 5% by weight or more, and more preferably 10% by weight or more. Here, the dissolution refers to a state of being transparent and uniform in a solvent, and does not include a form in which the resin is swollen in a transparent state or dispersed with a microgel, which is seen in a crosslinked resin.

  The good solvent for the high-refractive-index linear polymer of the present invention is not particularly limited as long as it is a solvent that dissolves the high-refractive-index linear polymer with the above-mentioned solubility, but a heterocyclic solvent such as tetrahydrofuran and pyrrolidone. Chlorinated solvents such as chloroform and methylene chloride; dimethylformamide, dimethyl sulfoxide and the like.

  Moreover, Tg of the high refractive index linear polymer of this invention is 0-180 degreeC normally, Preferably it is 40-180 degreeC, More preferably, it is 80-180 degreeC. If Tg is too high, there is a problem that it is difficult to mold by injection molding, and it tends to be colored, and if it is too low, there is a problem that it is easily deformed by a change in environmental temperature when used as an optical component.

[Production Method of High Refractive Index Linear Polymer]
The production method of the high refractive index linear polymer of the present invention represented by the general formula (1) is not particularly limited and can be produced by a known method, but preferably the high refractive index of the present invention. The linear polymer can be produced by the following method [1], [2] or [3].
[1] Method by polymerization of dicarboxylic acid and / or its acid halide compound and diamine compound [2] Method by polymerization of dithiol compound and divinyl compound [3] By polymerization of dicarboxylic acid and / or its acid halide compound and dialcohol compound Method

[1] Method by polymerization of dicarboxylic acid and / or acid halide compound thereof and diamine compound Monomer to be used in producing the high refractive index linear polymer of the present invention by polymerization of dicarboxylic acid and / or acid halide compound thereof and diamine compound As the kind, any dicarboxylic acid and / or its acid halide and diamine can be used.

(Dicarboxylic acid and / or acid halide compound thereof)
Preferred as the dicarboxylic acid and / or acid halide thereof is a compound represented by the following general formula [1-a].
G-D-A-D-G [1-a]
(In the formula, A and D have the same meanings as in the general formula (1)).
G is an acid halide group such as —COOH or —COCl. )

  Preferable specific examples of the dicarboxylic acid and / or its acid halide include the following.

  These may be used alone or in combination of two or more.

  The refractive index of the dicarboxylic acid and / or its acid halide used for the polymerization reaction is usually 1.4 or more, preferably 1.50 or more, more preferably 1.55 or more, and still more preferably 1.6 or more. A higher refractive index is preferable, but the upper limit is usually 1.9 or less.

(Diamine compound)
The diamine compound is not particularly limited, but any diamine compound represented by the following general formula [1-b] can be preferably used.
_{H 2 N-B-NH 2} [1-b]
(In the formula, B has the same meaning as in the general formula (1).)

  Specific examples of preferred diamine compounds include those having the structure exemplified as preferred examples of B, and preferred are diamines having the following structures.

  These may be used alone or in combination of two or more.

  The refractive index of the diamine compound subjected to the polymerization reaction in the present invention is usually 1.4 or more, preferably 1.50 or more, more preferably 1.55 or more, and still more preferably 1.6 or more. A higher refractive index is preferable, but the upper limit is usually 1.9 or less.

  The refractive index of the high refractive index linear polymer of the present invention is preferably 1.60 or more as described later, but in order to obtain a high refractive index linear polymer having a refractive index of 1.60 or more, By selecting the refractive index of dicarboxylic acid and / or its acid halide compound and diamine compound, it is preferable to increase the high refractive index of the obtained high refractive index linear polymer.

  For example, even when the refractive index of one of the two types of monomers subjected to the synthesis reaction of the high refractive index linear polymer is 1.55 or less, the refractive index of the other monomer is 1.55 or more, By taking the balance, a high refractive index linear polymer having a refractive index of 1.55 or more can be obtained.

(Polymerization method)
Various methods can be used as the polymerization method, and an example is a method in which dicarboxylic acid and / or its acid halide compound and diamine compound are mixed in a solvent, and then a catalyst is added and heated. A condensation reaction occurs by such a method, and a desired polymer can be obtained. As the catalyst, amines such as diethylamine and triethylamine are usually used.

  The amount of the monomer in the solvent is arbitrary, but it is usually 1 to 50% by weight, preferably 10 to 30% by weight. The amount of the catalyst is arbitrary, but it is usually 0.001-1% by weight, preferably 0.01-0.1% by weight, based on the monomer. Although the temperature and / or time of heating are also arbitrary, heating temperature is normally implemented between 20 degreeC and 150 degreeC.

[2] Method by polymerization of dithiol compound and divinyl compound When producing a high refractive index linear polymer by a method by polymerization of dithiol compound and divinyl compound, for example, a dithiol compound represented by the following general formula (3); It can manufacture by making the divinyl compound represented by following General formula (4) react.

HS-A-SH (3)
(In the formula, A has the same meaning as in the general formulas (1) and (2).)

（式中、Ｂ，Ｒ，Ｘは一般式（１），（２）におけると同義である。）

(In the formula, B, R and X have the same meanings as in the general formulas (1) and (2).)

(Diol compound)
As the diol compound, any diol compound represented by the general formula (3) can be used. In the general formula (3), preferred specific examples of A are as described above, but preferred specific examples of the dithiol compound. As examples, dithiol having the following structure can be given.

  These may be used alone or in combination of two or more.

  The refractive index of the dithiol compound used in the present invention is usually 1.4 or more, preferably 1.50 or more, more preferably 1.55 or more, and particularly preferably 1.6 or more. The higher refractive index of the dithiol compound is preferable, but the upper limit is usually 1.9 or less.

(Divinyl compound)
As the divinyl compound, any divinyl compound represented by the general formula (4) can be used.

  For the purpose of obtaining a high refractive index linear polymer, it is desirable to use a sulfur-containing (meth) acrylate compound represented by the following general formula (4-A) having a higher refractive index.

In General Formula (4-A), R ¹ represents a hydrogen atom or a methyl group, and R ² , Ar, Q, and Y have the same meanings as in General Formula (1A).

  Z represents —O— or —S—. m and n each represent an integer of 1 to 5, preferably 1 to 3, and p represents a number of 0 to 10, preferably 0 to 5.

In the general formula (4-A), a plurality of R ¹ , R ² , Ar, Z, Q, and Y may be the same or different.

  Specific examples of the sulfur-containing (meth) acrylate represented by the general formula (4-A) include p-bis (β- (meth) acryloyloxyethylthio) xylene, p-bis (β- (meta ) Acryloylthioethylthio) xylene, m-bis (β- (meth) acryloyloxyethylthio) xylene, m-bis (β- (meth) acryloylthioethylthio) xylene, α, α′-bis (β- ( (Meth) acryloyloxyethylthio) -2,3,5,6-tetrachloro-p-xylene, α, α′-bis (β- (meth) acryloylthioethylthio) -2,3,5,6-tetra Chloro-p-xylene, 4,4′-di (β- (meth) acryloyloxyethoxy) diphenyl sulfide, 4,4′-di (β- (meth) acryloylthioethoxy) diphenylsulfur 4,4′-di (β- (meth) acryloyloxyethoxyethoxy) diphenylsulfone, 4,4′-di (β- (meth) acryloylthioethoxyethoxy) diphenylsulfone, 4,4′-di ( β- (meth) acryloyloxyethylthio) diphenyl sulfide, 4,4′-di (β- (meth) acryloylthioethylthio) diphenyl sulfide, 4,4′-di (β- (meth) acryloyloxyethylthio) Diphenyl sulfone, 4,4′-di (β- (meth) acryloylthioethylthio) diphenyl sulfone, 4,4′-di (β- (meth) acryloyloxyethylthio) diphenyl ketone, 4,4′-di ( β- (meth) acryloylthioethylthio) diphenyl ketone, 2,4′-di (β- (meth) acryloyloxyethylthio) ) Diphenyl ketone, 2,4′-di (β- (meth) acryloylthioethylthio) diphenyl ketone, 4,4′-di (β- (meth) acryloyloxyethylthio) -3,3 ′, 5,5 '-Tetotabromodiphenyl ketone, 4,4'-di (β- (meth) acryloylthioethylthio) -3,3', 5,5'-tetotabromodiphenyl ketone, β, β'-bis (p- ( (Meth) acryloyloxyphenylthio) diethyl ether, β, β′-bis (p- (meth) acryloylthiophenylthio) diethyl ether, β, β′-bis (p- (meth) acryloyloxyphenylthio) diethylthioether, β, β′-bis (p- (meth) acryloylthiophenylthio) diethylthioether and the like can be mentioned.

  Among the compounds listed above, the divinyl compound is particularly preferably a polyvalent compound having two or more (meth) acryloyl groups in the molecule represented by the following general formulas (3-i) to (3-v). Examples of the functional (meth) acrylate compound include polyfunctional (meth) acrylate compounds represented by the following general formulas (3-i) and (3-ii).

（式中、Ｒ^１１及びＲ^１２は、それぞれ独立して、水素原子又はメチル基を表し、ｅ及びｆは、それぞれ独立して、１〜６の整数を示す。）

(In the formula, R ¹¹ and R ¹² each independently represent a hydrogen atom or a methyl group, and e and f each independently represent an integer of 1 to 6.)

（式中、Ｒ^２１及びＲ^２２は、それぞれ独立して、水素原子又はメチル基を表し、ｇ，ｈ，ｉ及びｊは、それぞれ独立して、１〜６の整数を示す。）

(In the formula, R ²¹ and R ²² each independently represent a hydrogen atom or a methyl group, and g, h, i and j each independently represent an integer of 1 to 6)

  These may be used alone or in combination of two or more.

  The refractive index of the divinyl compound used in the present invention is usually 1.4 or more, preferably 1.50 or more, more preferably 1.55 or more, and particularly preferably 1.6 or more. The higher refractive index of the divinyl compound is preferable, but the upper limit is usually 1.9 or less.

  The refractive index of the high refractive index linear polymer of the present invention is preferably 1.55 or more as described later, but in order to obtain a high refractive index linear polymer having a refractive index of 1.55 or more, It is important to appropriately select the refractive indexes of the dithiol compound and divinyl compound as monomers used as raw materials. For example, when the refractive index of one of the dithiol compound and the divinyl compound is less than 1.55, the refractive index of the other monomer is set to 1.55 or more, and the refractive index is balanced. The above high refractive index linear polymer can be obtained.

(Polymerization method)
As a method for producing the high refractive index linear polymer of the present invention, various methods can be used. As an example, after mixing the above dithiol compound and divinyl compound in a solvent, a catalyst is added and heated. By this, the following Michael addition reaction is caused and the method of obtaining a linear polymer is mentioned.

  In this case, one or more amines such as diethylamine and triethylamine are usually used as the catalyst.

  Since the dithiol compound and the divinyl compound theoretically react at a ratio of 1: 1, the dithiol compound and the divinyl compound are preferably used in a molar ratio of 1: 0.9 to 1.1 for the reaction.

  The solvent may be any one having excellent solubility of the dithiol compound and divinyl compound and the high refractive index linear polymer to be synthesized and having a boiling point of room temperature (20 ° C.) or more. For example, a complex such as tetrahydrofuran or pyrrolidone. Ring solvents; Chlorinated solvents such as chloroform and methylene chloride; dimethylformamide, dimethyl sulfoxide and the like. These solvents may be used alone or in combination of two or more.

  Moreover, although the quantity of the monomer in a solvent is arbitrary, it is 1-50 weight% normally, Preferably it implements at 10-30 weight%. Although the amount of the catalyst is also arbitrary, it is usually used in the range of 0.001 to 1% by weight, preferably 0.01 to 0.1% by weight, based on the monomer to be subjected to the reaction.

  The temperature and time of heating are also arbitrary. Regarding the heating temperature, in the general formula (1), when X is N, −30 to 20 ° C., when X is S, 0 to 100 ° C., and X is In the case of O, it is carried out between 20 ° C and 150 ° C. If the heating temperature is too high, the reaction rate is too fast and difficult to control, and if it is too low, the reaction does not proceed.

  In addition, when making the above-mentioned dithiol compound and a divinyl compound react, if it uses a radical initiator as a catalyst, it will become a three-dimensional crosslinked resin instead of a linear polymer. Therefore, in the present invention, in order to polymerize the dithiol compound and the divinyl compound linearly, it is important to make the catalyst amine-based.

[3] Method by polymerization of dicarboxylic acid and / or its acid halide compound and dialcohol compound There are no particular restrictions on the type of monomer used in the method of polymerization of dicarboxylic acid and / or its acid halide compound and dialcohol compound. Any dicarboxylic acid and / or its acid halide and dialcohol can be used.

(Dicarboxylic acid and / or acid halide thereof)
Preferred as the dicarboxylic acid and / or acid halide thereof is a compound represented by the following general formula [3-a].
G-D-A-D-G [3-a]
(In the formula, A and D have the same meanings as in the general formula (1)).
G is an acid halide group such as —COOH or —COCl. )

  Preferable specific examples of the dicarboxylic acid and / or its acid halide include the following.

  These may be used alone or in combination of two or more.

  The refractive index of the dicarboxylic acid and / or its acid halide used in the present invention is usually 1.4 or more, preferably 1.50 or more, more preferably 1.55 or more, and still more preferably 1.6 or more. A higher refractive index is preferable, but the upper limit is usually 1.9 or less.

(Dialcohol compound)
The dialcohol compound is not particularly limited, and any dialcohol compound represented by the following general formula [3-b] can be used.
HO-B-OH [3-b]
(In the formula, B has the same meaning as in the general formula (1).)

  Specific examples of preferred dialcohol compounds include those having the structure exemplified as preferred examples of B, and preferred are dialcohol compounds having the following structure.

  These may be used alone or in combination of two or more.

  The refractive index of the dialcohol compound is usually 1.4 or more, preferably 1.50 or more, more preferably 1.55 or more, and still more preferably 1.6 or more. A higher refractive index is preferable, but the upper limit is usually 1.9 or less.

  As described later, the refractive index of the high refractive index linear polymer of the present invention is preferably 1.60 or more. However, in order to obtain a linear polymer of 1.60 or more, the above dicarboxylic acid and / or It is preferable to increase the high refractive index of the resulting high refractive index linear polymer by selecting the refractive indices of the acid halide compound and dialcohol compound.

  For example, even when the refractive index of one of the two types of monomers subjected to the synthesis reaction of the high refractive index linear polymer is 1.55 or less, the refractive index of the other monomer is 1.55 or more, By taking the balance, a high refractive index linear polymer having a refractive index of 1.55 or more can be obtained.

(Polymerization method)
As the polymerization method, various methods can be used. As an example, after mixing dicarboxylic acid and / or its acid halide compound and dialcohol compound in a solvent, a method of adding a catalyst and heating, can be mentioned, By such a method, a condensation reaction occurs and a desired polymer can be obtained. As the catalyst, amines such as diethylamine and triethylamine are usually used.

  The amount of the monomer in the solvent is arbitrary, but it is usually 1 to 50% by weight, preferably 10 to 30% by weight. The amount of the catalyst is also arbitrary, but it is usually carried out between 0.001 to 1% by weight, preferably 0.01% to 0.1% by weight, based on the monomer. Although the temperature and time of heating are also arbitrary, heating temperature is normally implemented between 20 degreeC-150 degreeC.

[Molding method]
Since the high refractive index linear polymer of the present invention is excellent in moldability and processability, an optical material such as a lens can be obtained using this. In this case, for example, a method of molding the high refractive index linear polymer of the present invention by a technique such as injection molding or press molding may be mentioned.

  In molding the high refractive index linear polymer of the present invention, a composition may be added to which components other than the high refractive index linear polymer are added within a range that does not impair the physical properties of the resulting molded article. Examples of such components include nanoparticles, antioxidants, ultraviolet absorbers, ultraviolet stabilizers, dyes and pigments, and fillers.

Among these, as the nanoparticles, oxide nanoparticles such as titanium oxide, zinc oxide, tin oxide, indium tin oxide, antimony oxide, selenium oxide, cerium oxide, yttrium oxide, CdO, PbO, HfO ₂ , Sb ₂ O _5, etc. Titanates such as barium titanate and strontium titanate; nanoparticles of sulfides such as CdS, CdSe, ZnSe, CdTe, ZnS, HgS, HgSe, PdS, SbSe, selenides, tellurides and the like. These may be used alone or in combination of two or more.

  Moreover, what is called a core-shell type nanoparticle which coat | covered the nanoparticle with the other substance can also be used.

  Among these nanoparticles, preferred are titanium oxide, zirconium oxide and titanate nanoparticles, and particularly preferred are titanium oxide nanoparticles.

  The average particle size of these nanoparticles is preferably 1 to 100 nm. By suppressing the particle diameter of the nanoparticles to 100 nm or less, a nanoparticle-dispersed molded article having excellent transparency can be obtained. In addition, the particle diameter of a nanoparticle is shown by the value measured by XRD (powder X-ray analysis) etc. The particle size of the nanoparticles is preferably 50 nm or less, more preferably 30 nm or less.

  When blending such nanoparticles, the transparency decreases if the blending amount is too large, and if the blending amount is too small, the effect of increasing the refractive index is low. It is preferably 80% by weight, particularly 30 to 70% by weight.

  Hereinafter, the present invention will be described more specifically with reference to synthesis examples, examples, and comparative examples, but the present invention is not limited to the following examples.

<Synthesis Example 1: Synthesis of dicarboxylic acid 1>
The following dithiol (2-1) (MPS, manufactured by Sumitomo Seika Chemical Co., Ltd.) (2.0 g) was added to a 10 wt% KOH aqueous solution and heated at 50 ° C. for 1 hour with 16 g of ClCH ₂ COOH previously neutralized with KOH. Then, the target dicarboxylic acid 1 was obtained by neutralizing with hydrochloric acid and filtering. Yield 90%.

<Synthesis Example 2: Synthesis of Diamine 2>
1.89 g (0.025 mol) of 1,4-dibromobenzene, 6.88 g (0.025 mol) of 4-aminothiophenol and 9.12 g (0.66 mol) of potassium carbonate were used as a solvent NMP (N-methyl-2-pyrrolidone). ). The mixture was heated at 50 ° C. for 1 hour and further heated at 150 ° C. for 2 hours and 210 ° C. for 1 hour. NMP was removed by evaporation and the product was purified by reprecipitation from water. Further, recrystallization from ethanol gave the target diamine 2. Yield 85%.

<Synthesis Example 3: Synthesis of diamine 3>
1.89 g (0.025 mol) of 1,3-dibromobenzene, 6.88 g (0.025 mol) of 4-aminothiophenol and 9.12 g (0.66 mol) of potassium carbonate were dissolved in the solvent NMP. The mixture was heated at 50 ° C. for 1 hour and further heated at 150 ° C. for 2 hours and 210 ° C. for 1 hour. NMP was removed by evaporation and the product was purified by reprecipitation from water. Further, recrystallization from ethanol gave the target diamine 3. Yield 55%.

<Synthesis Example 4: Synthesis of acid chloride 1>
To 4 g of dicarboxylic acid 1, 10 ml of SOCl ₂ and 10 ml of methylene chloride were added and dissolved, and then transferred to a 50 ml flask. Then, 1 to 2 drops of DMF (dimethylformamide) was added as a catalyst. The reaction was carried out at 40 to 45 ° C. for 36 hours while the generated gas was trapped in the NaOH solution. The SOCl ₂ was removed under reduced pressure to give a crude product. Recrystallization from toluene gave the target acid chloride 1 in a yield of 50%.

<Synthesis Example 5: Synthesis of dicarboxylic acid 2>
2.0 g of the dithiol (2-1) (MPS, manufactured by Sumitomo Seika Co., Ltd.) was added to a 10% by weight aqueous KOH solution and heated at 70 ° C. for 6 hours with 16 g of 2-bromopropionic acid previously neutralized with KOH. . The target dicarboxylic acid 2 was obtained by neutralizing with hydrochloric acid and filtering. Yield 80%.

<Example 1>
0.75 g (0.003 mol) of the following dithiol compound (2-1) (MPS, manufactured by Sumitomo Seika Co., Ltd., refractive index 1.68) and the following divinyl compound (3-1) (MPMSA, manufactured by Sumitomo Seika Co., Ltd., refraction) 1.16 g (0.003 mol) was dissolved in 10 ml of tetrahydrofuran (THF). After adding 3 drops of triethylamine, the reaction was performed at 25 ° C. for 5 hours in a nitrogen atmosphere. 20 ml of THF was further added to the obtained polymer solution, and the solution was added dropwise to methanol under strong stirring to carry out reprecipitation purification of the polymer. The obtained polymer was filtered and dried at 70 ° C. for 2 hours to obtain a transparent polymer. The yield was 89.5%, and the weight average molecular weight (Mw) measured by GPC was 92,500.

  The structure of the obtained polymer is as follows.

<Example 2>
0.75 g (0.003 mol) of the following dithiol compound (2-1) (MPS, manufactured by Sumitomo Seika Co., Ltd., refractive index 1.68) and 1.16 g of the following divinyl compound (3-2) (refractive index 1.54) (0.003 mol) was dissolved in 10 ml of THF. After adding 3 drops of triethylamine, the reaction was carried out at 25 ° C. for 5 hours in a nitrogen atmosphere. 20 ml of THF was further added to the obtained polymer solution, and the solution was added dropwise to methanol under strong stirring to carry out reprecipitation purification of the polymer. The obtained polymer was filtered and dried at 70 ° C. for 2 hours to obtain a transparent polymer. The yield was 80.0%, and the weight average molecular weight (Mw) measured by GPC was 19,000.

（式中、Ｒ^２１及びＲ^２２はメチル基を表し、ｇ及びｊは２、ｈ及びｉは１の整数を示す。）

(In the formula, R ²¹ and R ²² represent a methyl group, g and j are 2, and h and i are integers of 1.)

  The structure of the obtained polymer is as follows.

<Example 3>
0.51 g (0.002 mol) of the following dithiol compound (2-1) (MPS, manufactured by Sumitomo Seika Co., Ltd., refractive index 1.68) and 1.01 g of the following divinyl compound (3-3) (refractive index 1.60) (0.002 mol) was dissolved in 7 ml of THF. After adding 5 drops of triethylamine, the reaction was carried out under a nitrogen atmosphere under THF reflux (65 ° C.) for 24 hours. The obtained polymer solution was added dropwise to methanol under strong stirring to carry out reprecipitation purification of the polymer. The obtained polymer was filtered and dried at room temperature under reduced pressure for 20 hours to obtain a transparent polymer. The yield was 80%, and the weight average molecular weight (Mw) measured by GPC was 21,000.

（式中、Ｒ^１１及びＲ^１２はメチル基を表し、ｅ及びｆは２の整数を表す。）

(In the formula, R ¹¹ and R ¹² represent a methyl group, and e and f represent an integer of 2.)

  The structure of the obtained polymer is as follows.

<Example 4>
The following dithiol compound (2-2) (Toyo Kasei Co., Ltd., refractive index 1.63) 0.62 g (0.004 mol) and the following divinyl compound (3-1) (Sumitomo Seika Co., Ltd., refractive index 1.63) 1.55 g (0.004 mol) was dissolved in 10 ml of THF. After adding 5 drops of triethylamine, the reaction was carried out at room temperature for 5 hours in a nitrogen atmosphere. The resulting polymer solution was diluted by adding 5 ml of THF, and dropped into methanol with strong stirring to perform reprecipitation purification of the polymer. The obtained polymer was filtered and dried at room temperature under reduced pressure for 20 hours to obtain a transparent polymer. The yield was 85%, and the weight average molecular weight (Mw) measured by GPC was 50,000.

  The structure of the obtained polymer is as follows.

<Example 5>
1.25 mmol of the following diamine 1 and the following dicarboxylic acid 1 were dissolved in an NMP solvent. Thereto was added a mixture of 2.5 mmol (about 0.9 ml) of triphenylosphate (TPP) and 1.2 ml of pyridine in 5 ml of NMP and 0.3 g of calcium chloride. The mixture was heated to 105 ° C. and reacted for 3 hours. As the condensation progressed, the solution gradually became viscous. The resulting viscous liquid was immediately added dropwise to 250 ml of methanol while stirring. The fibrous precipitate was collected by filtration, washed with methanol, and dried at 80 ° C. to obtain the target polymer. The yield was 90%, and the weight average molecular weight (Mw) measured by GPC was 110,000.

  The structure of the obtained polymer is as follows.

<Example 6>
1.25 mmol of the following diamine 2 and the following dicarboxylic acid 1 were dissolved in an NMP solvent. Thereto was added a mixture of 2.5 mmol (about 0.9 ml) of triphenylosphate (TPP) and 1.2 ml of pyridine in 5 ml of NMP and 0.3 g of calcium chloride. The mixture was heated to 105 ° C. and reacted for 3 hours. As the condensation progressed, the solution gradually became viscous. The obtained viscous liquid was immediately added dropwise to 500 ml of methanol while stirring. The fibrous precipitate was collected by filtration, washed with methanol, and dried at 80 ° C. to obtain the target polymer. The yield was 92%, and the weight average molecular weight (Mw) measured by GPC was 36,000.

  The structure of the obtained polymer is as follows.

<Example 7>
1.25 mmol of the following diamine 3 and the following dicarboxylic acid 1 were dissolved in an NMP solvent. Thereto was added a mixture of 2.5 mmol (about 0.9 ml) of triphenylosphate (TPP) and 1.2 ml of pyridine in 5 ml of NMP and 0.3 g of calcium chloride. The mixture was heated to 105 ° C. and reacted for 3 hours. As the condensation progressed, the solution gradually became viscous. The obtained viscous liquid was immediately added dropwise to 500 ml of methanol while stirring. The fibrous precipitate was collected by filtration, washed with methanol, and dried at 80 ° C. to obtain the target polymer. The yield was 90%, and the weight average molecular weight (Mw) measured by GPC was 20,000.

  The structure of the obtained polymer is as follows.

<Example 8>
0.2504 g (1 mmol) of the following commercially available dithiol compound (2-1) (MPS, manufactured by Sumitomo Seika Co., Ltd., refractive index: 1.68), 0.2226 g (2.2 mmol) of triethyleneamine, 2.5 ml Dry NMP was added to a 25 ml flask. 0.4034 g (1 mmol) of acid chloride 1 was dissolved in 2.5 ml of THF and added dropwise to the flask at 0 ° C. over 10 minutes. After dropping, the mixture was stirred at 0 ° C. for 2 hours and at room temperature for 5 hours. The obtained polymer solution was diluted with NMP and added dropwise to methanol with stirring to purify by reprecipitation. The resulting polymer was filtered and washed several times with methanol. The obtained polymer was dried at 70 ° C. for 24 hours to obtain the desired polymer. The yield was 90%, and it was slightly soluble in NMP and hardly soluble in the solvent, so the molecular weight could not be measured.

  The structure of the obtained polymer is as follows.

<Example 9>
0.2183 g (1 mmol) of commercially available 4,4′-thiodiphenol and 0.2225 g (2.2 mmol) of triethyleneamine, 2.5 ml of dry NMP were added to a 25 ml flask. 0.4034 g (1 mmol) of acid chloride 1 was dissolved in 2.5 ml of THF and added dropwise to the flask at 0 ° C. over 10 minutes. After dropping, the mixture was stirred at 0 ° C. for 2 hours and at room temperature for 5 hours. The obtained polymer solution was diluted with NMP and added dropwise to methanol with stirring to purify by reprecipitation. The resulting polymer was filtered and washed several times with methanol. The obtained polymer was dried at 70 ° C. for 24 hours to obtain the desired polymer. The yield was 92% and the molecular weight could not be measured because it was not soluble in the solvent.

得られた重合体の構造は下記の通りである。

The structure of the obtained polymer is as follows.

<Example 10>
1.25 mmol of diamine 3 and dicarboxylic acid 2 were dissolved in NMP solvent. Thereto was added a mixture of 2.5 mmol (about 0.9 ml) of triphenylosphate (TPP) and 1.2 ml of pyridine in 5 ml of NMP and 0.3 g of calcium chloride. The mixture was heated to 105 ° C and reacted for 3 hours. As the condensation progressed, the solution gradually became viscous. The obtained viscous liquid was immediately added dropwise to 250 ml of methanol while stirring. The fibrous precipitate was collected by filtration, washed with methanol, and dried at 80 ° C. to obtain the desired polymer. The yield was 90%, and the weight average molecular weight (Mw) measured by GPC was 20,000.

  The structure of the obtained polymer is as follows.

<Comparative Example 1>
0.75 g (0.003 mol) of the following dithiol compound (2-1) (MPS, manufactured by Sumitomo Seika Co., Ltd., refractive index 1.68) and the following divinyl compound (3-1) (MPMSA, manufactured by Sumitomo Seika Co., Ltd., refraction) (Rate 1.63) 1.16 g (0.003 mol) was dissolved in 10 ml of THF. After 20 mg of azoisobutyronitrile was added thereto, the reaction was carried out at 80 ° C. for 5 hours under a nitrogen atmosphere. 20 ml of THF was further added to the obtained polymer solution, and the solution was added dropwise to methanol under strong stirring to carry out reprecipitation purification of the polymer. The obtained polymer was filtered and dried at 70 ° C. for 2 hours to obtain a transparent polymer. The yield was 85%. With respect to this polymer, an attempt was made to measure the weight average molecular weight by GPC. However, since it was a crosslinked resin, its solubility in THF was poor and measurement was impossible.

  That is, in this comparative example, the diol compound (2-1) and the divinyl compound (3-1) were used as in Example 1, but the polymer was a linear polymer because the catalyst was a radical initiator. Instead, it became a three-dimensional cross-linked structure.

<Comparative Example 2 (Japanese Patent Laid-Open No. 60-226527)>
The polymer was synthesized using the method of Example 4 of JP-A-60-226527.
The dicarboxylic acid (chloride) used was a mixture (A) of terephthalic acid chloride and isophthalic acid chloride, and the diamine was 4,4′-bis (4-aminophenylthio) benzophenone (B). The structure of the obtained polymer is as follows.

  The polymers obtained in Examples 1 to 10 and Comparative Examples 1 and 2 were measured for refractive index, evaluated for solubility in THF, and measured for Tg by the following methods. The results are shown in Table 1.

(Refractive index measurement method 1)
The refractive indexes of the polymers of Examples 1 to 4 were obtained by preparing a 10 wt% THF solution of each polymer obtained, and using an Abbe refractometer DR-M2 manufactured by Atago Co., Ltd. 589.3 nm) the refractive index of the light was measured. The measured value was extrapolated to 100% by weight to obtain the refractive index of the polymer.

(Refractive index measurement method 2)
The refractive indexes of the polymers of Examples 5 to 10 and Comparative Example 2 were adjusted to 1 to 10% by weight THF or NMP solution of the obtained polymer, applied to a glass substrate and dried to obtain a thin film of each polymer. . The refractive index of the obtained thin film was measured by the prism coupling method, and the refractive index of the polymer with a wavelength (wavelength 633 nm) was obtained.

(Solubility discrimination method with THF)
A 10 wt% THF solution of each polymer obtained was prepared, and the transmittance of the solution was measured with a photoelectric colorimeter model 4C (manufactured by Hirama Rika Co., Ltd.) in a 1 cm quartz cell, and the transmittance was 80% or more. Those having good solubility (◯), transmittance of 80% or more but having undissolved residue were taken as solubility (Δ), and those having little solubility were taken as (×). When the polymer has a crosslinked structure, the solubility in THF is poor and the transmittance is not 80% or more. However, if the polymer is linear, the solubility in THF is good and the transmittance is 80% or more. Become.

(Measurement method of Tg)
Tg of the obtained polymer was measured using a TG-DTA apparatus.

  From the above results, according to the present invention, there is provided a linear polymer that has no problem of coloring, has a high refractive index, has a relatively low Tg, and can be used for various molding and processing, and has excellent solvent solubility. You can see that

Claims (14)

A high refractive index linear polymer having a repeating unit represented by the following general formula (1).

(In the formula, A and B represent a divalent organic group,
X represents an oxygen atom, -NH-, or a sulfur atom;
D represents a thioalkylene group having 1 to 8 carbon atoms.
Note that two D and X in the general formula (1) may be the same or different. )   The high refractive index linear polymer according to claim 1, wherein the glass transition temperature is 0 ° C or higher and 180 ° C or lower.   The high refractive index linear polymer according to claim 1 or 2, wherein the refractive index is 1.55 or more.   The high refractive index linear polymer according to any one of claims 1 to 3, wherein X is an oxygen atom or -NH-.   The high refractive index linear polymer according to claim 4, wherein X is -NH-.   The high refractive index linear polymer according to any one of claims 1 to 5, wherein D is a thioalkylene group having 1 to 4 carbon atoms. A high refractive index linear polymer comprising a repeating unit represented by the following general formula (2).

(In the formula, A and B represent a divalent organic group,
X represents an oxygen atom, -NH-, or a sulfur atom;
R represents a hydrogen atom or a methyl group.
Note that two R and X in the general formula (2) may be the same or different. ) The high refractive index linear polymer according to claim 7, wherein A is represented by the following general formula.

The high refractive index linear polymer according to any one of claims 7 and 8, wherein X is an oxygen atom, and B is represented by the following general formula (B-1) or (B-2).

(In formula, e and f represent the integer of 1-6 each independently.)

(In the formula, g, h, i and j each independently represent an integer of 1 to 6.)   The high-refractive-index linear polymer according to any one of claims 1 to 9, having a weight average molecular weight (Mw) of 1,000 to 10,000,000. The high refractive index linear polymer according to any one of claims 7 to 10, wherein a dithiol compound represented by the following general formula (3) and a divinyl compound represented by the following general formula (4) are reacted. Manufacturing method.
HS-A-SH (3)
(In the formula, A has the same meaning as in formula (2).)

(In the formula, B, R and X have the same meanings as in the general formula (2).)   The method for producing a high refractive index linear polymer according to claim 11, wherein the dithiol compound has a refractive index of 1.55 or more.   The method for producing a high refractive index linear polymer according to claim 11 or 12, wherein the divinyl compound has a refractive index of 1.55 or more.   The optical material formed by shape | molding the high refractive index linear polymer of any one of Claim 1 thru | or 10.