JP7625816B2 - Reactive liquid crystal polyester, polyester composition, polyester solution, and cured product - Google Patents

Description

The present invention relates to a reactive liquid crystal polyester, a polyester composition containing the reactive liquid crystal polyester, a polyester solution containing the reactive liquid crystal polyester, and a cured product obtained from the polyester composition.

In recent years, with the increase in the volume of information and communication, high-frequency information and communication has become more prevalent. This has created a demand for electrical insulating materials with better electrical properties, particularly low dielectric constants and low dielectric tangents, to reduce transmission loss in the high-frequency range.

Furthermore, printed circuit boards and electronic components that use these electrical insulating materials are exposed to high-temperature solder reflow during installation, so materials with high heat resistance, i.e., a high glass transition temperature, are required. In particular, lead-free solders with high melting points have recently been used due to environmental concerns, so there is an increasing demand for electrical insulating materials with even higher heat resistance.

In response to these demands, attention has been focused on liquid crystal polymers, such as liquid crystal polyesters, and in particular on thermosetting liquid crystal polymer materials that can form cured products with extremely high heat resistance by heat curing. For example, materials are known in which liquid crystal oligomers such as main chain thermotropic liquid crystal esters are end-capped with phenylacetylene, phenylmaleimide, or nadimide reactive terminal groups (see Patent Documents 1 to 3). In addition, a material has been disclosed that is obtained by reacting a thermosetting liquid crystal oligomer having one or more soluble structural units in the main chain and one or more thermosetting groups at the end of the main chain with a specific fluorine compound (see Patent Document 4). Furthermore, a material has been disclosed that is obtained by reacting the above-mentioned thermosetting liquid crystal oligomer with a nanofiller whose surface is substituted with an alkoxide metal compound (see Patent Document 5). Examples of these thermosetting liquid crystal polymer materials include materials in which a crosslinkable group is bonded to the end of a liquid crystal polymer via a spacer unit (see Patent Document 6), and materials having radical polymerizable groups such as unsubstituted or substituted maleimide, unsubstituted or substituted nadimide, ethynyl, and benzocyclobutene at both ends of a liquid crystal polyester have also been disclosed (see Patent Document 7).

However, the materials disclosed in Patent Documents 1 to 3 require high-temperature heating of 350°C or higher to harden, which makes the manufacturing process for the cured product complicated, and the components volatilize and decompose during hardening. In addition, when used as a sealant, for example, the product being sealed may deteriorate.

In the materials disclosed in Patent Documents 4 and 5, the liquid crystal polymer main chain contains soluble structural units, such as amide bonds or amine bonds, as essential structural units, which causes the problem that the dielectric constant and dielectric loss tangent of the resulting cured product are deteriorated.

In addition, the material disclosed in Patent Document 6 has a spacer unit such as an alkylene group as a linking group between the liquid crystal polymer and the crosslinkable group, which makes it susceptible to thermal decomposition, and the heat resistance of the resulting cured product is poor.

Furthermore, the material disclosed in Patent Document 7 has the problem that the resulting cured product is brittle.

In this context, several thermotropic liquid crystal materials with specific structures that have a divalent aromatic hydrocarbon group in the main chain of the liquid crystal polyester and a thermosetting group at the end have been proposed as thermosetting liquid crystal polyesters that can be cured at relatively low temperatures (e.g., 250°C or less) and that can give cured products with excellent physical properties such as heat resistance (see, for example, Patent Documents 8 and 9), and attempts have been made to keep the dielectric tangent low and improve heat resistance.

However, when the liquid crystal polyester-containing composition (solution) disclosed in Patent Documents 8 and 9 was used to impregnate glass cloth or the like, the composition had poor solvent solubility, and did not produce a cured product that was satisfactory in terms of both the low dielectric tangent required for electrical insulating material applications, particularly for high-frequency electrical insulating material applications, and heat resistance sufficient to withstand lead-free soldering.

Special Publication No. 2004-509190 U.S. Pat. No. 6,939,940 U.S. Pat. No. 7,507,784 JP 2011-111619 A JP 2011-084707 A Special Publication No. 2002-521354 U.S. Pat. No. 5,114,612 Patent No. 6342202 JP 2017-179120 A

The problem that the present invention aims to solve is to provide a cured product with low dielectric properties (particularly low dielectric tangent) and high heat resistance (high glass transition temperature) by using a reactive liquid crystal polyester with excellent solvent solubility and liquid crystallinity.

The inventors have conducted extensive research to solve the above problems and have discovered that a reactive liquid crystal polyester with excellent solvent solubility and liquid crystallinity, a polyester composition containing the reactive liquid crystal polyester, a polyester solution containing the reactive liquid crystal polyester, and a cured product obtained from the polyester composition are excellent in low dielectric properties (particularly low dielectric tangent) and high heat resistance (high glass transition temperature), thereby completing the present invention.

<Reactive Liquid Crystal Polyester>
That is, the present invention relates to a reactive liquid crystal polyester which contains a structural unit represented by the following general formula (1) containing a 2,2'-biphenylene group and has a thermally polymerizable functional group bonded to its terminal structure.
(In formula (1), ^D1 and ^D2 may be the same or different and represent a divalent aliphatic hydrocarbon group, a divalent alicyclic hydrocarbon group, or a divalent aromatic hydrocarbon group, and ^E1 and ^E2 may be the same or different and represent an ester bond [-(C=O)O- or -O(C=O)-].)

In the reactive liquid crystal polyester of the present invention, all or a part of ^D1 and ^D2 are preferably a cyclohexylene group.

In the reactive liquid crystal polyester of the present invention, the thermally polymerizable functional group is preferably at least one type of thermally polymerizable functional group selected from the group consisting of a hydroxyl group, a carboxyl group, a styryl group, a (meth)acryloyl group, and an allyl group.

In the reactive liquid crystal polyester of the present invention, the thermally polymerizable functional group is preferably at least one type of thermally polymerizable functional group selected from the group consisting of a styryl group, a (meth)acryloyl group, and an allyl group.

In the reactive liquid crystal polyester of the present invention, the molar ratio of the 2,2'-biphenylene group and the cyclohexylene group in the formula (1) is preferably 10/90 to 90/10.

In the reactive liquid crystal polyester of the present invention, the molar ratio of the cis isomer and the trans isomer of the cyclohexane ring in the cyclohexylene group is preferably 10/90 to 90/10.

The present invention relates to a polyester composition containing the reactive liquid crystal polyester.

The polyester composition of the present invention may contain the reactive liquid crystal polyester and a compound (2) having a functional group that reacts with the thermally polymerizable functional group.

The present invention relates to a polyester solution characterized in that the polyester composition further contains an aprotic polar solvent.

The present invention relates to a cured product obtained by reacting the polyester composition.

The reactive liquid crystal polyester of the present invention has excellent solvent solubility and liquid crystallinity, and a polyester solution containing the reactive liquid crystal polyester also has excellent solvent solubility. Furthermore, the cured product obtained from the polyester composition containing the reactive liquid crystal polyester is useful because it has low dielectric properties (particularly low dielectric tangent) and high heat resistance (high glass transition temperature).

The present invention is described in detail below.

<Reactive Liquid Crystal Polyester>
The present invention relates to a reactive liquid crystal polyester which comprises a structural unit represented by the following general formula (1) containing a 2,2'-biphenylene group and has a thermally polymerizable functional group bonded to a terminal structure.

In the above formula (1), ^D1 and ^D2 may be the same or different and represent a divalent aliphatic hydrocarbon group, a divalent alicyclic hydrocarbon group, or a divalent aromatic hydrocarbon group, and ^E1 and ^E2 may be the same or different and represent an ester bond [-(C=O)O- or -O(C=O)-]. The reactive liquid crystal polyester has two or more ester bonds.

The reactive liquid crystal polyester of the present invention is characterized by containing a 2,2'-biphenylene group. By containing a 2,2'-biphenylene group, the rigidity of the polyester main chain is alleviated, and the liquid crystallinity is expressed while improving the solvent solubility, which is preferable.

The reactive liquid crystal polyester of the present invention is characterized in that a thermally polymerizable functional group is bonded to the terminal structure. The reactive liquid crystal polyester has a thermally polymerizable functional group at the terminal, which allows the crosslinking reaction to proceed, the reactive liquid crystal polyester to be homopolymerized, or crosslinked with a crosslinking agent or a different resin component, and is preferable because it is possible to obtain a resin cured product with excellent heat resistance. The thermally polymerizable functional group is bonded to the terminal structure of the reactive liquid crystal polyester, but when there are multiple thermally polymerizable functional groups, they may be the same or different.

The thermally polymerizable functional group is preferably at least one type of thermally polymerizable functional group selected from the group consisting of hydroxyl group, carboxyl group, styryl group (vinylbenzyl ether group), (meth)acryloyl group, and allyl group, and more preferably at least one type of thermally polymerizable functional group selected from the group consisting of styryl group, (meth)acryloyl group, and allyl group. By having these thermally polymerizable functional groups (thermosetting groups) at the terminals of the molecular structure of the reactive liquid crystal polyester, thermal curing is possible, and the cured product obtained using the reactive liquid crystal polyester is excellent in heat resistance and low dielectric properties, which is preferable. In addition, when the thermally polymerizable functional group is at least one type of thermally polymerizable functional group selected from the group consisting of styryl group (vinylbenzyl ether group), (meth)acryloyl group, and allyl group, molecular mobility is low compared to polar groups such as hydroxyl group, so that lower dielectric properties are obtained, which is preferable. In addition, when there are multiple thermally polymerizable functional groups, the crosslinking density increases and heat resistance improves.

The reactive liquid crystal polyester of the present invention is characterized in that, in the above formula (1), D ¹ and D ² may be the same or different and represent a divalent aliphatic hydrocarbon group, a divalent alicyclic hydrocarbon group, or a divalent aromatic hydrocarbon group. The divalent aliphatic hydrocarbon group or the like of D ¹ and D ² improves the solvent solubility compared to aromatic hydrocarbon groups, which is preferable. Among them, it is preferable that all or a part of D ¹ and D ² is a cyclohexylene group. In addition, by having the cyclohexylene group, there are a cis isomer having a bent structure and a trans isomer having a rigid structure, which makes it possible to improve the solvent solubility while expressing liquid crystallinity, and the solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester are excellent, which is more preferable.

Examples of the divalent aliphatic hydrocarbon group include linear or branched alkylene groups having 1 to 18 carbon atoms, and linear or branched alkenylene groups having 2 to 18 carbon atoms. Examples of linear or branched alkylene groups having 1 to 18 carbon atoms include methylene, methylmethylene, dimethylmethylene, ethylene, propylene, and trimethylene groups. Examples of linear or branched alkenylene groups having 2 to 18 carbon atoms include vinylene, 1-methylvinylene, propenylene, 1-butenylene, and 2-butenylene groups.

Examples of the divalent alicyclic hydrocarbon group include divalent alicyclic hydrocarbon groups having 3 to 18 carbon atoms, such as cycloalkylene groups (including cycloalkylidene groups) such as a 1,2-cyclopentylene group, a 1,3-cyclopentylene group, a cyclopentylidene group, a 1,2-cyclohexylene group, a 1,3-cyclohexylene group, a 1,4-cyclohexylene group, and a cyclohexylidene group.

The divalent aromatic hydrocarbon group is a group in which two hydrogen atoms have been removed from the structural formula of an aromatic hydrocarbon (e.g., an aromatic hydrocarbon having 6 to 14 carbon atoms, such as benzene, naphthalene, anthracene, or phenanthrene).

In addition, the aromatic hydrocarbon ring of the divalent aromatic hydrocarbon group may have one or more types of substituents bonded thereto. Examples of the substituents include an alkyl group having 1 to 6 carbon atoms, an allyl group having 6 to 10 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryloxy group having 6 to 10 carbon atoms, and a halogen atom.

Examples of the alkyl group having 1 to 6 carbon atoms include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, s-butyl, t-butyl, pentyl, and hexyl.

Examples of the allyl group having 6 to 10 carbon atoms include a phenyl group and a naphthyl group.

Examples of the alkoxy group having 1 to 6 carbon atoms include linear or branched alkoxy groups such as a methoxy group, an ethoxy group, a butoxy group, and a t-butyloxy group.

Examples of the aryloxy group having 6 to 10 carbon atoms include a phenyloxy group and a 2-naphthyloxy group.

The reactive liquid crystal polyester of the present invention is characterized in that, in the above formula (1), E ¹ and E ² may be the same or different and represent an ester bond [-(C=O)O- or -O(C=O)-]. The reactive liquid crystal polyester has a plurality of ester bonds, which makes it possible to include a rigid structure and a bent structure in one molecule of the reactive liquid crystal polyester, and is preferable in terms of achieving both liquid crystallinity and solvent solubility. Here, the ester bond includes [-(C=O)O-] or [-O(C=O)-], which means that the compound having a 2,2'-biphenylene group used in synthesizing the reactive liquid crystal polyester includes both a case having a hydroxyl group and a case having a carboxyl group.

In the reactive liquid crystal polyester of the present invention, the molar ratio of the 2,2'-biphenylene group and the cyclohexylene group in the formula (1) is preferably 10/90 to 90/10, and more preferably 20/80 to 80/20. When the molar ratio is within the above range, both the solvent solubility and liquid crystallinity due to the 2,2'-biphenylene group and the cyclohexylene group can be secured, which is a preferred embodiment.

In the reactive liquid crystal polyester of the present invention, the molar ratio of the cis isomer and the trans isomer of the cyclohexane ring in the cyclohexylene group is preferably 10/90 to 90/10, and more preferably 20/80 to 80/20. When the molar ratio is within the above range, it becomes possible to include a rigid structure and a bent structure, which is a preferred embodiment.

From the viewpoint of liquid crystallinity in a molten state and solvent solubility, the reactive liquid crystal polyester of the present invention has a structural unit (repeating structural unit) containing a 2,2'-biphenylene group, but from the viewpoint of adjusting the liquid crystallinity and heat resistance, it is preferable that the reactive liquid crystal polyester contains a structural unit obtained by reacting at least one selected from the group consisting of an aliphatic diol, an alicyclic diol, an aromatic diol, an aliphatic dicarboxylic acid, an alicyclic dicarboxylic acid, an aromatic dicarboxylic acid, an aliphatic hydroxycarboxylic acid, an alicyclic hydroxycarboxylic acid, and an aromatic hydroxycarboxylic acid.

Examples of the aliphatic diol that can be used include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, neopentyl glycol, and 3-methylpentanediol.

Examples of the alicyclic diol that can be used include cyclobutanediol, cyclopentanediol, 1,4-cyclohexanediol, cycloheptanediol, cyclooctanediol, cyclohexanedimethanol, hydroxypropylcyclohexanol, tricyclo[5,2,1,0,2,6]decane-dimethanol, bicyclo[4,3,0]-nonanediol, dicyclohexanediol, tricyclo[5,3,1,1]dodecanediol, bicyclo[4,3,0]nonanedimethanol, tricyclo[5,3,1,1]dodecane-diethanol, hydroxypropyltricyclo[5,3,1,1]dodecanol, spiro[3,4]octanediol, butylcyclohexanediol, 1,1'-bicyclohexylidenediol, cyclohexanetriol, hydrogenated bisphenol A, and 1,3-adamantanediol.

Examples of the aromatic diol include 2,2'-dihydroxybiphenyl, 4,4'-dihydroxybiphenyl, hydroquinone, resorcinol, 2,6-naphthalenediol, 1,5-naphthalenediol, [1,1'-biphenyl]-4,4'-diol, 4,4'-dihydroxydiphenyl ether, bis(4-hydroxyphenyl)methanone, bisphenol A, bisphenol F, bisphenol S, (phenylsulfonyl)benzene, [1,1'-biphenyl]-2,5-diol, and derivatives thereof. Examples of the derivative include compounds in which the aromatic ring (aromatic ring) of the aromatic diol is substituted with a substituent having 0 to 20 carbon atoms (preferably 0 to 10 carbon atoms). Examples of the substituent include the same as the substituent in aromatic hydroxycarboxylic acid. The reactive liquid crystal polyester may have one type of structural unit derived from an aromatic diol, or may have two or more types.

As the aliphatic dicarboxylic acid, for example, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, eicosanedioic acid, etc. can be used.

As the alicyclic dicarboxylic acid, for example, 1,3-cyclopentanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, etc. can be used.

Examples of the aromatic dicarboxylic acid include phthalic acid, terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,2'-biphenyldicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 4,4'-oxybis(benzoic acid), 4,4'-thiobis(benzoic acid), 4-[2-(4-carboxyphenoxy)ethoxy]benzoic acid, and derivatives thereof. Examples of the derivative include compounds in which the aromatic ring (aromatic ring) of the aromatic dicarboxylic acid is substituted with a substituent having 0 to 20 carbon atoms (preferably 0 to 10 carbon atoms). Examples of the substituent include the same as the substituent in the aromatic hydroxycarboxylic acid. The reactive liquid crystal polyester may have one type of structural unit derived from an aromatic dicarboxylic acid, or may have two or more types.

Examples of the aliphatic hydroxycarboxylic acid that can be used include 16-hydroxyhexadecanoic acid, 15-hydroxypentadecanoic acid, 12-hydroxystearic acid, 2-hydroxyisobutanoic acid, and 2-hydroxy-2-methylbutanoic acid.

Examples of the alicyclic hydroxycarboxylic acid that can be used include 4-hydroxycyclohexanecarboxylic acid, 3-hydroxycyclohexanecarboxylic acid, 2-hydroxycyclohexanecarboxylic acid, 3-hydroxy-1-adamantaneacetic acid, and 4-(hydroxymethyl)cyclohexanecarboxylic acid.

Examples of the aromatic hydroxycarboxylic acid include 4-hydroxybenzoic acid, 3-hydroxybenzoic acid, 1-hydroxy-2-naphthoic acid, 3-hydroxy-2-naphthoic acid, 6-hydroxy-2-naphthoic acid, 5-hydroxy-1-naphthoic acid, 4'-hydroxy[1,1'-biphenyl]-4-carboxylic acid, and derivatives thereof. Examples of the derivatives include compounds in which the aromatic ring (aromatic ring) of the aromatic hydroxycarboxylic acid is substituted with a substituent having 0 to 20 carbon atoms (preferably 0 to 10 carbon atoms). Examples of the substituent include an alkyl group [e.g., a methyl group, an ethyl group, etc.]; an alkenyl group [e.g., a vinyl group, an allyl group, etc.]; an alkynyl group [e.g., an ethynyl group, a propynyl group, etc.]; a halogen atom [e.g., a chlorine atom, a bromine atom, an iodine atom, etc.]; a hydroxyl group; an alkoxy group [e.g., a C _1-6 alkoxy group (preferably a C _1-4 alkoxy group) such as a methoxy group, an ethoxy group, a propoxy group, an isopropyloxy group, a butoxy group, an isobutyloxy group, etc.]; an alkenyloxy group [e.g., a C _2-6 alkenyloxy group (preferably a C _2-4 alkenyloxy group) such as an allyloxy group, etc.]; an aryloxy group [e.g., a C _1-4 alkyl group, a C _2-4 alkenyl group, a halogen atom, a C 1-4 alkoxy group, etc., which may have a substituent on the aromatic ring (aromatic ring) such as a phenoxy group, a tolyloxy group, a _naphthyloxy group, etc. _6-14 aryloxy groups, etc.]; aralkyloxy groups [for example, C _7-18 aralkyloxy groups such as benzyloxy and phenethyloxy groups, etc.]; acyloxy groups [for example, C _1-12 acyloxy groups such as acetyloxy, propionyloxy, (meth)acryloyloxy, and benzoyloxy groups, etc.]; mercapto groups; alkylthio groups [for example, C _1-6 alkylthio groups (preferably C _1-4 alkylthio groups) such as methylthio and ethylthio groups, etc.]; alkenylthio groups [for example, C _2-6 alkenylthio groups (preferably C _2-4 alkenylthio groups) such as allylthio groups, etc.]; arylthio groups [for example, C _1-4 alkyl groups, C _2-4 alkenyl groups, halogen atoms, C _1-4 alkoxy groups, etc., which may have a substituent on the aromatic ring (aromatic ring) such as a phenylthio group, a tolylthio group, or a naphthylthio group, _6-14 arylthio groups, etc.]; aralkylthio groups [for example, C _7-18 aralkylthio groups such as benzylthio and phenethylthio groups, etc.]; carboxyl groups; alkoxycarbonyl groups [for example, C _1-6 alkoxy-carbonyl groups such as methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, and butoxycarbonyl groups, etc.]; aryloxycarbonyl groups [for example, C _6-14 aryloxy-carbonyl groups such as phenoxycarbonyl, tolyloxycarbonyl, and naphthyloxycarbonyl groups, etc.]; aralkyloxycarbonyl groups [for example, C _7-18 aralkyloxy-carbonyl groups such as benzyloxycarbonyl groups, etc.]; amino groups; mono- or di-alkylamino groups [for example, mono- or di-C methylamino, ethylamino, dimethylamino, and diethylamino groups, etc. _1-6 alkylamino group, etc.]; mono- or diphenylamino group [e.g., phenylamino group, etc.]; acylamino group [e.g., acetylamino group, propionylamino group, benzoylamino group, etc. C _1-11 acylamino group, etc.]; epoxy group-containing group [e.g., glycidyl group, glycidyloxy group, 3,4-epoxycyclohexyl group, etc.]; oxetanyl group-containing group [e.g., ethyloxetanyloxy group, etc.]; acyl group [e.g., acetyl group, propionyl group, benzoyl group, etc.]; oxo group; isocyanate group; and groups in which two or more of these are bonded via a C _1-6 alkylene group as necessary. The reactive liquid crystal polyester may have one type of structural unit derived from an aromatic hydroxycarboxylic acid, or may have two or more types.

When the reactive liquid crystal polyester has a hydroxyl group as a thermally polymerizable functional group at the molecular chain end, the hydroxyl group may be at only one end (one terminal) of the molecular chain, or at both ends (both terminals) of the molecular chain, although this is not particularly limited.

The hydroxyl group at the molecular chain end of the reactive liquid crystal polyester may be a phenolic hydroxyl group or an alcoholic hydroxyl group. In particular, from the viewpoint of the heat resistance of the cured product, it is preferable that the hydroxyl group at the molecular chain end of the reactive liquid crystal polyester is a phenolic hydroxyl group. The "phenolic hydroxyl group" includes hydroxyl groups bonded to substituted or unsubstituted benzene rings as well as hydroxyl groups bonded to other aromatic rings (such as naphthalene rings and anthracene rings).

When the reactive liquid crystal polyester has a carboxyl group as a thermally polymerizable functional group at the molecular chain end, it may have a carboxyl group at only one end (one terminal) of the molecular chain, or may have a carboxyl group at both ends (both terminals) of the molecular chain, although this is not particularly limited.

When the reactive liquid crystal polyester has an aromatic ring at the molecular chain end, the aromatic ring may be at only one end of the molecular chain, or at both ends of the molecular chain. The aromatic ring at the molecular chain end of the reactive liquid crystal polyester may have one or more substituents bonded to each ring. Examples of the substituent include known or conventional substituents, and include, but are not limited to, the substituents contained in the compounds exemplified as aromatic hydroxycarboxylic acids described below.

When the reactive liquid crystal polyester has a thermally polymerizable functional group at the molecular chain end, the thermally polymerizable functional group may be, but is not limited to, only one end of the molecular chain, or both ends of the molecular chain.

The thermally polymerizable functional group that the reactive liquid crystal polyester has at the molecular chain end thereof may be, for example, a styryl group, a (meth)acryloyl group, an allyl group, a maleimide group, a nadimide group, a phthalimide group, a cyanate group, a nitrile group, a phthalonitrile group, a styryl group, an ethynyl group, a propargyl ether group, a benzocyclobutane group, a biphenylene group, or a substitute or derivative thereof. The substitute or derivative may be a thermally polymerizable functional group in which a substituent (such as the substituent in the aromatic hydroxycarboxylic acid described above) is bonded to the thermally polymerizable functional group. Among these, from the viewpoint of keeping the polymerization temperature and dielectric loss low, a styryl group, a (meth)acryloyl group, or an allyl group is preferred.

<Method of producing reactive liquid crystal polyester>
The reactive liquid crystal polyester can be produced by polymerizing at least one selected from the group consisting of the above-mentioned aliphatic diols, alicyclic diols, aromatic diols, aliphatic dicarboxylic acids, alicyclic dicarboxylic acids, aromatic dicarboxylic acids, aliphatic hydroxycarboxylic acids, alicyclic hydroxycarboxylic acids, and aromatic hydroxycarboxylic acids by a known or conventional method, and the production method thereof is not particularly limited.

As a specific method for producing the reactive liquid crystal polyester, for example, a compound having a hydroxyl group, such as the above-mentioned hydroxycarboxylic acid or diol, is reacted with an excess amount of a fatty acid anhydride to carry out an acetylation reaction, and the resulting acetylated product is reacted with a compound having a carboxyl group, such as a hydroxycarboxylic acid or dicarboxylic acid (transesterification reaction).

In the acetylation reaction, the amount of the fatty acid anhydride added is preferably 1.0 to 1.2 times the equivalent of the hydroxyl group of the hydroxyl group-containing compound, and more preferably 1.05 to 1.1 times the equivalent. If the amount of fatty acid anhydride added is too small, the acetylated product and raw material monomers are sublimated during the transesterification reaction, and the reaction system tends to be easily blocked, while if the amount of fatty acid anhydride added is too large, the coloring of the resulting reactive liquid crystal polyester tends to become significant, which is not preferable.
The acetylation reaction is preferably carried out at 130 to 180° C. for 5 minutes to 10 hours, and more preferably at 140 to 160° C. for 10 minutes to 3 hours.
The fatty acid anhydride used in the acetylation reaction is not particularly limited, but examples thereof include acetic anhydride, propionic anhydride, butyric anhydride, isobutyric anhydride, valeric anhydride, pivalic anhydride, 2-ethylhexanoic anhydride, monochloroacetic anhydride, dichloroacetic anhydride, trichloroacetic anhydride, monobromoacetic anhydride, dibromoacetic anhydride, tribromoacetic anhydride, monofluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, glutaric anhydride, maleic anhydride, succinic anhydride, and β-bromopropionic anhydride, and two or more of these may be mixed and used. From the viewpoint of cost and handling, acetic anhydride, propionic anhydride, butyric anhydride, or isobutyric anhydride is preferred, and acetic anhydride is more preferred. More specifically, it can be produced, for example, by the method described in JP-A-2007-119610.

In the transesterification reaction, the amount of the acetyl group in the acetylated product is preferably 0.8 to 1.2 times the equivalent of the carboxyl group in the compound having a carboxyl group.
The transesterification reaction is preferably carried out while increasing the temperature to 400° C. at a rate of 0.1 to 50° C./min, and more preferably while increasing the temperature to 350° C. at a rate of 0.3 to 5° C./min.
During the transesterification reaction between the acetylated product and the compound having a carboxyl group, in order to shift the equilibrium, it is preferable to distill off the by-produced fatty acid and unreacted fatty acid anhydride outside the system by evaporation or the like.

The acetylation reaction and the transesterification reaction may be carried out in the presence of a catalyst. As the catalyst, a catalyst that has been known as a catalyst for polymerization of polyesters can be used, and examples of the catalyst include metal salt catalysts such as magnesium acetate, stannous acetate, tetrabutyl titanate, lead acetate, sodium acetate, potassium acetate, and antimony trioxide, and organic compound catalysts such as N,N-dimethylaminopyridine and N-methylimidazole. Among these catalysts, heterocyclic compounds containing two or more nitrogen atoms such as N,N-dimethylaminopyridine and N-methylimidazole are preferably used. The catalyst is usually added when the monomers are added, and it is not necessarily required to remove it after acetylation. If the catalyst is not removed, the transesterification reaction can be carried out as it is.
In addition, as the transesterification reaction, for example, a compound having a carboxyl group such as the above-mentioned hydroxycarboxylic acid or dicarboxylic acid (e.g., 1,4-cyclohexanedicarboxylic acid) is reacted with an excess amount of dichlorophenyl phosphate in a solvent such as pyridine, and then lithium chloride is added, and a compound having a hydroxyl group such as a hydroxycarboxylic acid or diol (e.g., 2,2'-biphenol and 4,4'-biphenol) is reacted to produce the polyol. More specifically, the amount of dichlorophenyl phosphate added is preferably 1.0 to 4.0 equivalents relative to the carboxyl group of the compound having a carboxyl group, and more preferably 2.0 to 3.0 equivalents. If the amount of dichlorophenyl phosphate added is too small, unreacted carboxyl groups remain, and the molecular weight tends to be low, and if the amount of dichlorophenyl phosphate is too large, it tends to react with the hydroxyl group and the molecular weight tends to be low, which is not preferable.
The reaction conditions with dichlorophenyl phosphate are preferably at 10 to 50° C. for 5 minutes to 2 hours, and more preferably at 20 to 40° C. for 10 minutes to 1 hour.
Next, the amount of lithium chloride added is preferably 1.0 to 2.0 times the equivalent of the hydroxyl group of the hydroxyl group-containing compound, and more preferably 1.2 to 1.5 times the equivalent. If the amount of lithium chloride added is too small, the hydroxyl group tends to react with dichlorophenyl phosphate, resulting in a lower molecular weight, whereas if the amount of lithium chloride added is too large, the transesterification reaction is inhibited, resulting in a lower molecular weight, which is not preferable.
The reaction conditions for the lithium chloride are preferably such that the reaction is carried out for 10 minutes to 1 hour at 110 to 120° C. In the transesterification reaction, the amount of hydroxyl groups is preferably 0.8 to 1.2 times the equivalent of carboxyl groups.
The transesterification reaction is preferably carried out by dropping a pyridine solution of a compound having a hydroxyl group over a period of 10 minutes to 1 hour following the reaction with lithium chloride at 110 to 120° C. for 1 to 5 hours.

The weight average molecular weight (Mw) of the reactive liquid crystal polyester is preferably 1000 to 50000, and more preferably 2000 to 20000. When the weight average molecular weight is within the above range, it is preferable that the polymer exhibits liquid crystallinity while being soluble in solvents, and a cured product with high heat resistance can be obtained. In particular, when the weight average molecular weight is 10000 or less, it is preferable that the polymer melts at a relatively low temperature, exhibits particularly excellent solubility in solvents, and has fast curing properties. The weight average molecular weight (Mw) of the reactive liquid crystal polyester can be determined by GPC measurement.

The pre-cure softening temperature of the reactive liquid crystal polyester is preferably 50 to 180°C, and more preferably 80 to 150°C. If the pre-cure softening temperature is within the above range, it is preferable in that liquid crystallinity is exhibited at a relatively low temperature.

The heat curing temperature of the reactive liquid crystal polyester is preferably 100 to 250°C, and more preferably 150 to 200°C. Within this range, the reactive liquid crystal polyester is preferable in that it can be heat cured while maintaining its liquid crystallinity, and that it has fast curing properties.

<Polyester Composition>
The present invention relates to a polyester composition comprising the reactive liquid crystal polyester. By comprising the reactive liquid crystal polyester, the polyester composition has excellent solvent solubility, is easy to prepare, is easy to handle, and can provide a cured product having excellent heat resistance and low dielectric properties.

The polyester composition of the present invention may contain the reactive liquid crystal polyester and a compound (2) having a functional group that reacts with the thermally polymerizable functional group (hereinafter, may be simply referred to as "compound (2)"). By containing compound (2) having a functional group that reacts with the thermally polymerizable functional group, the crosslinking reaction proceeds, and the composition has a high density crosslinked structure, which is preferable because it has excellent heat resistance and thermal expansion coefficient.

Examples of the compound (2) include compounds (2) having a functional group that reacts with the thermally polymerizable functional group of the reactive liquid crystal polyester, such as an α,β-unsaturated carbonyl group, an epoxy group, a maleimide group, an ester group, an acid anhydride group, a carboxyl group, a hydroxyl group, a nadimide group, a phthalimide group, a cyanate group, a nitrile group, a phthalonitrile group, a styryl group, an ethynyl group, a propargyl ether group, a benzocyclobutane group, a biphenylene group, an allyl group, or a vinyl group. Among these, it is preferable to use a compound having a maleimide group.

[Other resins, etc.]
The polyester composition of the present invention can be used without particular limitation as long as the purpose is not impaired, and can also contain alkenyl group-containing compounds such as bismaleimides, allyl ether compounds, allyl amine compounds, triallyl cyanurate, alkenyl phenol compounds, vinyl group-containing polyolefin compounds, etc. In addition, other thermosetting resins such as thermosetting polyimide resins, epoxy resins, phenolic resins, active ester resins, benzoxazine resins, cyanate resins, etc. can also be appropriately blended depending on the purpose.

[Hardening agent]
The polyester composition of the present invention may contain a curing agent. Examples of the curing agent include amine compounds, amide compounds, acid anhydride compounds, phenolic compounds, cyanate ester compounds, etc. These curing agents may be used alone or in combination of two or more kinds.

[Curing Accelerator]
The polyester composition of the present invention may also be appropriately used in combination with a curing accelerator, if necessary. Various types of curing accelerators can be used, including, for example, phosphorus-based compounds, tertiary amines, imidazoles, organic acid metal salts, Lewis acids, and amine complex salts. In particular, when used as a semiconductor encapsulation material, phosphorus-based compounds such as triphenylphosphine or imidazoles are preferred because of their excellent curability, heat resistance, electrical properties, and moisture resistance reliability. These curing accelerators may be used alone or in combination of two or more. The amount of the curing accelerator added is preferably in the range of 0.01 to 10 parts by mass relative to 100 parts by mass of the reactive liquid crystal polyester.

[Flame retardant]
The polyester composition of the present invention may contain a non-halogen flame retardant that does not substantially contain halogen atoms in order to exhibit flame retardancy, if necessary. Examples of the non-halogen flame retardant include phosphorus-based flame retardants, nitrogen-based flame retardants, silicone-based flame retardants, inorganic flame retardants, and organic metal salt-based flame retardants, which may be used alone or in combination.

[Filler]
The polyester composition of the present invention may contain an inorganic filler as required. Examples of the inorganic filler include fused silica, crystalline silica, alumina, silicon nitride, and aluminum hydroxide. When the amount of the inorganic filler is particularly large, it is preferable to use fused silica. The fused silica may be either crushed or spherical, but in order to increase the amount of fused silica and suppress the increase in the melt viscosity of the molding material, it is preferable to mainly use spherical silica. In order to further increase the amount of spherical silica, it is preferable to appropriately adjust the particle size distribution of the spherical silica. In addition, when the polyester composition is used for applications such as a conductive paste described in detail below, a conductive filler such as silver powder or copper powder can be used.

[Other compounding agents]
If necessary, various compounding agents such as a silane coupling agent, a release agent, a pigment, an emulsifier, etc. may be added to the polyester composition of the present invention.

<Polyester solution>
The present invention relates to a polyester solution characterized in that the polyester composition further contains an aprotic polar solvent. By using an aprotic polar solvent in the polyester composition containing the reactive liquid crystal polyester, it becomes possible to easily blend with other resins, crosslinking agents, curing agents, etc., and the polyester solution is preferable because it has excellent handling properties and storage stability.

Examples of the aprotic polar solvent include acetone, methyl ethyl ketone, methyl acetate, ethyl acetate, acetonitrile, tetrahydrofuran, N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, and dichloromethane. Among these, methyl ethyl ketone and dimethylacetamide are preferred from the viewpoints of handling and solubility.

<Cured Product>
The present invention relates to a cured product obtained by reacting the polyester composition. The cured product obtained by using the polyester composition is excellent in heat resistance, low dielectric properties, and low moisture absorption, and is therefore suitable for applications such as films, prepregs, printed wiring boards, and semiconductor encapsulants, and is preferable. In particular, the cured product uses the reactive liquid crystal polyester, and the reactive liquid crystal polyester expresses liquid crystallinity, which restricts the molecular motion of the polar moiety containing the ester bond contained in the structure, and the dielectric tangent of the obtained cured product tends to be low, and the low dielectric properties are improved, which is preferable. On the other hand, the solvent solubility tends to decrease as the liquid crystallinity of the reactive liquid crystal polyester increases, but in the case of the reactive liquid crystal polyester, the inclusion of a 2,2'-biphenylene group reduces the rigidity and provides excellent solvent solubility, which makes the polyester composition and the polyester solution excellent in handleability when preparing them, and makes the preparation of the cured product easier, which is preferable.

The cured product can be obtained by using the polyester composition (or the polyester solution), or by uniformly mixing the reactive liquid crystal polyester alone or in addition to the reactive liquid crystal polyester with the compound (2) and the above-mentioned curing agent and curing accelerator (catalyst), and can be easily made into a cured product by a method similar to that known in the art. Examples of the cured product include molded cured products such as laminates, cast products, adhesive layers, coatings, and films.

The curing reaction includes heat curing and ultraviolet curing reactions. Heat curing reactions are easily carried out without a catalyst, but if you want to make the reaction faster, it is effective to add a polymerization initiator such as an organic peroxide or an azo compound, or a basic catalyst such as a phosphine compound or a tertiary amine. Examples include benzoyl peroxide, dicumyl peroxide, azobisisobutyronitrile, triphenylphosphine, triethylamine, imidazoles, etc.

<Applications>
The cured product obtained by the polyester composition of the present invention has excellent heat resistance and low dielectric properties, and therefore can be suitably used for heat-resistant members and electronic members. In particular, it can be suitably used for prepregs, circuit boards, semiconductor encapsulants, semiconductor devices, build-up films, build-up boards, adhesives, resist materials, etc. It can also be suitably used for matrix resins of fiber-reinforced resins, and is particularly suitable as highly heat-resistant prepregs. In addition, the reactive liquid crystal polyester contained in the polyester composition exhibits excellent solubility in various solvents, and can be made into paint. The heat-resistant members and electronic members thus obtained can be suitably used for various applications, such as industrial machine parts, general machine parts, automobile, railway, vehicle parts, space and aviation related parts, electronic and electrical parts, building materials, containers and packaging parts, daily necessities, sports and leisure goods, and housing parts for wind power generation, but are not limited thereto.

Next, the present invention will be specifically described with reference to examples and comparative examples. In the following, "parts (g)" and "%" are by weight unless otherwise specified. A reactive liquid crystal polyester and a cured product obtained using the reactive liquid crystal polyester were synthesized under the conditions shown below, and the obtained cured product was measured or calculated under the following conditions and evaluated.

<GPC Measurement>
The following measuring device and measuring conditions were used to measure the reactive liquid crystal polyester obtained by the synthesis method shown below, and GPC measurement was performed. Based on the GPC measurement results (see FIG. 1 for Example 1), the synthesis of the reactive liquid crystal polyester was confirmed, and the weight average molecular weight (Mw) was calculated. Also, similar confirmation was performed for other examples than Example 1 (not shown).
Measuring device: "HLC-8320 GPC" manufactured by Tosoh Corporation
Column: Tosoh Corporation guard column "HXL-L" + Tosoh Corporation "TSK-GEL G2000HXL" + Tosoh Corporation "TSK-GEL G2000HXL" + Tosoh Corporation "TSK-GEL G3000HXL" + Tosoh Corporation "TSK-GEL G4000HXL"
Detector: RI (differential refractometer)
Data processing: Tosoh Corporation's "GPC Workstation EcoSEC-WorkStation"
Measurement conditions: Column temperature 40°C
Developing solvent: Tetrahydrofuran
Flow rate: 1.0 ml/min. Standard: The following monodisperse polystyrene with known molecular weight was used in accordance with the measurement manual for the above-mentioned "GPC Workstation EcoSEC-WorkStation."
(Polystyrene used)
"A-500" manufactured by Tosoh Corporation
"A-1000" manufactured by Tosoh Corporation
"A-2500" manufactured by Tosoh Corporation
"A-5000" manufactured by Tosoh Corporation
"F-1" manufactured by Tosoh Corporation
"F-2" manufactured by Tosoh Corporation
"F-4" manufactured by Tosoh Corporation
"F-10" manufactured by Tosoh Corporation
"F-20" manufactured by Tosoh Corporation
"F-40" manufactured by Tosoh Corporation
"F-80" manufactured by Tosoh Corporation
"F-128" manufactured by Tosoh Corporation
Sample: A tetrahydrofuran solution (1.0% by mass, calculated as solid content) of the reactive liquid crystal polyester obtained in each of the Examples and Comparative Examples was filtered through a microfilter (50 μl).

<NMR Measurement>
The following measuring device and measuring conditions were used to perform ^1H -NMR measurement of the reactive liquid crystal polyester obtained by the synthesis method shown below, and the synthesis of the reactive liquid crystal polyester was confirmed by the peak shift of aromatic hydrocarbons based on the NMR chart measurement results (see FIG. 2 for Example 1). The same confirmation was also performed for Examples other than Example 1 (not shown).
¹ H-NMR was measured using a JEOL RESONANCE "JNM-ECM400S" under the following conditions.
Magnetic field strength: 400MHz
Number of times of accumulation: 16 Solvent: DMSO-D6
Sample concentration: 20 mg/0.6 ml

<Evaluation of Liquid Crystallinity>
The liquid crystallinity of each of the reactive liquid crystal polyesters obtained in the examples and comparative examples was evaluated by the following procedure. Note that, when an isotropic material is inserted between crossed polarizers, light does not pass through, but when a material having optical anisotropy is inserted between crossed polarizers, light passes through.
First, the dimethylacetamide solution of each reactive liquid crystal polyester obtained in the examples and comparative examples is dried on a slide glass to prepare an isotropic coating film. Next, the appearance of the dark field when it is heated and melted on a hot stage (manufactured by Mettler Toledo) is observed at a magnification of 200 times with a polarizing microscope (manufactured by Nikon Corporation) to evaluate the liquid crystallinity. If the evaluation result is ◎, ○, or △, there is no problem in practical use.
◎: Liquid crystallinity is observed overall. ◯: Liquid crystallinity is observed in most areas, but not in some areas. △: Liquid crystallinity is observed in some areas. ×: Liquid crystallinity is hardly observed.

<Evaluation of Solvent Solubility>
The reactive liquid crystal polyester thus obtained was dissolved in dimethylacetamide at a ratio of non-volatile content (mass ratio) of 10%, 20%, 30%, 40%, 50%. The solvent solubility was evaluated from the appearance of the solution. If the evaluation result was ○, there was no problem in practical use.
◯: Completely dissolved △: Very little remains undissolved ×: Almost not dissolved or most remains undissolved

Example 1
[Synthesis of reactive liquid crystal polyester (A-1)]
In a 500mL flask equipped with a condenser, a stirrer, and a nitrogen inlet tube, 8.61g (0.05mol) of 1,4-cyclohexanedicarboxylic acid and 100mL of pyridine were placed and mixed and dissolved under a nitrogen atmosphere. Then, 34.92g (0.13mol) of dichlorophenyl phosphate was gradually added and reacted for 0.5 hours. Then, a pyridine solution in which 3.39g (0.08mol) of lithium chloride was dissolved in 75mL of pyridine was gradually added and reacted at 115°C for 0.5 hours. Then, a pyridine solution in which 7.45g (0.04mol) of 2,2'-biphenol and 3.72g (0.02mol) of 4,4'-biphenol were dissolved in 50mL of pyridine was gradually added and reacted at 115°C for 3 hours. Then, the reaction solution was dropped into a methanol/water mixture to precipitate a reactive liquid crystal polyester, which was then filtered and washed with methanol. Volatile components were removed by distillation using a vacuum dryer at 50° C. to obtain a reactive liquid crystal polyester (A-1) having a hydroxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-1) are shown in Table 1.

Example 2
[Synthesis of reactive liquid crystal polyester (A-2)]
A reaction operation was carried out under the same conditions as in Example 1, except that the amount of 1,4-cyclohexanedicarboxylic acid was changed to 10.33 g (0.06 mol), the amount of 2,2'-biphenol was changed to 6.20 g (0.033 mol), and the amount of 4,4'-biphenol was changed to 3.11 g (0.017 mol) in Example 1, to obtain a reactive liquid crystal polyester (A-2) having a carboxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility, and liquid crystallinity of the obtained reactive liquid crystal polyester (A-2) are shown in Table 1.

Example 3
[Synthesis of reactive liquid crystal polyester (A-3)]
In a 500 mL flask equipped with a condenser, a stirrer, and a nitrogen inlet tube, 10.0 g of the reactive liquid crystal polyester (A-1) obtained in Example 1, 200 mL of dimethylformamide, 5 mg of methoquinone, and 50 mg of butylated hydroxytoluene were added and mixed and dissolved at 50 ° C. under a nitrogen atmosphere. Then, 2.5 g of potassium carbonate, 0.4 g of tetrabutylammonium bromide, and 10.0 g of 4-chloromethylstyrene were added and reacted at 50 ° C. for 8 hours. Thereafter, the reaction solution was dropped into a methanol/water mixture to precipitate the reactive liquid crystal polyester, which was filtered and washed with methanol. The volatile components were distilled off in a vacuum dryer at 50 ° C. to obtain a reactive liquid crystal polyester (A-3) having a styryl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility, and liquid crystallinity of the obtained reactive liquid crystal polyester (A-3) are shown in Table 1.

Example 4
[Synthesis of reactive liquid crystal polyester (A-4)]
In a 500 mL flask equipped with a condenser, a stirrer, and a nitrogen inlet tube, 10 g of the reactive liquid crystal polyester (A-1) obtained in Example 1, 200 mL of dimethylformamide, 5 mg of methoquinone, 50 mg of butylated hydroxytoluene, and 0.30 g (2.4 mmol) of dimethylaminopyridine were placed and mixed at 85 ° C. under a nitrogen atmosphere. Then, when it was thought that all the solids had dissolved, 2.78 g (18 mmol) of methacrylic anhydride was added dropwise over 1 hour, and the mixture was reacted at 85 ° C. for another 3 hours. Thereafter, the reaction solution was dropped into a methanol/water mixture to precipitate the reactive liquid crystal polyester, which was filtered and washed with methanol. The volatile components were distilled off in a vacuum dryer at 50 ° C. to obtain a reactive liquid crystal polyester (A-4) having a methacryloyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility, and liquid crystallinity of the obtained reactive liquid crystal polyester (A-4) are shown in Table 1.

Example 5
[Synthesis of reactive liquid crystal polyester (A-5)]
In a 500 mL flask equipped with a condenser, a stirrer, and a nitrogen inlet tube, 10 g of the reactive liquid crystal polyester (A-1) obtained in Example 1, 200 mL of dimethylformamide, 5 mg of methoquinone, and 50 mg of butylated hydroxytoluene were added and mixed at 60 ° C. under a nitrogen atmosphere. Then, 2.0 g of potassium carbonate and 8.0 g of allyl bromide were added and reacted at 60 ° C. for 8 hours. Thereafter, the reaction solution was dropped into a methanol/water mixture to precipitate a reactive liquid crystal polyester, which was filtered and washed with methanol. The volatile components were distilled off in a vacuum dryer at 50 ° C. to obtain a reactive liquid crystal polyester (A-5) having an allyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility, and liquid crystallinity of the obtained reactive liquid crystal polyester (A-5) are shown in Table 1.

Example 6
[Synthesis of reactive liquid crystal polyester (A-6)]
A reactive liquid crystal polyester (A-6) having a hydroxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain was obtained by carrying out a reaction operation under the same conditions as in Example 1, except that 1,4-cyclohexanedicarboxylic acid in Example 1 was changed to 1,3-cyclohexanedicarboxylic acid. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-6) are shown in Table 2.

(Example 7)
[Synthesis of reactive liquid crystal polyester (A-7)]
In a 500mL flask equipped with a condenser, a stirrer, and a nitrogen inlet tube, 6.89g (0.04mol) of 1,4-cyclohexanedicarboxylic acid, 6.85g (0.02mol) of eicosanedioic acid, and 100mL of pyridine were added and mixed and dissolved under a nitrogen atmosphere. Then, 34.92g (0.13mol) of dichlorophenyl phosphate was gradually added and reacted for 0.5 hours. Then, a pyridine solution in which 3.39g (0.08mol) of lithium chloride was dissolved in 75mL of pyridine was gradually added and reacted at 115°C for 0.5 hours. Then, a pyridine solution in which 9.31g (0.05mol) of 2,2'-biphenol was dissolved in 50mL of pyridine was gradually added and reacted at 115°C for 3 hours. Then, the reaction solution was dropped into a methanol/water mixture to precipitate a reactive liquid crystal polyester, which was then filtered and washed with methanol. The volatile components were removed by distillation using a vacuum dryer at 50° C. to obtain a reactive liquid crystal polyester (A-7) having a carboxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-7) are shown in Table 2.

(Example 8)
[Synthesis of reactive liquid crystal polyester (A-8)]
In a 500 mL flask equipped with a condenser, a stirrer, and a nitrogen inlet tube, 12.11 g (0.05 mol) of 2,2'-biphenyldicarboxylic acid and 100 mL of pyridine were placed and mixed and dissolved under a nitrogen atmosphere. Then, 34.92 g (0.13 mol) of dichlorophenyl phosphate was gradually added and reacted for 0.5 hours. Then, a pyridine solution in which 3.39 g (0.08 mol) of lithium chloride was dissolved in 75 mL of pyridine was gradually added and reacted at 115 ° C. for 0.5 hours. Then, a pyridine solution in which 3.72 g (0.02 mol) of 4,4'-biphenol and 4.65 g (0.04 mol) of 1,4-cyclohexanediol were dissolved in 50 mL of pyridine was gradually added and reacted at 115 ° C. for 3 hours. Then, the reaction solution was dropped into a methanol/water mixture to precipitate a reactive liquid crystal polyester, which was filtered and washed with methanol. The volatile components were removed by distillation using a vacuum dryer at 50° C. to obtain a reactive liquid crystal polyester (A-8) having a hydroxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-8) are shown in Table 2.

(Example 9)
[Synthesis of reactive liquid crystal polyester (A-9)]
In a 500mL flask equipped with a condenser, a stirrer, and a nitrogen inlet tube, 17.13g (0.05mol) of eicosanedioic acid and 100mL of pyridine were placed and mixed and dissolved under a nitrogen atmosphere. Then, 34.92g (0.13mol) of dichlorophenyl phosphate was gradually added and reacted for 0.5 hours. Then, a pyridine solution in which 3.39g (0.08mol) of lithium chloride was dissolved in 75mL of pyridine was gradually added and reacted at 115°C for 0.5 hours. Then, a pyridine solution in which 7.45g (0.04mol) of 2,2'-biphenol and 3.72g (0.02mol) of 4,4'-biphenol were dissolved in 50mL of pyridine was gradually added and reacted at 115°C for 3 hours. Then, the reaction solution was dropped into a methanol/water mixture to precipitate a reactive liquid crystal polyester, which was then filtered and washed with methanol. Volatile components were removed by distillation using a vacuum dryer at 50° C. to obtain a reactive liquid crystal polyester (A-9) having a hydroxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-9) are shown in Table 2.

(Example 10)
[Synthesis of reactive liquid crystal polyester (A-10)]
A reaction was carried out under the same conditions as in Example 9, except that 17.13 g of eicosane diacid in Example 9 was changed to 16.41 g (0.048 mol) of eicosane diacid and 0.36 g (2.1 mmol) of 1,4-cyclohexane dicarboxylic acid, to obtain a reactive liquid crystal polyester (A-10) having hydroxyl groups, which are thermally polymerizable functional groups, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-10) are shown in Table 2.

(Example 11)
[Synthesis of reactive liquid crystal polyester (A-11)]
A reaction was carried out under the same conditions as in Example 9, except that 17.13 g of eicosane diacid in Example 9 was changed to 15.60 g (0.046 mol) of eicosane diacid and 0.76 g (4.4 mmol) of 1,4-cyclohexane dicarboxylic acid, to obtain a reactive liquid crystal polyester (A-11) having a hydroxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-11) are shown in Table 2.

Example 12
[Synthesis of reactive liquid crystal polyester (A-12)]
A reaction was carried out under the same conditions as in Example 9, except that 17.13 g of eicosane diacid in Example 9 was changed to 11.25 g (0.033 mol) of eicosane diacid and 2.95 g (0.017 mol) of 1,4-cyclohexane dicarboxylic acid, to obtain a reactive liquid crystal polyester (A-12) having a hydroxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-12) are shown in Table 2.

Example 13
[Synthesis of reactive liquid crystal polyester (A-13)]
In a 500mL flask equipped with a condenser, a stirrer, and a nitrogen inlet tube, 8.61g (0.05mol) of 1,4-cyclohexanedicarboxylic acid and 100mL of pyridine were placed and mixed and dissolved under a nitrogen atmosphere. Then, 34.92g (0.13mol) of dichlorophenyl phosphate was gradually added and reacted for 0.5 hours. Then, a pyridine solution in which 3.39g (0.08mol) of lithium chloride was dissolved in 75mL of pyridine was gradually added and reacted at 115°C for 0.5 hours. Then, a pyridine solution in which 6.14g (0.033mol) of 2,2'-biphenol and 3.14g (0.027mol) of 1,4-cyclohexanediol were dissolved in 50mL of pyridine was gradually added and reacted at 115°C for 3 hours. Then, the reaction solution was dropped into a methanol/water mixture to precipitate a reactive liquid crystal polyester, which was then filtered and washed with methanol. The volatile components were removed by distillation using a vacuum dryer at 50° C. to obtain a reactive liquid crystal polyester (A-13) having a hydroxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-13) are shown in Table 2.

(Example 14)
[Synthesis of reactive liquid crystal polyester (A-14)]
A reaction was carried out under the same conditions as in Example 13, except that the amount of 2,2'-biphenol was changed to 2.05 g (0.011 mol) and the amount of 1,4-cyclohexanediol was changed to 5.69 g (0.049 mol) in Example 13, to obtain a reactive liquid crystal polyester (A-14) having a hydroxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-14) are shown in Table 3.

(Example 15)
[Synthesis of reactive liquid crystal polyester (A-15)]
A reaction was carried out under the same conditions as in Example 13, except that the amount of 2,2'-biphenol was changed to 1.02 g (5.5 mmol) and the amount of 1,4-cyclohexanediol was changed to 6.33 g (0.055 mol) in Example 13, to obtain a reactive liquid crystal polyester (A-15) having a hydroxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility and liquid crystallinity of the obtained reactive liquid crystal polyester (A-15) are shown in Table 3.

(Examples 16 to 20)
[Synthesis of reactive liquid crystal polyesters (A-16) to (A-20)]
The reaction was carried out under the same conditions as in Example 1, except that the molar ratio of cis-isomer in the cyclohexane group of 1,4-cyclohexanedicarboxylic acid in Example 1 was changed from 60% to 100% in Example 16, 90% in Example 17, 30% in Example 18, 10% in Example 19, and 0% in Example 20, to obtain reactive liquid crystal polyesters (A-16) to (A-20) having hydroxyl groups, which are thermally polymerizable functional groups, at both ends of the molecular chain. The weight average molecular weight (Mw), solvent solubility, and liquid crystallinity of the obtained reactive liquid crystal polyesters (A-16) to (A-20) are shown in Table 3.

(Comparative Example 1)
[Synthesis of reactive liquid crystal polyester (A-21)]
In a 500 mL flask equipped with a condenser, a stirrer, and a nitrogen inlet tube, 171.26 g (0.5 mol) of eicosanedioic acid, 111.73 g (0.6 mol) of 4,4'-biphenol, 147.01 g (1.44 mol) of acetic anhydride, and 0.14 g of 1-methylimidazole were added, and the temperature was gradually raised to 140°C under a nitrogen atmosphere, and then the mixture was reacted for 2 hours while maintaining the temperature to complete the acetylation reaction. Next, the temperature was gradually raised to 220°C to distill off acetic acid and unreacted acetic anhydride. Thereafter, the flask was gradually depressurized to 1 mmHg to distill off the volatile components, thereby obtaining a reactive liquid crystal polyester (A-21) having a hydroxyl group, which is a thermally polymerizable functional group, at both ends of the molecular chain. The solvent solubility of the obtained reactive liquid crystal polyester (A-21) is shown in Table 3. In addition, since the solvent solubility is poor, the weight average molecular weight (Mw) and liquid crystallinity were not evaluated.

The meanings of the abbreviations in Tables 1 to 3 above are as follows.
22BP...2,2'-biphenol 44BP...4,4'-biphenol 14CHDO...1,4-cyclohexanediol 22BPA...2,2'-biphenyldicarboxylic acid 14CHDA...1,4-cyclohexanedicarboxylic acid 13CHDA...1,3-cyclohexanedicarboxylic acid EicA...Eicosanedioic acid A-1...Reactive liquid crystal polyester (A-1)
CMS: 4-chloromethylstyrene MAH: methacrylic anhydride AB: allyl bromide 22BP group: 2,2'-biphenylene group CH group: cyclohexylene group (within the cyclohexane ring)

<Preparation of resin film>
The reactive liquid crystal polyester obtained alone, the mixture obtained by melt-mixing the reactive liquid crystal polyester obtained with the bismaleimide, and the bismaleimide alone were each placed in a 5 cm square mold, sandwiched between stainless steel plates, and set in a vacuum press. The pressure was increased to 1.0 MPa at room temperature (15 to 25 ° C). Next, the pressure was reduced to 10 torr, and the mixture was heated to a predetermined temperature (225 ° C or 280 ° C in this embodiment) over 30 minutes. After leaving it for another 2 hours, it was gradually cooled to room temperature (40 ° C or less). A uniform resin film (cured product) with an average film thickness of 100 μm was produced.

<Evaluation of dielectric properties>
The dielectric constant and dielectric loss tangent were measured for the in-plane dielectric properties of the obtained resin film (cured product) by a split post dielectric resonator method at a frequency of 10 GHz using a network analyzer N5247A from Keysight Technologies, Inc. Note that the dielectric loss tangent is practically acceptable if it is 10×10 ⁻³ or less, preferably 8×10 ⁻³ or less, and more preferably 7.5×10 ⁻³ or less, and the dielectric constant is practically acceptable if it is 3 or less, preferably 2.8 or less, and more preferably 2.6 or less.

<Evaluation of heat resistance>
The obtained resin film (cured product) was heated from room temperature (40°C or less) at a temperature increase rate of 10°C/min using a PerkinElmer DSC device (Pyris Diamond), and held at 250°C for 30 minutes. The sample was then cooled to room temperature (40°C or less) at a temperature decrease rate of 10°C/min, and then heated again at a temperature increase rate of 10°C/min to measure the glass transition temperature (Tg) (°C) of the resin film (cured product). Note that as long as the glass transition temperature (Tg) is 100°C or more, there is no practical problem, and it is preferably 150°C or more.

[Production of Liquid Crystal Polyester Cured Product (B-1)]
(Example 21)
10.0 g of the reactive liquid crystal polyester (A-1) obtained in Example 1 was melted at 150°C, and melt mixed with 5.0 g of polyphenylmethane maleimide (product name "BMI-2300" manufactured by Daiwa Kasei Co., Ltd.) as a maleimide derivative (bismaleimide) for 1 hour, and then 0.2 g of diaminodiphenylmethane was mixed and the mixture was heat pressed at 225°C by the above-mentioned method for producing a resin film to obtain a liquid crystal polyester cured product (B-1). The heat resistance (glass transition temperature (Tg)) and dielectric properties of the obtained liquid crystal polyester cured product (B-1) are shown in Table 4.

[Production of Liquid Crystal Polyester Cured Product (B-2)]
(Example 22)
A cured liquid crystal polyester (B-2) was obtained by hot pressing 10.0 g of the reactive liquid crystal polyester (A-3) obtained in Example 3 at 280° C. by the above-mentioned method for producing a resin film. The heat resistance (glass transition temperature (Tg)) and dielectric properties of the obtained cured liquid crystal polyester (B-2) are shown in Table 4.

[Production of Liquid Crystal Polyester Cured Product (B-3)]
(Example 23)
10.0 g of the reactive liquid crystal polyester (A-4) obtained in Example 4 was hot-pressed at 280° C. by the above-mentioned method for producing a resin film to obtain a cured liquid crystal polyester (B-4). The heat resistance (glass transition temperature (Tg)) and dielectric properties of the obtained cured liquid crystal polyester (B-3) are shown in Table 4.

[Production of Liquid Crystal Polyester Cured Product (B-4)]
(Example 24)
10.0 g of the reactive liquid crystal polyester (A-5) obtained in Example 5 was melted at 150° C., and melt-mixed with 5.0 g of polyphenylmethane maleimide (product name "BMI-2300" manufactured by Daiwa Kasei Co., Ltd.) as a maleimide derivative for 1 hour, and then 0.2 g of diaminodiphenylmethane was mixed and the mixture was heat-pressed at 225° C. by the above-mentioned method for producing a resin film to obtain a liquid crystal polyester cured product (B-4). The heat resistance (glass transition temperature (Tg)) and dielectric properties of the obtained liquid crystal polyester cured product (B-4) are shown in Table 4.

[Production of Cured Product (B-5)]
(Comparative Example 2)
5.0 g of a maleimide derivative, polyphenylmethane maleimide (product name "BMI-2300" manufactured by Daiwa Kasei Co., Ltd.) was melted at 150°C for 1 hour, and then 0.2 g of diaminodiphenylmethane was mixed therewith. The mixture was then hot-pressed at 225°C by the above-mentioned method for producing a resin film to obtain a maleimide cured product (B-5). The heat resistance (glass transition temperature (Tg)) and dielectric properties of the obtained cured product (B-5) are shown in Table 4.

Note: In Table 4, "250<" indicates that the temperature exceeds the maximum temperature (250° C.) during measurement of the glass transition temperature (Tg).

From the evaluation results in Tables 1 to 3 above, it was confirmed that reactive liquid crystal polyesters with excellent solvent solubility and liquid crystallinity were obtained in Examples 1 to 8 and 12 to 19 by using reactive liquid crystal polyesters with the desired structure. It was confirmed that in Examples 9 to 11 and 20, the solvent solubility decreased due to the high non-volatile content, but it was confirmed that the composition (solution) containing the liquid crystal polyester could be impregnated into glass cloth or the like, and that there was no practical problem. On the other hand, in Comparative Example 1, it was confirmed that the solvent solubility was very low and there was a practical problem because the structural unit contained only a rigid structure in which all ester bonds were derived from 4,4'-biphenylene groups, rather than a reactive liquid crystal polyester with the desired structure.

From the evaluation results in Table 4 above, it was confirmed that in Examples 21 to 24, the cured products obtained using reactive liquid crystal polyesters with the desired structure were able to satisfy heat resistance and low dielectric properties. On the other hand, in Comparative Example 2, the cured product did not use reactive liquid crystal polyesters with the desired structure, but only commercially available polyphenylmethanemaleimide, and therefore was unable to simultaneously satisfy both heat resistance and low dielectric properties.

The cured product obtained using the reactive liquid crystal polyester of the present invention has excellent high heat resistance and low dielectric properties, and therefore can be suitably used for heat-resistant components and electronic components, and in particular, can be suitably used for prepregs, semiconductor encapsulants, circuit boards, build-up films, build-up boards, etc., as well as adhesives and resist materials. It can also be suitably used as a matrix resin for fiber-reinforced resins, and is suitable as a highly heat-resistant prepreg.

1 is a GPC chart of the reactive liquid crystal polyester obtained in Example 1. 1 is a ¹ H-NMR spectrum of the reactive liquid crystal polyester obtained in Example 1.

Claims (8)

A reactive liquid crystal polyester comprising a structural unit represented by the following general formula (1) containing a 2,2'-biphenylene group and having a thermally polymerizable functional group bonded to a terminal structure:

(In formula (1), D ¹ and D ² may be the same or different and represent a divalent aliphatic hydrocarbon group, a divalent alicyclic hydrocarbon group, or a divalent aromatic hydrocarbon group, all or a part of D ¹ and D ² are cyclohexylene groups, and further, the molar ratio of cis isomers and trans isomers of the cyclohexane ring in the cyclohexylene group is 10/90 to 90/10, and E ¹ and E ² may be the same or different and represent an ester bond [-(C=O)O- or -O(C=O)-].) 2. The reactive liquid crystal ester according to claim 1, wherein the thermally polymerizable functional group is at least one type of thermally polymerizable functional group selected from the group consisting of a hydroxyl group, a carboxyl group, a styryl group, a (meth)acryloyl group, and an allyl group. 3. The reactive liquid crystal ester according to claim 1, wherein the thermally polymerizable functional group is at least one type of thermally polymerizable functional group selected from the group consisting of a styryl group, a (meth)acryloyl group, and an allyl group. 4. The reactive liquid crystal polyester according to claim 1 , wherein the molar ratio of the 2,2'-biphenylene group and the cyclohexylene group in the formula (1) is from 10/90 to 90/10. A polyester composition comprising the reactive liquid crystal polyester according to any one of claims 1 to 4 . 6. The polyester composition according to claim 5 , further comprising a compound (2) having a functional group reactive with the thermally polymerizable functional group. A polyester solution comprising the polyester composition according to claim 5 or 6 , and further comprising an aprotic polar solvent. A cured product obtained by reacting the polyester composition according to claim 5 or 6 .