Vinyl polymer, adhesive composition, adhesive, adhesive sheet, polymerizable composition, and method for producing vinyl polymer

Abstract

To provide: a vinyl polymer which has low melt viscosity even with high molecular weight and can obtain sufficient adhesive force and holding power when used as an adhesive composition after curing with active energy rays; an adhesive composition and an adhesive using the vinyl polymer; a method for producing the vinyl polymer; and a polymerizable composition.SOLUTION: A vinyl polymer contains: a structure derived from a specific chain transfer agent (A); a constituent unit derived from a monomer (B) which generates an active species by photoexcitation to form a crosslinked structure; and a constituent unit derived from a vinyl monomer (C) other than the monomer (B). The adhesive composition and the adhesive use the vinyl polymer. A method for producing the vinyl polymer includes a step (i) of polymerizing the polymerizable composition containing the chain transfer agent (A), the monomer (B), the vinyl monomer (C) and a polymerization initiator (D).SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a vinyl polymer, an adhesive composition, an adhesive, an adhesive sheet, a polymerizable composition, and a method for producing a vinyl polymer.

Background Art

[0002] In the fields of adhesion such as dicing related and adhesives, coating fields such as coating agents, inks and paints, and electronic material fields such as underfills, in order to meet various requirements such as improving the material performance that can withstand the use environment, simplifying the manufacturing process, and energy saving, materials, particularly polymer materials, have been developed. When using a general polymer (chain polymer) material as an adhesive or a paint, the polymer is often dissolved in a solvent to reduce its viscosity for use. On the other hand, a multi-branched polymer has a lower viscosity compared to a chain polymer of the same molecular weight, so that a solvent is not required or only a small amount is sufficient, and it is expected to be effective in reducing harmful volatile organic compounds (VOCs) in applications such as paints and adhesives. As a method for synthesizing such a multi-branched polymer, for example, a method using an addition-fragmentation chain transfer (AFCT) agent (Non-Patent Document 1, Patent Documents 1 and 2) and a method using catalytic chain transfer with cobalt (Patent Document 3) are known.

[0003] In recent years, as an adhesive composition that can be applied on a substrate and cured by irradiation with active energy rays, a composition containing a copolymer obtained by polymerizing an alkyl acrylate having an alkyl group having 1 to 4 carbon atoms, an unsaturated carboxylic acid such as acrylic acid, and a benzophenone derivative having a (meth)acryloyloxy group is known (Patent Document 4).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Document

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Generally, when adjusting the adhesive performance, the glass transition temperature, molecular weight, and molecular weight distribution are changed. In particular, when used as a coating agent that cures by irradiation with active energy rays, by increasing the molecular weight before curing, it can be cured more efficiently, so that the irradiation energy can be reduced. On the other hand, when using a high molecular weight polymer as a photocurable coating agent, there is a problem that the coating property is poor because the melt viscosity at the same temperature becomes high.

[0007] An object of the present invention is to provide a vinyl polymer having a low melt viscosity even at a high molecular weight, and a vinyl polymer that can obtain sufficient adhesive strength and holding power when used as an adhesive composition after curing with active energy rays, an adhesive composition using the vinyl polymer, and an adhesive. Another object of the present invention is to provide a method for producing the vinyl polymer and a polymerizable composition that can be used in such a production method.

Means for Solving the Problems

[0008] The present invention includes the following configurations. [1] A vinyl polymer comprising a structure derived from a chain transfer agent (A) represented by the following formula (1), a constitutional unit derived from a monomer (B) that generates active species upon photoexcitation and forms a crosslinked structure, and a constitutional unit derived from a vinyl monomer (C) other than the chain transfer agent (A) and the monomer (B). [Chemical formula] (In formula (1), R’ is a hydrogen atom, a halogen atom, -OC(=O)R”, -C(=O)NH 2 , -CN, -C(=O)OR”, or an aryl group. Y is -SR”, a halogen atom, -SO 2 R”, -P(=O)(OR”) 2 , -SnR” 3 , -SiR” 3、 or -C(=O)OR”. R” is each independently an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group.) [2] The vinyl polymer according to [1], wherein the mechanism for generating active species upon photoexcitation of the monomer (B) is a hydrogen abstraction type. [3] The vinyl polymer according to [1] or [2], wherein the monomer (B) is a monomer having at least one selected from the group consisting of a benzophenone skeleton, a thioxanthone skeleton, an anthraquinone skeleton, and skeletons derived therefrom. [4] The vinyl polymer according to any one of [1] to [3], having a weight average molecular weight of 20,000 to 700,000. [5] The vinyl polymer according to any one of [1] to [4], which is a vinyl polymer having a branched structure. [6] An adhesive composition containing the vinyl polymer according to any one of [1] to [5]. [7] An adhesive obtained by irradiating the adhesive composition according to [6] with active energy rays. [8] An adhesive comprising the adhesive composition according to [6] or [7]. [9] An adhesive sheet containing the adhesive according to [7] or [8].

[10] A polymerizable composition comprising a chain transfer agent (A) represented by the following formula (1), a monomer (B) that generates active species by photoexcitation and forms a crosslinked structure, a vinyl monomer (C) other than the chain transfer agent (A) and the monomer (B), and a polymerization initiator (D). [Chemical formula] (In formula (1), R’ is a hydrogen atom, a halogen atom, -OC(=O)R”, -C(=O)NH 2 , -CN, -C(=O)OR”, or an aryl group. Y is -SR”, a halogen atom, -SO 2 R”, -P(=O)(OR”) 2 , -SnR” 3 , -SiR” 3、 or -C(=O)OR”. Each R” is independently an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group.)

[11] A method for producing a vinyl polymer, comprising step (i) of subjecting a polymerizable composition comprising a chain transfer agent (A) represented by the following formula (1), a monomer (B) that generates active species by photoexcitation and forms a crosslinked structure, a vinyl monomer (C) other than the chain transfer agent (A) and the monomer (B), and a polymerization initiator (D) to polymerization. [Chemical formula] (In formula (1), R’ is a hydrogen atom, a halogen atom, -OC(=O)R”, -C(=O)NH 2 , -CN, -C(=O)OR”, or an aryl group. Y is -SR”, a halogen atom, -SO 2 R”, -P(=O)(OR”) 2 , -SnR” 3 , -SiR” 3、 or -C(=O)OR”. Each R” is independently an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group.)

[12] The method for producing a vinyl polymer according to

[11] , wherein the conversion rate of the vinyl monomer (C) in step (i) is 85% or more.

[13] The production method of the vinyl polymer according to

[11] or

[12] , wherein the content of the chain transfer agent (A) in the polymerizable composition is 0.01 to 10 parts by mass with respect to 100 parts by mass in total of the monomer (B) and the vinyl monomer (C).

[14] The production method of the vinyl polymer according to any one of

[11] to

[13] , wherein the weight average molecular weight of the vinyl polymer is 20,000 to 700,000.

[15] The production method of the vinyl polymer according to any one of

[11] to

[14] , wherein the vinyl polymer has a branched structure.

Advantages of the Invention

[0009] According to the present invention, there can be provided a vinyl polymer having a low melt viscosity even if it has a high molecular weight, and having sufficient adhesive force and holding force when used as an adhesive after curing by active energy rays, a pressure-sensitive adhesive composition using the vinyl polymer, and an adhesive. Further, according to the present invention, there can be provided a production method of the vinyl polymer and a polymerizable composition that can be used in such a production method.

Embodiments for Carrying Out the Invention

[0010] In the present invention, the numerical range represented by "~" means a numerical range including the numerical values before and after "~" as the lower limit value and the upper limit value, respectively. "(Meth)acryl" means acrylic or methacrylic. "(Meth)acrylate" means acrylate or methacrylate. "(Meth)acrylo" means acrylo or methacrylo. "Vinyl monomer" is a compound having a polymerizable double bond.

[0011] [Vinyl Polymer] The vinyl polymer according to the embodiment has a structure derived from the chain transfer agent (A), a structural unit derived from the monomer (B) (hereinafter, also simply referred to as "monomer (B)") that generates active species by photoexcitation and forms a crosslinked structure, and a structural unit derived from a vinyl monomer (C) other than the chain transfer agent (A) and the monomer (B). The following will be described in order.

[0012] (Chain transfer agent (A)) The chain transfer agent (A) is a compound represented by the following formula (1).

[0013] [Chemical formula]

[0014] In the above formula (1), R’ is a hydrogen atom, a halogen atom, -OC(=O)R”, -C(=O)NH 2 , -CN, -C(=O)OR”, or an aryl group. Y is -SR”, a halogen atom, -SO 2 R”, -P(=O)(OR”) 2 , -SnR” 3 , -SiR” 3、 or -C(=O)OR”. Each R” is independently an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group.)

[0015] Examples of the halogen atom in R’ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. As the halogen atom, a chlorine atom or a bromine atom is preferable. When R’ is a halogen atom, it shows an appropriate chain transfer constant value in the step (i) described later.

[0016] Examples of the aryl group in R’ include an aryl group having 6 to 18 carbon atoms. Examples of the aryl group having 6 to 18 carbon atoms include a phenyl group, a benzyl group, and a naphthyl group. The aryl group may have a substituent. Examples of the substituent include an alkyl group, an aryl group, a carboxy group, an alkoxycarbonyl group, a carbamoyl group, a cyano group, a hydroxy group, an amino group, an amide group, a halogen atom, an allyl group, an epoxy group, an alkoxy group, and a group showing hydrophilicity or ionicity. Examples of the group exhibiting hydrophilicity or ionic property include, for example, an alkali salt of a carboxy group, an alkali salt of a sulfoxy group, a poly(alkylene oxide) group such as a polyethylene oxide group and a polypropylene oxide group, and a cationic substituent such as a quaternary ammonium base.

[0017] Examples of the halogen atom in Y include, for example, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. As the halogen atom, a chlorine atom or a bromine atom is preferable. When Y is a halogen atom, it shows an appropriate value of the chain transfer constant in step (i) described later.

[0018] Examples of the alkyl group in R” include, for example, a linear or branched alkyl group having 1 to 20 carbon atoms. Specific examples of the linear or branched alkyl group having 1 to 20 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, a t-butyl group, an i-butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, and an icosyl group.

[0019] Examples of the cycloalkyl group in R” include, for example, a cycloalkyl group having 3 to 20 carbon atoms. Specific examples of the cycloalkyl group having 3 to 20 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, and an adamantyl group.

[0020] Examples of the aryl group in R” include, for example, an aryl group having 6 to 18 carbon atoms. Specific examples of the aryl group having 6 to 18 carbon atoms include a phenyl group, a benzyl group, and a naphthyl group.

[0021] Examples of the heterocyclic group in R” include heterocyclic groups having 5 to 18 carbon atoms containing an oxygen atom, a nitrogen atom or a sulfur atom as a hetero atom. Specific examples of the heterocyclic group include a γ-lactone group, an ε-caprolactone group and a morpholine group.

[0022] Note that the alkyl group, cycloalkyl group, aryl group and heterocyclic group in R” may have a substituent. Examples of the substituent include an alkyl group, an aryl group, a carboxy group, an alkoxycarbonyl group, a carbamoyl group, a cyano group, a hydroxy group, an amino group, an amide group, a halogen atom, an allyl group, an epoxy group, an alkoxy group, and a group exhibiting hydrophilicity or ionic property. Examples of the group exhibiting hydrophilicity or ionic property include an alkali salt of a carboxy group, an alkali salt of a sulfoxy group, a poly(alkylene oxide) group such as a polyethylene oxide group and a polypropylene oxide group, and a cationic substituent such as a quaternary ammonium base.

[0023] R” is preferably an alkyl group or a cycloalkyl group, more preferably an alkyl group, still more preferably a linear or branched alkyl group having 1 to 6 carbon atoms, and particularly preferably a linear alkyl group having 1 to 6 carbon atoms.

[0024] Examples of the chain transfer agent (A) include 2-(halomethyl)acrylic acid esters in which R” in R’ is a linear alkyl group having 1 to 6 carbon atoms, such as methyl 2-(bromomethyl)acrylate, ethyl 2-(bromomethyl)acrylate, and propyl 2-(bromomethyl)acrylate; and 2-(arylsulfonylmethyl)acrylic acid esters in which R” in R’ is a linear alkyl group having 1 to 6 carbon atoms, such as methyl 2-(phenylsulfonylmethyl)acrylate, ethyl 2-(phenylsulfonylmethyl)acrylate, and propyl 2-(phenylsulfonylmethyl)acrylate. Among them, 2-(halomethyl)acrylic acid esters and 2-(arylsulfonylmethyl)acrylic acid esters in which R” in R’ is a linear alkyl group having 1 to 6 carbon atoms are preferred, 2-(bromomethyl)acrylic acid esters and 2-(phenylsulfonylmethyl)acrylic acid esters in which R” in R’ is a linear alkyl group having 1 to 6 carbon atoms are more preferred, methyl 2-(bromomethyl)acrylate, ethyl 2-(bromomethyl)acrylate, propyl 2-(bromomethyl)acrylate, methyl 2-(phenylsulfonylmethyl)acrylate, propyl 2-(phenylsulfonylmethyl)acrylate, ethyl 2-(phenylsulfonylmethyl)acrylate, and methyl 2-(phenylsulfonylmethyl)acrylate are even more preferred, and ethyl 2-(bromomethyl)acrylate and methyl 2-(phenylsulfonylmethyl)acrylate are particularly preferred. These chain transfer agents (A) can be used alone or in combination of two or more.

[0025] (Other chain transfer agents) In the vinyl polymer according to the embodiment, other chain transfer agents may be used in combination with the chain transfer agent (A). That is, the vinyl polymer according to the embodiment may further have a structure derived from other chain transfer agents other than the chain transfer agent (A). As the other chain transfer agent, a chain transfer agent in which a growing terminal radical of the polymer extracts a hydrogen atom in the chain transfer agent molecule to generate a radical is preferred, such as -OH, -SH, -C(=O)OH, -NH 2 , -NHR 1, and -SO 3 A chain transfer agent having at least one group selected from the group consisting of H is more preferable. However, the above R 1 is an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group.

[0026] Examples of other chain transfer agents include mercapto group-containing chain transfer agents such as n-dodecyl mercaptan; secondary hydroxyl group-containing chain transfer agents such as isopropyl alcohol, etc. Other chain transfer agents can be used alone or in combination of two or more.

[0027] (Monomer (B) that generates active species by photoexcitation and forms a crosslinked structure) Monomer (B) generates active species by photoexcitation of active energy rays such as ultraviolet rays and electron beams, and forms a crosslinked structure. Examples of the active species include radicals, cations, and anions, and radicals are preferable from the viewpoint of reactivity.

[0028] The mechanism for generating active species by photoexcitation of monomer (B) is preferably of the hydrogen abstraction type. Examples of monomer (B) include monomers having at least one selected from the group consisting of a benzophenone skeleton, a thioxanthone skeleton, an anthraquinone skeleton, and skeletons derived therefrom. Since these skeletons include a benzophenone skeleton, an excited triplet state of the benzophenone skeleton is generated by photoexcitation, and a carbon radical A having a secondary hydroxyl group is formed by hydrogen abstraction from a hydrocarbon group. It is considered that this carbon radical A combines with a carbon radical B generated by hydrogen abstraction to form a crosslinked structure having a tertiary hydroxyl group and two phenyl groups at the crosslinking point. The crosslinked structure preferably contains, for example, a diphenylhydroxymethyl group. The phenyl group in the crosslinked structure may or may not have a substituent.

[0029] From the viewpoint of reactivity, the benzophenone derivative represented by the following formula (4) is preferable as monomer (B).

[0030]

Chem.

[0031] In formula (4), R A and R B each independently represent an alkyl group, an alkoxy group, a hydroxyl group, a carboxy group, or a halogen atom. n is an integer from 0 to 5. m is an integer from 0 to 4. X represents a (meth)acryloyloxy group or a (meth)acryloyloxyalkyleneoxy group.

[0032] R A and R B As the alkyl groups of R A and R B , linear or branched alkyl groups having 1 to 10 carbon atoms are preferred, and linear or branched alkyl groups having 1 to 5 carbon atoms are more preferred. As the alkoxy group, linear or branched alkoxy groups having 1 to 10 carbon atoms are preferred, and linear or branched alkoxy groups having 1 to 5 carbon atoms are more preferred. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. n is preferably an integer from 0 to 3, and more preferably 0. m is preferably an integer from 0 to 3, and more preferably 0.

[0033] As the alkylene group in the (meth)acryloyloxyalkyleneoxy group of X, an alkylene group having 2 to 10 carbon atoms is preferred, and an alkylene group having 2 to 6 carbon atoms is more preferred. Examples of the (meth)acryloyloxyalkyleneoxy group include a 2-(meth)acryloyloxyethoxy group, a 2-(meth)acryloyloxypropoxy group, and the like.

[0034] Examples of the monomer represented by the formula (4) include 4-acryloyloxybenzophenone, 4-methacryloyloxybenzophenone, 4-[2-(acryloyloxy)ethoxy]benzophenone, 4-[2-(methacryloyloxy)ethoxy]benzophenone, 2-hydroxy-4-acryloyloxybenzophenone, 2-hydroxy-4-methacryloyloxybenzophenone, 2-hydroxy-4-(2-acryloyloxy)ethoxybenzophenone, 2-hydroxy-4-(2-methyl-2-acryloyloxy)ethoxybenzophenone, 2-hydroxy-4-acryloyloxy-5-tert-butylbenzophenone, and 2-hydroxy-4-acryloyloxy-2',4'-dichlorobenzophenone. Among them, 4-methacryloyloxybenzophenone and 4-[2-(methacryloyloxy)ethoxy]benzophenone are preferred. As the monomer (B), one kind may be used alone, or two or more kinds may be used in combination.

[0035] (Vinyl monomer (C)) The vinyl monomer (C) is not particularly limited as long as it is a monomer other than the chain transfer agent (A) and the monomer (B), and a (meth)acrylate compound is preferred. Examples of the (meth)acrylate compound include alkyl (meth)acrylate having an alkyl group with 1 to 30 carbon atoms, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, glycidyl (meth)acrylate, methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate, ethoxyethoxyethyl (meth)acrylate, polyethylene glycol (meth)acrylate and its alkyl ether, benzyl (meth)acrylate, phenyl (meth)acrylate, 3-(triethoxysilyl)propyl (meth)acrylate, and 2-(dimethylamino)ethyl (meth)acrylate and its quaternary alkylammonium salt.

[0036] As the alkyl (meth)acrylate having an alkyl group with 1 to 30 carbon atoms, an alkyl (meth)acrylate having a linear or branched alkyl group with 1 to 10 carbon atoms is preferable, an alkyl acrylate having a linear or branched alkyl group with 1 to 10 carbon atoms is more preferable, an alkyl acrylate having a linear alkyl group with 1 to 6 carbon atoms and an alkyl acrylate having a branched alkyl group with 3 to 10 carbon atoms are particularly preferable, and n-butyl acrylate and 2-ethylhexyl acrylate are most preferable. These vinyl monomers (C) can be used alone or in combination of two or more.

[0037] In addition, the vinyl polymer according to the embodiment may contain a small amount of other structural units other than the structural units derived from the (meth)acrylate-based compound as long as the effects of the present invention are not impaired. The other structural units are not particularly limited as long as they are structural units derived from a vinyl monomer capable of radical polymerization. Examples of the vinyl monomer capable of radical polymerization include styrene-based monomers such as α-methylstyrene, vinyltoluene, and styrene, vinyl ether-based monomers such as methyl vinyl ether, ethyl vinyl ether, and isobutyl vinyl ether, fumaric acid, monoalkyl esters and dialkyl esters of fumaric acid, maleic acid, monoalkyl esters and dialkyl esters of maleic acid, itaconic acid, monoalkyl esters and dialkyl esters of itaconic acid, (meth)acrylonitrile, (meth)acrylamide, butadiene, isoprene, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl ketone, vinyl pyridine, and vinyl carbazole. These vinyl monomers capable of radical polymerization can be used alone or in combination of two or more.

[0038] The vinyl monomer (C) is preferably used such that the ratio (mol%) of the total number of moles of acrylic acid and acrylate compounds to the total number of moles of the vinyl monomer (C) is 50 mol% or more. Thereby, a vinyl polymer in which x described later is 50 mol% or more can be obtained. The ratio (mol%) of the total number of moles of acrylic acid and acrylate compounds to the total number of moles of the vinyl monomer (C) is more preferably 60 mol% or more, and even more preferably 70 mol% or more.

[0039] The vinyl polymer according to the embodiment preferably has a structure represented by the following formula (2).

[0040]

Chemical formula

[0041] The meanings of the symbols in formula (2) are as follows. R and R 1 ~R n are each independently a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group. Z is a group derived from a radical polymerization initiator, a group derived from the chain transfer agent (A), or a group derived from another chain transfer agent. X 1 ~X n are each independently a hydrogen atom, a methyl group, or a structure represented by formula (3), and at least one of X 1 ~X n is a structure represented by formula (3). R n and X n in, n is a natural number from 2 to 10,000.

[0042]

Chemical formula

[0043] The meanings of the symbols in formula (3) are as follows. R and R 1 ~R nis, independently of each other, a hydrogen atom, an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group, Z is a group derived from a radical polymerization initiator, a group derived from a chain transfer agent (A), or a group derived from another chain transfer agent, and X 1 ~X n is, independently of each other, a hydrogen atom, a methyl group, or a structure represented by the formula (3). R n and X n in which n is a natural number from 2 to 10,000.

[0044] R and R in the formula (2) 1 ~R n and R in the formula (3) 1 ~R n are independent of each other, and X in the formula (2) 1 ~X n and X in the formula (3) 1 ~X n are independent of each other.

[0045] Since at least one of X 1 ~X n in the formula (2) is a structure represented by the formula (3), the vinyl polymer according to the embodiment has a branched structure.

[0046] The fact that the vinyl polymer according to the embodiment has the structures represented by the formulas (2) and (3) means that in the 1 1H-NMR measurement of the vinyl polymer according to the embodiment, there are peaks with chemical shift values of 5.5 to 5.6 ppm and 6.1 to 6.2 ppm, and 13 in the 13C-NMR measurement, it can be confirmed that there is a peak with a chemical shift value of 38 to 41 ppm. Here, 1 The peaks with chemical shift values of 5.5 to 5.6 ppm and 6.1 to 6.2 ppm in the 1H-NMR measurement mean the presence of terminal double bonds in the vinyl polymer according to the embodiment. Also, 13 The peak with a chemical shift value of 38 to 41 ppm in the 13C-NMR measurement means that the vinyl polymer according to the embodiment has a branched structure represented by the formula (3).

[0047] In the vinyl polymer according to the embodiment, as shown in the formula (2), it is preferable that a terminal double bond is introduced. This terminal double bond has polymerizability and is useful because a graft copolymer can be easily synthesized by copolymerizing with a vinyl monomer.

[0048] The vinyl polymer according to the embodiment preferably has a structural unit derived from the monomer (B) and, as shown in the formulas (2) and (3), a structural unit derived from (meth) acrylic acid or a (meth) acrylate compound.

[0049] In the vinyl polymer according to the embodiment, in the formulas (2) and (3), X 1 ~X n When the ratio of the number of moles of hydrogen atoms to the total number of moles of hydrogen atoms and methyl groups contained in is x, x is preferably 50 mol% or more, more preferably 60 mol% or more, and even more preferably 70 mol% or more. When x is 50 mol% or more, the vinyl polymer according to the embodiment has a high degree of branching. Note that x is a value obtained from the charging ratio of acrylic acid and acrylate compounds in the monomer (B) and the vinyl monomer (C) which are raw materials.

[0050] The weight average molecular weight (Mw) of the vinyl polymer according to the embodiment is not particularly limited, but is preferably 20,000 to 700,000, more preferably 50,000 to 600,000, even more preferably 70,000 to 500,000, particularly preferably 100,000 to 400,000, and most preferably 150,000 to 350,000. By using such a vinyl polymer as a raw material, a molded body and a coating film excellent in elastic modulus and mechanical strength can be obtained. The weight average molecular weight is a value calculated by converting the value measured by gel permeation chromatography (GPC) into standard polystyrene conversion.

[0051] The 130 ° C melt viscosity, which is the melt viscosity at 130 ° C of the vinyl polymer according to the embodiment before curing, is preferably 10 to 300 Pa·s, more preferably 15 to 200 Pa·s, and even more preferably 20 to 150 Pa·s. When the solution viscosity of the vinyl polymer according to the embodiment is equal to or lower than the upper limit value, low viscosity can be achieved, resulting in excellent handleability. When the solution viscosity of the vinyl polymer according to the embodiment is equal to or higher than the lower limit value, the process suitability such as coating film formation becomes high. Note that the melt viscosity at 130 °C before curing can be measured by the method described in the examples.

[0052] The vinyl polymer according to the embodiment described above has a branched structure introduced by using the chain transfer agent (A), has a low melt viscosity even at a high molecular weight, and can be more efficiently photocrosslinked due to the increase in molecular weight. In addition, the vinyl polymer according to the embodiment can obtain sufficient adhesive strength and holding power. This is presumably because the vinyl polymer has a branched structure, and the reactive points are densely present compared to a linear polymer having the same composition and the same molecular weight, enabling more efficient curing.

[0053] [Polymerizable composition] The polymerizable composition according to the embodiment includes a chain transfer agent (A), a monomer (B), a vinyl monomer (C), and a polymerization initiator (D), and may also contain a solvent as necessary. By subjecting the polymerizable composition according to the embodiment to polymerization, the vinyl polymer according to the above-described embodiment can be obtained.

[0054] (Polymerization initiator (D)) The polymerization initiator (D) is not particularly limited, and conventionally known compounds can be used, but a radical polymerization initiator is preferred. Examples of the radical polymerization initiator include azo-based radical polymerization initiators and peroxide-based radical polymerization initiators.

[0055] Specific examples of the azo-based radical polymerization initiator include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile). Specific examples of the peroxide-based radical polymerization initiator include 2,4-dichlorobenzoyl peroxide, t-butyl peroxypivalate, o-methylbenzoyl peroxide, bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, t-butyl peroxy-2-ethylhexanoate, cyclohexanone peroxide, benzoyl peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, lauroyl peroxide, diisopropylbenzene hydroperoxide, t-butyl hydroperoxide, and di-t-butyl peroxide. The radical polymerization initiator may be used alone or in combination of two or more.

[0056] (Solvent) The solvent is not particularly limited. For example, alcohol solvents (such as methanol and ethanol), aromatic hydrocarbon solvents (such as toluene, ethylbenzene, xylene, and anisole), ketone solvents (such as acetone, methyl isobutyl ketone, and methyl ethyl ketone), and ester solvents (such as butyl acetate and ethyl acetate) can be mentioned. The solvent can be used alone or in combination of two or more.

[0057] (Composition of the polymerizable composition) The content of the chain transfer agent (A) in the polymerizable composition is preferably 0.01 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the vinyl monomer (C). When the content of the chain transfer agent (A) is at least the lower limit value, a branched structure can be appropriately introduced into the obtained vinyl polymer. When the content of the chain transfer agent (A) is at most the upper limit value, properties such as the elastic modulus, mechanical strength, and durability of the vinyl polymer can be sufficiently obtained.

[0058] The content of the monomer (B) in the polymerizable composition is preferably 0.001 to 30 parts by mass, more preferably 0.005 to 20 parts by mass, and even more preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the vinyl monomer (C).

[0059] The content of the polymerization initiator (D) in the polymerizable composition is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 5 parts by mass, and even more preferably 0.1 to 1 part by mass with respect to 100 parts by mass of the vinyl monomer (C). When the content of the polymerization initiator (D) is within the above range, an appropriate polymerization rate can be obtained in the step (i) described below.

[0060] The content of the solvent in the polymerizable composition is preferably 0 to 300 parts by mass, more preferably 10 to 200 parts by mass, and even more preferably 20 to 150 parts by mass with respect to 100 parts by mass of the vinyl monomer (C). When the content of the solvent is within the above range, an appropriate polymerization rate can be obtained in the step (i) described below, and the solution viscosity after the formation of the vinyl polymer is reduced, resulting in excellent handleability.

[0061] (Other additives) The polymerizable composition according to the embodiment may contain other additives. Examples of other additives include pigments, ultraviolet absorbers, release agents, defoaming agents, plasticizers, viscosity modifiers, etc. Known compounds can be used as these additives.

[0062] [Method for producing vinyl polymer] The method for producing a vinyl polymer according to the embodiment includes the following step (i). Step (i): A step of subjecting a polymerizable composition containing a chain transfer agent (A), a monomer (B), a vinyl monomer (C), and a polymerization initiator (D) to polymerization. Hereinafter, the step (i) will be described in detail.

[0063] [Step (i)] In the step (i), a polymerizable composition containing a chain transfer agent (A), a monomer (B), a vinyl monomer (C), and a polymerization initiator (D) is subjected to polymerization. The polymerizable composition may contain a solvent and other additives as necessary. According to the method for producing a vinyl polymer according to the embodiment, a vinyl polymer having a branched chain or a graft copolymer which is a vinyl polymer having a graft chain can be produced by the step (i).

[0064] As used herein, the "graft copolymer" is a polymer having one or more blocks connected as a side-chain polymer structure to a main-chain polymer structure. In a polymer having a branched chain, the structures of the main-chain polymer and the side-chain polymer may be different or the same. On the other hand, in a graft copolymer, the structures of the main-chain polymer and the side-chain polymer are different in the type (structure) of monomer units, or even if they are the same monomer units, the composition or sequence distribution is different.

[0065] Conventional methods for producing graft copolymers include, for example, a method in which a macromonomer having a radically polymerizable double bond at the end is produced as a side-chain polymer structure and then radically polymerized with a monomer that is a constituent unit of the main-chain polymer, a method in which a main-chain polymer having a reaction point and a macromonomer having a reaction point are produced in advance and then reacted, and a method in which after producing the main-chain polymer, a radical is generated on the main-chain polymer using an initiator having a hydrogen abstraction ability, and a monomer that is a constituent unit of the side-chain polymer is reacted to produce a side-chain polymer structure. Here, the "macromonomer" means a polymer having a radically polymerizable group or an addition-reactive functional group. Any of these methods requires two or more polymerization steps. In contrast, according to the method for producing a vinyl polymer according to the embodiment, a vinyl polymer having a branched chain or a graft chain can also be produced by only one-step polymerization step, that is, only by the step (i). The method for producing a vinyl polymer according to the embodiment may further include a polymerization step after the second step.

[0066] The polymerization method of the polymerizable composition is not particularly limited, and for example, conventionally known polymerization methods such as bulk polymerization method, solution polymerization method, suspension polymerization method, emulsion polymerization method can be used. The polymerization reaction may be carried out in the presence of air, but from the viewpoint of the efficiency of radical polymerization, it is preferably carried out in an inert gas atmosphere such as nitrogen or argon. As a method of carrying out in an inert gas atmosphere, known methods are used. For example, a method of blowing an inert gas into the polymerizable composition, a method of repeating freezing, degassing and melting can be used.

[0067] The polymerization temperature is not particularly limited, but from the viewpoint of the polymerization rate, it is preferably 0 to 150 ° C, more preferably 20 to 120 ° C. The polymerization time is not particularly limited, but it is preferably 0.5 to 48 hours, more preferably 4 to 48 hours.

[0068] From the viewpoint of improving the molecular weight and branching degree of the obtained vinyl polymer, the conversion rate of the vinyl monomer (C) in step (i) is preferably 85% or more, more preferably 90% or more, still more preferably 95% or more, and particularly preferably 98% or more. Here, the conversion rate (%) of the vinyl monomer (C) is determined from the measurement values of 1H-NMR measurement using a nuclear magnetic resonance apparatus (manufactured by JEOL Ltd., ECZ400S, 400 MHz) with CDCl 3 used 1 as the measurement solvent. Specifically, the conversion rate (%) of the vinyl monomer (C) can be calculated as the ratio of the integrated value of the peaks derived from the remaining vinyl monomer (C) to the integrated value of the peaks derived from the constitutional units derived from the vinyl monomer (C) in the produced vinyl polymer, using the integrated value of the peaks derived from the remaining vinyl monomer (C) and the integrated value of the peaks derived from the constitutional units derived from the vinyl monomer (C) in the produced vinyl polymer, with respect to the total amount of the remaining vinyl monomer (C) and the amount of the constitutional units derived from the vinyl monomer (C) in the produced vinyl polymer.

[0069] The vinyl polymer obtained in step (i) may be used mainly as a vinyl polymer or as an additive for other resins. When used mainly as a vinyl polymer, it can be used as various molded articles such as sheets, films, various housings and covers, and light guides as melt-moldable molding materials. It can also be used as a paint or an adhesive by coating after dissolving in a solvent.

[0070] When using a vinyl polymer as an additive for other resins, examples of the resin as the main component include acrylic resins such as polymethyl methacrylate, polyolefins, polyamides, unsaturated polyesters, saturated polyesters such as polyethylene terephthalate and polybutylene terephthalate, polycarbonates, polystyrenes, ABS resins, AS resins, polyvinyl chlorides, polylactic acids, polyvinylidene fluorides, and the like. Functions that the vinyl polymer imparts to other resins include flexibility, toughness, impact resistance, weather resistance, processability, mold release property, scratch resistance, surface hardness, compatibility, crystal size control, ductility, and the like. Examples of methods for mixing with other resins include physical mixing, melt mixing, and methods of dissolving or dispersing before polymerization or curing.

[0071] [Adhesive composition] The vinyl polymer according to the foregoing embodiment can be used in an adhesive composition. The adhesive composition according to the embodiment may further contain other components other than the vinyl polymer according to the foregoing embodiment. Other components that can be contained in the adhesive composition are not particularly limited, and examples thereof include solvents, fillers, crosslinking agents, tackifying resins, antioxidants, light stabilizers, metal deactivators, anti-aging agents, moisture absorbers, rust preventives, hydrolysis inhibitors, and reaction catalysts.

[0072] The adhesive composition according to the embodiment may be in the form of a liquid adhesive composition containing a solvent or in the form of a hot-melt type adhesive composition not containing a solvent.

[0073] [Adhesive, adhesive sheet] The adhesive according to the embodiment is an adhesive composed of the adhesive composition according to the embodiment. The adhesive according to the embodiment may use the adhesive composition according to the embodiment in an uncured state, or may be one cured by irradiating active energy rays. From the viewpoint of versatility, ultraviolet rays are preferable as the active energy rays.

[0074] The pressure-sensitive adhesive sheet according to the embodiment is a pressure-sensitive adhesive sheet containing the pressure-sensitive adhesive according to the embodiment, and has a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition according to the embodiment. The pressure-sensitive adhesive layer may be composed of the pressure-sensitive adhesive composition, or may be composed of a cured product obtained by irradiating the pressure-sensitive adhesive composition with ultraviolet rays. From the viewpoint of the handleability of the pressure-sensitive adhesive sheet, a pressure-sensitive adhesive layer composed of a cured product obtained by curing the pressure-sensitive adhesive composition with ultraviolet rays is preferable. The irradiation amount of ultraviolet rays is preferably 1 to 150 mJ / cm 2 and more preferably 5 to 100 mJ / cm 2 and even more preferably 10 to 50 mJ / cm 2 is even more preferable.

[0075] The pressure-sensitive adhesive sheet according to the embodiment may be in a form consisting only of a pressure-sensitive adhesive layer formed by shaping the pressure-sensitive adhesive composition according to the embodiment into a sheet shape, or may be in a form of a laminate in which a release substrate is laminated on one or both sides of a pressure-sensitive adhesive layer formed by shaping the pressure-sensitive adhesive composition according to the embodiment into a sheet shape. According to the embodiment

[0076] The thickness of the pressure-sensitive adhesive layer can be appropriately set according to the application, preferably 10 to 500 μm, and more preferably 20 to 100 μm.

[0077] The use of the pressure-sensitive adhesive sheet according to the embodiment is not particularly limited. For example, it can be used for bonding window films for vehicles, buildings, etc., bonding labels in label displays, bonding various panels in display displays such as liquid crystal panels, and bonding transparent plate materials such as glass.

Examples

[0078] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the examples described below, and various modifications are possible without departing from the gist of the present invention.

[0079] [Raw materials] The abbreviations of the raw materials used in the examples and comparative examples are shown below. (Chain transfer agent (A)) EBMA: Ethyl 2-(bromomethyl)acrylate (manufactured by Chemclear Co., Ltd.) ASME: Methyl 2-(benzenesulfonylmethyl)acrylate (produced in Production Example 1)

[0080] (Other chain transfer agents) IPA: Isopropyl alcohol (manufactured by Tokyo Chemical Industry Co., Ltd.)

[0081] (Monomer (B)) 4-ABP: 4-Acryloyloxybenzophenone (manufactured by Sino-biochemical Laboratory)

[0082] (Vinyl monomer (C)) nBA: n-Butyl acrylate (manufactured by Mitsubishi Chemical Corporation) AAc: Acrylic acid (manufactured by Mitsubishi Chemical Corporation)

[0083] (Polymerization initiator (D)) AIBN: 2,2’-Azobis(isobutyronitrile) (manufactured by Fujifilm Wako Pure Chemical Corporation)

[0084] [Measurement method and evaluation method] <Weight-average molecular weight of vinyl polymer> The weight-average molecular weight of the vinyl polymer was measured using gel permeation chromatography (GPC) (HLC-8320 manufactured by Tosoh Corporation). After preparing a 0.2 mass% tetrahydrofuran solution of the vinyl polymer, 10 μL of the solution was injected into an apparatus equipped with columns manufactured by Tosoh Corporation (TSKgel SuperHZM-M (inner diameter 4.6 mm, length 15 cm), HZM-M (inner diameter 4.6 mm, length 15 cm), HZ-2000 (inner diameter 4.6 mm, length 15 cm), TSKguardcolumn SuperHZ-L (inner diameter 4.6 mm, length 3.5 cm)). The measurement was carried out under the conditions of a flow rate of 0.35 mL / min, an eluent of tetrahydrofuran (stabilizer BHT), and a column temperature of 40°C, and the weight-average molecular weight (Mw) was calculated in terms of standard polystyrene conversion.

[0085] <Conversion rate of vinyl monomer (C)> The conversion rate (%) of the vinyl monomer (C) was determined from the measurement values of 1H-NMR measurement using a nuclear magnetic resonance apparatus (manufactured by JEOL Ltd., ECZ400S, 400 MHz) with CDCl 3 used as the measurement solvent. 1 Specifically, it was calculated as the ratio of the amount of the structural unit derived from the vinyl monomer (C) in the generated vinyl polymer to the total of the amount of the remaining vinyl monomer (C) and the amount of the structural unit derived from the vinyl monomer (C) in the generated vinyl polymer, using the integrated value of the peaks derived from the remaining vinyl monomer (C) and the integrated value of the peaks derived from the structural unit derived from the vinyl monomer (C) in the generated vinyl polymer.

[0086] <Melt viscosity at 130 °C> The vinyl polymer composition obtained in each example was diluted with ethyl acetate so that the solid content became 33.3% by mass, and it was visually confirmed that there was no undissolved polymer, and a resin composition in a liquid state at normal temperature (23 °C) was obtained. The resin composition was applied onto a PET film subjected to a peeling treatment with an applicator and dried at 90 °C for 1 hour to form an adhesive layer with a thickness of 50 μm. The melt viscosity of the adhesive layer was measured using a viscoelasticity measuring device HAAKE MARS. The viscosity (η*) value measured at 130 °C and a frequency of 0.02 Hz using a cone plate with a diameter of 35 mm was taken as the value of the melt viscosity at 130 °C before irradiation.

[0087] <Adhesive strength> The peeled PET of the adhesive test piece obtained in each example was peeled off to expose the adhesive layer, and it was bonded to a 30 mm × 110 mm stainless steel (SUS) plate using a 3 kg hand roller so that the bonding surface became 25 mm × 70 mm. The peel strength (N / 25 mm) with respect to the SUS plate was measured at a peel angle of 180° and a tensile speed of 300 mm / min and taken as the adhesive strength. When measuring the adhesive strength, the case where the adhesive layer could be peeled at the interface between the two adhesive surfaces and there was no roughness on the peeled surface was defined as "interface peeling", and the case where the interface between the two adhesives became unclear, the adhesive layer was broken, and irregularities occurred on the peeled surface, resulting in a fish-scale-like appearance was defined as "cohesive failure".

[0088] <Retention force> At one end of the adhesion test piece obtained in each example, the release PET was peeled off to expose the adhesive layer, and it was horizontally bonded to a 30 mm × 110 mm SUS plate using a 3 kg hand roller so that the bonding surface was 25 mm × 25 mm. It was left in a thermo-hygrostat test machine at a temperature of 80 °C for 15 minutes. Immediately after that, the SUS plate was installed so that a force was applied in the shear direction to the bonding surface, a 1.0 kg load was applied with the other end of the test piece facing down, and the holding time was measured and used as the holding force. The holding time was measured with a maximum of 24 hours. In the table, the examples where the holding time reached the upper limit are described as "24<".

[0089] [Production Example 1: Synthesis of ASME] Methyl methacrylate (48.06 g, 480.0 mmol) and methanol (252.8 g) were placed in a 2.0 L separable flask, cooled to 0 °C, and then iodine (144.2 g, 568.0 mmol) and sodium benzenesulfinate dihydrate (201.8 g, 1008 mmol) were added little by little and stirred at room temperature for 5 hours. Next, dichloromethane (800.0 mL) was added for dilution, saturated aqueous sodium carbonate solution (160.0 mL) and 5% aqueous sodium bisulfite solution (160.0 mL) were added, and after liquid separation, 30.00 g of magnesium sulfate was added to the organic layer for drying, and then the solvent was distilled off. Next, dichloromethane (280.0 mL) was added, triethylamine (97.14 g, 960.0 mmol) was added dropwise over 30 minutes, and then stirred at room temperature for 2 hours. Next, after distilling off the solvent, column chromatography was performed using silica gel (3.000 kg) to obtain 61.00 g of white solid ASME.

[0090] [Production Example 2] [Preparation of Vinyl Polymer] To a 250 mL separable flask, 2.50 parts by mass of EBMA as a chain transfer agent (A), 0.13 parts by mass of 4-ABP as a monomer (B), 94.8 parts by mass of nBA as a vinyl monomer (C), 5.0 parts by mass of AAc, 0.31 parts by mass of AIBN as a polymerization initiator (D), and 102.5 parts by mass of ethyl acetate as a solvent were added. The temperature was raised to 65 °C and stirred for 2 hours. Then the temperature was raised to 70 °C and stirred for 4 hours. Then, after cooling to room temperature, the obtained resin composition was recovered from the flask to obtain a vinyl polymer composition (P-1). The conversion rate of the vinyl monomer (C) and the evaluation results of the obtained vinyl polymer composition (P-1) are shown in Table 1.

[0091] [Production Examples 3-8] A polymerizable composition was prepared in the same manner as in Production Example 1 except that the amounts of the chain transfer agent (A), other chain transfer agents, monomer (B), and vinyl monomer (C) were changed as shown in Table 1, and this was subjected to polymerization to obtain vinyl polymer compositions (P-2) to (P-7). The conversion rate of the vinyl monomer (C) and the evaluation results of the obtained vinyl polymer compositions (P-2) to (P-7) are shown in Table 1.

[0092]

Table 1

[0093] [Example 1] The vinyl polymer composition (P-1) was diluted with ethyl acetate so that the solid content was 33.3% by mass, and it was visually confirmed that there was no undissolved polymer, and a resin composition in a liquid state at room temperature (23 °C) was obtained. Next, the resin composition was coated on a PET film with a thickness of 38 μm using an applicator and dried at 90 °C for 1 hour to form an adhesive layer. Using an 85 mW high-pressure mercury lamp, ultraviolet rays (UV-C) were irradiated onto the PET film (PET) on which the adhesive layer was formed in air to cure the adhesive layer. The UV-C irradiation dose was 35 mJ / cm 2(Measured values obtained using an integrated light quantity meter UV POWER PUCK II (S / N 13685, manufactured by EIT, USA)). A peeled PET film (peeled PET) was overlaid on its upper surface to obtain a laminate having a structure of peeled PET - adhesive layer - PET. The thickness of the adhesive layer was 50 μm. The cured laminate was cut into strips with a width of 25 mm and a length of 250 mm to obtain adhesive test pieces. The evaluation results of the obtained adhesive test pieces are shown in Table 2.

[0094] [Examples 2 - 5, Comparative Examples 1 - 3] Adhesive test pieces were obtained in the same manner as in Example 1, except that the vinyl polymer composition used was changed as described in Table 2. The evaluation results of the obtained adhesive test pieces are shown in Table 2.

[0095]

Table 2

[0096] All of the adhesive test pieces obtained in Examples 1 - 5 had a low melt viscosity before curing and exhibited both good adhesive strength and high holding power after curing. On the other hand, for the adhesive test pieces obtained in Comparative Examples 1 - 3, although they had the same composition ratio and molecular weight as the vinyl copolymers in Examples 1 - 5 because a chain transfer agent with a different structure was added instead of chain transfer agent (A) during the production of the vinyl polymer, their melt viscosity was high. If the melt viscosity is too high, it is inferior in handleability and thus not industrially preferable. In particular, in Comparative Example 3, adhesive residue due to cohesive failure occurs and it is inferior in holding power compared to Example 5 with the same composition, so it is not suitable for use as an adhesive.

Claims

1. A vinyl polymer comprising: a structure derived from a chain transfer agent (A) represented by the following formula (1); a constituent unit derived from a monomer (B) that generates an active species upon photoexcitation and forms a crosslinked structure; and a constituent unit derived from a vinyl monomer (C) other than the chain transfer agent (A) and the monomer (B). 【Chemistry 1】 In formula (1), R' is a hydrogen atom, a halogen atom, -OC(=O)R", -C(=O)NH ２ , -CN, -C(=O)OR", or an aryl group. Y is -SR", a halogen atom, -SO ２ R”, ​​-P (=O) (OR”) ２ , -SnR" ３ , -SiR ３、 or -C(=O)OR", where each R" is independently an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group.

2. 2. The vinyl polymer according to claim 1, wherein a mechanism for generating an active species by photoexcitation of the monomer (B) is a hydrogen abstraction mechanism.

3. 3. The vinyl polymer according to claim 1, wherein the monomer (B) is a monomer having at least one skeleton selected from the group consisting of a benzophenone skeleton, a thioxanthone skeleton, an anthraquinone skeleton, and skeletons derived therefrom.

4. 3. The vinyl polymer according to claim 1, having a weight average molecular weight of 20,000 to 700,000.

5. 3. The vinyl polymer according to claim 1, which is a vinyl polymer having a branched structure.

6. A pressure-sensitive adhesive composition comprising the vinyl polymer according to claim 1 .

7. A pressure-sensitive adhesive obtained by irradiating the pressure-sensitive adhesive composition according to claim 6 with active energy rays.

8. A pressure-sensitive adhesive comprising the pressure-sensitive adhesive composition according to claim 6.

9. A pressure-sensitive adhesive sheet comprising the pressure-sensitive adhesive according to claim 7 or 8.

10. A polymerizable composition comprising: a chain transfer agent (A) represented by the following formula (1); a monomer (B) that generates an active species upon photoexcitation and forms a crosslinked structure; a vinyl monomer (C) other than the chain transfer agent (A) and the monomer (B); and a polymerization initiator (D). 【Chemistry 2】 In formula (1), R' is a hydrogen atom, a halogen atom, -OC(=O)R", -C(=O)NH ２ , -CN, -C(=O)OR", or an aryl group. Y is -SR", a halogen atom, -SO ２ R”, ​​-P (=O) (OR”) ２ , -SnR" ３ , -SiR ３、 or -C(=O)OR", where each R" is independently an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group.

11. A method for producing a vinyl polymer, comprising: a step (i) of subjecting a polymerizable composition to polymerization, the polymerizable composition comprising: a chain transfer agent (A) represented by the following formula (1); a monomer (B) that generates an active species upon photoexcitation to form a crosslinked structure; a vinyl monomer (C) other than the chain transfer agent (A) and the monomer (B); and a polymerization initiator (D): 【Chemistry 3】 In formula (1), R' is a hydrogen atom, a halogen atom, -OC(=O)R", -C(=O)NH ２ , -CN, -C(=O)OR", or an aryl group. Y is -SR", a halogen atom, -SO ２ R”, ​​-P (=O) (OR”) ２ , -SnR" ３ , -SiR ３、 or -C(=O)OR", where each R" is independently an alkyl group, a cycloalkyl group, an aryl group, or a heterocyclic group.

12. The method for producing a vinyl polymer according to claim 11, wherein the conversion rate of the vinyl monomer (C) in the step (i) is 85% or more.

13. The method for producing a vinyl polymer according to claim 11 or 12, wherein the content of the chain transfer agent (A) in the polymerizable composition is 0.01 to 10 parts by mass per 100 parts by mass of the total of the monomer (B) and the vinyl monomer (C).

14. The method for producing a vinyl polymer according to claim 11 or 12, wherein the weight average molecular weight of the vinyl polymer is from 20,000 to 700,000.

15. The method for producing a vinyl polymer according to claim 11 or 12, wherein the vinyl polymer has a branched structure.

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