JP4407313B2 - Fluorine-containing compound, fluorine-containing polymer and production method thereof - Google Patents

Description

  The present invention relates to a novel fluorine-containing compound, a fluorine-containing polymer and a method for producing the same.

  As the fluorine-containing polymer having a functional group, functional group-containing fluorine-containing polymers used for fluorine-based ion exchange membranes and curable fluorine resin coatings are known, but these are all linear polymers having a basic skeleton. And obtained by copolymerization of a fluoroolefin typified by tetrafluoroethylene and a monomer having a functional group.

  Polymers containing a functional group and having a fluorinated alicyclic structure in the main chain are also known. As a method for introducing a functional group into a polymer having a fluorinated alicyclic structure in the main chain, polymerization may be used. A method using terminal groups of the obtained polymer, a method in which a polymer is treated at a high temperature to oxidatively decompose the side chain or terminal of the polymer to form a functional group, a monomer having a functional group is copolymerized, and if necessary For example, a method of introducing a product by adding a treatment such as hydrolysis is known (see, for example, Patent Documents 1, 2, 3, and 4).

  As a method for introducing a functional group into a polymer having a fluorinated aliphatic ring structure in the main chain, there is the method described above, but in the method of introducing a functional group by treating the terminal group of the polymer, the functional group concentration is low, There is a disadvantage that sufficient functional group characteristics cannot be obtained. Further, in the method of introducing a monomer having a functional group by copolymerization, if the functional group concentration is increased, problems such as a decrease in mechanical properties due to a decrease in glass transition temperature (Tg) occur.

Japanese Patent Laid-Open No. 4-189880 JP-A-4-226177 JP-A-6-220232 International Publication No. 02/064648 Pamphlet

The problem to be solved by the present invention is to provide a fluorine-containing compound, a fluorine-containing polymer and a method for producing the same, which have a high functional group concentration and can obtain sufficient functional group characteristics and have high transparency in a wide wavelength range. That is. Furthermore, as a chemically amplified resist, in particular, it has excellent transparency to dry ultraviolet rays such as KrF and ArF excimer lasers and vacuum ultraviolet rays such as F ₂ excimer lasers, dry etching properties, and also excellent sensitivity, resolution dissolution rate, flatness, etc. It is to provide a base polymer for a photoresist composition that provides a resist pattern.

  The present invention is the following invention which has been made to solve the above-mentioned problems.

The present invention provides a fluorinated diene represented by the following formula (1).
CF ₂ = CFCH ₂ CH (C (CF ₃ ) ₂ OH) CH ₂ CR ¹ = CHR ² (1) where R ¹ and R ² are each independently a hydrogen atom, an alkyl group having 10 or less carbon atoms, Or a cyclic aliphatic hydrocarbon group, at least one of which is a cyclic aliphatic hydrocarbon group.

  The present invention provides a fluorine-containing polymer (A) having a monomer unit obtained by cyclopolymerization of the fluorine-containing diene represented by the above formula (1) and a method for producing the same.

  According to the present invention, a fluoropolymer having an aliphatic ring structure in the main chain and a hydroxyl group in the side chain can be produced. The fluorine-containing polymer obtained by the present invention has high chemical stability and heat resistance. In addition, since hydroxyl groups are introduced into the side chains, sufficient hydroxyl characteristics can be expressed without causing a decrease in Tg, which has been difficult to achieve with conventional fluoropolymers. In particular, since the ring side chain has a highly acidic hydroxyl group, the solubility in an alkaline aqueous solution is improved. Furthermore, it has high transparency in a wide wavelength region.

According to the present invention, a fluorine-containing diene represented by the following general formula (1) (hereinafter referred to as fluorine-containing diene (1)), a fluorine-containing polymer (A And a manufacturing method thereof.
CF ₂ = CFCH ₂ CH (C (CF ₃ ) ₂ OH) CH ₂ CR ¹ = CHR ² (1)
In the formula (1), R ¹ and R ² each independently represent a hydrogen atom, an alkyl group having 10 or less carbon atoms, or a cyclic aliphatic hydrocarbon group, at least one of which is a cyclic aliphatic hydrocarbon group Represents.

A part of carbon atoms in the alkyl group may be substituted with a hetero atom or a carbonyl group, and a part of hydrogen atoms in the alkyl group may be substituted with a fluorine atom, an alkyl group or a fluoroalkyl group. Good.
The cycloaliphatic hydrocarbon group is preferably a hydrocarbon group having at least one cyclic structure, and more preferably a saturated hydrocarbon group having at least one cyclic structure. Further, the cycloaliphatic hydrocarbon group is preferably a cycloaliphatic hydrocarbon group having 4 or more carbon atoms, more preferably a saturated hydrocarbon group having 4 or more carbon atoms, and a saturated hydrocarbon having 4 to 10 carbon atoms. A hydrogen group is particularly preferred. Specifically, monocyclic saturated hydrocarbon groups such as cyclobutyl group, cycloheptyl group and cyclohexyl group as shown below, bicyclic saturated hydrocarbon groups such as 4-cyclohexylcyclohexyl group, and 1-decahydronaphthyl group Or a polycyclic saturated hydrocarbon group such as 2-decahydronaphthyl group, a bridged cyclic saturated hydrocarbon group such as 1-norbornyl group and 1-adamantyl group, and a spiro hydrocarbon group such as spiro [3.4] octyl group. Etc.

  In addition, a part of the carbon atoms of the cycloaliphatic hydrocarbon group may be substituted with a heteroatom such as an oxygen atom, a nitrogen atom, or a sulfur atom or a carbonyl group, and one of the hydrogen atoms of the cycloaliphatic hydrocarbon group may be substituted. Part may be substituted with a fluorine atom, an alkyl group (preferably having 1 to 6 carbon atoms) or a fluoroalkyl group (preferably having 1 to 6 carbon atoms).

The fluorine-containing diene of the present invention can be synthesized by a known method. For example, using CH ₂ ═CHC (CF ₃ ) ₂ OH as a starting material and adding a CF ₂ ClCFClI to a double bond in the presence of a radical initiator to make CF ₂ ClCFClCH ₂ CHIC (CF ₃ ) ₂ OH, CH ₂ = C _(Cy) is reacted with CH 2 MgCl (Grignard _{reagent), CF 2 ClCFClCH 2 CH (} C (CF 3) 2 OH) was a CH 2 C (Cy) = CH 2, be dechlorinated Can be obtained. Here, Cy represents a cyclic aliphatic hydrocarbon group. By using a Grignard reagent having various structures instead of the Grignard reagent, various fluorine-containing dienes (1) can be obtained as follows.

  Specific examples of the fluorine-containing diene (1) of the present invention include the following dienes including the above-mentioned dienes, but are not limited thereto.

  The fluorinated diene (1) is cyclized and polymerized under relatively mild conditions to obtain a cyclized polymer having a hydroxyl group in the side chain of the ring produced by the polymerization.

  It is considered that the following monomer units (a) to (c) are generated by cyclopolymerization of the fluorinated diene (1). From the results of spectroscopic analysis and the like, the fluoropolymer (A) is a polymer having a structure containing one or more monomer units selected from the monomer unit (a), the monomer unit (b), and the monomer unit (c); Conceivable.

The fluorine-containing polymer (A) is a monomer unit in which the hydroxyl group of the monomer unit (1) is blocked in addition to the monomer unit obtained by cyclopolymerization of the fluorine-containing diene (1) (hereinafter referred to as the monomer unit (1)). (Hereinafter referred to as a blocked monomer unit (1)). The proportion of the blocked monomer unit (1) is preferably 50 mol% or less, particularly preferably 15 to 40 mol%, based on the total of the monomer unit (1) and the blocked monomer unit (1). Blocking refers to replacing a hydrogen atom of a hydroxyl group with a blocking group. Specific examples of the blocked hydroxyl group include OCH ₃ , OCF ₃ , O (t—C ₄ H ₉ ), OCH ₂ OCH ₃ , OCH ₂ OC ₂ H ₅ , OCH ₂ OCH ₂ CF ₃ , OCOO (t _{-C 4 H 9), OCH (} CH 3) OC 2 H 5, include those shown in 2-tetrahydropyranyloxy group, and the following.

  The fluorine-containing polymer (A) having the monomer unit (1) and the blocked monomer unit (1) comprises a blocked fluorine-containing diene obtained by blocking the hydroxyl group of the fluorine-containing diene (1), and a fluorine-containing diene ( It can be obtained by copolymerizing 1). It can also be obtained by blocking part of the hydroxyl group of the monomer unit (1) of the fluoropolymer (A) having the monomer unit (1).

  The fluorine-containing polymer (A) contains, in addition to the monomer unit (1), monomer units derived from other radical polymerizable monomers (excluding the blocked monomer unit (1)) as long as the characteristics thereof are not impaired. But you can. Hereinafter, other radical polymerizable monomers are referred to as other monomers. The proportion of monomer units derived from other monomers is preferably 50 mol% or less, particularly preferably 15 mol% or less.

  Examples of other monomers that can be exemplified include α-olefins such as ethylene, propylene, and isobutylene, fluorine-containing olefins such as tetrafluoroethylene and hexafluoropropylene, and perfluoro (2,2-dimethyl-1,3-dioxole). Fluorine-containing cyclic monomers, perfluorodienes capable of cyclopolymerization such as perfluoro (butenyl vinyl ether), 1,1,2,3,3-pentafluoro-4-trifluoromethyl-4-hydroxy-1, Hydrofluorodienes such as 6-heptadiene and 1,1,2-trifluoro-4- [3,3,3-trifluoro-2-hydroxy-2-trifluoromethylpropyl] -1,6-heptadiene, acrylic Acrylic esters such as methyl acid and ethyl methacrylate, vinyl acetate, vinyl benzoate, Vinyl esters such as vinyl adamantyl acid, ethyl vinyl ether and cyclohexyl vinyl ether, cyclohexene, norbornene, cyclic olefins such as norbornadiene, maleic anhydride, and vinyl chloride.

The fluorine-containing polymer (A) of the present invention can be obtained by copolymerizing the fluorine-containing diene (1) with another monomer that can be homopolymerized or copolymerized under a polymerization initiation source. The polymerization initiation source is not particularly limited as long as the polymerization reaction proceeds radically, and examples thereof include a radical generator, light, and ionizing radiation. In particular, radical generators are preferred, and examples of radical generators include peroxides, azo compounds, and persulfates. Of these, the following peroxides are preferred.
_{C 6 H 5 -C (O)} O-OC (O) -C 6 H 5
_{C 6 F 5 -C (O)} O-OC (O) -C 6 F 5
_{C 3 F 7 -C (O)} O-OC (O) -C 3 F 7
_{(CH 3) 3 C-C} (O) O-OC (O) -C (CH 3) 3
_{(CH 3) 2 CH-C} (O) O-OC (O) -CH (CH 3) 2
_{(CH 3) 3 C-C} 6 H 10 -C (O) O-OC (O) -C 6 H 10 -C (CH 3) 3

  The polymerization method is not particularly limited, and the so-called bulk polymerization in which the monomer is directly subjected to polymerization, fluorinated hydrocarbon, chlorinated hydrocarbon, fluorinated chloride capable of dissolving or dispersing the fluorinated diene (1) and other monomers. Solution polymerization performed in hydrocarbons, alcohols, hydrocarbons and other organic solvents, suspension polymerization performed in the presence or absence of a suitable organic solvent in an aqueous medium, emulsion polymerization performed by adding an emulsifier to an aqueous medium, etc. Is exemplified.

  The temperature and pressure at which the polymerization is carried out are not particularly limited, but are preferably set appropriately in consideration of various factors such as the boiling point of the monomer, the heating source, and the removal of the polymerization heat. For example, a suitable temperature can be set between 0 ° C. and 200 ° C., and a practically suitable temperature can be set if it is about room temperature to 100 ° C. The polymerization pressure may be reduced or increased. Practically, suitable polymerization can be carried out even at atmospheric pressure to about 100 atm, and even at atmospheric pressure to about 10 atm.

  The molecular weight of the fluorine-containing polymer (A) of the present invention is not particularly limited as long as it can be uniformly dissolved in the organic solvent (C) described later and can be uniformly applied to the substrate, but the number average molecular weight in terms of polystyrene is usually 1,000. From 100,000 to 100,000 is suitable, and preferably from 2,000 to 30,000. If the number average molecular weight is 1,000 or more, the resulting resist pattern may be defective, the remaining film ratio after development may decrease, or the shape stability during pattern heat treatment may decrease. There is little nature. Moreover, when the number average molecular weight is 100,000 or less, the coating property of the resist composition described later can be kept good, and good developability can be maintained.

  The fluorine-containing polymer (A) of the present invention can be used as a base polymer for photoresist. It can be used as a resist composition by preparing a composition containing a fluorine-containing polymer (A), an acid-generating compound (B) that generates an acid upon irradiation with light, and an organic solvent (C). Hereinafter, taking the fluorine-containing polymer (A) having the monomer unit (1) and the blocked monomer unit (1) as a preferred embodiment of the fluorine-containing polymer (A) as an example, the fluorine-containing polymer (A) is used as the base polymer. The resist composition (hereinafter referred to as resist composition (D)) will be described in detail.

  The acid generating compound (B) that generates an acid upon irradiation with light generates an acid upon exposure. With this acid, part or all of the blocking groups of the blocked monomer units in the fluoropolymer (A) are cleaved (deblocked). As a result, the exposed portion becomes readily soluble in an alkaline developer, and a positive resist pattern can be formed with the alkaline developer. As the acid generating compound (B) that generates an acid upon receiving such light irradiation, an acid generating compound that is used in a normal chemically amplified resist material can be employed, and an onium salt, a halogen-containing compound, a diazoketone. A compound, a sulfone compound, a sulfonic acid compound, etc. can be mentioned. Examples of these acid generating compounds (B) include the following.

  Examples of onium salts include iodonium salts, sulfonium salts, phosphonium salts, diazonium salts, pyridinium salts, and the like. Specific examples of preferred onium salts include diphenyliodonium triflate, diphenyliodonium pyrenesulfonate, diphenyliodonium dodecylbenzenesulfonate, bis (4-tert-butylphenyl) iodonium triflate, bis (4-tert-butylphenyl) iodonium dodecylbenzene. Sulfonate, triphenylsulfonium triflate, triphenylsulfonium nonanate, triphenylsulfonium perfluorooctane sulfonate, triphenylsulfonium hexafluoroantimonate, 1- (naphthylacetomethyl) thiolanium triflate, cyclohexylmethyl (2-oxocyclohexyl) Sulfonium triflate, dicyclohexyl (2-oxocyclohexyl) Honium triflate, dimethyl (4-hydroxynaphthyl) sulfonium tosylate, dimethyl (4-hydroxynaphthyl) sulfonium dodecylbenzenesulfonate, dimethyl (4-hydroxynaphthyl) sulfonium naphthalenesulfonate, triphenylsulfonium camphorsulfonate, (4-hydroxyphenyl) ) Benzylmethylsulfonium toluenesulfonate and the like.

  Examples of the halogen-containing compound include a haloalkyl group-containing hydrocarbon compound and a haloalkyl group-containing heterocyclic compound. Specific examples include (trichloromethyl) -s- such as phenyl-bis (trichloromethyl) -s-triazine, methoxyphenyl-bis (trichloromethyl) -s-triazine, and naphthyl-bis (trichloromethyl) -s-triazine. Examples include triazine derivatives and 1,1-bis (4-chlorophenyl) -2,2,2-trichloroethane.

  Examples of the sulfone compound include β-ketosulfone, β-sulfonylsulfone, and α-diazo compounds of these compounds. Specific examples include 4-trisphenacylsulfone, mesitylphenacylsulfone, bis (phenylsulfonyl) methane, and the like. Examples of the sulfonic acid compounds include alkyl sulfonic acid esters, alkyl sulfonic acid imides, haloalkyl sulfonic acid esters, aryl sulfonic acid esters, and imino sulfonates. Specific examples include benzoin tosylate and 1,8-naphthalenedicarboxylic imide triflate. The acid generating compound (B) can be used alone or in admixture of two or more.

  The organic solvent (C) is not particularly limited as long as it dissolves both the fluorine-containing polymer (A) and the acid-generating compound (B). Alcohols such as methyl alcohol and ethyl alcohol, ketones such as acetone, methyl isobutyl ketone and cyclohexanone, acetates such as ethyl acetate and butyl acetate, aromatic hydrocarbons such as toluene and xylene, propylene glycol monomethyl ether, propylene glycol Examples include glycol monoalkyl ethers such as monoethyl ether, and glycol monoalkyl ether esters such as propylene glycol monomethyl ether acetate and carbitol acetate.

  The proportion of each component in the resist composition (D) is usually 0.1 to 20 parts by mass of the acid generating compound (B) and 50 to 2000 parts by mass of the organic solvent (C) with respect to 100 parts by mass of the fluoropolymer (A). Is appropriate. Preferably, they are 0.1-10 mass parts of acid generating compounds (B) and 100-1000 mass parts of organic solvent (C) with respect to 100 mass parts of fluoropolymer (A).

  By setting the amount of the acid generating compound (B) used to be 0.1 parts by mass or more, sufficient sensitivity and developability can be given, and by setting it to 10 parts by mass or less, the transparency to radiation is sufficient. Thus, a more accurate resist pattern can be obtained.

  The resist composition (D) has an acid-cleavable additive for improving the pattern contrast, a surfactant for improving the coating property, a nitrogen-containing basic compound for adjusting the acid generation pattern, and adhesion to the substrate. In order to improve the property, an adhesion assistant, a storage stabilizer or the like can be appropriately blended depending on the purpose in order to improve the storage stability of the composition. The resist composition of the present invention is preferably used after being uniformly mixed with each component and then filtered through a 0.1 to 2 μm filter.

  A resist film is formed by applying and drying the resist composition (D) on a substrate such as a silicone wafer. As the coating method, spin coating, flow coating, roll coating or the like is employed. Light irradiation is performed on the formed resist film through a mask on which a pattern is drawn, and then development processing is performed to form a pattern.

As the irradiated light, far ultraviolet rays such as g-rays with a wavelength of 436 nm, i-rays with a wavelength of 365 nm, KrF excimer laser with a wavelength of 248 nm, ArF excimer laser with a wavelength of 193 nm, F ₂ excimer laser with a wavelength of 157 nm, and vacuum ultraviolet rays. Is mentioned. The resist composition (D) is a resist composition useful for applications in which ultraviolet light having a wavelength of 250 nm or less, particularly ultraviolet light having a wavelength of 200 nm or less (ArF excimer laser light or F ₂ excimer laser light) is used as a light source.

  Various alkaline aqueous solutions are applied as the developing solution. Examples of the alkali include sodium hydroxide, potassium hydroxide, ammonium hydroxide, tetramethylammonium hydroxide, triethylamine and the like.

  Next, although the Example of this invention is described concretely, this invention is not limited to these.

Abbreviations used in the following examples are as follows.
THF; tetrahydrofuran, BPO; benzoyl peroxide, PFB; perfluorobutyryl peroxide, PSt; polystyrene, R225; dichloropentafluoropropane (solvent).

Example 1
_{[CF 2 = CFCH 2 CH (} C (CF 3) 2 OH) Synthesis of _{CH 2 C (c-Hex)} = CH 2]
_CF 2 ClCFClI of 500g glass reactor 1L, put _{CH 2 = CHC (CF 3)} 2 OH of 344g and BPO of 32.6 g, was heated for 71 hours at 95 ° C.. The reaction crude liquid was distilled under reduced pressure to obtain 544 g of CF ₂ ClCFClCH ₂ CHI (C (CF ₃ ) ₂ OH). 344 g of CF ₂ ClCFClCH ₂ CHI (C (CF ₃ ) ₂ OH) synthesized above and 1.7 L of dehydrated THF were placed in a 5 L glass reactor, and cooled to −70 ° C. Thereto, 2 L of a 2M THF solution of CH ₂ = C (c-Hex) CH ₂ MgCl was added dropwise over 4 hours (here, c-Hex represents a cyclohexyl group). After heating up to 0 degreeC and stirring for 16 hours, 1.6 L of saturated ammonium chloride aqueous solution was added and it heated up to room temperature. The reaction mixture was partitioned, and the organic layer was concentrated by an evaporator and then under reduced pressure to obtain distilled to 250g of _{CF 2 ClCFClCH 2 CH (C (} CF 3) 2 OH) CH 2 C (c-Hex) = CH 2 . A 1 L glass reactor was charged with 97 g of zinc and 300 g of water and heated to 90 ° C. There _{CF 2 ClCFClCH 2 CH (C (} CF 3) 2 OH) synthesized above was added dropwise to _{CH 2 C (c-Hex)} = CH 2 of 250 g, and stirred for 24 hours. After stirring for 2 hours by dropwise addition of hydrochloric acid 70mL the reaction solution, it was separated by filtration, vacuum distillation to 100g of _{CF 2 = CFCH 2 CH (C} (CF 3) 2 OH) CH 2 C (c-Hex ) = CH ₂ was obtained.

NMR spectrum
¹ H-NMR (399.8 MHz, solvent: CDCl ₃ , standard: tetramethylsilane)
δ (ppm):
1.28 (m, 16H), 3.49 (m, 1H), 4.66 (m, 2H).

¹⁹ F-NMR (376.2 MHz, solvent: CDCl ₃ , standard: CFCl ₃ )
δ (ppm):
-73.6 (m, 6F), -104.1 (m, 1F), -123.1 (m, 1F), -175.4 (m, 1F).

(Example 2)
4 g of the monomer obtained in Example 1 and 2.2 g of ethyl acetate were charged into a glass pressure-resistant reactor having an internal volume of 30 mL. Next, 6.23 g of a 3 wt% R225 solution of PFB was added as a polymerization initiator. After the system was frozen and degassed, it was sealed and polymerized in a constant temperature shaking tank (20 ° C.) for 41 hours. After the polymerization, the reaction solution was dropped into hexane to reprecipitate the polymer, followed by vacuum drying at 90 ° C. for 21 hours. As a result, 1.33 g of an amorphous polymer having a fluorine-containing ring structure in the main chain was obtained. The PSt equivalent molecular weight measured by GPC using THF as a solvent was a number average molecular weight (Mn) 15600, a weight average molecular weight (Mw) 25100, and Mw / Mn = 1.61. Tg measured by differential scanning calorimetry (DSC) was 118 ° C., and the polymer was a white powder at room temperature. The obtained polymer was soluble in acetone, THF, methanol, and R225.

It was confirmed by ¹⁹ F-NMR and ¹ H-NMR that the polymer was a cyclized polymer having the following monomer units (d), (e), and (f).

(Example 3)
A 200 ml glass reactor was charged with 4 g of the polymer obtained in Example 2, 2.7 g of a 6.6 wt% methanol solution of sodium hydroxide and 80 g of methanol, and stirred at room temperature for 20 hours. The reaction solution was concentrated with an evaporator and then dissolved in 120 g of dehydrated THF. Next, 0.38 g of chloromethyl methyl ether was added and stirred at room temperature for 90 hours. The reaction solution was filtered through celite and concentrated with an evaporator. The concentrate was dissolved in R225, washed with water and separated. The R225 layer was dropped into hexane to reprecipitate the polymer, followed by vacuum drying at 110 ° C. for 16 hours. As a result, 3.3 g of an amorphous polymer having a fluorine-containing ring structure in the main chain was obtained. ^{According to 19} F-NMR and ¹ H-NMR analyses, the methoxymethylation rate of this polymer was 32 mol%. The PSt equivalent molecular weight measured by GPC using THF as a solvent was a number average molecular weight (Mn) 15800, a weight average molecular weight (Mw) 25900, and Mw / Mn = 1.64. Tg measured by differential scanning calorimetry (DSC) was 120 ° C., and the polymer was a white powder at room temperature. The obtained polymer was soluble in acetone, THF, methanol, and R225.

The fluorine-containing polymer of the present invention can be used as a base polymer for photoresists, for example, ion exchange resins, ion exchange membranes, fuel cells, various battery materials, optical fibers, electronic members, transparent film materials, agricultural film films. It can be used for adhesives, fiber materials, weather-resistant paints, and the like.

Claims (4)

Fluorine-containing diene represented by the following formula (1).
CF ₂ = CFCH ₂ CH (C (CF ₃ ) ₂ OH) CH ₂ CR ¹ = CHR ² (1)
However, R ¹ and R ² each independently represent a hydrogen atom, an alkyl group having 10 or less carbon atoms, or a cyclic aliphatic hydrocarbon group, and at least one of them is a cyclic aliphatic hydrocarbon group. The fluorine-containing diene according to claim 1, wherein one of R ¹ and R ² is a cyclic aliphatic hydrocarbon group, and the other is a hydrogen atom.   A fluorine-containing polymer (A) having a monomer unit obtained by cyclopolymerization of the fluorine-containing diene according to claim 1 or 2. A method for producing a fluorine-containing polymer (A), wherein the fluorine-containing diene according to claim 1 or 2 is cyclopolymerized.