JPH03500661A - Monomers, oligomers and polymers of biscyclobutalene crosslinked by at least one bond of benzoxazole, benzothiazole or benzimidazole - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] At least 1 of benzoxazole, benzothiazole or benzimidazole Monomers and polymers of biscyclobutadine cross-linked by two bonds − The U.S. government has a paid license to this invention, (WriEI+t-Paterson Air Force Ba5e>) Defined by Contract No. F33615-85-C-5092 awarded by The patentee has the right to require another person to license the license on reasonable terms. Under limited hfs circumstances.

This is co-located with U.S. Patent Application No. 205.141 (filed June 9, 1988). This is a partial continuation application.

The present invention relates to monomers and oligomers of biscyclobutarene and polypolymers based on them. Regarding Ma. More particularly, the invention provides at least one benzoxazole, Monomers crosslinked by benzothiazole or benzimidazole bonds, Concerning oligomers and polymers.

Polymers based on biscyclobutarene monomers are described in U.S. Pat. No. 4,540,76. It is disclosed in No. 3. These polymers contain bis-dichlorobutarene monomers. Manufactured by exposure to temperatures sufficient for weight. These polymers - Excellent thermal stability at high temperatures, good chemical resistance to most industrial solvents , has good physical and mechanical properties and low water sensitivity. These polymers are composite It is useful in the manufacture of bodies, coatings, films, and as an adhesive.

The polymer of U.S. Pat. No. 4,540,763 has excellent thermal stability at high temperatures. However, many applications in high-performance industries, such as the aerospace industry, rely on thermal stability at high temperatures. It requires long-term high-temperature thermal stability in air. US Patent No. Unfortunately, many of the 4.540°763 polymers do not have the long lengths necessary for high performance applications. Does not have thermal oxidative stability for a period of time. Polyvalent organic and inorganic bridges of biscyclobutarene Bridge groups are susceptible to oxidation reactions when exposed to high temperatures for long periods of time. Aliphatic crosslinking groups are especially Easily oxidized.

Considering the shortcomings of the prior art, bisdichloride, which has excellent long-term thermo-oxidative stability, It is desirable to produce polymers based on butyrene monomers and oligomers.

In one aspect, the present invention provides biscyclobutarene monomers and compounds based thereon. Concerning biscyclobutarene oligomers.

The biscyclobutarene monomer contains at least one type of benzoxazole, benzoxazole, etc. Cross-linked by divalent radicals with thiazole or benzimidazole bonds It consists of two dichlorobutarenes. Biscyclobutarene oligomer is Lobutarene carboxylic acid; diaminodihydroxyarene, dihydroxythio either luarene or tetraaminoarene; and aromatic diacid or aromatic Any of the group diacid chlorides includes the reaction products.

In other embodiments, the invention provides biscyclobutarene monomers or biscyclobutarenes of the invention. It consists of a method for producing a polymer from lobtalene oligomers. This method is a monomer or by exposing the oligomer to ring-opening polymerization conditions.

Polymers based on biscyclobutrene monomers or oligomers have long-term high Has thermal oxidative stability at warm temperatures. Divalent radicals benzoxazole and benzothiazo Because the molecule or benzimidazole linkages contribute to the thermo-oxidative stability of the crosslinking elements, , the thermo-oxidative stability of the polymer is enhanced. These polymers are advanced composite As matrix resin and for bonding the substrate Useful as a high performance adhesive. They also require handling in harsh environments. It is also useful for other applications.

Figures 1 to 4 [2I are thermal oxidation stabilizers of polymers based on preferred oligomers of the present invention. This is a qualitative graph.

For the purposes of this invention, cyclobutarene is defined as having one or more cyclobutane rings or Substituted or unsubstituted aromatic compound with one or more substituted cyclobutane rings fused together . The aromatic ring of dichlorobutarene is nitro, chloro, bromo or monomer of the present invention. - by other groups that do not adversely affect the thermo-oxidative stability of the polymer based on Can be replaced. The dichlorobutane ring is similarly supported by similar thermooxidatively stable groups. will be replaced. The most preferred cyclobutarene is benzocyclobutene.

The monomer of the present invention is a bis dichlorobutarene monomer.

The cyclobuthalene group of the monomer has at least one benzoxazole, benzothi Cross-linked by divalent radicals with azole or benzimidazole bonds Ru. Benzoxazole, benzothiazole or benzimida within the scope of the invention Methods for making sol bonds are described in U.S. Pat. No. 4.53, which is hereby incorporated by reference. 3.693. Benzoxazole, benzothiazole or benzoxazole Bis(benzoxazole, benzoxazole, A thiazole or benzimidazole) bond is preferred.

"In the formula, Z-〇, S　n　, NR,': R' is hydrogen, an aromatic group, or is an aliphatic group, Ar is an aromatic ring or aromatic ring system] Ar can be a heterocyclic group preferably a carboxyl group, more preferably a hydrocarbyl group. It is also understood that Each Ar is a single aromatic ring, a fused ring system or a direct divalent bond or An unfused ring system containing two or more aromatic groups linked by one or more divalent groups R1 It is understood that this is possible. Benzoxazole, benzothiazole or benz Preferably, the imidazole linkage corresponds to one of the following formulas: 2 is oxygen or sulfur atom or R゛ ■ -N- (R' is hydrogen or a monovalent aliphatic radical or aromatic radical ) and; R is methyl, halo, phenyl or phenoxy; F3 CF: 1 is sulfur, sulfinyl, or sulfonyl; [n is 0.1 or 2; n is 0, 1.2 or 3] As used herein, the term "arylene" refers to a divalent aromatic radical. do. A preferred arylene is phenylene.

Most preferred benzoxazole linkages have the formula: Most preferred benzoxazole A preferred monomer having a ring bond is a bisbenzocyclobutene monomer of the formula: Yes: Preferred monomers are dichlorobuthalene carboxylic acid and diaminodihydroxy Arenes and hydroxy, thio, or amine groups react against amine groups at high temperatures. diaminodihydroxyarene, diaminodithiolea in the ortho position Produced by condensation reaction with arene or tetraamine arene. diclob Talenecarboxylic acid is a carboxylic acid, such as benzocyclobutene-4-carboxylic acid. Defined as dichlorobutalene substituted with ruboxyl. This reaction is called a contraction reaction. Requires a reaction reagent to act as a dehydrating solvent and solubilize the monomers formed . Ueda etc.'s Jay Boy 1 Mar Lee (J Nee Tomoe Menbei) Cod L3 Not Contributed Engineering) Part A: Polymer Chem, (Poly+ner Chem,) 24.1 A preferred reagent disclosed on page 019 (1986) is methanesulfonic acid and It is a mixture with phosphorus oxide. wafer for the production of polybenzoxazole polymers. The process conditions disclosed by Da are generally suitable for making the monomers of the present invention.

As an example of monomer preparation, the monomer of formula (I) is benzocyclobutene-4-carboxylic. 2 moles of carboxylic acid and 1 mole of 1,3-diamino-4,6-cyhydrokidibenzene. By reacting in the presence of about 10% by weight phosphorus pentoxide in methanesulfonic acid. It can be manufactured using Approximately 15% by weight of phosphorus pentoxide present at the beginning of the condensation reaction There should be enough phosphorus pentoxide so that it can be calculated from the condensation water that the following has been consumed: be. The reaction mixture was stirred at about 100°C for about 3 hours under a nitrogen atmosphere and then brought to room temperature. Cool to warm. The monomers precipitate out of the mixture by contact with cold water and are removed by filtration. will be collected.

In other embodiments of the invention, cyclobutalenecarboxylic acid, diaphragm, as discussed above, Minodihydroxyarene, diaminodithiolarene or tetraaminoarene By reacting the lane with either an aromatic diacid or an aromatic diacid chloride. A reactive biscyclobutane oligomer is thus produced. produced by this reaction The resulting biscyclobutane oligomer is divalent polybenzoxazole, polybenzo Crosslinked by thiazole or polybenzimidazole. Describing the invention aromatic diacids or aromatic diacid chlorides, such as aromatic dinitriles, diene Alkaline esters, diamides, imidate esters, and diacids or diacid chlorides Contains metal salts and alkaline metal salts. For example, aromatic diesters are Aromatic diesters are produced by reacting diacid chlorides or diacid chlorides with phenol. can do. For the purpose of the present invention, the biscyclobutane oligomer has the following formula: Some AB-type benzoxazoles, benzothiazoles, and benzoxazoles as shown. Imidazole can also be used: In the formula, Q is a carboxylic acid or fl/) rhodanide (e.g. ζf-COOH or - COCβ) or its derivative or (imaginary precursor).

The necessary reaction conditions are the same as those described in 3 for the production of the monomers of the present invention (3). . From the preferred biscyclobutane oligomer zocyclobutene-4-carboxylic acid is manufactured and has the following formula: [wherein L is benzoxazole or benzothiazo represented by any of the following formulas] Z is an oxygen, sulfur atom or a benzimidazole bond. R.

-N- (R' is hydrogen or a monovalent aliphatic radical or aromatic radical ) and; R is methyl, halo, phenyl or phenyloxy: R1 is a direct bond -〇-, arylene, oxygen, carbonyl, CF.

is sulfur, sulfinyl, or sulfonyl; +n is 0, 1 or 2; n is 0.1.2 or 3; Ar is arylene, biarylene, oxygen, carbonyl, sulfur, sulfinyl two arylene groups bridged by sulfonyl or sulfonyl; p is either O or an integer of 1 or more, preferably 0 or 1 to 100 The code is preferably any integer up to 0. Preferred arylene is phenylene; preferred oligomers are those in which Ar is phenylene. phenylene, biphenylene, and oxygen, carbonyl, sulfur, sulfinyl or It is shown when it is two phenyl groups bridged by sulfonyl. preferred and combined is a bisbenzoxazole bond 1 corresponding to the following formula: More preferred biscyclo In the butarene oligomer, Ar in the formula is biphenylene, oxygen, or carbon. It is indicated when it is either of two phenylene groups bridged by a bondyl.

The most preferred bis dichlorobutarene oligomer is one in which Ar is biphenylene; Indicated when the subscript n is O and has the following formula: Reactive biscyclobuthalene oligomers have a broad subscript p for each component of the mixture. Exists as a mixture of oligomers varying in range. Manufactured by the method of the invention The average value of the subscript p for the oligomers used in the reaction is Talene carboxylic acid diamino dihydroxyarene, diaminodithiol arene or tetraaminoarenes; and aromatic diacids or aromatic Calculated by the relative proportion of any of the diacid chlorides.

In other embodiments of the invention, two or more diaminodihydroxyarenes or dia Minodithiol arene or tetraamino arene with cyclobutarene carbo acid and either an aromatic diacid or an aromatic diacid chloride. asymmetrical In this way, reactive biscyclobutarene oligomers with divalent crosslinking elements can be prepared. It can be manufactured using Reactive bisdiclobutares with asymmetric crosslinking elements can be handled more easily than bis-shift lobe cranes with symmetrical bridging elements. possible (symmetry results in crystallization, making it difficult to melt the monomer or oligomer) ). Similar results can be obtained using two or more aromatic diacids or aromatic diacid chlorides. It will be done.

The biscyclobuthalene monomer and reactive oligomer of the present invention are subjected to cyclic polymerization conditions. A highly cross-linked three-dimensional polymer that is thermo-oxidatively stable at elevated temperatures for long periods of time when exposed to Reamer tissue can be produced. In a preferred embodiment, the produced polymer loss of less than 10 weight after exposure to 316°C in air for 900 hours, preferably Shows less than 10% weight loss after exposure to 343'C in air for 200 hours. child In this regard, "ring-opening polymerization" refers to the polymerization of open cyclobutane rings of cyclobuthalene groups and other polymers. Reaction with an open cyclobutane ring or a group that can react with an open cyclobutane ring do.

When the cyclobutane ring of the cyclobuthalene group is opened, it becomes a dienephilic group (diene form a conjugated diene (orthoquinodimethane) that can react with typical In other words, open rings react with other open rings. U.S. Patent No. 4,540,763 is an open ring Some of the possible reactions that can occur when the two react with each other are disclosed. The open ring is By 77' Iser and 7 F eiser (F eiser and F eiser) Organic Chemistry (○rFianie Chemistry) 3rd edition (1980) to produce olefins by the Diels-Alder reaction. or acetylene groups.

The cyclobutane ring of the dichlorobuthalene group is capable of supporting monomers or reactive oligomers. Can be released by exposure to high heat.

A temperature of 200°C to 300°C is typically sufficient to weigh the ring. heavy solvent Alternatively, no catalyst is required, but a copper salt catalyst lowers the required temperature. gamma ray and electron beam rays can also open the ring, but hot rays are not applied by conventional methods. It is preferable because it can be obtained.

The monomers and oligomers of the present invention contain at least one cyclobuthalene-reactive functionality. It can be copolymerized with other monomers and reactive oligomers having groups. Things to choose The monomers or oligomers are advantageously reacted with the monomers and oligomers of the invention to A thermooxidatively stable copolymer composition is formed. Preferred comonomers and oligomers are Maleimides, olefins, acetylenes, cyanates and U.S. Pat. No. 4,540, No. 763 and concurrent U.S. Patent Application No. 835.013 (filed February 28, 1986). also have at least one cyclobutarene group, as described in It is. A particularly preferred comonomer has the formula: Using reaction conditions similar to those necessary for the production of the monomers of the invention described in 3 reactions with benzocyclobutene-4-carboxylic acid and orthoaminophenol It can be manufactured by

The following examples illustrate the invention but do not limit the scope of the invention. Bis-dichlorobutarene with a divalent crosslinking element containing sesame:. system 500ml resin reaction kettle equipped with magnetic stirring bar and nitrogen supply port benzocyclobutene-4-carboxylic acid (4,70 x 10-2 mol) ), 4,4°-biphenyldicarboxyl chloride (2,35 x 10-2 mol) , 1,3-diamino-4,6-cyhydroxybenzene (4,7040-2 mol) , 25.0 g of phosphorus pentoxide and 225 g of methanesulfonic acid are charged. Nitrogen the mixture Stir under atmosphere and heat to 100°C. After 3 hours, the reaction mixture was cooled to room temperature. However, when it is poured into the pulverized powder 11, a precipitate is formed. Hydroxylation of the pH of the resulting aqueous slurry Adjust pH to 9 with ammonium. Precipitation? Collected by filtration and washed with water. After thorough washing and drying in a vacuum oven at 90°C for 8 hours, the yield was 95%. The desired product is obtained.

Possible-1 Production of polymer from biscyclobutarene oligomer of fflJ 1 and ζ Tamemoto U Benzocyclobutene oligomer obtained from Example 1 A portion of the sample is placed in a compression mold having a disk-shaped space. This mold is 16 Heat to 0’C and apply enough pressure to completely fill the mold space with the oligomer stream. 9 The mold was then heated to 270°C under pressure for 3 hours, after which the pressure was maintained. Allow to cool to room temperature. When the mold is opened after cooling to room temperature, the shape of the mold space changes. A solid polymer disk appears that conforms to the . Remove the polymer disc from the mold and Place the disc in a circulating air furnace at 316'C (600°). The polymer is removed and weighed to determine the isothermal weight loss of the polymer. After each measurement, Return Ma to the furnace.

The other part of the oligomer obtained from Example 1 was similarly polymerized in a compression mold, and the resulting polymer was Charge the reamer to a circulating air oven at 343°C (650°). Again, the copolymer The disks are removed from the oven at various times and weighed to determine isothermal weight loss.

The isothermal weight loss measurements at each temperature are shown in Table 1 and the results at 316°C are the polymer weight suggests that more than 90% of the substance remains after exposure for more than 900 hours in air do. The results at 343°C indicate that approximately 90% of the polymer weight was in air for more than 200 hours. % remains after exposure. These results are valid for divalent chains containing benzoxazole. Biscyclobutarene oligomers with bridge elements exhibit excellent performance at high temperatures for long periods of time. This indicates that it has excellent thermal oxidative stability.

Using the method of Example 1, a biscyclobutarene oligomer of the following formula is prepared: using the method described in this example at 316°C and 343°C. Analyzed for thermal oxidative stability at °C.

Isothermal weight loss measurements at each temperature are shown in FIGS. 3 and 4.

Again, the results at both temperatures indicate immediate thermal oxidative stability at elevated temperatures for long periods of time. show.

Takumi-l Three bisbenzimidazole-linked biscyclobutarene monomers Under a nitrogen atmosphere, 2.78 parts by weight of 3,3'-diaminobenzidine, benzodichloro Reaction in which 4.32 parts by weight of butenoic acid chloride and 951.5 parts by weight of polyphosphorus were stirred Place in a container and cover with nitrogen. Next, reaction 8 was completed and the contents were stirred and heated to 95°C. React for 24 hours at a temperature of . At the end of the above period, empty the contents of the reactor into water. ゛When coagulated in a blender, a Karaji-colored powder is obtained, which is passed through r. Collected, reslurried in a blender and brought to a slightly basic pH with NaOH. Adjust. The product obtained′! ! : Collected by filtration and washed twice with water. , dried in a vacuum oven at 80°C.

The generated phase was then subjected to proton nuclear magnetic resonance spectroscopy (1R to proton N), differential Performing scanning calorimetry (DSC) and infrared (I[) spectroscopy; Verify that the following structure matches: Production of end-coated polybenzimidazole oligomers with benzocyclobutene 3,3′-diaminobenzidine 2 was added to a mechanically stirred reactor under a nitrogen atmosphere. ．． 57 parts by weight, 2.0 parts by weight of benzodichlorobutene acid chloride, 45.2 parts by weight of polyphosphoric acid parts by weight, and charged with 1.77 parts by weight of 4.4°-oxybis(benzoyl chloride). , then cover with nitrogen, seal the reactor and bring its contents to a temperature of 95 °C with stirring. Heat and maintain under these conditions (i.e. 95°C with stirring) for 24 hours. . At this time Mf&, the reactor contents congealed as a yellow powder in the water in the blender. Allow to harden and wash with water and then with dilute aqueous NaOH. After the last water wash When dried at 60 °C in a vacuum oven, an olive green powder was obtained. Ru.

The product was analyzed by proton NMR analysis, IR spectroscopy and differential scanning calorimetry. Polybenzimidazole oligo end-coated with benzocyclobutene It was affirmed that it was Ma.

Eclipse-1 Production of penzocycloboon (, Koyoru n, n'zothiazole) Stirring under nitrogen atmosphere 2.78 parts by weight of 2,5-diano-1,4-dithiolbenzene was added to the stirred reactor; 3.78 parts by weight of 4-benzocyclobutenoic acid chloride and 39.4 parts by weight of polyphosphoric acid and cover with nitrogen. The reactor was then sealed and the contents heated to 95°C with stirring. and maintain this temperature for 24 hours.

At the end of the above period, the contents of the reactor were mixed into a yellow-green powder according to the method described in Example 3 above. Collect as waste.

Proton N M R1 analysis by differential scanning calorimetry and IR spectroscopy suggests that the reaction products formed correspond to the following refinement formula: By repeating the method of Examples 1 to 5, the same procedure can be performed with other oligomers and monomers of the present invention. A variety of excellent results can be obtained.

Purification (no change in content) Procedural amendment form) 1. Display of incidents PCT/US89102458.

2. Name of the invention At least one of benzoxazole, benzothiazole or benzimidazole Monomers, oligomers and polyesters of biscyclobutene cross-linked by two bonds. Mar 3, person who corrects Relationship to the incident: Patent applicant address Name: The Dow Chemical Company 4, Agent Address: Shin-Otemachi Building, 206-ku, 2-2-1 Otemachi, Chiyoda-ku, Tokyo 5. Date of amendment order: November 6, 1990 (shipment date) 6. Subject of amendment (1) Translation of the specification and claims written by type printing (2) Translation of drawings Sentence

Claims (1)

[Claims] 1. at least one benzoxazole, benzothiazole or benzimida Two cyclobutarene monomers cross-linked by a divalent radical containing a zole bond - biscyclobutarene monomer. 2. The benzoxazole bond has the following formula: ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ [In the formula, Z is oxygen or sulfur atom or ▲Mathematical formula, chemical formula, table, etc.▼(R' is hydrogen or a monovalent aliphatic radical or an aromatic radical); R is methyl R, halo, phenyl or phenyloxy; R1 is a direct bond ▲ mathematical formula, chemical There are formulas, tables, etc.▼Arylene, oxygen, carbonyl, sulfur, sulfinyl or is sulfonyl; m is 0, 1 or 2; n is 0, 1, 2 or 3] The biscyclobutarene monomer according to claim 1, represented by any of the following. 3. Biscyclo according to claim 2, wherein the monomer is a bisbenzocyclobutene monomer. Lobutarene monomer. 4. The benzoxazole bond has the formula: ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ The biscyclob according to claim 3, which is a bisbenzoxazole bond represented by Talene monomer. 5. The biscyclob according to claim 4, wherein the monomer has a bisbenzoxazole bond. Talene monomer. 6. formula: ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ Biscyclo according to claim 5 Butarene monomer. 7. Cyclobuthalene carboxylic acid; diaminodihydroxyarene, diaminodihydroxyarene theolarenes or tetraaminoarenes; and aromatic diacids or aromatic diacids; Biscyclobutarene oligomers consisting of acid chloride reaction products. 8. Cyclobuthalenecarboxylic acid is benzocyclobutene-4-carboxylic acid The biscyclobutarene oligomer according to claim 7. 9. formula: ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ [In the formula, L is the formula: ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ [In the formula, Z is O, S or ▲Mathematical formula, chemical formula, table, etc.▼(R' is hydrogen or is a monovalent aliphatic radical or an aromatic radical); R is methyl, b, phenyl or phenyloxy; R1 is a direct bond ▲ Numerical formula, chemical formula, table etc.▼Arylene, oxygen, carbonyl, sulfur, sulfinyl, or sulfur is sulfonyl; m is 0, 1 or 2; n is 0, 1, 2 or 3; Ar is arylene, biarylene, oxygen, carbonyl, sulfur, sulfinyl two arylene groups bridged by sulfonyl or sulfonyl; p is an integer of 0 or 1 or more) benzoxazole, benzothiazole or benz, denoted by either The biscyclobutare according to claim 8, which is an imidazole bond. 10. L is the formula: ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ The biscyclobutarene oligomer according to claim 9, which is represented by: 11. Ar is phenylene, biphenylene, oxygen, carbonyl, sulfur, sulfur Claim 1: Two phenylene groups bridged by finyl or sulfonyl The biscyclobutarene oligomer described in 0. 12. Two Ar bridges linked by biphenylene, oxygen, or carbonyl The biscyclobutarene oligomer according to claim 11, which is a phenylene group. 13. The biscyclobutarene oligo according to claim 12, wherein Ar is biphenylene. Ma. 14. formula: ▲Contains mathematical formulas, chemical formulas, tables, etc.▼ The biscyclobutarene oligomer according to claim 13, which is represented by: 15. Claim 1 comprising the step of exposing the monomer of Claim 1 to ring cleavage polymerization conditions. Process for producing polymers from the monomers described. 16. The polymer comprises a monomer according to claim 1 and at least one second monomer. 16. The method according to claim 15, wherein the copolymer is a copolymer of a polymer or an oligomer. 17. the second monomer or oligomer has at least one cyclobutarene group; 17. The method according to claim 16. 18. The second monomer or oligomer has a formula: ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ 18. The method of claim 17, as indicated by: 19. A claim comprising the step of exposing the oligomer according to claim 7 to ring cleavage polymerization conditions. A method for producing a polymer from the oligomer of No. 7. 20. The polymer comprises the oligomer according to claim 7 and at least one second oligomer. 20. The method according to claim 19, wherein the copolymer is a copolymer of - or a monomer. 21. the second oligomer or monomer has at least one cyclobutarene group; 21. The method of claim 20. 22. The second monomer or oligomer has a formula: ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ 22. The method of claim 21, which is represented by: