WO1993025386A1

WO1993025386A1 - Thermally resistant glass article

Info

Publication number: WO1993025386A1
Application number: PCT/US1993/001031
Authority: WO
Inventors: Karen B Lake; Wells. C. Cunningham
Original assignee: Ensign-Bickford Coatings Company
Priority date: 1992-06-16
Filing date: 1993-02-05
Publication date: 1993-12-23
Also published as: AU3611293A

Abstract

A thermally resistant article includes a silaceous substrate and a coating layer on the substrate wherein the coating layer is formed by the cured reaction product of a maleimide compound having at least two maleimide functional groups per molecule. A method for enhancing the strength of a silaceous substrate includes applying a layer of a maleimide coating composition to the core and cross-linking the coating composition to form a strength enhancing coating layer on the core.

Description

THERMALLY RESISTANT GLASS ARTICLE

TECHNICAL FIELD

The present invention relates to strength

enhancement of silaceous substrates and more

particularly to strength enhancement of silaceous optical fibers under high temperature conditions.

BACKGROUND OF THE INVENTION

Optical fibers include a small diameter fiber core having an index of refraction such that incident light may be internally reflected within the fiber core and thereby transmitted along the length of the fiber core. Typically, optical fiber cores are made from a brittle material, e.g. quartz or aluminosilicate glass. In order to enhance the strength of the

brittle, small diameter optical fiber core and to avoid damage to the surface of the fiber core, a coating layer is typically applied onto the surface of the fiber core using, e.g. nylon, polyethylene,

polyurethane, epoxy, silicone or acrylate coating compositions. The performance of conventional optical fiber coating compositions is inadequate at temperatures greater than about 300 F and therefore limits the temperature range within which such optical fibers may be used.

SUMMARY OF THE INVENTION

A thermally resistant article is disclosed. The thermally resistant optical fiber comprises a silaceous substrate and a coating layer on the substrate. The coating layer comprises the cured reaction product of a reactive coating composition. The reactive coating composition comprises a maleimide compound having at least one and preferably two maleimide functional groups per molecule. The thermally resistant article exhibits improved strength at elevated temperatures, is suitable for continuous use at temperatures up to about 400°C and is tolerant of brief excursions up to about 500°C.

In a preferred embodiment, the silaceous substrate is selected from the group consisting of glasses, glass ceramics, silaceous ceramic materials and combinations thereof.

In a preferred embodiment, the coating composition comprises a mixture of a maleimide compound having at least two maleimide functional groups per molecule and a silane coupling agent.

In a preferred embodiment, the coating composition comprises a mixture of a maleimide compound having at least two maleimide functional groups per molecule and a comonomer.

In a preferred embodiment, the thermally resistant article comprises an optical fiber.

A method for enhancing the strength of a silaceous substrate is also disclosed. The method includes applying a layer of a coating composition to the silaceous substrate wherein the coating composition comprises a maleimide compound having at least two maleimide functional groups per molecule and cross linking the coating composition to form a strength enhancing coating layer on the core.

BRIEF DESCRIPTION OF THE DRAWING:

The FIGURE shows a plot of the weight (expressed as a percentage of original weight) of a sample of a thermally resistant optical fiber of the present invention versus temperature.

DETAILED DESCRIPTION OF THE INVENTION

The thermally resistant article of the present invention includes a silaceous substrate and a strength enhancing coating layer on the substrate.

The silaceous substrate of the article of the present invention may comprise any silica-containing material, e.g. any glass, glass-ceramic, silaceous ceramic or combination thereof. Specific examples of suitable silaceous substrate materials include

borosilicate glass, silica, lithium aluminosilicate, KF glasses, and SSe glasses.

While the present invention is specifically described herein by reference to the preferred

embodiment of an optical fiber, it will be appreciated by one skilled in the art that the coating composition and process set forth herein may be used to increase the tensile and/or flexural strength of any silaceous substrate to provide strength enhanced elavated

temperature resistant articles other than optical fibers. For example, the coating compositions set forth herein may be used as an adhesive in glass/glass or glass/metal laminates, as a molding compound or as an encapsulant. The coating layer is the cured reaction product of a reactive coating composition. The reactive coating composition includes a maleimide compound.

The maleimide compound of the coating composition of the present invention may be any compound which includes at least two reactive maleimide functional groups per molecule. The coating composition may include a mixture of maleimide compounds.

For example, the maleimide compound may be any maleimide compound according to the structural formula:

wherein:

R¹ and R² independently are hydrogen or lower

(C1 to C4) alkyl;

R³ is an organic linking group that lacks any functional groups that would interfere with preparation of the maleimide groups or with the reactivity of the maleimide groups formed;

n = 1 ; and

m = 2 if n = 1, or m≥ 1 if n ≥1.

Preferably R¹ and R² are each hydrogen or

methyl. Most preferably, R¹ and R² are each

hydrogen.

R³ may be, e.g. an alkyl, cycloalkyl, aryl or aralkyl group and may be bonded to the maleimide groups through an oxygen atom.

Oligomeric polyfunctional maleimides, wherein n >

1 are suitable as the maleimide compound. Preferably, the oligomeric polyfunctional maleimide is of

relatively low molecular weight, i.e. wherein n is greater than 1 but less than about 10. An exemplary oligomeric polyfunctional maleimide is known as Thermax MP-2000X, is commercially available from Kennedy and Klim, Inc. of Little Silver, New Jersey and has the structural formula:

wherein:

Ml is a maleimide functional group, and

R₄ is either H or CH₃.

Preferably, the maleimide compound is a monomeric bismaleimide compound, i.e. any compound according to formula (1) above in which n = 1 and m = 2.

Suitable bismaleimides may be prepared, e.g. by reaction of maleic anhydride with a suitable diamine.

Examples of suitable diamines include aromatic

diamines, e.g. 4,4'- , 2,4'-, 3,3'- and 2,2'- diaminophenylmethane, aliphatic diamines, e.g. hexa- methylenediamine, dodecamethylenediamine,

cycloaliphatic diamines, e.g. 1,4

eyelohexylmethanediamine, 3,3'-, 4,4'- 2,4' and 2,2' dicyclohexylmethanediamines and aralkyldiamines, e.g. xylylenediamine. Other suitable diamines for use in preparing bismaleimides include 4,4' diaminophenyl oxide, 1,3-bis [3-aminophenoxy] benzene, 2,2'-,

2,4'- 3,3'-, 4,4'- diaminobenzo-phenone.

Examples of suitable bismaleimide compounds include N,N' ethylenedimaleimide, N,N' -hexamethylenedimaleimide, N,N'

dodoecamethylenedimaleimide, 2,2 - bis [4 - (4 -maleimide phenoxy) phenyl] propane, N,N' - (4,4

diphenylmethane) bismaleimide, N,N' - 4 methyl - 1,3 -phenylene) bismaleimide, 6 - maleimido - 1 - (4' -maleimidophenyl) - 1,3,3 - trimethyl-indone, N,N' - o -phenylene - bismaleimide and N,N' p - phenylene

bismaleimide, N,N' m phenylene bismaleimide, N,N' - (oxy - p - phenylene) dimaleimide, N,N' methylene - p -phenylene) - dimaleimide, N,N' - 2,4 -tolylenedimaleimide, N,N' - p - xylene dimaleimide, N,N' oxydipropylenedimaleimide, N,N'

phenylethylenedimaleimide and N,N'

phenylpropylenedimaleimide.

The coating composition of the present invention may include from about 40 weight percent to about 99.5 weight percent of the maleimide compound. Preferably, the coating composition includes from about 60 weight percent to about 95 weight percent of the maleimide compound.

The maleimide compound may be the sole

polymerizable compound in the reactive coating

composition. Alternatively, the reactive coating composition may include a comonomer. Suitable

comonomers include any monomeric species which may be copolymerized with the maleimide compound, e.g. epoxy resins, monomers having reactive acetylenically

unsaturated or ethylenically unsaturated functional groups, oxazolines and monomers capable of undergoing Michael addition reactions. Preferably, the comonomer is a multifunctional comonomer to provide a highly crosslinked cured

copolymeric coating layer.

A suitable epoxy resin comonomer is any monomeric or oligomeric compound which includes at least one epoxy, i.e. oxirane, functional group per molecule. Specific examples of epoxy compounds suitable as comonomers in the coating of the present invention include the diglycidyl ether of bisphenol A (such as EPON resins from Shell); glycidylethers of phenol or cresol-formaldehyde resins (e.g., epoxy novolac

oligomers such as DOW DEN resins); cycloaliphatic monomers such as 1, 4-vinylcyclohexene dioxide,

3-4-epoxycyclohexylmethyl-3, 4-epoxy-cyclohexane carboxylate; aromatic glycidyl amine resins such as glycidyl-p-aminophenol,

N,N,N;N'-tetraglycidyl-4,4'-methylene

bis(diaminobenzene), triglycidyl isocyanurate;

aliphatic glycidyl ethers such as trimethylolpropane triglycidylether and neopentyl glycol diglycidyl ether.

Suitable comonomers having acetylenically or ethylenically unsaturated functional groups may be any monomeric compound having at least one acetylenically or ethylenically unsaturated functional group per molecule.

Examples of suitable unsaturated comonomers include acrylic acids as well as amides and esters derived therefrom, e.g. acrylic acid, methacrylic acid, methylmethacrylate, acrylamide,

triethyleneglycol dimethacrylate, 1,4-butanediol diacrylate, trimethylolpropanetriacrylate and

1,3-Butylene glycol dimethacrylate. Also included are unsaturated materials such as, styrene,

n-vinylpyrrolidone and maleate esters. Unsaturated comonomers having multiple unsaturated sites are preferred. Diallyl and divinyl compounds have been found to be particularly suitable ethylenically unsaturated comonomers. Examples of suitable diallyl and divinyl compounds include diallyl phthalate,

N,N'-diallyltartardiamide, 1,3 divinyltetra-methyldisiloxane,

3 ,9-divinyl-2,4,8,10-tetraoxaspiro[5,5] undecane, diallyl maleimide, 1,3 diallyl urea, and diallyl-carbonate.

Suitable oxazoline comonomers include 2 - methyl oxazoline and bis (2 - oxazolinyl) methane.

Suitable comonomers which are capable of

undergoing Michael addition reaction include primary amino compounds and thiol compounds. Specific and preferred examples include 3,3' diaminodiphenylsulfone and dicarboxylic acid dihydrazides, 1,4 - bis

(4-aminophenoxy) benzene; oxydianiline; bis

(p-aminocyclohexyl) methane and

4,4'-diaminophenylmethane.

The coating composition of the present invention may include from about 0 weight percent to about 60 weight percent of the comonomer. Preferably, the coating composition includes from about 5 weight percent to about 30 weight percent of the comonomer.

The reactive coating composition may include a silane coupling agent. Silane coupling agents suitable for use in the coating composition of the present invention include any organosilane monomer having one or more groups capable of reacting with the silaceous substrate and a nonhydrolyzable organic functional group capable of undergoing reaction to form a chemical bond with the maleimide compound described above. Suitable organosilane coupling agents are those of the general formula:

wherein:

R⁴ is a nonhydrolyzable organic functional group which is capable of reacting with a

maleimide functional group, e.g.

(meth)acryloxyalkyl, vinyl, allyl, glyeidoxyalkyl or aminoalkyl, mercaptan;

R⁵ is a nonhydrolyzable nonfunctional

organic group, e.g. alkyl;

X is a hydroxyl group or hydrolyzable group, e.g. alkoxy, acetoxy, amino or halo; and

n = 0, 1 or 2.

The hydroxyl or hydrolyzable group X is capable of undergoing reaction with, or of undergoing hydrolysis and subsequent reaction with, silanol groups on the silaceous substrate to chemically bond the organosilane monomer to the surface of the substrate. The

nonhydrolyzable organic functional group is capable of undergoing reaction with the maleimide or with the comonomer of the coating composition to chemically bond the organosilane monomer within the cured coating layer. Respective reactions between the hydroxyl or hydrolyzable group X and the silaceous substrate and between the functional group R and the reactive

maleimide compound or a comonomer of the coating composition provide a chemical bonding between the cured coating layer and the silaceous substrate.

Preferably, n = 0 or 1, the organic functional group R is a group capable of undergoing free radical or cationic polymerization and the hydrolyzable group X is alkoxy. Most preferably, n = 0 and the organic functional group R is (meth)acryloxyalkyl,

glycidoxyalkyl or aminoalkyl, and the hydrolyzable group X is methoxy or ethoxy. Specific examples of suitable organosilane coupling agents include

3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)aeryloxypropyltriethoxysilane, 3-(meth)-acryloxypropylmethyldiethoxysilane, 3-(meth)acryloxypropylmethyldichlorosilane, allyltrimethoxysilane,

vinylmethyldiethoxy-silane,

3-glycidoxypropyltrimethoxysilane,

3-aminopropyltrimeth-oxysilane and

p-aminophenyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,

N-vinylbenzyl-N-2(trimethoxysily propyl amino ethyl) NH₄Cl. Methacryloxypropyl- trimethoxysilane,

3-glycidoxypropyltrimethoxysilane and

aminophenyltrimethoxysilane are particularly preferred as the organosilane. Mixtures of two or more

organosilane coupling agents are also suitable as the organosilane coupling agent.

The coating composition of the present invention may include from about 0.5 weight percent to about 20 weight percent of the silane coupling agent.

Preferably, the coating composition includes from about 5 weight percent to about 15 weight percent silane coupling agent.

Maleimide coating compositions of the present invention which do not include a polymerization

initiator compound may be cured by heating to a

temperature of about 200°C to 300°C for a time

period of about 1-3 hours. Optionally, the coating composition may further comprise a polymerization initiator. With the addition of a suitable polymerization initiator, the reactive maleimide coating composition may be cured by several different routes, i.e. the coating composition may be cured by photoinitiated free radial reactions, by thermally initiated free radical reactions, by cationic reactions, by Zwitterionic reactions, by cycloaddition reactions, by Michael addition reactions, by base catalyzed reactions and by combinations thereof.

Preferred photoinitiators of the coating

composition of the present invention are

photoinitiators which dissociate or decompose upon exposure to actinic radiation to yield a free radical. Conventional photosensitizing compounds may be used in combination with the photoinitiator. Photoinitiators which dissociate upon exposure to radiation having a wavelength in the range of 40 nm to 400 nm are

particularly preferred. Suitable photoinitiator compounds include, e.g. benzil, benzophenone,

camphorquinone, benzoin n-butyl ether, thioxanthone, 2-hydroxy-methyl-1-phenyl-propan-1-one,

1-hydroxycyclohexyl-phenylketone, isopropyl

thioxanthone, 2,2-dimethoxy-2-phenyl-2-benzyl-2-N-dimethylamino and 1- (4-morpholinophenyl-butanone). Preferred

photoinitiators include 2-hydroxy-methyl-1-phenyl-propan-1-one and 1-hydroxycyclohexylphenylketone.

The coating composition of the present invention may be heat cured by including a thermal initiator, e.g. a compound which decomposes upon heating to yield free radical, in the coating composition. The thermal initiator may be substituted for the photoinitiator to provide heat curable composition or may be included in addition to the photoinitiator to provide a composition that may be cured by exposure to heat and/or radiation. Suitable thermal initiators include, e.g.

2, 2'-azobis (2, 4 dimethylvaleronitrile), 2-2'-azobis

(isobutyl-nitrile), 2, 2' azobis (methylbutylnitrile),

1, 1'-azobis (cyanocyclohexane) and mixtures thereof. 2, 2' azobis (isobutylnitrile) is preferred as the thermal initiator.

Alternatively, the coating composition of the present invention may be cured by a cationic reaction either thermally or photolytically, using a suitable acid initiator, e.g. onium salts, diazonium salts or

Lewis acids.

Alternatively, the coating composition of the present invention may be cured by thermal reactions

(which appear to be Zwitterionic in nature) by

including a compound having acid-base properties, e.g. an imidazole derivative, in the coating composition as a polymerization initiator.

Alternatively, the coating composition of the present invention may be cured by base catalyzed reactions by including a basic catalyst, e.g. a metal alkoxide, in the composition as a polymerization initiator.

Alternatively, the coating composition of the present invention may be cured by cycloaddition reaction if a triplet sensitizer or Lewis acid is included in the composition as a polymerization initiator.

The coating composition of the present invention may include any effective amount of the polymerization initiator. Preferably, the coating composition of the present invention includes from about 0.1 weight percent to about 5 weight percent of the polymerization initiator. The coating composition may be diluted with a suitable solvent, e.g. methylethylketone (MEK),

1-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), a propyleneglycol monomethyl-ether acetate (PM), ethyl lactate or dimethylsulfoxide (DMSO).

Various additives known in the art, e.g. leveling agents, surfactants (a nonionic fluorinated alkyl ether known as FC-430 available from 3M has been found to be a particularly suitable surfactant for use in the coating composition of the present invention), and wetting agents may be added to the coating composition in accord with the demands of the particular

application method.

The coating composition of the present invention may be applied to the silaceous substrate by

conventional methods, e.g. dipping, spraying, rolling, curtain-coating.

In a preferred embodiment of the present

invention, the coating composition of the present invention may by applied to optical fiber by

conventional methods, i.e. by use of a conventional coating die. Significantly, the coating composition may be diluted using the above listed solvents to a solution suitable for application in a coating die, i.e. to a solids level, e.g. from about 50 weight percent solids to about 70 weight percent solids, sufficient to allow application of a coating layer having a thickness between about 5 microns and 10 microns on an exemplary 200 micron diameter fiber in one pass. E X A M P L E S

A. EXAMPLES 1 - 5: GENERAL PROCEDURE

Testing of the coating compositions set forth in EXAMPLES 1- 5 was carried out in accord with the procedure set forth below. Particular conditions and exceptions to the procedure are noted in the EXAMPLES.

Each composition was diluted with solvent, applied to microscope slides and cured.

Soda-lime silica microscope slides (nominally 1" × 3" × 0.04") were visually inspected for flaws, e.g. nicks, scratches. Slides exhibiting visually

detectable flaws were discarded. The thickness of each of the remaining slides were recorded. One side of each of the slides was then abraded with 60 mesh grit at about 80 psi. The abraded slides were then soaked in distilled water for 24 hours, allowed to dry in air at ambient temperature and then heat treated in an oven at 600°C for 1 hour. The heat treated slides were stored in a dessicator.

Slides were removed from the dessicator and curtain coated with a solution of coating composition. The coated slides were, hung vertically in air for approximately 10 minutes and the excess was blotted from the bottom edge a second time.

The coated slides were cured as noted in the tabulated results, i.e. by exposure to elevated

temperature, by exposure to UV radiation or by a combination thereof.

The coated slides to be heat cured were placed on a rack and cured by heating in an oven for a particular length of time at a particular temperature. The specific cure conditions for each heat cured sample tested are set forth in the TABLES of results. The coated slides to be UV cured were aligned in a rack and cured by passing the rack under a FUSION

SYSTEMS 300 WPI "H bulb" high pressure mercury lamp. The flawed side of each slide was alternately oriented upwardly and downwardly with the successive passes.

The slides were subjected to UV radiation at an

intensity of about 900 mW/cm² for 5-6 seconds per pass. The number of passes required to obtain a

tackfree coating was recorded for each side.

The coated slides were either stored under ambient conditions or soaked in distilled water overnight prior to testing, as noted in the results given below.

The slides were tested with an INSTRON 1122

testing apparatus using a 4 point bend flexural test fixture with a span ratio of 2 and a crosshead speed of 0.2 in/min with the flawed side of the slide in tension.

The strength enhancement (S.E.) ratio is a

quantity indicative of the improved flexural strength imparted to the silaceous substrate by the strength enhancing coating layer of the present invention and is determined by comparing results obtained with coated slides and those obtained with noncoated slides under the same test conditions. "Ambient" strength

enhancement values were derived by testing coated slides that had been stored under ambient conditions and tested under ambient conditions. "High Humidity" strength enhancement values were derived by testing coated slides that had been stored submerged overnight in water and tested wet at room temperature. B. EXAMPLES 1 - 5 CORRELATION OF RESULTS OBTAINED

WITH COATED MICROSCOPE SLIDES TO PREDICTED RESULTS WITH COATED OPTICAL FIBERS

In Examples 1 - 5 below, the strength enhancement provided by various coating compositions is determined using coated glass microscope slides, according to the procedure described above. To date, no strength enhancement data has been obtained regarding the preformance of the maleimide coatings of the present invention as strength enhancing coatings on thermally resistant optical fibers. However, in preliminary work with polyimide coatings, strength enhancement data obtained with coated optical fibers have shown a strong positive correlation with strength enhancement data obtained with coated microscope slides and it appears that strength enhancement results obtained with coated mircroscope slides may be used as a basis for reliable qualitative predictions regarding strength enhancement results on optical fibers. In the results presented in EXAMPLES 1 - 5 below, a high strength enhancement ratio with a particular coating composition on a microscope slide may be interpreted as an indication that a high strength enhancement ratio would likely be obtained with an analogous coated optical fiber and a low strength enhancement ratio for a particular coating composition on a microscope slide would indicate that a low strength enhancement ratio would likely be obtained with an analogous coated optical fiber. EXAMPLE 1

The following bismaleimide coating compositions were prepared:

COMPOSITION 1 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 70

2,4 ethylmethylimidazole 0.8 diglycidyl ether of bisphenol A 18

3-glycidoxypropyltrimethoxysilane 11 surfactant (FC-430, 3M) 0.2

COMPOSITION 2 WEIGHT PERCENT

2-2-bis [4-(4-maleimidophenoxy)

phenyl] propane 87

2,4-ethylmethylimidazole 2

3,-glycidoxypropyltrimethoxysilane 10 surfactant (FC-430, 3M) 1.0

COMPOSITION 3 WEIGHT PERCENT

2-2-bis [4-(4-maleimidophenoxy)

phenyl] propane 89.7 3,-glycidoxypropyltrimethoxysilane 10 surfactant (FC-430) (3M) 0.3

Coated samples were prepared for testing. The compositions were each diluted with NMP (to 30 percent solids), curtain coated on glass slides, heat cured and tested under ambient and high humidity conditions.

The number of samples tested(n), cure conditions, coating thickness, test conditions, mean stress at break and S.E. ratio are set forth in TABLE 1.

The results presented in TABLE 1 show that the coating compositions tested provided very significant improvements in S.E. ratio, i.e. an increase by a factor of about 2 under both ambient and high humidity testing conditions.

Compositions 1 - 3 were also diluted to 30 percent solids in NMP, coated on slides, cured and tested as above, and, in addition, the cured samples were

subjected to heat ageing under high temperature

conditions (350°C) prior to testing. The number of samples tested(n), cure and heat ageing conditions, coating thickness, test conditions, mean stress at break and S.E. ratio obtained for each composition tested are set forth in TABLE 2.

The results presented in TABLE 2 show that coating compositions tested provided improved S.E. ratio after high temperature ageing under ambient conditions, but that the S.E. ratio dropped significantly when the heat aged samples were tested under high humidity conditions.

EXAMPLE 2

The following bismaleimide coating compositions were prepared: COMPOSITION 4 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 90

3-glycidoxypropyltrimethoxysilane 10

COMPOSITION 5 WEIGHT PERCENT 2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 77

3-glycidoxypropyltrimethoxysilane 13 acetophenone 10 EXAMPLE 2 ( Cont ' d . )

COMPOSITION 6 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 77 benzophenone 10

3-glycidoxypropyltrimethoxysilane 13

COMPOSITION 7 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 77

2-hydroxy-2-methyl-1-phenyl-propan-1-one 10

3-glycidoxypropyltrimethoxysilane 13

COMPOSITION 8 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 67

3-glycidoxypropyltrimethoxysilane 13

2-hydroxy-2-methyl-1-phenyl-propan-1-one 20

Coated samples were prepared and tested.

Compositions 4 - 8 were each diluted with MEK (to 30 percent solids), coated on microscope slides, cured by exposure to UV radiation and tested under ambient conditions. The number of samples tested(n), cure conditions (expressed as number of passes by UV

source), coating thickness, mean stress at break and S.E. ratio for each composition tested are set forth in TABLE 3.

The results presented in TABLE 3 show that

bismaleimide coating compositions may be photocured and that the photocured coatings provide an improvement in S.E. ratio of about 20 percent under ambient conditions. EXAMPLE 3

A coating composition was prepared:

COMPOSITION 9 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 84

3-glycidoxypropyltrimethoxysilane 13 triarylsulfoniumhexafluoroantimonate 3

(UVI 6974, Union Carbide)

Coated samples were prepared and tested.

Composition 9 was diluted with MEK to 30 percent

solids, coated on microscope slides, UV cured,

thermally post-cured and tested under ambient

conditions. The number of samples tested(n), UV cure conditions (expressed as number of passes by UV

source), thermal post cure conditions, coating

thickness, mean stress at break and S.E. ratio for each composition tested are set forth in TABLE 4.

The results presented in TABLE 4 show that a thermal post cure of 1 - 3 hours at 200°C increased the S.E. ratio of a photocured coating layer from about 1.2 to about 1.9. Further post cure, i.e. 4 hours at 200 C resulted in a decrease in S.E. ratio from about 1.9 to about 1.8. The results suggest that exposure to UV radiation alone is not sufficient to fully cure coating composition 9. EXAMPLE 4

The following bismaleimide coating compositions were prepared.

COMPOSITION 10 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 60 diallyl maleate 30

3-glycidoxypropyltrimethoxysilane 10

COMPOSITION 11 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 60 diallyl urea 30

3-glycidoxypropyltrimethoxysilane 10

COMPOSITION 12 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 60 diallyl carbonate 30

3-glycidoxypropyltrimethoxysilane 10

COMPOSITION 13 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 60 diallyl phthalate 30

3-glycidoxypropyltrimethoxysilane 10

COMPOSITION 14 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 60

N,N'-diallyltartardiamide 30

3-glycidoxypropyltrimethoxysilane 10 EXAMPLE 4 (Cont ' d . )

COMPOSITION 15 WEIGHT PERCENT

2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 60

3,9-divinyl-2,4,8,10

tetraoxaspiro[5,5] undecane 30

3-glycidoxyproρyltrimethoxysilane 10

COMPOSITIONS 16 - 22

Compositions 16 - 22 are analogous to Compositions 4 and 10 - 15 described above, except that N,

N'-(4,4'-diphenylmethane) bismaleimide was substituted for 2,2 bis [4-(4 maleimidophenoxy) phenyl] propane.

Coated samples were prepared and tested.

Compositions 4 and 10 - 22 were diluted to 30 percent solids with solvent (MEK was used as the solvent for

Compositions 4 and 10 - 15, NMP was used as the solvent for Compositions 16 - 22), coated on microscope slides, heat cured and tested under ambient conditions. The number of samples tested(n), cure conditions, coating thickness, mean stress at break, and S.E. ratio for each composition tested are set forth in TABLE 5.

EXAMPLE 5

The following example again uses composition 15 which is repeated below.

COMPOSITION 15 WEIGHT PERCENT 2,2-bis [4-(4-maleimidophenoxy)

phenyl] propane 60

3,9-divinyl-2,4,8,10

tetraoxaspiro[5,5]undecane 30

3-glycidoxypropyltrimethoxysilane 10 Coated samples were prepared and tested.

Compositions 12 and 23 were diluted to 30 percent solids with MEK, applied to microscope slides, heat cured and tested under ambient conditions. In

addition, several cured samples were subjected to further heat ageing after cure and prior to testing.

The number of samples tested(n), cure conditions, heat ageing conditions, test conditions, mean stress at break and S.E. ratio for each composition tested are set forth in TABLE 6.

The results presented in TABLES 5 - 6 show that flexibilizing comonomers copolymerized with 2,2-bis

[4-(4-maleimidophenoxy) phenyl] propane, did not

negatively affect the S.E. ratio of heat aged samples, but copolymerization of flexibilizing monomers with N,N'-(4,4'-diphenylmethane) bismaleimide adversely affected the S.E. ratio provided by the coatings. EXAMPLE 6

An optical fiber (of nominal 200 micron diameter) was coated with a layer of composition number 24

(applied as a 54% solution in MEK) and cured by UV and thermal to provide a thermally resistant optical fiber comprising an 8 micron cured coating layer. Cure conditions were: 8" oven at 200°C; UV treatment with one 300 watt Fusion "H" bulb lamp; 2 foot cure oven at 350°C. A portion of the thermally resistant optical fiber (a 2.0512 mg sample) was subjected to

thermogravimetric analysis at a heating rate of

40°C/minute. Results of the analysis are given in the FIGURE as the weight of sample remaining, expressed as a percentage of the original sample weight, versus temperature.

The coating layer exhibited very good thermal stability up to a temperature of about 400°C, with the sample weight then decreasing at a slow rate up to a pronounced drop off between about 550°C and

620°C. Based on this preliminary analysis, it would appear that the thermally resistant optical fiber could potentially be applied in applications which require continued exposure to temperatures up to about 400°C, and would be able to tolerate brief excursions up to about 500°C.

COMPOSITION 24 Weight Percent

2-2-bis [4-(4-maleimidophenoxy)

phenyl] propane 70 diglycidyl ether of bisphenol A 17

2,4-ethylmethylimidazole 1

2-hydroxy-2-methyl-1-phenyl-propan-1-one 1

3-glycidoxy propyl trimethoxysilane 11 TABLE 1

COATING MEAN S.E. THICKNESS TEST

COMPOSITION n STRESS RATIO CURE CONDITIONS (microns) CONDITIONS noncoated 7 12720 1.00 - - - - - - - - - - - - AMBIENT

1 8 26900 2.11 90' @ 90°C + 2h @ 225°C 28.9 AMBIENT

2 12 24720 1.94 90' @ 90°C + 2h @ 225°C 39.7 AMBIENT noncoated 10 12940 1.00 - - - - - - - - - - - - AMBIENT

3 10 27230 2.10 60' @ 80°C + 4h @ 200°C 24.9 AMBIENT noncoated 8 11560 1.00 - - - - - - - - - - - - HIGH

HUMIDITY

3 8 22580 1.95 60' @ 80°C + 4h @ 200°C - - - - HIGH

HUMIDITY

TABLE 2

HIGH TEMPERATURE STABILITY

COATING

COATING n MEAN S.E. THICKNESS TEST COMPOSITION STRESS RATIO CURE CONDITIONS (microns) CONDITIONS noncoated 11 12600 1.00 - - - - - - - - AMBIENT

1 13 23450 1.86 1h @ 100°C + 1h @ 200°C 11.2 AMBIENT

2 8 19550 1.55 1h @ 100ºC + 1h @ 200°C 24.4 AMBIENT

3 9 24990 1.98 1h @ 100°C + 1h @ 200°C 14.8 AMBIENT noncoated 13 12570 1.00 1h @ 350°C AMBIENT

1 11 17880 1.42 1h @ 100°C + 1h @ 200° 30.3 AMBIENT

+ 1h @ 350°C

2 12 20430 1.63 1h @ 100°C + 1h @ 200°C 24.6 AMBIENT

+ 1h @ 350°C

3 9 21510 1.71 1h @ 100°C + 1h @ 200°C 22.9 AMBIENT

+ 1h @ 350°C

noncoated 9 11690 1.00 - - - - HIGH HUMIDITY

1 8 19610 1.68 1h @ 100°C + 1h @ 200°C HIGH HUMIDITY

2 7 18660 1.60 1h @ 100°C + 1h @ 200°C HIGH HUMIDITY

3 10 20590 1.76 1h @ 100°C + 1h @ 200°C HIGH HUMIDITY noncoated 10 11280 1.00 1h @ 350°C - - - - HIGH HUMIDITY

TABLE 2 (Continued)

HIGH TEMPERATURE STABILITY

COATING

COATING n MEAN S.E. THICKNESS TEST

COMPOSITION STRESS RATIO CURE CONDITIONS (microns) CONDITIONS

1 10 13850 1.23 1h @ 100°C + 1h @ 200°C coating HIGH HUMIDITY

+ 1h @ 350°C peeled

2 10 13150 1.17 1h @ 100°C + 1h @ 200°C coating HIGH HUMIDITY

+ 1h @ 350°C peeled

3 10 13220 1.17 1h @ 100°C + 1h @ 200°C coating HIGH HUMIDITY

+ 1h @ 350°C peeled

TABLE 3

COATING

COATING MEAN SE CURE THICKNESS COMPOSITION n STRESS RATIO CONDITIONS (microns) noncoated 12 13131 1.00 - - - - - - - -

4 11 15815 1.20 15/1 X 40.1 noncoated 12 12895 1.00 - - - - - - - -

5 10 15261 1.18 7/2 X 44.2

6 11 15045 1.17 5/1 X 27.9

7 12 15842 1.23 3/2 X 57.2

8 11 14486 1.14 1 X 29.4

TABLE 4

COATING

COATING n MEAN SE THICKNESS TEST

COMPOSITION STRESS RATIO CURE CONDITIONS (microns) CONDITIONS uncoated 10 12708 1.00 - - - - - - - - Ambient

9 11 15646 1.23 7 X 45.2 Ambient

9 11 24476 1.93 7X + 1h @ 200°C 31.8 Ambient

9 11 24310 1.91 7X + 2h @ 200°C 22.0 Ambient

9 8 24175 1.90 7X + 3h @ 200°C 29.8 Ambient

9 10 22449 1.77 7X + 4h @ 200°C 44.2 Ambient

TABLE 5

COATING

COATING n MEAN SE THICKNESS TEST

COMPOSITION STRESS RATIO CURE CONDITIONS (microns) CONDITIONS noncoated 13 13327 1.00 - - - - - - - - Ambient 4 9 26956 2.02 3h @ 200°C 52.9 Ambient

10 10 25923 1.95 3h @ 200°C 31.4 Ambient

11 10 23311 1.75 3h @ 200°C 15.2 Ambient

12 11 26209 1.97 3h @ 200°C 16.7 Ambient noncoated 9 13111 1.00 - - - - - - - - Ambient

13 11 25594 1.95 4.5h @ 200 300°C - - - - Ambient

14 11 17097 1.30 4.5h @ 200 300°C - - - - Ambient

15 10 24873 1.90 4.5h @ 200 300°C - - - - Ambient

20 11 19919 1.52 4.5h @ 200 300°C - - - - Ambient

21 12 19169 1.46 4.5h @ 200 300°C - - - - Ambient

22 11 18998 1.45 4.5h @ 200 300°C - - - - Ambient noncoated 13 13327 1.0 - - - - - - - - Ambient

16 11 24058 1.81 3h @ 200°C 4.1 Ambient

17 8 18944 1.42 3h @ 200°C 20.6 Ambient

18 11 20264 1.52 3h @ 200°C 13.0 Ambient

19 9 21708 1.63 3h @ 200°C 19.0 Ambient

TABLE 6

COATING MEAN SE TEST COMPOSITION STRESS RATIO CURE CONDITIONS CONDITIONS

uncoated 12 13596 1.00 - - - - Ambient

12 10 23885 1.76 1.5h @ 200°C Ambient

15 5 15433 1.14 1.5h @ 200°C Ambient

15 4 20545 1.51 3h @ 200°C Ambient

15 3 19423 1.43 4h @ 200°C Ambient

12 12 17899 1.32 1.5h @ 200°C + 1h @ 325°C Ambient

15 10 16882 1.24 1.5h @ 200°C + 1h @ 325°C Ambient

While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been

described by way of illustrations and not limitations.

What is claimed is:

Claims

CLAIM 1. A thermally resistant article, comprising: a silaceous substrate; and

a thermally resistant strength enhancing coating layer on the substrate, said layer comprising the cured reaction product of a reactive coating composition, said composition comprising a maleimide compound having at least one maleimide functional group per molecule.

CLAIM 2. The article of Claim 1, wherein said

substrate comprises a material selected from the group of glasses, glass-ceramics, silaceous ceramics and combinations thereof.

CLAIM 3. The article of Claim 1, wherein the article comprises a thermally resistant optical fiber and the substrate comprises a fiber core.

CLAIM 4. The article of Claim 3, wherein the fiber core is cylindrical and the coating layer

circumferentially surrounds the fiber core.

CLAIM 5. The article of Claim 1, wherein the maleimide a compound comprises a bismaleimide compound.

CLAIM 6. The article of Claim 1, wherein the maleimide compound is selected from the group consisting of N,N' ethylenedi-maleimide, N,N' - hexamethylenedimaleimide, N,N' dodoecamethylenedimaleimide, 2,2 - bis [4 - (4 -maleimidephenoxy) phenyl] proppne, N,N' - (4,4

diphenylmethane) bismaleimide, N,N' - 4 methyl - 1,3 -phenylene) bismaleimide, 6 - maleimido - 1 - (4' -maleimide-ophenyl) - 1,3,3 - trimethylindone, N,N' - o- phenylenediamine - bismaleimide and N,N' p -phenylene bismaleimide, N,N' m phenylene bismaleimide, N,N' - (oxy - p - phenylene) dimaleimide, N,N'

methylene - p - phenylene) - dimaleimide, N,N' - 2,4 -tolylenedimaleimide, N,N' - p - xylene dimaleimide, N,N' oxydipropylenedimaleimide, N,N'

phenylethylenedimaleimide and

N,N'-p-phenylpropylenedimaleimide.

CLAIM 7. The fiber of Claim 1, wherein the coating composition comprises a mixture of the maleimide compound and a silane coupling agent.

CLAIM 8. The article of Claim 7, wherein the silane coupling agent has at least one reactive

organofunctional group that is copolymerizable with the maleimide compound and at least two functional groups selected from the group consisting of hydride,

hydroxyl, hydrolyzable inorganic functional groups and hydrolyzable organic functional groups.

CLAIM 9. The article of Claim 8, wherein the silane coupling agent is selected from the group consisting of 3-glycidoxypropyltrimethoxysilane,

aminophenyltrimethoxysilane,

2-(3,4-epoxycyclohexyl)ethyl (triethoxysilane),

N-vinylbenzyl-N-2(trimethoxysilylpropylaminoethylNH₄Cl) and methacryloxypropyltrimethoxysilane.

CLAIM 10. The article of Claim 7, wherein the mixture comprises up to about 20 weight % silane coupling agent,

CLAIM 11. The article of Claim 1, wherein the coating composition comprises a mixture of the maleimide

compound and a comonomer capable of undergoing

copolymerization with the maleimide compound.

CLAIM 12. The article of Claim 11, wherein the

comonomer comprises an epoxy resin having at least one epoxy functional group per molecule.

CLAIM 13. The article of Claim 12, wherein the epoxy resin is selected from the group consisting of

diglycidylether of bisphenol A, polyglycidylether of cresol novolac resin and

3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane

carboxylate.

CLAIM 14. The article of Claim 11, wherein the

comonomer comprises an acetylenically or ethylenically unsaturated compound having at least one unsaturated functional group per molecule.

CLAIM 15. The article of Claim 14, wherein the

ethylenically unsaturated compound is selected from the group consisting of diallyl phthalate,

N,N'-diallyltartardiamide, 1,3 divinyltetra-methyldisiloxane,

3,9-divinyl-2,4,8,10-tetraoxaspiro[5,5] undecane, diallyl maleate, 1,3 diallyl urea, and

diallyl-carbonate.

CLAIM 16. The article of Claim 11, wherein the

comonomer comprises an oxazoline compound.

CLAIM 17. The article of Claim 16, wherein the

oxazoline compound is selected from the group

consisting of 2-methyl-oxazoline and

bis(2-oxazoliny1)methane.

CLAIM 18. The article of Claim 11, wherein the

comonomer comprises a compound capable of undergoing Michael addition reaction with the maleimide compound.

CLAIM 19. The article of Claim 18, wherein the

comonomer is selected from the group consisting of 3,3', diaminodiphenyl-sulfone and 1,4-bis(4

aminophenoxy)benzene.

CLAIM 20. The article of Claim 11, wherein the

comonomer comprises a silane coupling agent having at least one reactive organofunctional group that is copolymerizable with the maleimide compound and at least two functional groups selected from the group consisting of hydride, hydroxyl, hydrolyzable inorganic functional groups and hydrolyzable inorganic functional groups.

CLAIM 21. The article of Claim 11, wherein the silane coupling agent is selected from the group consisting of 3-glycidoxypropyl-trimethoxysilane, aminophenyltrimethoxysilane,

2-(3,4-epoxycyclohexyl)ethyl (triethoxysilane),

N-vinylbenzyl-N-2(trimethoxysilylpropylaminoethylNH₄Cl) and methacryloxy-propyltrimethoxysilane.

CLAIM 22. The article of Claim 1, wherein the reactive coating composition further comprises a curing

initiator.

CLAIM 23. THe article of Claim 22, wherein the

initiator comprises a photoinitiator.

CLAIM 24. The article of Claim 22, wherein the

initiator is a cationic initiator.

CLAIM 25. The article of Claim 22, wherein the

initiator is a thermal initiator.

CLAIM 26. The article of Claim 11, wherein the coating composition comprises from about 50 parts by weight to about 100 parts by weight of the maleimide compound, from about 25 parts by weight to about 50 parts by weight comonomer, and

from about 5 parts of weight to about 15 parts by weight of a silane coupling agent.

CLAIM 27. A method for enhancing the strength of a silaceous substrate, comprising:

applying a layer of a temperature resistant, strength enhancing coating composition to the

substrate, said coating composition comprising a maleimide compound having at least two reactive

maleimide functional groups per molecule, and

cross linking the coating composition to form a coating layer on the core.

CLAIM 28. The method of Claim 27, wherein the substrate is selected from the group consisting of glasses, glass-ceramics, silaceous ceramic materials and

combinations thereof.

CLAIM 29. The method of Claim 27, wherein the silaceous substrate is an optical fiber core.

CLAIM 30. The method of Claim 29, wherein the fiber core is cylindrical and the coating layer

circumferentially surrounds the fiber core.

CLAIM 31. The method of Claim 26, wherein the coating composition comprises a mixture of the maleimide compound and a silane coupling agent.

CLAIM 32. The method of Claim 31, wherein the silane coupling agent has at least one reactive

CLAIM 33. The method of Claim 32, wherein the silane coupling agent is selected from the group consisting of 3-glycidoxypropyl-trimethoxysilane,

aminophenyltrimethoxysilane

2-(3,4-epoxycyclohexyl)ethyl (triethoxysilane),

CLAIM 34. The method of Claim 31, wherein the mixture comprises up to about 20 weight % silane coupling agent.

CLAIM 35. The-method of Claim 27, wherein the coating composition comprises a mixture of the maleimide

compound and a comonomer capable of undergoing

copolymerization with the maleimide compound.

CLAIM 36. The method of Claim 35, wherein the comonomer comprises an epoxy resin having at least one epoxy functional per molecule.

CLAIM 37. The method of Claim 36, wherein the epoxy resin is selected from the group consisting of

diglycidylether of bisphenol A, polyglycidylether of cresol novolac resin and

3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane

carboxylate.

CLAIM 38. The method of Claim 35, wherein the comonomer comprises an acetylenically or ethylenically

unsaturated compound having at least one unsaturated functional group per molecule.

CLAIM 39. The method of Claim 38, wherein the

N,N'-diallyltartardiamide, 1,3 divinyltetra-methyldisiloxane,

diallyl-carbonate.

CLAIM 40. The method of Claim 35, wherein the comonomer comprises an oxazoline compound.

CLAIM 41. The method of Claim 40, wherein the oxazoline compound is selected from the group consisting of

2-methyl-oxazoline and bis(2-oxazolinyl)methane.

CLAIM 42. The method of Claim 35, wherein the comonomer comprises a compound capable of undergoing Michael addition reaction with the maleimide compound.

CLAIM 43. The method of Claim 42, wherein the comonomer is selected from the group consisting of 3,3',

diaminodiphenyl-sulfone and

1,4-bis(4-aminoρhenoxy)benzene.

CLAIM 44. The method of Claim 35, wherein the comonomer comprises a silane coupling agent having at least one reactive organofunctional group that is copolymerizable with the maleimide compound and at least two functional groups selected from the group consisting of hydride, hydroxyl, hydrolyzable inorganic functional groups and hydrolyzable inorganic functional groups.

CLAIM 45. The method of Claim 44, wherein the silane coupling agent is selected from the group consisting of 3-glycidoxypropyl-trimethoxysilane,

aminophenyltrimethoxysilane

2-(3,4-epoxycyclohexyl)ethyl (triethoxysilane),

CLAIM 46. The method of Claim 27, wherein the mixture further comprises a curing initiator.

CLAIM 47. The method of Claim 46, wherein the initiator comprises a photoinitiator.

CLAIM 48. The method of Claim 46, wherein the initiator is a cationic initiator.

CLAIM 49. The method of Claim 46, wherein the initiator is a thermal initiator.

CLAIM 50. The method of Claim 27, wherein the coating composition is cross linked by heating the coated substrate.

CLAIM 51. The method of Claim 27, wherein the coating composition is cross linked by irradiating the coated substrate.

CLAIM 52. The method of Claim 27, wherein the coating composition is crosslinked by cationic reaction.