HK1122583B - Dimercaptan terminated polythioether polymers and methods for making and using the same - Google Patents

Description

Dithiol-terminated polythioether polymers and methods for making and using the same

Technical Field

The present invention relates to dithiol-terminated polythioether polymers. The invention also relates to methods for the preparation and use of these polymers.

Background

Thiol-terminated sulfur-containing polymers are known to be very useful as aerospace sealants due to their fuel resistance properties through crosslinking. Commercially available polymeric materials having sufficient sulfur content to exhibit such desirable properties are polysulfide polymers such as described in U.S. patent No.2466963, and polythioether polymers containing alkyl side chains such as described in U.S. patent No. 4366307. The materials used herein also have the desired properties of a liquid state at room temperature.

Another desirable combination of properties for aerospace sealants that is more difficult to obtain is the combination of long application times or "pot life" (the time the sealant remains workable) and short cure times (the time required to reach a predetermined strength). Aerospace sealants also require high temperature resistance. Compositions that are liquid at room temperature, have a low Tg with excellent pot life and/or excellent performance characteristics are desirable for aerospace applications.

Disclosure of Invention

The present invention relates to a dithiol-terminated polythioether polymer of formula (I):

wherein each R is₁Are the same and are represented by formula (II):

x is O or S; a is 2 to 6; b is 1 to 5; c is 2 to 10; n is 1 or greater; and R is₂Is a residue of a diene, a triene or an organic compound having a terminal leaving group, other than a divinyl ether residue.

Methods for preparing and using the polymers of formula (I) are also within the scope of the invention.

Detailed Description

The present invention relates to a dithiol-terminated polythioether polymer of formula (I):

wherein each R is₁Are the same and are represented by formula (II):

x is O or S; a is 2 to 6; b is 1 to 5; c is 2 to 10; n is 1 or greater; and R is₂Is a diene residue other than a divinyl ether residue, a triene residue, or an organic compound residue having a terminal leaving group. "diene residue", "triene residue" and "residue of an organic compound having a terminal leaving group" are to be understood as meaning the moieties which remain upon reaction of a diene, a triene or a compound having a leaving group, respectivelyAnd (4) dividing. In certain embodiments, X is O and a, b, and c are all 2, n is 1, and R is₂Is a vinylcyclohexene residue.

The polythioether polymers of the invention are liquid at ambient temperature and pressure, have a low Tg, and have excellent fuel resistance. As used herein, the term "ambient pressure" means about 77F (25℃.) and one atmosphere. "Low Tg" means a glass transition temperature of-50 ℃ or less. In a certain embodiment of the invention, the Tg is-55 ℃ or less, such as-60 ℃ or less or even-70 ℃ or less. Low Tg indicates excellent low temperature toughness in the cured formulation, which can be determined by known methods, such AS those described in Aerospace Material Specification (AMS)3267 § 4.5.4.7, Aerospace Material Specification (AMS)8802B § AS 5127/17.6 and military Specification (MI L-S) MIL-S-29574, and by methods similar to those described in ASTM D522-88. Typically, good low temperature toughness means no reduction in adhesion to the substrate, no cracking, no crazing, etc. Polythioether polymers of the invention can also exhibit highly desirable fuel resistance characteristics when cured. One measure of the fuel resistance of polymers is their percent volume swell after prolonged exposure to fuel, which can be quantitatively determined using methods the same as or similar to those described in ASTM D792 or AMS 3269. In certain embodiments, polythioether polymers of the invention, when cured, have a percent volume swell of 25% or less after 1 week immersion in a type 1 Jet Reference Fluid (JRF) at 140 ° F (60 ℃) and atmospheric pressure. In certain embodiments, the volume swell percentage is 20% or less.

Polythioether polymers of the invention can have a number average molecular weight of 200-8000, such as 200-4000 or 200-520.

The polythioether polymers of the invention are polyfunctional, i.e., they have two or more functional groups. The minimum two functional groups are terminal thiol groups. Or by R₁And/or R₂Partially to perform functionalization. For example, if R₂For a triene residue, the functionality of the polythioether may be greater than 2. These polymers can be prepared by 2 moles of the formula (I)Reaction of a compound of II) with 1 mol of a diene, triene or other organic compound having a terminal leaving group:

HS-R₁-SH (III)

wherein R is₁As previously described. Any suitable diolefin, triene or other organic compound may be used, including cycloaliphatic, aliphatic and aromatic diolefins and trienes. The diolefin is not a divinyl ether. One particularly suitable diene is vinylcyclohexene, such as 4-vinyl-1-cyclohexene, which is understood to have the following formula (IV):

it is understood that when the diene is 4-vinyl-1-cyclohexene, the polymer of the invention has the following structure (V):

other suitable compounds include triallyl cyanurate and di-or trihalides such as dichloroalkanes and trichloroalkenes.

In certain embodiments, formula (III) is dimercaptodioxaoctane (DMDO).

In certain embodiments of the present invention, such as when formula (III) is DMDO and the diene is vinylcyclohexene, polythioether polymers are obtained that can be used to reduce the viscosity of the composition; in this manner, the compounds of the present invention can act as reactive diluents. This provides a significant advantage over the prior art; compositions using the polymers of the present invention have low viscosity without the use of solvents. Therefore, the amount of solvent used in the case of using a solvent according to the present invention can be minimized. The absence and/or minimal use of solvent has significant benefits on environmental impact because little or no solvent is "flashed" off as the solvent evaporates, and the handling of the compositions of the invention is improved over other compositions having higher solvent content. In addition, the use of the polymers of the present invention in the composition may slow the curing of the composition, which may provide longer pot life and/or longer time to apply the composition to a substrate. Accordingly, the present invention further relates to compositions comprising the polythioether polymers described above.

In addition to the polythioether polymers described above, the compositions of the invention also include one or more additional sulfur-containing compounds, a curing agent, and one or more additional additives. "Sulfur-containing compound" and like terms refer to any compound or mixture of compounds in which at least one component contains a sulfur molecule. Examples may include those known in the art, such as polysulfides and/or polythioethers, such as those commercially available from Akzo Noble corporation under the name THIOPLAST and Toray corporation under the name THIOKOL LP, and as described in U.S. patent nos.6,172,179; polythioethers such as those described in U.S. Pat. Nos. 5,912,319 and 4,609,762. In certain embodiments, the sulfur-containing compounds include polymer blends that contain a polysulfide component and a polythioether component, such as described in U.S. application Ser. No.10/935,857, which is incorporated herein by reference. It is recognized that the polymers of the present invention are themselves sulfur-containing compounds and are used in the compositions of the present invention without any other sulfur-containing compounds. The term "curing agent" refers to a material that may be added to the composition of the present invention to accelerate the curing or gelling time of the sulfur-containing compound. "cure" and like terms refer to the point at which the composition reaches a 30 durometer "A" cure hardness as determined by ASTM D2240. Any suitable curing agent may be used. In certain embodiments, the curing agent includes an oxide that can oxidize the terminal thiol groups to form disulfide bonds. Suitable curing agents include, for example, lead dioxide, manganese dioxide, calcium dioxide, sodium perborate monohydrate, calcium peroxide, zinc peroxide, dichromate, and epoxies.

In the composition of the present inventionVarious additives such as fillers, adhesion promoters and plasticizers are used. The fillers used in the compositions of the invention, particularly for aerospace applications, include those commonly used in the art, such as carbon black, calcium carbonate (CaCO)₃) Silica, nylon, microspheres, and the like. In one embodiment, the composition includes from 10 to 70 weight percent of the selected filler or combination of fillers, such as from 10 to 50 weight percent, based on the total weight of the composition.

One or more adhesion promoters may be used. Suitable adhesion promoters include phenolics such as methyl on phenolic resins available from Occidental Chemicals, and/or organosilanes such as epoxy, thio or amino functional silanes such as A-187 and A-1100 available from OSispecialties. In one embodiment, the adhesion promoter is used in an amount of 0.1 to 15 weight percent based on the total weight of the formulation.

Plasticizers may be used in the composition and are generally present in an amount ranging from 1 to 8 weight percent based on the total weight of the formulation. Useful plasticizers include phthalates, chlorinated paraffins, and hydrogenated terphenyls.

The compositions may also contain one or more organic solvents, such as ethyl acetate, typically used in amounts of 0 to 15 wt%, such as less than 15 wt% or less than 10 wt%, based on the total weight of the formulation.

The compositions of the present invention may also optionally contain other standard additives such as pigments, thixotropes, inhibitors, catalysts and shielding agents.

Useful pigments include pigments conventional in the art, such as carbon black and metal oxides. The pigment is present in an amount of 0.1 to 10 weight percent based on the total weight of the composition.

Thixotropes, such as fumed silica or carbon black, are used in amounts of 0.1 to 5 weight percent based on the total weight of the composition.

Certain compositions of the present invention comprise, based on the total weight of the composition, 1 to 30 weight percent, e.g., 5 to 20 weight percent, of the thiol-terminated polythioether polymer of the invention; 20 to 70 wt.%, for example 35 to 50 wt.%, of a sulfur-containing compound other than the polymer of the present invention; 1 to 50 wt%, such as 5 to 25 wt% or 10 wt% of a curing agent; and 10 to 50 wt%, such as 5 to 30 wt% or 25 wt% of other additives. For compositions in which the polymer of the present invention is the only sulfur-containing compound, these weight percentages are adjusted accordingly.

The compositions of the present invention are typically packaged as two-component or "2K" systems. One component comprises a polythioether polymer of the invention, and optionally other sulfur-containing compounds, and may also contain one or more of various types of additives, such as fillers, extenders, adhesion promoters, accelerators and/or inhibitors; the second component typically comprises a curing agent and may also contain one or more of a variety of additives, such as plasticizers, fillers, accelerators, and/or inhibitors. The two components were mixed immediately before use. For example, the two components may be mixed in a specially ordered cartridge/stick system, such as SEMKIT commercially available from PRC-DeSoto International, inc. Alternatively, the components may be mixed together and the mixture maintained at a temperature below the reactivity of the curing agent. "reactive" means capable of chemical reaction and includes any degree of reaction of the reactants, from partial to complete. Storage temperatures below-40 ℃ are generally suitable to inhibit or prevent reaction between the curing agent and the polythioether polymer component.

A particularly suitable use of the composition of the present invention is in all grades of sealants. The sealant of the present invention refers to sealants comprising any of the above-described thiol-terminated polythioether polymers. "sealant" and like terms refer to a composition that is resistant to atmospheric conditions such as moisture and/or temperature, and/or at least partially impedes the transport of substances such as water, fuel, and/or other liquids and gases. Moreover, the sealant generally has adhesive properties. The sealant is typically classified according to viscosity. Class a sealants typically have a viscosity of 100-. Since these sealants are typically brush coated, this grade of sealant is considered a "brush coating". Class B sealants typically have a viscosity of 6000-. Such sealants may be used on fillet seals and are commonly used as fuel tank sealants. Class C sealants typically have viscosities between class A and class B sealants, such as 1000-. Class C sealants can be applied by a variety of means, such as brushes, rollers, or extrusion guns, and can also be used for "fayseal". Accordingly, the present invention further relates to a sealant comprising any of the above compositions.

The compositions of the present invention can be applied to a variety of substrates, for example, titanium, stainless steel, aluminum, and primed, organically coated and chromate forms thereof, epoxies, polyurethanes, graphite, fiberglass composites, KEVLAR, acrylics and polycarbonates. As noted above, the compositions of the present invention are particularly useful in aerospace applications, such as aerospace sealants and linings for fuel tanks, fuselages and the like. The aerospace sealant materials of the invention can exhibit characteristics including high temperature resistance, fuel resistance, and/or flexural strength. The formulations described herein may also be well suited for applications in which the temperature is extreme, chemically harsh environments, and/or subjected to mechanical vibration. The present formulations may also be used outside the aerospace field.

The polymers of the present invention are generally ungelled, that is to say the polymer blends have a measurable intrinsic viscosity. The cured formulations of the present invention generally have good low temperature toughness for aerospace applications, since the formulations can withstand varying environmental conditions, such as temperature and pressure, as well as physical conditions, such as joint shrinkage and expansion and/or vibration.

The viscosities described herein are determined according to ASTM D-2849, paragraph 79-90, using a Brookfield viscometer at a temperature of about 25 ℃ and a pressure of about 760 mm Hg.

The invention further relates to a method of sealing a hole comprising applying to a surface associated with the hole any of the sealants described herein. An adhesion promoter may be applied to the surface prior to the sealant if desired. "hole" refers to a void, gap, slit, or other opening. In certain embodiments, the aperture is located on an aircraft or aerospace vehicle.

Unless otherwise indicated, all numbers such as those expressing values, ranges, amounts or percentages used herein are to be understood as being preceded by the term "about", even if the term does not appear. All numerical ranges recited are intended to include all sub-ranges subsumed therein. Plural encompasses singular and vice versa. For example, when reference is made herein to "a" polythioether polymer, one or more polythioether polymers can be used, at least one of which is in the present invention. Similarly, one or more sulfur-containing compounds, one or more curing agents and/or one or more additives of any kind may be used in the compositions of the present invention. In addition, the term "polymer" as used herein is meant to refer to prepolymers, oligomers, and homopolymers and copolymers; the prefix "poly" refers to two or more.

Examples

The following examples are intended to illustrate the invention and should not be construed as limiting the invention in any way.

Example 1

1, 8-dimercapto-3, 6-dioxaoctane (616.95 g, 3.38 moles, CAS #14970-87-7) was added to a 1 liter four-necked round bottom flask equipped with a mechanical stirrer, thermometer, and two aeration devices (one for nitrogen and the other for gas). The flask was filled with nitrogen and the contents were heated to 32 ℃.

4-vinylcyclohexene (183.05 g, 1.69 mol, CAS #100-40-3) was added to the stirring dithiol over 3 hours, 15 minutes. A mild exotherm occurred during the addition, but the temperature was maintained at 42-45 ℃. The reaction mixture was heated at 55 ℃ for 3 hours. One of five parts (140 grams each) of a free radical initiator (VAZO-52(2, 2' azobis) 2, 4-dimethylvaleronitrile CAS #4419-11-8, commercially available from DuPont) was added at 55-60 deg.C each at 2 hour intervals. The reaction mixture was evacuated at 70-75 deg.C/7-8 mm Hg for 2 hours to obtain a clear colorless product. Yield: 800 g (100%); mercaptan equivalent weight: 238 (theoretical value: 236); viscosity: 1.331 poise.

Example 2

A class B sealant was prepared by mixing the components listed in table 1 in a two-shaft cowles type batch mixer under vacuum of 27 inches of mercury or greater until homogeneous. Components A and B were mixed in a weight ratio of 100: 12 to make the final sealant.

TABLE 1

Component A

¹Made according to U.S. patent No.4,623,711 (molecular weight approximately 2200).

²Made according to U.S. patent No.4,623,711 (molecular weight approximately 2500).

³Thiokol LP-55 polysulfide polymer, commercially available from Toray Fine Chemicals.

⁴Made according to U.S. Pat. No.6,172,179 (molecular weight approximately 3000).

⁵ORGASOL, commercially available from Atofina.

⁶EXPANCEL, commercially available from Akzo.

⁷Commercially available from OSi.

⁸Commercially available from OSi.

TABLE 1(continuation)

Component B

Components	Weight percent of
		MnO2	55
Plasticizer9	38
		Stearic acid	0.6
Sodium stearate	0.7
		Molecular sieve powder10	0.7
Dipentamethylenechloride/thiuram/polysulfide mixtures11	5.0

⁹Partially hydrogenated terphenyl (HB-40), commercially available from Solutia.

¹⁰3 angstroms of alkali aluminum silicate powder, commercially available from UOP.

¹¹Akrochem promoterPowder of propellant DPTT, commercially available from Akrochem.

As shown in table 2, the sealant of sample 2 performed well after testing as required by BMS 5-142 target specifications.

TABLE 2

Testing performance	Require that	Sample 2
			Viscosity (poise)	6000-13000	8400
Specific weight (maximum)	1-10	1.04
			Non-volatile content,% minimum	90-0	96
Flow (inch)	0.10-0.50	0-10
			Coating time after 1 hour, g/min (minimum)	15	48
Non-stick time, hour (max)	12	＜2
			Cure Rate after 24 hours (minimum)	30	346 hours
Percent weight loss (maximum)	16.0	7.26
			Toughness of	Without cracking, crazing, or delaminating	By passing
Dry tensile Strength psi (minimum)	150	210
			Class III*Tensile Strength in submersion psi (minimum)	150	225
Percent dry elongation (minimum)	150	220
			Class III immersion elongation% (maximum)	150	220
MoistureAnd (maximum) fuel stability of distilled water, class III at 120 ℉ for 5 days*120 F.5 days	20.05.0	19.32.34

Sprayed reference fluids TT-S-735A III

Sample 2 also had good peel strength and showed hydrocarbon fluid resistance when tested using the same specifications.

While particular embodiments of the present invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Claims (8)

1. A composition comprising a dithiol-terminated polythioether polymer of formula (I):

wherein each R is₁Are the same and are represented by formula (II):

x is O or S; a is 2 to 6; b is 1 to 5; c is 2 to 10; n is 1 or greater; and R is₂Is a residue of a diene, a triene or an organic compound having a terminal leaving group, other than a divinyl ether residue, characterized in that the composition further comprises a polymer blend comprising a polysulfide and a polythioether.

2. The composition of claim 1 wherein X is O; a is 2; b is 2; c is 2; n is 1, and R₂Is a vinylcyclohexene residue.

3. A sealant comprising the composition of claim 1 or 2 and a curing agent.

4. The sealant of claim 3, wherein the curing agent is MnO₂。

5. The sealant of claim 3, wherein the viscosity is 1 to 2000Pas (10 to 20000 poise).

6. A process for preparing a composition according to claim 1 or 2, which comprises reacting 2 moles of a compound of formula (II)

And 1 mole of a diene, triene, or organic compound having a terminal leaving group, and adding a polymer blend comprising a polysulfide and a polythioether.

7. A method of sealing an aperture comprising applying the sealant of claim 3 to a surface associated with the aperture.

8. The method of claim 7, wherein the surface is a surface of an aircraft or aerospace vehicle.