Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere
  • C09K3/10—Materials in mouldable or extrudable form for sealing or packing joints or covers
  • C09K3/1006—Materials in mouldable or extrudable form for sealing or packing joints or covers characterised by the chemical nature of one of its constituents
  • C09K3/1012—Sulfur-containing polymers, e.g. polysulfides
• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K3/00—Materials not provided for elsewhere
  • C09K3/10—Materials in mouldable or extrudable form for sealing or packing joints or covers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G75/00—Macromolecular compounds obtained by reactions forming a linkage containing sulfur with or without nitrogen, oxygen, or carbon in the main chain of the macromolecule
  • C08G75/12—Polythioether-ethers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G75/00—Macromolecular compounds obtained by reactions forming a linkage containing sulfur with or without nitrogen, oxygen, or carbon in the main chain of the macromolecule
  • C08G75/02—Polythioethers
  • C08G75/04—Polythioethers from mercapto compounds or metallic derivatives thereof
  • C08G75/045—Polythioethers from mercapto compounds or metallic derivatives thereof from mercapto compounds and unsaturated compounds
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L81/00—Compositions of macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing sulfur with or without nitrogen, oxygen or carbon only; Compositions of polysulfones; Compositions of derivatives of such polymers
  • C08L81/02—Polythioethers; Polythioether-ethers

Definitions

• the present invention relates to a sealant or potting formulation prepared from a mercapto-terminated polymer produced by the reaction of polythiol(s) and polyvinyl ether monomer(s), the formulation having good low temperature flexibility and fuel resistance.
• polysulfide polyformal polymers described, e.g., in U.S. Pat. No. 2,466,963, and the alkyl side chain containing polythioether polyether polymers described, e.g., in U.S. Pat. No. 4,366,307 to Singh et al.
• Materials useful in this context also have the desirable properties of low temperature flexibility characterized by a low glass transition temperature (T g ) and liquidity at room temperature.
• the disclosed condensation reaction has a maximum yield of about 75% of the desired condensation product.
• the acid-catalyzed reaction of ⁇ -hydroxysulfide monomers yields significant quantities of an aqueous solution of thermally stable and highly malodorous cyclic byproducts, such as 1-thia-4-oxa- cyclohexane which limits the suitable application of the disclosed polymers.
• Another desirable feature in polymers suitable for use in aerospace sealants is high temperature resistance. While incorporating sulfur to carbon bonds into a polymer generally enhances high temperature performance, the polysulfide polyformal polymers disclosed in U.S. Pat. No. 2,466,963 have multiple -S-S- linkages in the polymer backbones which result in compromised thermal resistance.
• sealant, coating and electrical potting formulations or compositions that can provide good pot life as well as good performance properties, such as fuel resistance, flexural strength, thermal resistance and longevity in use.
• the present invention provides a sealant or potting formulation prepared from components comprising (a) at least one ungelled mercapto- terminated polymer prepared by reacting reactants comprising at least one polyvinyl ether monomer and at least one polythiol material; (b) at least one curing agent reactive with a mercapto group of the mercapto-terminated polymer; and (c) at least one additive selected from the group consisting of fillers, adhesion promoters, plasticizers and catalysts.
• sealant or potting formulation prepared from components comprising: (a) at least one ungelled mercapto-terminated polymer prepared from reactants comprising diethylene glycol divinyl ether and dimercapto dioxaoctane; (b) at least one curing agent reactive with a mercapto group of the mercapto-terminated polymer; and (c) at least one additive selected from the group consisting of fillers, adhesion promoters, plasticizers and catalysts.
• the above sealant formulations are useful in a variety of applications, such as for example aerospace applications or as electrical potting compounds.
• FIG. 1 depicts linear graphs of extrusion rate (E) versus time (T) for sealant compositions of the invention in comparison to extrusion rate curves for known types of sealant composition
• FIG. 2 is a semi-log graph of the extrusion rate curve of a polythioether sealant composition of the invention ( ⁇ ) and a prior art polysulfide sealant composition ( ⁇ ).
• the sealant and potting formulations of the present invention comprise one or more ungelled mercapto-terminated polymers or polythioethers. It has surprisingly been discovered that polythioethers prepared from the combination of polythiol(s) with polyvinyl ether monomer(s) according to the present invention result in ungelled mercapto-terminated polymers that are liquid at room temperature and pressure and that have desirable physical and rheological properties, and that furthermore are substantially free of malodorous cyclic by-products. The inventive materials also are substantially free of deleterious catalyst residues, and have superior thermal resistance properties.
• the mercapto-terminated polymers useful in the sealant and potting formulations of the present invention are preferably liquid at room temperature and pressure and cured sealants including such polymers have excellent low temperature flexibility and fuel resistance.
• room temperature and pressure denotes conditions of approximately 77°F. (25°C) and 1 atmosphere (760 mm Hg) pressure.
• the mercapto-terminated polymer is ungelled or substantially free of crosslinking.
• ungelled is meant that the mercapto-terminated polymer is substantially free of crosslinking and has an intrinsic viscosity when dissolved in a suitable solvent, as determined, for example, in accordance with ASTM- D1795 or ASTM-D4243.
• the intrinsic viscosity of the mercapto-terminated polymer is an indication of its finite molecular weight.
• a gelled reaction product on the other hand, since it is of essentially infinitely high molecular weight, will have an intrinsic viscosity too high to measure.
• the mercapto-terminated polymer has a glass transition temperature (T g ) that is not higher than -50°C, more preferably not higher than -55°C and most preferably not higher than -60°C.
• T g glass transition temperature
• the glass transition temperature of the mercapto-terminated polymer ranges from -85°C to-50°C, and more preferably -70°C to -50°C, as determined by differential scanning calorimetry (DSC).
• DSC differential scanning calorimetry
• Low temperature flexibility can be determined by known methods, for example, by the methods described in AMS (Aerospace Material Specification) 3267 ⁇ 4.5.4.7, MIL-S (Military Specification) -8802E ⁇ 3.3.12 and MIL-S-29574, and by methods similar to those described in ASTM (American Society for Testing and Materials) D522-88, which are incorporated herein by reference. Cured formulations having good low temperature flexibility are desirable in aerospace applications because the formulations are subjected to wide variations in environmental conditions, such as temperature and pressure, and physical conditions such as joint contraction and expansion and vibration.
• An advantage of the formulations of the present invention is that they exhibit very desirable fuel resistance characteristics when cured, due at least in part to the use of the mercapto-terminated polymers discussed herein.
• the fuel resistance of a cured sealant can be determined by percent volume swell after prolonged exposure of the cured sealant to a hydrocarbon fuel, which can be quantitatively determined using methods similar to those described in ASTM D792 or AMS 3269, which are incorporated herein by reference.
• the cured sealant can be prepared from 100 parts by weight of mercapto-terminated polymer, 50 parts by weight of precipitated calcium carbonate and an epoxy curing agent in a 1 :1 equivalent ratio of mercapto groups to epoxy groups.
• the epoxy curing agent is prepared from a 60:40 weight ratio of EPON 828 bisphenol A diglycidyl ether (available from Shell Chemical) to DEN 431 bisphenol A novolac resin (available from Dow Chemical).
• the cured sealants of the present invention have a percent volume swell not greater than 40%, and preferably not greater than 25% after immersion for one week at 140°F (60°C) and ambient pressure in jet reference fluid (JRF) type 1. More preferably, the percent volume swell of the cured polymers is not greater than 20%, and more preferably ranges from zero to 20%.
• Jet reference fluid JRF type 1 as employed herein for determination of fuel resistance, has the following composition (see AMS 2629, issued July 1 , 1989), ⁇ 3.1.1 et seq., available from SAE (Society of Automotive Engineers, Warrendale, Pennsylvania) (that is incorporated herein by reference): Toluene 28 ⁇ 1 % by volume
• the ungelled mercapto-terminated polymers have a number average molecular weight ranging from about 500 to about 20,000 grams per mole, more preferably from about 1 ,000 to about 10,000, and most preferably from about 2,000 to about 5,000, the molecular weight being determined by gel-permeation chromatography using a polystyrene standard.
• Liquid mercapto-terminated polymers within the scope of the present invention can be difunctional, that is, linear polymers having two end groups, or polyfunctional, that is, branched polymers having three or more end groups.
• the mercapto-terminated polymers are prepared by reacting reactants comprising one or more polyvinyl ether monomers and one or more polythiol materials.
• Useful polyvinyl ether monomers include divinyl ethers having the formula (V):
• R 2 is C2-6 n-alkylene, C2-6 branched alkylene, C 6- 8 cycloalkylene or C ⁇ -io alkylcycloalkylene group or -[(CH2-) p -0-] q -(-CH 2 -)r and m is a rational number ranging from 0 to 10
• p is an independently selected integer ranging from 2 to 6
• q is an independently selected integer ranging from 1 to 5
• r is an independently selected integer ranging from 2 to 10.
• the materials of formula V are divinyl ethers.
• divinyl ether monomers as described herein can provide polymers having superior fuel resistance and low temperature performance as compared to prior art polymers prepared from alkenyl ether and conjugated dienes such as 1 ,3 butadiene copolymerized with a dithiol such as DMDS.
• Preferred divinyl ethers include those compounds having at least one oxyalkylene group, more preferably from 1 to 4 oxyalkylene groups such as those compounds in which m is an integer from 1 to 4. More preferably, m is an integer from 2 to 4. It is also possible to employ commercially available divinyl ether mixtures in producing mercapto- terminated polymers according to the invention.
• m in formula V can also take on rational number values between 0 and 10.0; preferably between 1.0 and 10.0; very preferably between 1.0 and 4.0, particularly between 2.0 and 4.0.
• the polyvinyl ether material can have one or more pendant groups selected from alkyl groups, hydroxyl groups, alkoxy groups and amine groups.
• Useful divinyl ethers in which R 2 is C 2-6 branched alkylene can be prepared by reacting a polyhydroxy compound with acetylene.
• Exemplary compounds of this type include compounds in which R 2 is an alkyl-substituted methylene group such as -CH(CH 3 )- (for example "PLURIOL®” blends such as PLURIOL® E-200 divinyl ether (BASF Corp.
• alkyl-substituted ethylene for example -CH 2 CH(CH 3 )- such as "DPE” polymeric blends including DPE-2 and DPE-3 (International Specialty Products of Wayne, New Jersey)
• divinyl ethers include fluorinated compounds or compounds in which R 2 is polytetrahydrofuryl (poly-THF) or polyoxyalkylene, preferably having an average of about 3 monomer units.
• Two or more polyvinyl ether monomers of the formula V can be used in the foregoing method.
• two polythiols of formula IV discussed below
• one polyvinyl ether monomer of formula V one polythiol of formula IV and two polyvinyl ether monomers of formula V
• two polythiols of formula IV and two polyvinyl ether monomers of formula V and more than two compounds of one or both formulas, can be used to produce a variety of polymers according to the invention, and all such combinations of compounds are contemplated as being within the scope of the invention.
• the polyvinyl ether monomer comprises 20 to less than 50 mole percent of the reactants used to prepare the mercapto-terminated polymer, and preferably 30 to less than 50 mole percent.
• Suitable polythiol materials for preparing the mercapto-terminated polymer include compounds, monomers or polymers having at least two thiol groups.
• Useful polythiols include dithiols having the formula (IV): HS— R 1 — SH (IV) where R 1 can be a C 2- e n-alkylene group; C 3-6 branched alkylene group, having one or more pendant groups which can be, for example, hydroxyl groups, alkyl groups such as methyl or ethyl groups; alkoxy groups, C ⁇ -s cycloalkylene; C 6- ⁇ o alkylcycloalkylene group; -[(-CH 2 )p-X3q-(-CH 2 )r-; or -[(- CH 2 ) p -X]q-(-CH 2 )r in which at least one -CH 2 - unit is substituted with a methyl group and in which p is an independently selected integer ranging from 2 to 6, q
• dithiols include one or more heteroatom substituents in the carbon backbone, that is, dithiols in which X includes a heteroatom such as O, S or another bivalent heteroatom radical; a secondary or tertiary amine group, i.e., -NR 6 -, where R 6 is hydrogen or methyl; or another substituted trivalent heteroatom.
• X is O or S
• R 1 is -[(-CH 2 -)p-0-] q -(-CH 2 -) r - or -[(-CH 2 -)p-S-] q -(-CH 2 -)r-.
• p and r are equal, and most preferably both have the value of 2.
• Useful polythiols include but are not limited to dithiols such as 1 ,2- ethanedithiol, 1 ,2-propanedithiol, 1 ,3-propanedithiol, 1 ,3-butanedithiol, 1 ,4- butanedithiol, 2,3-butanedithiol, 1 ,3-pentanedithiol, 1,5-pentanedithiol, 1,6- hexanedithiol, 1 ,3-dimercapto-3-methylbutane, dipentenedimercaptan, ethylcyclohexyldithiol (ECHDT), dimercaptodiethylsulfide, methyl-substituted dimercaptodiethylsulfide, dimethyl-substituted dimercaptodiethylsulfide, dimercaptodioxaoctane, 1 ,5
• the polythiol material can have one or more pendant groups selected from lower alkyl groups, lower alkoxy groups and hydroxyl groups.
• Suitable alkyl pendant groups include C 1 -C 6 linear alkyl, C 3 -C 6 branched alkyl, cyclopentyl, and cyclohexyl.
• Such compounds include methyl-substituted DMDS, such as HS-CH 2 CH(CH 3 )-S-CH 2 CH 2 -SH, HS- CH(CH 3 )CH 2 -S-CH 2 CH 2 -SH and dimethyl substituted DMDS such as HS- CH 2 CH(CH 3 )-S-CH(CH 3 )CH 2 -SH and HS-CH(CH 3 )CH 2 -S-CH 2 CH(CH 3 )-SH.
• Two or more different polythiols can be used if desired to prepare useful polythioethers.
• the polythiol material has a number average molecular weight ranging from 90 to 1000 grams per mole, and more preferably 90 to 500 grams per mole.
• Relative amounts of dithiol and divinyl ether materials used to prepare the polymers are chosen to yield terminal mercapto groups (-SH).
• These mercaptan-terminated polymers can include thiol terminal groups that are not further reacted ("uncapped"), or include one or more thiol groups that are further reacted with other materials to provide reactive or non-reactive terminal or pendant groups ("capped").
• Capping the polymers of the present invention enables introduction of additional terminal functionalities, for example, hydroxyl or amine groups, to the polymers, or in the alternative, introduction of end groups that resist further reaction, such as terminal alkyl groups.
• the stoichiometric ratio of polythiol to divinyl ether materials is less than one equivalent of polyvinyl ether to one equivalent of polythiol, resulting in mercapto-terminated polymers. More preferably, the stoichiometric ratio is selected to fully terminate the polymer with mercapto groups.
• Hydroxyl- or amino-functional terminal polymers can be produced, for example, by reacting a vinyl terminated material with mercaptoalcohols such as 3-mercaptopropanol or mercaptoamines such as 4-mercaptobutylamine, respectively, or by reacting a mercaptan terminated material with a vinyl terminated material having hydroxyl functionality such as butane diol monovinyl ether or amine functionality such as aminopropyl vinyl ether.
• the mercapto-terminated polymer comprises 30 to 90 weight percent of the sealant formulation on a basis of total weight of the sealant formulation, and more preferably 30 to 60 weight percent.
• the reactants from which the mercapto-terminated polymers are prepared can further comprise one or more free radical catalysts.
• Preferred free radical catalysts include azo compounds, for example azobis-nitrile compounds such as azo(bis)isobutyronitrile (AIBN); organic peroxides such as benzoyl peroxide and t-butyl peroxide; inorganic peroxides and similar free-radical generators.
• the reaction can also be effected by irradiation with ultraviolet light either with or without a cationic photoinitiating moiety. Ionic catalysis methods, using either inorganic or organic bases, e.g., triethylamine, also yield materials useful in the context of this invention.
• Mercapto-terminated polymers within the scope of the present invention can be prepared by a number of methods. According to a first preferred method, (n+1) moles of a material having the formula IV:
• Capped analogs to the foregoing mercapto-terminated polymers can be prepared by reacting a material having the formula IV or a mixture of at least two different compounds having the formula IV and a material having the formula V or a mixture of at least two different compounds having the formula V in a stoichiometric ratio of less than one equivalent of dithiol per vinyl equivalent of formula V, with about 0.05 to about 2 moles of a material having the formula VI
• CH 2 CH-(CH 2 ) s-O— R 5 (VI) or a mixture of two different materials having the formula VI, in the presence of an appropriate catalyst.
• Materials of the formula VI are alkyl ⁇ -alkenyl ethers having a terminal ethylenically unsaturated group which react with terminal thiol groups to cap the polythioether polymer.
• s is an integer from 0 to 10, preferably 0 to 6, more preferably 0 to 4 and R 5 is an unsubstituted or substituted alkyl group, preferably a C ⁇ _ 6 n-alkyl group which can be substituted with at least one -OH or -NHR 7 group, with R 7 denoting H or C ⁇ - 6 alkyl.
• Exemplary useful R 5 groups include alkyl groups, such as ethyl, propyl and butyl, hydroxyl-substituted groups such as 4-hydroxybutyl; amine substituted groups such as 3-aminopropyl; etc.
• an equivalent of polyvinyl ether is reacted with dithiol or a mixture of polythiols.
• a preferred linear structured mercapto-terminated polymer useful in the seaiant and potting formulations of the present invention has the structure of formula (I):
• R 1 denotes a C2- 10 n-alkylene, C2-6 branched alkylene, C 6- 8 cycloalkylene or C ⁇ -io alkylcycloalkylene group, heterocyclic, -[(-CH2)p-X]q-(-CH 2 ) r -; or
• R 2 denotes a C 2-10 n-alkylene, C 2-6 branched alkylene, C 6-8 cycloalkylene or C ⁇ - 14 alkylcycloalkylene group, heterocyclic, -[(-CH 2 ) p -X] q -(-CH 2 ) r ;
• X denotes one selected from the group consisting of O, S and -NR 6 -;
• R 6 denotes H or methyl;
• m is an independently selected rational number from 1 to 50; and n is an independently selected integer from 1 to 60;
• p is an independently selected integer ranging from 2 to 6;
• q is an independently selected integer ranging from 1 to 5; and
• r is an independently selected integer from 2 to 10.
• R 1 is C 2 -C 6 alkyl and R 2 is C 2 -C 6 alkyl.
• the polythioether has the formula (II): wherein
• A denotes a structure having the formula I, y is O or l ,
• R 5 denotes d- 6 alkyl group which is unsubstituted or substituted with at least one — OH or -NHR 7 group, and
• R 7 denotes H or a C ⁇ -6 n-alkyl group.
• polythioethers of the formula II are linear, difunctional polymers which can be uncapped or capped.
• the polymer includes terminal thiol groups or capped derivatives thereof.
• the polymer includes terminal vinyl groups or capped derivatives thereof.
• the polythioether has the following structure: HS — R 1 — [— S — (CH 2 ) 2 — O — [— R 2 — O -] m - (CH 2 ) 2 — S — R 1 -] n - SH
• the foregoing polymers are produced, for example, by reacting a divinyl ether or mixture thereof with an excess of a dithiol or mixture thereof, as discussed in detail below.
• the mercapto-terminated polymers are essentially free of sulfone, ester or disulfide linkages, and more preferably free of such linkages.
• the absence of these linkages can provide good fuel and temperature resistance and good hydrolytic stability.
• "essentially free of sulfone, ester or disulfide linkages” means that less than 2 mole percent of the linkages in the mercapto-terminated polymer are sulfone, ester or disulfide linkages.
• Disulfide linkages are particularly susceptible to thermal degradation
• sulfone linkages are particularly susceptible to hydrolytic degradation.
• Mercapto-terminated polymers useful in the formulations of the present invention have a mercapto functionality of at least 2.
• Polyfunctional analogs of the foregoing difunctional mercapto-terminated polymers can be prepared by reacting one or more compounds of formula IV and one or more compounds of formula V, in appropriate amounts, with one or more polyfunctionalizing agents.
• the polyfunctionalizing agent preferably includes from 3 to 6 such moieties, and thus is denoted a "z-valent” polyfunctionalizing agent, where z is the number (preferably from 3 to 6) of such moieties included in the agent, and hence the number of separate branches which the polyfunctional mercapto-terminated polymer comprises.
• the polyfunctionalizing agent can be represented by the formula
• R 1 , R 2 , n and m denote structures and values discussed above with reference to Formula I,
• R 8 denotes a moiety which is reactive with a terminal vinyl group or mercapto group, and z is an integer from 3 to 6.
• Polyfunctional polythioethers according to the present invention can preferably have the formula (III):
• Y is O or l
• R 5 denotes C ⁇ - ⁇ alkyl that is unsubstituted or substituted with at least one -OH or -NHR 7 group
• R 7 denotes H or a C ⁇ -6 n-alkyl group, s is an integer from 0 to 10, z is an integer from 3 to 6, and
• Partially capped polyfunctional polymers i.e., polymers in which some but not all of the branches are capped, are also within the scope of the present invention.
• Preferred trifunctionalizing agents include triallylcyanurate (TAC), which is reactive with dithiol, and 1 ,2,3-propanetrithiol, which is reactive with polyvinyl ether.
• TAC triallylcyanurate
• Agents having mixed functionality i.e., agents that include moieties which are typically separate moieties that react with both thiol and vinyl groups, can also be employed.
• polyfunctionalizing agents include trimethylolpropane trivinyl ether, and the polythiols described in U.S. Pat. No. 4,366,307; U.S. Pat. No. 4,609,762 and U.S. Pat. No. 5,225,472, the disclosures of each of which are incorporated in their entireties herein by reference. Mixtures of polyfunctionalizing agents can also be used.
• Polyfunctionalizing agents having more than three reactive moieties afford "star" polymers and hyperbranched polymers.
• two moles of TAC can be reacted with one mole of a dithiol to afford a material having an average functionality of 4.
• This material can then be reacted with a diene and a dithiol to yield a polymer, which can in turn be mixed with a trifunctionalizing agent to afford a polymer blend having an average functionality between 3 and 4.
• Inventive polymers as described above have a wide range of average functionality.
• trifunctionalizing agents afford average functionalities from about 2.05 to 3.0, preferably about 2.1 to 2.6.
• (n+1) moles of a compound or compounds having the formula IV, (n) moles of a compound or compounds having the formula V, and a z-valent polyfunctionalizing agent in an amount sufficient to obtain a predetermined molecular weight and functionality, are combined to form a reaction mixture.
• the mixture is then reacted in the presence of a suitable catalyst as described above to afford mercapto-terminated polyfunctional polymers.
• Capped analogs of the foregoing mercapto-terminated polyfunctional polymers are prepared by inclusion in the starting reaction mixture of about 0.05 to about (z) moles one or more appropriate capping compounds VI.
• inventive polymers preferably are prepared by combining at least one compound of formula IV and at least one compound of formula V, optionally together with one or more capping compounds VI and/or VII as appropriate, and/or a polyfunctionalizing agent, followed by addition of an appropriate catalyst, and carrying out the reaction at a temperature from about 50 to about 120°C for a time from about 2 to about 24 hours.
• the reaction is carried out at a temperature from about 70 to about 90°C for a time from about 2 to about 6 hours.
• the inventive reaction is an addition reaction, rather than a condensation reaction, the reaction typically proceeds substantially to completion, i.e., the inventive mercapto-terminated polymers are produced in yields of approximately 100%. No or substantially no undesirable by-products are produced. In particular, the reaction does not produce appreciable amounts of malodorous cyclic by-products such as are characteristic of several known methods for producing polythioethers. Moreover, the polymers prepared according to the invention are substantially free of residual catalyst. Methods of making the foregoing polyfunctional inventive polymers are discussed in detail below.
• the mercapto-terminated polymer has a viscosity of less than about 500 poise at a temperature of about 25°C and a pressure of about 760 mm Hg determined according to ASTM D-2849 ⁇ 79-90 using a Brookfield viscometer.
• the mercapto-terminated polymer or combination of mercapto- terminated polymers as detailed herein preferably is present in the polymerizable sealant composition in an amount from about 30 wt% to about 90 wt%, more preferably about 40 to about 80 wt%, very preferably about 45 to about 75 wt%, with the wt% being calculated based on the weight of total solids of the composition.
• the sealant or potting formulations of the present invention further comprise one or more curing agents, such as polyolefins, polyacrylates, metal oxides, polyepoxides and mixtures thereof as appropriate.
• Curing agents useful in polymerizable sealant compositions of the invention include polyepoxides or epoxy functional resins, for example, hydantoin diepoxide, bisphenol-A epoxides, bisphenol-F epoxides, novolac type epoxides, aliphatic polyepoxides, and any of the epoxidized unsaturated and phenolic resins.
• useful curing agents include unsaturated compounds such as acrylic and methacrylic esters of commercially available polyols, unsaturated synthetic or naturally occurring resin compounds, TAC, and olefinic terminated derivatives of the compounds of the present invention.
• useful cures can be obtained through oxidative coupling of the thiol groups using organic and inorganic peroxides (e.g., Mn0 2 ) known to those skilled in the art. Selection of the particular curing agent may affect the T g of the cured composition. For example, curing agents that have a T g significantly lower than the T g of the polythioether may lower the T g of the cured composition.
• the composition can comprise about 90% to about 150% of the stoichiometric amount of the selected curing agent(s) based upon -SH equivalents, preferably about 95 to about 125%.
• Fillers useful in the polymerizable compositions of the invention for aerospace application include those commonly used in the art, such as carbon black and calcium carbonate (CaC0 3 ). Potting compound fillers illustratively include high band gap materials such as zinc sulfide and inorganic barium compounds.
• the compositions include about 10 to about 70 wt% of the selected filler or combination of fillers, more preferably about 10 to 50 wt% based upon the total weight of the composition.
• the sealant and potting compositions of the present invention can comprise one or more adhesion promoters.
• Suitable adhesion promoters include phenolics such as METHYLON phenolic resin available from Occidental Chemicals, organosilanes such as epoxy, mercapto or amino functional silanes such as A-187 and A-1100 available from OSi Specialities.
• an adhesion promoter is employed in an amount from 0.1 to 15 wt% based upon total weight of the formulation.
• Common substrates to which the sealant compositions of the present invention are applied can include titanium, stainless steel, aluminum, anodized, primed, organic coated and chromate coated forms thereof, epoxy, urethane, graphite, fiberglass composite, KEVLAR®, acrylics and polycarbonates.
• a plasticizer is present in the sealant formulation in an amount ranging from 1 to 8 weight percent based upon total weight of the formulation.
• Plasticizers that are useful in polymerizable compositions of the invention include phthalate esters, chlorinated paraffins, hydrogenated terphenyls, etc.
• the formulation can further comprise one or more organic solvents, such as isopropyl alcohol, in an amount ranging from 0 to 15 percent by weight on a basis of total weight of the formulation, preferably less than 15 weight percent and more preferably less than 10 weight percent.
• a typical sealant formulation is provided in Example 18.
• organic amine catalysts are organic tertiary amines.
• Specific catalysts which are useful in the present invention are triethylene diamine, diazabicyclo (2,2,2) octane (DABCO) (preferred), diazabicycloundecene (DBU), 2,4,6- tri(dimethylamino methyl) phenol (DMP-30) and tetramethyl guanidine (TMG).
• DABCO diazabicyclo (2,2,2) octane
• DBU diazabicycloundecene
• DMP-30 2,4,6- tri(dimethylamino methyl) phenol
• TMG tetramethyl guanidine
• the reaction time when utilizing the organic amine catalysts, and particularly the organic tertiary amine catalysts is in general between about one hour to about 20 hours which is a considerable difference compared to using no amine catalyst.
• the amount of catalyst ranges from 0.05 wt% to 3 wt%, based on the total weight of the starting reactants.
• sealant or potting formulations preferably are cured at ambient temperature and pressure, however the formulations generally can be cured at a temperature ranging from about 0°C to about 100°C.
• polymerizable sealant compositions of the invention can optionally include one or more of the following: pigments; thixotropes; retardants; and masking agents.
• Useful pigments include those conventional in the art, such as carbon black and metal oxides. Pigments preferably are present in an amount from about 0.1 to about 10 wt% based upon total weight of the formulation.
• Thixotropes for example fumed silica or carbon black, are preferably used in an amount from about 0.1 to about 5 wt% based upon total weight of the formulation.
• An additional advantage of sealant formulations according to the invention is their improved curing behavior.
• the extent of cure of a sealant formulation as a function of time is often difficult to measure directly, but can be estimated by determining the extrusion rate of the composition as a function of time.
• the extrusion rate is the rate at which a mixed sealant formulation, i.e., a sealant formulation together with an accelerator system, is extruded from an applicator device. As the sealant formulation is mixed with the accelerator system, curing begins, and the extrusion rate changes with time.
• the extrusion rate thus is inversely related to the extent of cure.
• the extent of cure is low, the viscosity of the mixed ungelled sealant formulation is low and thus the extrusion rate is high.
• the viscosity becomes very high, and the extrusion rate thus becomes low.
• the extrusion rate can be measured according to AMS Method 3276 (section 4.5.10), which is incorporated herein by reference.
• AMS Method 3276 section 4.5.10
• a mixed sealant formulation should have a low viscosity, and thus a high extrusion rate, for a length of time sufficient to allow even application of the sealant formulation to the area requiring sealing, but then should cure rapidly after application, i.e., their extrusion rate should quickly decrease.
• Sealant formulations according to the present invention are characterized by this desirable extrusion curve, as illustrated qualitatively in curve C.
• Sealant formulations according to the present invention can have, depending on the particular formulation, initial extrusion rates as high as 500 g/min or higher, together with low extrusion rates on the order of about 5 to 10 g/min or less after curing times on the order of one hour.
• the initial extrusion rate of a sealant containing a polymer of the present invention is about 550 g/min, then falls rapidly to about 20 g/min after 70 minutes.
• a known polysulfide polymer based sealant (cured with MnO 2 ) has an initial extrusion rate of about 90 g/min, which slowly falls to about 20 g/min after 70 minutes.
• Another preferred curable sealant formulation combines one or more plasticizers with the mercapto-terminated polymer(s), curing agent(s) and filler(s) described above.
• a plasticizer allows the polymerizable formulation to include mercapto-terminated polymers which have higher T g than would ordinarily be useful in an aerospace sealant or potting compound, i.e., use of a plasticizer effectively reduces the T g of the formulation, and thus increases the low-temperature flexibility of the cured polymerizable formulation beyond that which would be expected on the basis of the T g of the mercapto-terminated polymers alone.
• liquid polythioethers were prepared by stirring together one or more dithiols with one or more divinyl ethers and a trifunctionalizing agent. The reaction mixture was then heated and a free radical catalyst was added. All reactions proceeded substantially to completion (approximately 100% yield).
• the polymer was yellow and had low odor.
• Example 3 In a 100 mL flask, 33.2 g (0.21 mol) of DEG-DVE and 26.48 g (0.244 mol) of 1 ,2-propanedithiol were mixed with 0.75 g (0.003 mol) of TAC and heated to 71 °C. To the heated reaction mixture was added 0.15 g (0.8 mmol) of VAZO® 67. The reaction proceeded substantially to completion after 7 hours to afford 60 g (0.03 mol, yield 100%) of a resin having a T g of -61 °C and a viscosity of 22 poise. The polymer had a noticeable PDT (propane dithiol) odor.
• reaction mixture was maintained at 80°C, and the reaction proceeded substantially to completion after 3 hours to afford 200 g (0.06 mol, yield 100%) of a polymer having a T g of -66°C and a viscosity of 55 poise.
• Example 8 In a small glass jar, 9.11 g (0.036 mol) of PLURIOL® E-200 divinyl ether, 5.71 g (0.031 mol) of DMDO, 1.52 g (7.8 mmol) of ECHDT, 5.08 g (0.031 mol) of DMDS and 4.11 g (0.024 mol) of hexanediol divinyl ether (HD-DVE) were mixed with 0.39 g (1.6 mmol) of TAC (heated briefly to dissolve the TAC) and heated to 82°C. To the heated reaction mixture was added 0.6 g (3.1 mmol) of VAZO® 67.
• the reaction proceeded substantially to completion after about 45 hours to afford 2.6 g (7.8 mmol, yield 100%) of a polymer having a T g of -66°C and a viscosity of 304 poise.
• the polymer had a cloudy appearance.
• control polymer The polymer described in Example 3 of U.S. Pat. No. 4,366,307 was used as a control.
• This polymer (the "control polymer") had an odor of 3.
• the polymers prepared in Examples 1-8 were then cured. Curing was carried out using the uncompounded resins with a curing agent and DABCO accelerator.
• the curing agent had the following composition:
• epoxy novolac 1 (equivalent weight 175.5) 22 wt % hydantoin epoxy 2 (equivalent weight 132) 34 wt % calcium carbonate 34 wt % carbon black 5 wt % silane adhesive promoter 5 wt %
• % volume swell 100 x [(W 2 + w 3 )-(w ⁇ + w )]/(w- ⁇ - W 2 )
• control polymer had an odor of 1-2 when cured.
• Polythioethers having a number average molecular weight of 2100 and an average SH functionality F of 2.1 were prepared by combining a divinyl ether with a dithiol as shown in Table 2 and reacting the materials as previously described herein.
• the uncompounded polythioethers were then cured using 15 g of the curing agent described above and 0.30 g of DABCO.
• the following quantities were measured: viscosity (uncured material, poise p); Shore A hardness (cured material, Rex durometer value); % weight gain (cured material) after one week at 140°F (60°C) and atmospheric pressure in JRF type 1 ; and T g (cured material, °C). Results were as follows: TABLE 2
• Example 9 Each resultant uncompounded polymer was cured as in Example 9 (15 g of the curing agent composition and 0.30 g of DABCO). For each polymer, the following properties were measured: T g (resin, °C); T g (cured, °C); viscosity (p); % swell in JRF type 1 ; % weight gain in JRF type 1 ; and % weight gain in water. Results are given in Table 3.
• Each of these polymers had a number average molecular weight of about 3000 and a SH functionality F of 2.2.
• Each resultant uncompounded polymer was cured as in Example 10.
• T g resin, °C
• T g cured, °C
• viscosity p
• % swell in JRF type 1 % weight gain in JRF type 1 ; and % weight gain in water. Results are given in Table 4.
• Example 13 In a 250 mL 3-neck flask equipped with a stirrer, thermometer and condenser, 26.7 g (0.107 mol) of TAC, 56.4 g (0.357 mol) of DEG-DVE and 117.0 g (0.642 mol) of DMDO are mixed and heated to 77°C (about 170°F). To the mixture is added 0.8 g (4.2 mmol) of VAZO 67 catalyst. The reaction mixture is reacted at 82°C (about 180°F) for about 6 hours to afford 200 g (0.07 mol, yield 100%) of a high viscosity liquid polythioether resin having an equivalent weight of 800 and a SH functionality F of about 3.5.
• Example 14 Sealant Composition
• a sealant composition including the DMDO/DEG-DVE polythioether polymer of Example 1 was compounded as follows (amounts in parts by weight):
• the compounded polymer was mixed intimately with the epoxy resin curing agent of Examples 9-11 above, in the weight ratio of 10:1 and cured at ambient temperature and humidity. Tensile strength and elongation were evaluated according to ASTM 3269 and AMS 3276. The die used to prepare the test samples is described in ASTM D 412. The die used to prepare test samples for tear strength testing is described in ASTM D1004. The following physical properties were obtained for the cured composition: Cure hardness at 25°C 60 Shore A
• a sealant composition including the ECHDT/DEG-DVE polythioether polymer of Example 9 was compounded as follows (amounts in parts by weight):
• the compounded polymer was mixed intimately with an epoxy resin curing agent of Examples 9-12 above in the weight ratio of 10:1 and cured at ambient temperature and humidity.
• the following physical properties were obtained for the cured composition:
• a sealant composition including the DMDO/DEG-DVE polythioether polymer of Example 1 was compounded as follows (amounts in weight percent):
• the phenolic/polysulfide adhesion promoter was prepared by reacting about 31% VARCUM 29202 phenolic resin, 66% Thiokol LP-3 polysulfide and 3% of a polymer prepared according to Example 4 of U.S. Patent No. 4,623,711 (at a ratio of 1 mole dithiol to 1 mole polysulfide) (incorporated by reference herein) at a temperature of about 150°F (65°C) for 45 mins, then heated to 230°F (110°C) over a 45-60 minute period, then heated at 230°F (110°C) for 165 mins.
• a sealant formulation according to the present invention was prepared by mixing 100 grams of the Base Composition with 18.5 grams of the Accelerator.
• compositions of the present invention are useful in aerospace applications such as aerospace sealants and linings for fuel tanks; and as electrical potting or encapsulant compounds.
• An aerospace sealant material according to the present invention can exhibit properties including extreme temperature performance, fuel resistance and flexural strength.
• the formulations detailed herein are well suited for use as potting compounds to encapsulate electrical and electronic components that can experience temperature extremes, chemically harsh environments and mechanical vibrations.

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