Fluoroalkyl acrylate polymeric propellant compositions

United States Patent Office

3,255,059

Patented June 7, 1966

255 059 FLUOROALKYL ACRYLATE POLYMERIC PROPELLANT COMPOSITIONS

Charles L. Hamermesh, Canoga Park, and Chester F. Makuch, Woodland Hills, Calif., assignors to North American Aviation, Inc.

No Drawing. Filed July 9, 1962, Ser. No. 208,642

Claims. (Cl. 149—19)

Propellant performance is a function of propellant density. The importance of propellant density with its effect on the range and payload is exemplified by various volume limited missiles. The direction of past efforts to obtain such high density systems has ben through the replacement of the oxidizer by more dense ingredients. This approach has always resulted in severe reduction in specific impulse in the more dense system. Additionally other problems were numerous. For example, the mixture of lithium perchlorate and ammonium perchlorate resulted in propellants which were very difficult to cast. In an effort directed to the use of the very high density metals such as zirconium and titanium, the formulations developed were quite difficult to cast. Other shortcomings of this system were the sensitivity of such propellants, poor combustion efficiency, and very low delivered impulse. Very little effort has been directed to the development of binders with increased density.

This invention concerns novel fluoropolymers. More particularly, the invention pertains to fluoropolymers used as solid propellant binders and additionally is directed to a new method for vulcanizing rubber-type compounds.

An object of this invention is to provide a new solid propellant binder composition. An additional object of this invention is to provide a solid propellant binder composition having a high density.

A further object of this invention is to provide a solid propellant binder composition having high stability and thermo-sensitivity.

One other object of this invention is to provide a novel solid propellant formulation.

A still further object of this invention is to provide a self-curing diolefin polymer.

Other objects and advantages will become apparent from the following detailed description.

This invention concerns a novel polymeric propellant binder prepared from the reaction of fluoroalkyl acrylate esters selected from the class consisting of 1,1,-dihydroperfluoroalkyl acrylate and α,α,ω,-trihydrofluoroalkyl acrylate esters having from two to 11 carbon atoms in the alkyl group and at least one-co-monomer having both an ethylenic linkage and a functional group capable of entering into cross-linking after polymerization. When reacting the fluoro acrylate ester with more than one comonomer, only one of such co-monomers need possess both the ethylenic linkage and a functional group capable of entering into .cross-linking; the remaining comonomers need possess only an ethylenic linkage. The number of various co-monomers to be reacted with the fluoroacrylate esters is immaterial and any number can be used so long as the above criteria is met.

The proportion by weight percent of fluoroacrylate ester to the other co-monomers, varies from 99:1 to 1:99. A more preferred range of proportions of acrylate to monomer is 50:50 to 95:5. However, since the presence of fluorine is highly desirable, the preferred range of the proportion of fluoroacrylate ester to monomer is 75:25 to 90:10.

It has been discovered that a castable propellant composition can be. obtained at 78 percent solids loading if, for example, an 80:20 coarse: Fine' ammonium perchlorate were employed in a solid propellant formulation.

A solid propellant grain can be formulated having from 10 to 40 weight percent of the binder of this invention, from 50 to 85 weight percent of oxidizer and from 0 to 25 weight percent of fuel. Composition containing 62 weight percent of the ammonium perchlorate, 16 weight percent of aluminum, 18.4 weight percent of the novel binder and 3.6 weight percent of a highly-fluorinated surfactant such as fluoroalkyl pyromellitate produces a propellant having a density of 1.95 g./cc. and a calculated impulse of 258 seconds which is considerably above the current state-of-the-art for high density systems.

The fluoroalkyl acrylate ester utilized in this invention has the following general formula:

Ri R, O 0=0-(^-00^-(0 FiA-X I

H wherein X is selected from the class consisting of hydrogen and fluorine, and n is an integer from 1 to 10, such that when X is hydrogen, n is an even integer, where Ri and R₂ are selected from the class consisting of hydrogen, alkyl and cycloalkyl radicals of 1 to 8 carbon atoms, cyano, halogen, phenyl radicals and alkanoic acids of 1 to 6 carbon atoms such that at least one of said Ri and R₂ is hydrogen.

In the above formula when X is a hydrogen, the compound is an α,α,ω-trihydrofluoroalkyl acrylate ester and when X is a fluorine, the compound is 1,1-dihydroperfluoroalkyl acrylate ester. Illustrative members of the above acrylates include: 1,1,3-trihydrotetrafluoropropyl acrylate; 1,1,5-trihydrooctafluoropentyl acrylate; 1,1,7trihydrododecafluoroheptyl acrylate; 1,1,3 - trihydrotetrafluoropropyl β - methylacrylate; 1,1,7 - trihydrododecafluoroheptyl β - chloroacrylate; 1,1,11 - trihydroeicosafluoroundecyl β - fluoroacrylate; 1,1,9 - trihydrohexadecafluorononyl β - butylacrylate; 1,1,5 - trihydrooctafluoropentyl a. - acetic acid acrylate; 1,1,7 - trihydrododecafluoroheptyl β - cyanoacrylate; 1,1,9 - trihydrodecafluorohexyl a - phenylacrylate; 1,1,7 - trihydrotetradecafluorooctyl β - fluoroacrylate; 1,1 - dihydroperfluoroethyl acrylate; 1,1 - dihydroperfluorooctyl acrylate; 1,1 - dihydropeifluorobutyl a - octylacrylate; 1,1 - dihydroperfluoropentyl a - cyanoacrylate; 1,1dihydroperfluorohexyl β - butanoic acid acrylate; 1,1dihydroperfluoroheptyl a - hexanoic acid acrylate; 1,1 - dihydroperfluorodecyl β - phenylacrylate; 1,1dihydroperfluorononyl a - cyanoacrylate; 1,1 - dihydroperfhiorodecyl acrylate..

Particularly preferred acrylates are 1,1,7-trihydrododecafluoroheptyl acrylate and 1,1,9-trihydrohexadecafluorononyl acrylate.

The acrylate esters, as described above, can be prepared via an esterification process through the reaction of an acid halide with a fluoro alcohol:

Ri r₃ o

HOCHa—(CFa)_n—X + C=G— C-Cl --->

H

Ri Ra O I I II C=C-G-OCI-r_!-(CF₂)„-X + HCl

I H where η, X, R_x and R₂ are as defined above.

Alternatively, the esters may be prepared by direct reaction of a fluoro alcohol with an organic acid and the simultaneous removal of the water formed by the reaction. An appropriate hydrocarbon solvent such as benzene, toluene or xylene and an acid catalyst such as p-toluenesulfonic acid may be used. The preparation of the starting fluoro alcohols where X is hydrogen is well known and described in United States Patent 2,559,3,255,059

628 and in Industrial and Engineering Chemistry, vol. 51, page 829 (1959). Generally the fluoro alcohols where X is hydrogen are prepared by the free radical telomerization of tetrafluoroethylene with methanol. It is because of this method of preparation that n will always be an even integer when X is hydrogen since the structure will contain a plurality of ethylene groups. Where X is fluorine, the starting alcohols are the reduction products of the corresponding perfluoro acids. These acids are prepared from the electrochemical fluorination of organic compounds as described in Industrial and Engineering Chemistry, vol. 43, pp. 2332—34 (1951). The preparation of the fluoropolymer where X is fluorine is described in United States patent 2,642,416.

At least one of the co-monomers which is reacted with the fluoroalkyl acrylates to form the novel polymers of this invention must be a compound having both an ethylenic linkage and a functional group capable of entering into cross-linking after the polymerization with the acrylates for curing purposes as will be described below. The reason for this requirement is that the polymer formed from the reaction of the acrylate ester and monomer is essentially a prepolymer which much be capable of further polymerization or cross-linking when used as a binder for a solid propellant. In such an application, the liquid prepolymer is mixed with the solid fuel and oxidizer ingredients of the propellant and then further polymerized or cured through the remaining reactive sites on the comonomer. When more than one co-monomer is utilized, then such additional co-monomer or co-monomers need only possess an ethylenic linkage. Non-limiting examples of the co-monomers that may be utilized in the invention include the vinyl halides such as iodoethene, bromoethene, fluoroethene, chloroethene; vinylidene halides including vinylidene chloride, vinylidene iodide, and the like; unsaturated dibasic acids, their esters and their amines such as 2,3-dicarboxy propene, dibromofumarate, dichloromaleate, difluoromaleate, bromomaleate, iodofumarate, methyl maleate, diethyl fumarate, dibutyl fumarate, propyl fumarate, fumaramide, maleamide, and the like; vinyl esters of carboxylic acids having 1 to 10 carbon atoms including vinyl acetate and the like; and N-substituted acrylamides and methacrylamides including N-methylacrylamide, N-propyl methacrylamide, N-hexyl acrylamide and the like; allyl and methylallyl monomers including allylamine, N-methylallylamine, allyl bromide, allyl alcohol, allyl chloride, allyl cyanide, allyl fluoride, allyl glycidyl ether, allyl isodide, allyl mercaptan, allyl sulphide, and the like; isopropenyl monomers including isopropenyl bromide; isopropenyl chloride, isopropenyl fluoride, and the like; vinyl compounds including vinyl alcohol, vinyl bromide, vinyl fluoride, vinyl cyanide, vinyl sulphide, vinyl tribromide, vinyl ether, vinyl naphthalene, and the like; vinyl ethers including ethenyloxyethene, propenyloxyethene, and the like; acrylates and methylacrylates including ethyl acrylate, methyl acrylates, propyl methylacrylates, hydroxy propyl methacrylate, hexyl acrylate, and the like; glycidyl acrylates, glycidyl methacrylates, and the like; and styrene.

The polymers of this invention may be prepared, by utilization of either emulsion or bulk polymerization. In the emulsion polymerization, the fluoroacrylate monomer and the co-monomer are reacted in an aqueous media. To obtain a liquid product, high percentages of chain transfer agents such as for example, dodecyl mercaptan, are employed. Even at high mercaptan content, mixtures containing the highly-fluorinated acrylates such as 1,1,9-trihydroundecafluorononyl acrylate do not yield liquid products which are more desirable for use as propellant binders. The emulsion polymerization process requires a step for the removal of water from the resin prior to its use in the propellant formulation since water is intolerable in a solid propellant formulation.

It is preferred that bulk polymerization be utilized for the preparation of the compounds. Bulk polymerization is one in which no solvent or dispersing medium is employed. The products of this invention obtained are generally liquid even in the highly-fluorinated acrylates by the use of this process. Additionally, there is no need to isolate the undesirable water from the final composition. In this process, molecular weight and viscosity of the resinous products of this invention are controlled by the amount of chain transfer agent utilized. Additionally, the time of reaction does not affect the chain length of the polymers. Since the polymer is initiated and propagated and terminated in a millisecond, the length of the chain as described is controlled by the presence of the chain transfer agent rather than time of reaction. Such chain transfer agents include, for example, dodecyl mercaptan and carbon tetrachloride. Some of the comonomers utilized in preparing the polymers of the invention such as allyl glycidyl ether are chain transfer agents themselves and thus, very little mercaptan is necessitated in preparing polymers from such co-monomers. Chain initiators such as benzoyl peroxide, cumene hydroperoxide, and the like may be utilized in the bulk polymerization to affect the speed of the reaction, the exotherm and to some extent the molecular weight range of the product obtained.

It is believed that the method of preparing the polymers of this invention will be better understood from the following detailed examples.

Example I

To a clean one liter open glass flask was added 90 grams of 1,1,7-trihydrododecafluoroheptyl acrylate, 10 grams of glycidyl methacrylate as the two monomers to be used. Additionally added were three grams of dodecyl mercaptan to act as a chain transfer agent and 0.33 gram of benzoyl peroxide as the initiator. The composition was then stirred and placed on a heating mantle to bring up to the temperature of reaction. The reaction temperature was 55° C. and the compounds were maintained at this temperature for five and one half hours. The flask was then removed from the heat mantle and the contents were allowed to cool to room temperature. The normallyliquid polymer of this invention was obtained. Conversion to polymer is at least 90 percent and can be determined by the amount of non-volatile solids remaining after completion of the process.

Example II

The method set forth in Example I was followed to prepare a polymer of this invention. The temperature employed was 55° C. and the reaction time was eight hours. The following formula was used:

Grams

1,1,7-trihydrododecafluoroheptyl acrylate90.0

Allyl glycidyl ether10.0

Dodecyl mercaptan 3.3

Benzoyl peroxide .6

The liquid polymer of this invention was obtained. The acrylate used was 1,1,3-trihydrotetrafluoropropyl acrylate as the fluoroacrylate in the above yields a liquid polymer of this invention.

Example III

Procedure set forth in Example I was repeated employing a temperature of 65° C. and a reaction time of five hours. The formula used was;

Grams

1,1,9-trihydrohexadecafluorononyl acrylate98.00

Glycidyl methacrylate 2.00

Dodecyl mercaptan .80

Benzoyl peroxide .33

A liquid polymer was obtained. A liquid polymer is also obtained utilizing 50 grams of each the fluoroacrylate and methacrylate set forth above.

3,255,059 s

Example IV

The procedure set forth above was repeated employing a reaction temperature of 65° C. and reaction time of five hours to obtain a liquid polymer. The following formula was used:

Grams

1,1,9-trihydrohexadecafluorononyl acrylate90.0

Hydroxy propyl methacrylate10.0

Dodecyl mercaptan 1.1

Benzoyl peroxide 3.3

A liquid polymer was obtained. A likewise good polymer is produced substituting 1,1-dihydroperfluorobutyl acrylate as the fluoroacrylate in the above formula.

Example V

The above procedure set forth in Example I was again used with a temperature of 65° C. and reaction time of four hours. The following formula was utilized:

Grams

1,1,9-trihydrohexadecafluorononyl acrylate90.00

Allyl glycidyl ether 8.00

Acrylic acid 2.00

Dodecyl mecaptan 0.06

Benzoyl peroxide 0.66

The liquid polymer of this invention was obtained. Additionally, the substitution of 1,1-dihydroperfluoropentyl <xcyano-acrylate as the fluoroacrylate in the above formula yields a liquid polymer.

Example VI

The procedure of Example I was utilized with a temperature of 65 ° C. and a reaction time of three hours to obtain a liquid polymeric product. The following formula was used:

Grams

1,1,9-trihydrohexadecafluorononyl acrylate91.00

Acrylonitrile 4.0

Acrylic acid 6.00

Dodecyl mercaptan 1.25

Benzoyl peroxide 0.50

The liquid polymer of this invention was obtained. Substituting allyl bromide and hydroxy propyl methacrylate as the two co-monomers in the above formula yields a liquid polymer of this invention.

Example VII

The procedure of Example I was again repeated with a temperature of 65° C. and a reaction time of eight hours to obtain the liquid products of this invention. The following formula was used:

Grams

1,1,9-trihydrohexadecafluorononyl acrylate______ 80.002-ethyl hexyl acrylate15.00

Acrylic acid 1.25

Benzoyl peroxide .40

Example VIII

This example illustrates the preparation of the polymers of this invention by emulsion polymerization technique. To a one liter glass flask open to the atmosphere was added 300 grams of distilled water, 1.15 grams of potassium sulphate as the initiator, and two grams of Duponol WAQ which is the sodium salt of technical grade lauryl alcohol sulphate as the emulsifying agent. Additionally added was 6.6 grams of dodecyl mercaptan as a chain transfer agent. Finally -added is 95 grams of 1,1,7-trihydrododecylfluoroheptyl acrylate and five grams of glycidyl acrylate. The order in which the above ingredients are added is generally of no moment. In part or all of the compounds may be added at the beginning of the reaction. The emulsion is then agitated and heated to the reaction temperature of 55° C. Throughout the run, total non-volatile solids determinations are made to show the course of the reaction. When conversion of mono mer to polymer is better than 90 percent, the reaction is stopped. In this example, time was nine hours. The flask is removed from the heat and the emulsion polymer is then dried. The process of drying consists of adding the resultant emulsion to a barium chloride solution. The coagulated polymer is' then washed with distilled water until no white precipitate occurs when silver nitrate is added to a small sample of the wash water. At this time, all of the wash water is then poured off the polymer. The wet polymer is then. spread in a thin layer over a large-surfaced glass dish and dried in an oven at 60° C. for approximately 12 hours. The resultant liquid in the glass dish is the polymer of this invention.

Though a portion of the invention is directed to the utilization of novel polymers for use as binders in solid propellant applications, it has also been discovered that the homopolymers of the fluoroacrylate esters yield solid polymeric products for utility in fields such as additives to marine paints to lend a protective coating to the material painted.

Example IX

In this example, a homopolymer of 1,1,9-trihydrohexadecylfluorononyl acrylate was prepared according to the bulk polymerization method set forth in -Example I. Utilized was 100 grams of the acrylate ester while 0.8 gram of dodecyl mercaptan and one gram of benzoyl peroxide was used. The reaction temperature was 65° C. and the reaction- time was seven hours. A solid polymeric product was obtained.

The' above examples have utilized non-volatile components in their formulation of the polymer. When a volatile component is desired, such as the use of vinyl chloride as a monomer, the reaction is carried out in what is termed a “bottle polymerizer.” The ingredients including the gaseous component are weighed and loaded into a 32-ounce glass bottle which is essentially a beverage bottle. The bottle is then capped and sealed. It is then affixed to a rotating arm in a water bath which is maintained at the desired reaction temperature. The bottle is affixed so that it rotates end-over-end in the bath serving to constantly stir the ingredients as the polymerization occurs. At the end of the reaction the bottle is removed from the bath, uncapped and the resultant polymer is available. The emulsion polymerization previously described can also be carried out in a bottle polymerizer when volatile monomers are used.

As previously discussed, the polymers of this invention have peculiar utility as binders for solid propellant formulations. The ordinary solid propellant is comprised of a fuel and an oxidizer for such fuel contributing to the combustibility of the material. Since the fuel -and oxidizer are usually in the form of solid minute particles not possessing cohesive properties a binder material is necessitated to hold the particles in intimate relationship with one another in a solid usable mass of propellant. When the binder is in the form of a liquid polymer, such as in this particular application, the fuel oxidizer and binder are intimately mixed, then poured into a mill having the configuration of the desired propellant grain. The propellant is then cast in the mould by curing the material at a given temperature. In the curing process, the polymer becomes solidified and the solid propellant grain desired is obtained. The solid propellant is then removed from the mould and is ready for use in its desired application.

There are several variable factors involved in the production of a solid propellant grain as can readily be seen. These factors all contribute to the desired properties of such a grain. Generally speaking, the. binder material contributes relatively little to the propulsive qualities of the propellant grain as compared to the contribution made by the oxidizer and fuel utilized. Thus, it is desired to maintain the binder content as relatively low

3,255,059 as possible. In other words, the art strives for high solids loading in the production of solid propellants. This means that there is a high percentage of the solid particles of oxidizer and fuel in the binder matrix. Obviously a point is reached where the percentage of the solid materials in the binder matrix is so high that the binder is unable to adequately serve in its function as a matrix material. This limitation depends to a great degree on the structure of the binder itself. One of the particular advantages of the fluoro polymers of this invention is that they have a high solids loading ability for such a dense system. The propellant compositions utilizing the binder material of the invention have been prepared having as high as 80 percent solids loading.

The second major problem concerned with solid propellants in addition to solids loading is the ease of castability. This ease of castability is related to how readily the propellant composition flows into the mould in which it is to be cast. If the amount of liquid binder material decreases in the propellant composition, the ease of castability in turn decreases since the composition takes on the characteristics of the solids present in the formulation. Thus a propellant composition prior to casting will flow more easily when there is 50 percent binder as compared to a composition wherein there is only 15 percent binder. Additionally, the ease of castability is affected by the type of binder material used. Propellant compositions utilizing only 20 percent of the fluoro-polymer binders of this invention are castable, further emphasizing the excellent application of the materials.

The oxidizer materials used may be compounds such as metals perchlorates and metal nitrates. The metal perchlorates employed as oxidizing agents or oxygen carriers in the compositions are anhydrous and have the general formula:

M(C1O₄)_x wherein

M is NH₄ or a metal, and x is the valence of M.

Since the propellant composition is required to withstand high temperature storage, it is preferable that the melting point and the decomposition temperatures of the oxidizer be as high as possible. The perchlorates of the Group I-A, Group I-B, and Group II-A metals are found to have the required high temperature stability and are employed in the preparation of propellant compositions by the process of this invention. Hence, the metal perchlorates used in the preparation of the propellant compositions include lithium perchlorate, sodium perchlorate, potassium perchlorate, rubidium perchlorate, and cesium perchlorate which are the perchlorates of the metals of Group I—A of the Periodic Tables of Elements; silver perchlorate which is a perchlorate of the Group I-B metal; and magnesium perchlorate, calcium perchlorate, strontium perchlorate, and barium perchlorate which are the perchlorates of the Group II—A metals. In addition to the metal perchlorates, the compound ammonium perchlorate finds extensive use in propellant compositions. Examples of the nitrates of the Group I-A, and I-B and II-B which are employed in preparing propellant compositions by the process of this invention are compounds such as lithium nitrate, sodium nitrate, potassium nitrate, magnesium nitrate, calcium nitrate, barium nitrate, strontium nitrate, etc. Ammonium nitrate is also used.

In addition, other oxidizers include bis(2,2,2-trinitroethyl)nitramine; hydroxylamine; nitronium perchlorate; hydrazine nitrate; hydrazine perchlorate; hydroxylamine perchlorate; hydroxylamine nitrate; bis (trinitroethyl) carbonate; nitrosyl tetrafluorochlorate; nitrosyl perchlorate, nitroguanidine nitrate; guanidine perchlorate; guanidine nitrate; 1,2-diaminoguanidine monoperchlorate; nitrylperchlorate; tetranitromethane; diperchlorylacetylene; diperchlorylhydrazine; perchlorylfluoride; perchloric acid dihydrate; lithium-aluminum superoxide; trinitroethyl orthocarbonate; and hexamethylenetetramine tetraperchlorate; cyclotrimethylenetrinitramine; cyclotetramethylene-tetranitramine; linear polymethylenenitramine intermediate and hydrazine nitroform.

The fuel which constitutes from 0 to 25 weight percent of the propellant is normally one or more metals of Groups I-A, II-A, III-A, and Groups I-B through VIIB, and Group VIII of the Periodic Table. Thus, the metal fuel may contain Group I-A elements such as lithium, Group II-A metals such as beryllium or magnesium. Illustrative of the Group III-A metals is aluminum. The metals of Group I-B through VII-B include copper, silver, zinc, cadmium, titanium, zirconium, vanadium, niobium, chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, ruthenium, rhodium, osmium, palladium, and platinum. In certain missile applications, it is desired to prevent detection of the rocket. Such detection is normally accomplished from the metal oxide particles in the exhaust of the rocket. Thus, it is feasible to eliminate the metal fuel particles and utilize only the oxidizer with binder which will function sufficiently as a propellant. An example of such a formulation is one containing 12 weight percent of a binder of this disclosure and 88 weight percent of an oxidizer such as ammonium perchlorate.

Additionally, the metal fuel can take the form of wires or fibers embedded in the grain as disclosed in co-pending application Serial No. 144,265, filed October 10, 1961.

Other substances which are employed in the preparation of propellants by the process of this invention include minor amounts of burning catalysts, well known in propellant compositions. These are composed of one or a mixture of two or more metal oxide powders in amounts sufficient to improve the burning rate of the composition. The amounts usually range from about 0.01 to about three weight percent, based on the weight of the oxidizer employed. The particle size of the powders can range from about 10 to about 250 microns in diameter. Non-limiting examples of metals that serve as burning catalysts are copper, vanadium, chromium, silver, molybdenum, zirconium, antimony, manganese, iron, cobalt, and nickel. Examples of metal oxide burning catalysts are ferric oxide, aluminum, copper oxide, chromic oxide, as well as the oxides of the other metals mentioned above. Additionally, materials may be added to the propellant formulation which serve as coolants to reduce the temperature of the exhaust gases. Such compounds include hydrazine azide, hydrazine azide hydrazinate, carbonates such as ammonium carbonate, crotonates such as ammonium crotonate, compounds containing boron and nitrogen which yield B-N as exhaust products such as pentaborane-amine adducts.

The particle size of the oxidizer utilized in the propellant formulations of the invention varies from 10 to 400 microns. Though a single modal oxidizer may be used, particularly preferred are bi-modal blends. An example of such a bi-modal blend is a 70:30 percent blend of 200 micron: 10 micron ammonium perchlorate. In addition to the bi-modal blends of oxidizer, tri-modal blends may be utilized to get even further fluidity in the propellant. The fuel particles may vary in size from 10 to 100 microns. A typical particle size of such a fuel particle is 35 microns. In addition to a single modal fuel, bi-modal blends can readily be used. The preparation of propellant formulations of this invention will be better understood from the following examples.

Example X

To a vertical blade mixer such as a Baker-Perkins mixer for solid propellants was added 73.6 grams of 90:10, 1,1,9-trihydrohexadecafluorononyl acrylate-glycidyl methacrylate co-polymer of this invention as the binder for the propellant. Next is added 64 grams of 35 micron aluminum particles as the fuel.

3,255,069

Additionally, the castability may be improved if a highly-fluorinated surfactant is added to the composition during the mixing thereof. A typical surfactant utilized is Zonyl E-7 which is fluoro-alcohol pyromellitate. In this example, 14.4 grams of Zonyl E-7 was added. The propellant prepared in this example has a density of 1.95 grams per cubic centimeter and calculated specific impulse of 258 seconds. Specific impulse is defined by the formula:

Z_sp=F/JT where

4p= specific impulse in 16/(16/sec.), F=thrust in pounds, and

W—weight flow rate of propellant in Ib./sec.

This calculated impulse is based on 1000 p.s.i. chamber pressure expanded to 14.7 p.s.i.a. and with shifting equilibrium. The mixer is then started to disperse the metal within the binder. After the metal is dispersed then 248 grams of 200:20 micron coarse:fine ammonium perchlorate blend is added to the mixer. The composition is then mixed until the aluminum and ammonium perchlorate is evenly dispersed throughout the binder matrix. If the reactive groups on the co-monomer require an external cross-linking agent in order to react, such as crosslinking agent is added to the mixer just before the mixing is completed. Such a cross-linking agent is MAPO which is tris[l-(-2-methyl)aziridinyl]phosphine oxide or PAPI which is polymethylene polyphenylisocyanate. An example of a co-monomer that requires such a cross-linking agent is acrylic acid. The mixing is then stopped and the resultant propellant composition is then poured into the mould used to cast the propellant grain. A mould is used in this application in order to enable testing of mechanical properties. Conventional casting directly in the motor casing can be utilized, however. The casting is then placed in a conventional oven maintained at a temperature of 200° F. for 25 hours. The curing time for the propellant compositions of the invention varied depending upon the constituents used in the binder material. Generally, the cure time is from 18 hours up to seven days. Additionally, the curing temperature may also vary and as can readily be appreciated, the higher the curing temperature, the fewer hours needed to heat the propellant formulation. The cure' temperature can vary from 110° F. up to 200° F. When the propellant is to be used in an actual motor, it is cast directly in the motor casing and is bonded to the casing by secondary valence forces.

Example XI

The above procedure of making the propellant formulation was repeated utilizing as the binder 2.074 grams of 1,1,9 - trihydrohexadecafluorononyl acrylate - glycidyl methacrylate. Used as a surfactant was 0.364 grams of Zonyl E-7. The fuel was 1.8 grams of aluminum having a particle size of 35 microns. A highly energetic oxidizer in the form of 5.8 grams of hydrazine nitroform was added to the formulation. The resultant propellant had a density of 1.90 grams per cubic centimeter and had a calculated specific impulse of 270 seconds. The above composition was prepared utilizing 26 percent binder, 16 percent aluminum and 58 percent ammonium perchlorate. Successful ballistic properties were obtained. Obviously, propellant formulations of higher percentage binder can be prepared as previously described. However, the lower binder content is preferable for the reasons set forth above. Thus, it is preferred to keep the binder content below 25 weight percent.

Another aspect of this invention is the unusual and unexpected results obtained when a diolefin such as butadiene as a co-monomer is reacted and polymerized with the fluoroacrylate esters of this invention. The polymerization is essentially the procedure set forth in the exam10 pies relating to the bottle polymerization process used. It has been unexpectedly found that the liquid pre-polymers obtained are self-curing upon being heated at 70° F. to 400° F. from about fifteen minutes to seven days. Obviously, the higher the cure temperature, the shorter the cure time required. The ability of the mixture to self-cure is of particular moment since the normal step of vulcanization utilizing conventional sulphur recipes or other method of vulcanization using external agents has been eliminated. Thus, the reaction transpires in the absence of sulphur or other vulcanizing agents. The elimination of the vulcanization process has particular utility in the field of manufacturing synthetic rubber materials wherein present-day rubber compositions require this step of vulcanization. Propellant formulations utilizing these diolefin pre-polymers as a binder cure at temperatures between 110° F. and 200° F. Additional diolefins include propadiene, 1,3-pentadiene, 1,4-pentadiene, isoprene, 1,5-hexadiene, and the like.

The diolefin acrylate ester polymers are self-curing at any ratio of monomers used. Thus, liquid pre-polymers are obtained within weight percent ratios of 1:99 to 99:1, of butadiene to fluoroacrylate ester. The ability to have a self-curing system with a wide range of proportions of diolefin lends flexibility to the desired properties of the polymers obtained. By eliminating the usual external curatives, to cause the vulcanization or curing, several problems in the rubber industry are eliminated, such as oxidative cracking of the rubber when such curvatives are employed.

The technique for polymerization of the polymer is dependent on the end use of application. If a propellant is desired, bulk polymerization to yield a liquid product is preferred for the reasons previously disclosed. If a given stock rubber is desired, emulsion polymerization to yield a high molecular weight solid product will be utilized. Additionally, when a stock-rubber end product is desired, solution polymerization may be employed to prepare the pre-polymers of the fluoro acrylate ester and diolefin. The solution polymerization may be carried out by four different methods: (1) utilizing sodium naphthalide as a catalyst in a solvent such as tetrahydrofuran or cyclohexane, (2) using sodium as a catalyst with xylene as the solvent, (3) the Alfin process which comprises using a sodium alkyl catalyst such as ethyl sodium or isopropyl sodium in an aliphatic solvent such as heptane, and (4) by the Ziegler process using a mixed catalyst of titanium tetrachloride and aluminum alkyl such as trimethyl aluminum in an aliphatic solvent.

Since butadiene is the most commonly-used diolefin, the discussion will be generally limited to its application. Because butadiene has a boiling point of —3 ° C. and is thus normally a gas, the bulk polymerization to form the pre-polymer is carried out using the bottle polymerizer as previously described. The amount of chain transfer agent which may be used, dodecyl mercaptan, for example, can vary from 0 to 10 parts per hundred parts of monomers with a preferred range of 0.25 to 0.5 part per hundred parts of monomers being utilized. The higher the amount of chain transfer agent used, the lower the molecular weight of the pre-polymer obtained since the average chain length will be shorter. The amount of the transfer agent that is utilized will thus depend upon whether the desired pre-polymer to be obtained will have physical properties of liquid, gel, or semi-solid state. The catalyst that is used in the reaction which may be benzoyl peroxide, for example, may vary up to two parts per hundred parts of polymer with a preferred range of 0.1 to one part per hundred parts. Particularly preferred is 0.5 part per hundred parts of monomers. Since the catalyst speeds up the reaction, it is important not to have too great an amount present. The heat of reaction, could be increased to a point where the polymerization would run away and become uncontrolled, possibly causing an explosion. The reaction temperature or the temperature

3,255,059 ¹¹ of the bath used may vary from 30 to 80° C. with a preferred range of 45 to 65° C. The reaction is normally run from 18 to 45 hours yet it could be run for a week, though such is generally not necessary to obtain the desired polymeric product.

Example XII

To a 32-ounce bottle polymerizer was added 190 grams of 1,1,9-trihydrohexadecyltrifluorononyl acrylate and 10 grams of butadiene. Additionally added was 0.20 grams of dodecyl mercaptan and 1.8 grams of benzoyl peroxide as the initiator. The bath temperature was maintained at 60° C. and the reaction time was 20 hours. The resulting polymer was a gel. This gel cured with no additional curing agent when maintained for one hour at 200° F. When the above procedure was repeated using 1,1,5-trihydrooctafluoropentyl acrylate as the fluoro acrylate ester, a self-curing polymer is obtained.

Example XIII

The process in Example XII was repeated using the following formula:

Grams

1,1,9-trihydrohexadecyltrifluorononyl acrylate — 540.00

Butadiene 60.00

Dodecyl mercaptan 4.98

Benzoyl peroxide 1.80

The bath temperature was also 60° C. and the reaction time was 20 hours. A liquid polymeric product was yielded from the above reaction. This product was selfcuring with no additional additive when heated at 200° F. for one hour.

Example XIV

The procedure in Example XII was repeated utilizing the following formula:

Grams

1,1,9-trihydrohexadecyltrifluorononyl acrylate — 150.00

Butadiene 50.00

Dodecyl mercaptan .10

Benzoyl peroxide 2.00

The preceding composition was heated at a bath at 60° C. for 40 hours yielding a liquid polymeric product of this invention. This product self-cured with no additional agent v/hen heated to 200° F. for one hour. When 1,1,7-trihydrododecafluoroheptyl acrylate is substituted as the ester in the above formula, a similar polymeric product of this invention was obtained which possesses a selfcuring characteristic.

Example XV

The procedure in Example XII is repeated using the formula set forth below:

Grams

1,1,9-trihydrohexadecyltrifluorononyl acrylate __ 100.00

Butadiene ________________________________ 100.00

Dodecyl mercaptan_________________________ 0.10

Benzoyl peroxide__________________________ 2.00

The above reactants were heated at 60° C. for 40 hours yielding a liquid polymeric product which was self-curing when heated for one hour at 200° F. When 1,1,dihydroperfluorooctyl acrylate is substituted as the ester in the above formula, a liquid polymer of this invention is obtained having self-curing properties.

Example XVI

The procedure in Example XII is repeated using the formula set forth below:

Grams

1,1,9-trihydrohexadecyltrifluorononyl acrylate — 20.0

Butadiene 180.0

Dodecyl mercaptan 0.0

Benzoyl peroxide 1-8

The above formula was heated at 60° C. for 44 hours yielding a liquid polymeric product of this invention that has self-curing properties. Substituting isoprene in the above example as the diolefin also yields a polymer of the invention having self-curing properties.

In addition to the co-monomers of the fluoroacrylate esters with the diolefins, additional co-monomers may be utilized as needed to give desired properties. Thus, any of the co-monomers, as previously set forth in the case together with the acrylate ester and diolefin, will form a self-curing polymeric system. The proportion of the co-monomer can vary from 1 to 90 percent depending on the end property desired. An example of such a system is the polymer prepared from 1,1,9-trihydrohexadecylfluorononyl acrylate, butadiene and acrylic acid.

Systems employing co-monomers in addition to butadiene form polymers of this invention. Though the fluoro acrylate ester diolefin-type polymers are found to be selfcuring conventional cross-linking agents such as MAPO can be added to facilitate the curing process. This procedure can be pursued, for example, when a ter-polymer of the acrylate ester diolefin and a co-monomer having both an ethylenic linkage and a functional group entering into cross-linking is used as a binder in a solid propellant application. An example is the ter-polymer of 1,1,9-trihydrohexadecyltrifluorononyl acrylate, butadiene and acrylic acid.

Example XVII

The procedure in Example XII was repeated utilizing the following formula:

Grams

1,1,9-trihydrohexadecyltrifluorononyl acrylate — 160.00

Butadiene 20.00

Allyl glycidyl ether 16.00

Acrylic acid 8.00

Dodecyl mercaptan ·03

Benzoyl peroxide 1.80

The above formula was heated at 60° C. for 20 hours yielding a liquid self-curing polymer.

Example XVIII

The procedure in Example XII was repeated utilizing the following formula:

Grams

1,1,9-trihydrohexadecyltrifluorononyl acrylate — 540.00

Butadiene 48.00

Allyl glycidyl ether 12.00

Dodecyl mercaptan .96

Benzoyl peroxide 3.60

The above formula was heated at 60° C. for 20 hours yielding a liquid self-curing polymer. When 1,1,5-trihydrooctafluoropentyl acrylate is used as the ester in the above formula, a likewise liquid self-curing polymer is obtained.

Example XIX

The procedure in Example XII was repeated utilizing the following formula:

Grams

1,1,9-trihydrohexadecyltrifluorononyl acrylate — 170.0

Butadiene 20.0

Acrylic acid 10.0

Dodecyl mercaptan 1.8

Benzoyl peroxide 1.5

The above formula was heated at 60° C. for 20 hours producing a self-curing liquid polymer.

Example XX

A self-curing butadiene-acrylate ester polymer of this invention was prepared utilizing solution polymerization. To a 32-ounce gram bottle was added 45 grams of butadiene and 450 grams of distilled tetrahydrofuran. The bottle was sealed with butyl rubber-lined crown cap. One-half gram of sodium naphthalide in a tetrahydrofuran (2 percent solution) through the self-sealing cap with a syringe. The bottle was then heated in a water bath maintained at 40° C. until conversion to the polymer was 90 percent or better. The time to reach this 90 percent

3,255,059 conversion was from one to two hours. At this time five grams of 1,1,9-trihydrohexadecafluorononyl acrylate was inserted into the .bottle by way of a syringe through the cap and the reaction was run to complete conversion at 40° C. The resultant thick solution of tetrahydrofuranpolymer was then poured from the bottle into the 100 grams of methanol in order to coagulate the polymer. The coagulated polymer was separated and then dried in a glass tray overnight in an oven maintained at 45° C.

Example XXI

The polymer prepared in Example XVI was utilized as a binder for a solid propellant formulation. The propellant formulated utilized 2.074 grams of the polymer prepared in Example XVI. The fuel utilized was 1.8 grams of aluminum having a particle size of 35 microns. Additionally, 5.8 grams of hydrazine nitraform was added to the formulation as the oxidizer. The resultant propellant .had a density of 1.92 grams per cubic centimeter and a calculated impulse of 270 seconds.

As can be seen from the above description and examples, the diolefin-fluoroalkyl acrylate polymer system has substantially advanced the art of producing rubber-like materials. It is now possible to prepare cured rubber-like materials without the aid of vulcanizing agents through the formation of the self-curing polymers described.

Although the invention has been described and illustrated in detail, it is to be clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.