United States Patent (19) 11 Patent Number: 4,531,989 Ducote et al. (45) Date of Patent: Jul. 30, 1985

54 AMINE BONDING AGENTS IN POLYESTER Attorney, Agent, or Firm-Anthony T. Lane; Robert P. BNDERS Gibson; Jack W. Voigt 75) Inventors: Marjorie E. Ducote; Charles L. (57) ABSTRACT Greer, Jr., both of Huntsville, Ala. Amine salts which are adducts of an donor selected from ammonium , ammo 73) Assignee: The t St. s America Fih nium sulfate, , and equal molar mix prey R the tary of the ture of ammonium perchlorate and ammonium formate rmy, Washington, D.C. and cyanoethyl substituted tetraethylene pentamine (TEPAN) or the glycidol reaction product of cyano (21)21 Appl. No.:No 596,345 ethyl substituted tetraethylene pentamine (TEPANOL) (22) Filed: Apr. 3, 1984 are employed as a bonding agent in a solid composition employing a polyester binder of polydie 51 int. Cl...... C06B 45/10 thyleneglycoladipate. (52) U.S. C...... 149/19.2; l, Unlike hydroxy-terminated polybutadiene wherein a bonding agent is solubilized and still can function as a 58 Field of Search ...... 149/19.2, 19.4, 19.5, bonding agent for inorganic ammonium oxidizer salts in 149/20 the propellant matrix, polyester binders that solubilize the bonding agent renders the bonding agent ineffectual (56) References Cited as a bonding agent. Therefore, with a polyester binder- it U.S. PATENT DOCUMENTS was found that the bonding agent could not be soluble 4,000,023 12/1976 Oberth et al...... 149/19.4 in the prebinder to be effective in improving mechanical 4,019,933 4/1977 Cuksee et al...... 49/19.4 properties. It was, however, necessary for the bonding 4, 110, 135 8/1978 Graham et al...... 149/19.4 agent to be finely dispersed since it is driven to the 4, 128,441 12/1978 Cuksee et al...... 149/19.4 inorganic oxidizer salt surfaces where it homopolymer 4,332,632 6/1982 Conyers et al...... 9/9-' izes around or reacts with a second reactant, usually the 4,410,376 10/1983 Bruenner et al. .... 149/19.4 propellant curative to form a shell which will subse

: 1838 Rationas a sess so a so 88: quently react with the binder thus chemically reinforc 2013, '76, f.i. 14676 ing the binder/inorganic oxidizer salt matrix. Primary Examiner-Edward A. Miller 11 Claims, 1 Drawing Figure U.S. Patent Jul. 30, 1985 4,531,989

O STRESS O MODULUS

2O 2OO

OO OOO

2OO 2.O 2.2 2.4 2.6 2.8 3.O %. IPDI 4,531,989 1. 2 binder. Further, bonding agents such as cyanoethyl AMINE BONDINGAGENTS IN POLYESTER substituted tetraethylene pentamine (TEPAN) dis BINDERS closed in U.S. Pat. No. 4,000,023 and the glycidol reac tion product of cyanoethyl substituted tetraethylene DEDICATORY CLAUSE pentamine (TEPANOL) have been employed as bond The invention described herein may be manufac ing agents for polyurethane containing ammonium per tured, used, and licensed by or for the Government for chlorate oxidizing agent. These bonding agents governmental purposes without the payment to us of (TEPAN or TEPANOL), in use, produced a disadvan any royalties thereon. tage in that is liberated during the propellant 10 mix and cure cycles due to displacement of ammonia BACKGROUND OF THE INVENTION from ammonium perchlorate (AP) by amine groups in The function of a bonding agent in an ammonium the bonding agent. The amine-ammonium perchlorate perchlorate oxidized solid propellant is to adequately reaction required subsequent ammonia removal from coat the ammonium perchlorate (AP) surfaces, a point the mix because ammonia could consume part of the of disagreement in the propellant field is whether it is 15 isocyanate curing agent and thus interfere with the cure desirable for a bonding agent to be soluble in the liquid and the mechanism for achieving more desirable me prebinder. It has been postulated that adequate coating chanical properties. would occur when the bonding agent is dissolved in the The above problems were obviated by reacting prebinder; however, recent experimentations indicated TEPAN or TEPANOL with a selected ammonium that most bonding agents that are soluble tend to remain 20 oxidizer salt to form an adduct of TEPAN or TEPA dissolved in the binder even after the solid ingredients NOL and selected oxidizer salt. These adducts of se are added. Some function as a bonding agent still ap lected ammonium oxidizer salts, e.g., ammonium per pears to take place in hydroxy-terminated polybutadi chlorate (AP), (AN), ammonium ene even with solubility of the bonding agent. Better sulfate (AS) and ammonium formate (AF), and their use bonding and thus superior mechanical properties and 25 in employing HTPB binders are disclosed sometimes better aging characteristics have been ob and claimed in copending patent application Ser. No. tained with highly miscible rather than soluble bonding 488,249 by Ducote et al., filed June 9, 1983, and now agent condidates. It is believed that the partial insolubil U.S. Pat. No. 4,493,741. ity of such a bonding agent causes it to be driven to the The present invention relates to bonding agents for surface of the solids where it is needed to perform its 30 function. At the same time, the partial solubility, misci solid propellants employing polyester binders. bility, must be great enough to insure even, adequate Therefore, an object of this invention is to provide coverage of the solids, especially the oxidizer such as excellent bonding agents for use in propellants employ ammonium perchlorate, (AP). The bonding agent cov ing polyester binders. ering the AP surface subsequently reacts with compo 35 A further object of this invention is to provide a nents in the binder, especially the curing agent so that bonding agent which has excellent performance as a the encapsulated AP is mechanically and chemically bonding agent with co-oxidizer ammonium salts in a bound to the elastic binder, thus reinforcing the matrix polyester binder propellant system. system to give superior physical properties. If the bond SUMMARY OF THE INVENTION ing agent is soluble in the binder and there is no force such as a chemical reaction to drive the bonding agent Amine salts when finely dispersed in a solid propel to the surface of the AP, e.g., amine containing bonding lant composition employing a polyester binder improve agent, much of the bonding agent tends to remain dis the propellant mechanical properties. When finely dis solved in the binder and subsequently reacts "in situ' persed (rather than dissolved) the amine salt is driven to with the binder ingredients, especially the polymer and 45 the ammonium oxidizer salt surfaces where is encapsu the curing agent, rather than first encapsulting the AP. lates the ammonium oxidizer and subsequently reacts A state of the art bonding agent HX752, a difunc with the binder, thus chemically reinforcing the binder tional aziridine, is soluble in both hydroxyterminated /ammonium salt oxidizer matrix. polybutadiene (HTPB) and polyester binders at 140°F. The solid propellant is comprised of a binder of the In HTPB propellants with proper processing proce 50 polyester polydiethyleneglycoladipate, polycaprolac dures HX752 performs as an adequate bonding agent. It tone which functions as a trifunctional polymer for is chosen many times because of availability and ease of crosslinking, dioctyladipate plasticizer, isophorone di incorporation into the propellant. However, when isocyanate curing agent, and triphenylbismuth and ma HX752 was used in a polyester binder with AP oxidizer, leic anhydride. Solid oxidizers of ammonium perchlo no bonding occurred. 55 rate and ammonium sulfate are employed. Since HTPB binders have been more widely used in The partially cyanoacrylated tetraethylene pent propellants the problem described above has not come amine (TEPAN) is treated with ammonium perchlorate to light because "state-of-the-art bonding agents' func to yield the adduct of TEPAN and AP. This adduct tion to some degree as bonding agents in HTPB propel contains a ratio of ammonium ion from AP in ratio of lant regardless of their solubility relationship in the 60 1.8 per mole of TEPAN. TEPAN adduct salt is referred prebinder. The decrease in bonding agent performance to as amine salt TC18. TC18 when employed as an has, perhaps by necessity, been compensated for in additive in a baseline polyester binder propellant com HTPB propellants by experimentally adjusting the position maintained greater strain at maximum stress amount of the bonding agent to achieve the desired values at 74 F. an 130 F. processing condition as com strain at maximum stress/break for a required mission. 65 pared with a baseline propellant composition containing Recent propellant developments show that some no bonding agent or as compared with a baseline pro state-of-the-art bonding agents used in HTPB propel pellant composition containing a prior art aziridine lants do not function as bonding agents in a polyester bonding agent. 4,531,989 3 BRIEF DESCRIPTION OF THE DRAWING TABLE III MECHANICAL PROPERTIES The single FIGURE of drawing depicts plottings of At 74 F. At - 130 F. mechanical property data for improved propellant con Stain at Stain at 5 taining the amine Salt as bonding agent as compared to Max Max Max Max control propellants cured with various levels of curing Mix Stress StraBrk Modulus Stress StraBrk Modulus agent but containing no bonding agent. No. psi % psi psi 2. psi M5.7 80 16.6/20,8 697 42 3.6/20.0 456 DESCRIPTION OF THE PREFERRED M5.9 42 27.7/82.5 29 10 M 86 18. A36.9 748 56 15.0/2.4 50 EMBODIMENT M12 64 25.0/312 139 14 19.0/20. 1086 A solid propellant which contains a polyester binder requires a bonding agent that is finely dispersed since a Two mixes of the baseline composition as shown in bonding agent that is soluble in a polyester binder has Table I were processed without bonding agent, e.g., been found to be ineffective as a bonding agent. This 5 mixes M5.7 and M5.9 of Tables II and III. The binder finding is unexpected since the prior art propellants was comprised of the polymer PGA(R18), a polyester, containing hydroxy-terminated polybutadiene (HTPB) PCP 0310, a trifunctional polymer for crosslinking, binder function with aziridine bonding agents and DOA as the plasticizer, IPDI curing agent and TPB and amine bonding agents even when soluble in HTPB. MA as the cure catalyst system. The solid oxidizers were AP and AS. A bonding agent to function properly in a propellant The low stress and strain at both 74 and 130 F. of systern must coat the oxidizer (AP) surfaces. If the oxi mixes M5.7 and M5.9 indicated the necessity of intro dizer (AP) surfaces are not adequately coated with the ducing a bonding agent to the composition for the re bonding agent the AP is only partially bonded to the quired mission. binder matrix, and the soluble bonding agent remaining 25 A state-of-the-art bonding agent for HTPB propel in the binder matrix reacts with the polymer and/or lants HX752, a difunctional aziridine, was added to the curing agent. baseline composition in Mix M11. The HX752 was solu The amine salt, formed as the adduct of partially ble in the polyester prebinder. Unexpectedly no in cyanoacrylated tetraethylene pentamine (TEPAN) and provements in physical properties occurred when the ammonium perchlorate, is finely dispersed as an addi HX752 was added to the polyester binder. This indi tive and functions efficiently as a bonding agent in a cated that the usual AP bonding agents used in other polyester binder propellant containing the ingredients polymer systems might not function in the polyester set forth below in Table I. binder. The amine salt, TC18, was found to be not solu ble in the polyester binder, however, it was readily TABLE I 35 dispersable. Being widely dispersed was found to be BASELINE COMPOSITION preferred to solubility since the polyamine and amine Polydiethyleneglycoladipate. PGA (R-18) 2279-22.29 salts act by another mechanism. TC18, for example, was Isophorone diisocyanate, IPDI found to coat the oxidizer surfaces after being finely Polycaprolactone, PCP-0320 3.72 dispersed and subsequently attaching themselves chemi Dioctyladipate piasticizer, DOA 400 cally to the ammonium ion in ammonium oxidizer salts, Ammonium Sulfate, AS 6.00 e.g., AP and AS in the propellant composition, after Annoniurn Perchlorate, AP 67.00 which further interaction is achieved to form a secure Triphenylbismuth, TPB O.O15 bond of the oxidizer with the binder matrix. Since Maleic Anhydride, MA 0.015 TEPAN requires special processing to compensate for 45 ammonia formation during mixing, an amine salt was Table II, below, sets forth composition variations of selected for evaluation. To minimize ammonia libration curing agent and bonding agent in the mixes shown. and to keep mix time short, the amine salt, TC18 (reac tion product of 1.8 moles of ammonium perchlorate and TABLE II 1.0 TEPAN), was determined to be the best candidate COMPOSITION VARATIONS 50 for Mix M12. Mix No. % PD Bonding Agent/% The TC18 was not soluble in the prebinder but could M5.7 2.75 Norte be readily dispersed. Processing was not affected. End M5.9 2.60 None of mix viscosity for mixes M5.7 and M5.9 was 3.7 kp at M11 2.57 HX752 - 0.20 140 F. and 3.5 kp at 140 F. for Mix M12. M12 2.64 TC8 - 0.20 55 As shown in Table III, stress, strain and modulus significantly increases in M12 at both 74 and 130 F. HX752 is a difunctional aziridine which functions as a Whereas stress decreases by 48% from 74 to 130 F. in bonding agent in HTPB propellants. HX752 is soluble Mix 5.7, stress decreased by only 14% when TC18 in HTPB at 140 F., and though solubility is not thought bonding agent was incorporated. Even though M12 60 was cured to a higher modulus (harder) it still had 34% to be desirable, HX752 does perform as a bonding agent greater strain at maximum stress at 74 F. than M5.7. in HTPB propellants. Unexpectedly, no improvement Extrapolation of mechanical property data from in physical properties occurrred when the HX752 was M5.7 and M5.9, as shown in the single figure of draw added to the polyester binder system. Finely dispersed ing, indicates that if the cure stoichiometry were re TC18 did function quite well as a bonding agent in 65 duced in M12 so that it had a modulus 700 psi (Point A) propellant M12 employing a polyester binder as evi (directly comparable to modulus of M5.7) it would still denced by the mechanical properties comparisons in have a maximum stress of 123 psi (point B), which is Table III below. 54% greater than the 80 psi stress (Point C) of M5.7. 4,531,989 5 6 The data above conclusively show that finely dis persed polyamines and amine salts perform effectively SPECIAL COMMENTS ABOUT TEPAN as bonding agents in polyester binders. The results of ADDUCT AND AMINE GROUPS this data is graphically depicted in the drawing which EQUIVALENTS REQUIRED TO BE REACTED shows the improved stress and modulus values for Mix WITH IN POLYAMINE M12 as compared with mixes M5.7 and M5.9. More that 25% of the amine groups in the polyamine Although the complete disclosures of TEPAN and must be reacted to minimize ammonia evolution when TEPANOL adducts, their preparations and uses in the amine salt adduct is employed in a propellant com HTPB propellants are provided in patent application position as a bonding agent. O Prereaction of approximately 36% of amine groups in Ser. No. 488,249, filed June 9, 1983, their preparation, the polyamine appears to be optimum to minimize am code numbers, and bonding agent identification are monia evolution and obtain optimum physical proper provided below for convenience. ties without the necessity of a dispersing aid. PROCEDURE FOR PREPARATION OF TEPAN Processing time can be greatly reduced with the use ADDUCT 15 of amine salt bonding agents with no loss in propellant mechanical properties or processibility, and without The quantities of ammonium oxidizer salt and equipment change. TEPAN to give the desired adduct ratio are calculated, Since ammonia evolution is minimized, mechanical and the ammonium salt is dissolved in about five times property reproducibility may be expected to be in its weight of distilled water (the quantity of water is not 20 creased even with a reduction in mix time. critical). The salt solution is then added slowly to We claim: TEPAN with stirring at room temperature. Ammonia is 1. A solid propellant composition employing a high liberated during and for a time after addition of the salt solids loading of about 67 parts of an ammonium oxi solution, as detected by odor. After approximately one dizer salt selected from ammonium perchlorate, ammo hour at room temperature the mixture is loosely cov 25 nium nitrate, ammonium sulfate, and annonium for ered and placed in a 70° C.-80 C. oven for three days. mate; a polyester binder system comprised of from Then the adduct solution is transferred to an evaporat about 22.29 to about 22.79 parts of the polyester ing dish and dried by initial open exposure in the polydiethyleneglycoladipate, a trifunctional polymer 70-80 C. oven followed by final drying under vac for crosslinking of about 3.72 parts of polycaprolactone, uum. Many of the adducts tended to pick up water 30 and a plasticizer of about 4.00 parts of dioctyladipate; a when exposed to ambient laboratory air, so finished curing agent of isophorone diisocyanate of about 2.64 adducts are stored in desiccators until used. parts; a curing catalyst of triphenylbismuth and maleic Table IV discloses bonding agent identification and anhydride of 0.015 parts each respectively; and a finely mole ratios of the ammonium ion and amines in the 35 dispersed amine salt adduct of about 0.20 parts as a bonding agents that can be used in a similar manner as bonding agent that is insoluble in said polyester binder TC18. system, said finely dispersed amine salt bonding agent being an adduct of an ammonium salt selected from the TABLE IV ammonium salts consisting of ammonium perchlorate, BONDINGAGENT IDENTIFICATION 40 ammonium nitrate, ammonium sulfate, and ammonium Moles Amine Aid Pet Unreact formate and an amine compound selected from the Salt Annonium Mole ed Amine polyamine compounds consisting of cyanoethyl substi Bonding Ion Donor Poly- Equiv tuted tetraethylene pentamine and the glycidol reaction Agents (Aid) armine Armine alents product of cyanoethyl substituted tetraethylene pent TC-10 Ammonium 1.0 TEPAN 4.0 45 amine. Perchlorate 2. In a solid propellant composition as set forth in TC-2 Annonium 1.2 TEPAN 3.8 claim 1 wherein said amine salt adduct bonding agent is Perchlorate further defined as being the reaction product produced TC-8 Ammonium 8 TEPAN 3.2 by the process which comprises: Perchlorate TC-20 Ammonium 2.0 TEPAN 30 50 (i) dissolving a molar quantity from about 1.0 to about Perchlorate 2.0 of said ammonium salt in about five times its TS-18 Ammonium Sulfate 1.8 TEPAN 3.2 weight of water to form a solution of said ammo TS-36 Annonium Sulfate 3.6 TEPAN .2 nium salt; TF-20 Annonium Formate 2.0 TEPAN 3.0 (ii) slowly adding said ammonium salt solution to said TC-12 Amnonium Fornate 0.6 TEPAN 3,8 & Ammonium 0.6 TEPAN 55 polyamine compound which is present in a molar Perchlorate quantity of about 1.0 while stirring at room temper TOC 145 Ammonium 145 TEPANOL 3.5S ature; Perchlorate (iii) reacting said ammonium salt solution and said "TEPAN has about five amine equivalents present as secondary and a few tertiary polyamine compound together for about one hour amines (confirmed by IR). 60 at room temperature to form an amine salt adduct solution while permitting the liberation of ammo The number after each amine salt bonding agent des nia; ignates its adduct ratio. The codes for the various ad (iv) covering loosely said amine salt adduct solution duct are identified below. after about one hour reaction time and placing TC-TEPAN-AP (ammonium perchlorate) 65 same in a 70° C.-80 C. oven to continue said react TS-TEPAN-AS (ammonium sulfate) ing for about three days; TF-TEPAN-AF (ammonium formate) (v) transferring said amine salt solution to an evapo TFC-TEPAN-50/50 equivalents AP and AF rating dish and drying initially by open exposure in 4,531,989 7 8 a 70 C.-80 C. oven followed by final drying wherein said polyamine compound is the glycidol reac under vacuum; and tion product of cyanoethyl substituted tetraethylene (vi) recovering said dried amine salt adduct and stor pentamine. ing said dried annine salt adduct in a suitable con 9. The solid propellant composition of claim 2 tainer to prevent absorption of moisture. 5 wherein said ammonium salt is annonium perchlorate 3. The solid propellant composition of claim 2 and wherein said polyamine compound is the glycidol wherein said ammonium salt is ammonium perchlorate reaction product of cyanoethyl substituted tetraethyl and wherein said polyamine compound is cyanoethyl ene pentamine. substituted tetraethylene pentamine. 10. The solid propellant composition of claim 2 4. The solid propellant composition of claim 2 10 wherein said ammonium salt is ammonium formate and wherein said ammonium salt is ammonium nitrate and wherein said polyamine compound is cyanoethyl substi wherein said polyamine compound is the glycidol reac tuted tetraethylene pentamine. tion product of cyanoethyl substituted tetraethylene 5. The solid propellant composition of claim 2 pentamine. wherein said ammonium salt is ammonium sulfate and 15 11. The solid propellant composition of claim 2 wherein said polyamine compound is cyanoethyl substi wherein said polyamine compound during processing tuted tetraethylene pentamine. has from about 25 percent to about 36 percent of its 6. The solid propellant composition of claim 2 amine groups reacted with said selected annonium salt wherein said ammonium salt is ammonium formate and to yield said amine salt adduct bonding agent which wherein said polyamine compound is cyanoethyl substi minimizes in situ ammonia generation in the propellant tuted tetraethylene pentamine. composition and decreases mixing time required for 7. The solid propellant composition of claim 2 mixing the propellant composition without sacrificing wherein said ammonium salt is annonium nitrate and the mechanical properties achieved from using said wherein said polyamine compound is the glycidol reac amine salt adduct as the bonding agent for said propel tion product of cyanoethyl substituted tetraethylene 25 lant composition as compared with a like propellant pentamine. composition employing said polyamine compound as 8. The solid propellant composition of claim 2 the bonding agent. wherein said ammonium salt is ammonium sulfate and k k k ck ck

30

35

45

SO

55

60

65