Explosive and thermic compositions or charges – Structure or arrangement of component or product – Solid particles dispersed in solid solution or matrix
Reexamination Certificate
1990-11-21
2002-02-26
Carone, Michael J. (Department: 2203)
Explosive and thermic compositions or charges
Structure or arrangement of component or product
Solid particles dispersed in solid solution or matrix
C149S019600, C523S180000, C525S186000, C525S450000, C528S486000
Reexamination Certificate
active
06350330
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to novel thermoplastic block polymers and methods of making same; and high-energy compositions, such as propellants, explosives, gasifiers, and the like, containing such block polymers therein as binders, which are chemically uncured.
2. Description of the Prior Art
Solid high-energy compositions, such as propellants, explosives, gasifiers, or the liked comprise solid particulates, such as fuel particulates and/or oxidizer particulates, dispersed and immobilized throughout a binder matrix comprising an elastomeric polymer.
Conventional solid composite propellant binders utilize cross-linked elastomers in which prepolymers are cross-linked by chemical curing agents, as typically disclosed in U.S. Pat. No. 4,361,526 and European Patent No. 266,973. As outlined in detail in the referenced U.S. patent there are important disadvantages to using cross-linked elastomers as binders. Cross-linked elastomers must be cast within a short period of time after addition of the curative, which time period is known as the “pot life”. Disposal of a cast, cross-linked propellant composition is difficult, except by burning, which poses environmental problems. Furthermore, current state-of-the art propellant compositions have serious problems that include, but are not limited to use of nonenergetic binder, high end-of mix viscosities, toxic isocyanate curatives, thermally labile urethane linkages, and vulnerability to unscheduled detonation.
Although advantages of thermoplastic elastomers relative to cured elastomers for use in high-energy compositions are appreciated by those skilled in the art, particularly for use in rocket motors, there are reasons why one might not rush to substitute thermoplastic elastomers for cured elastomers in specific applications. Rocket motors are expensive to design, test and produce. Typically, a rocket motor is developed to use a particular propellant composition which has certain mechanical and burn characteristics. If a rocket motor design is successful, there is reluctance to make changes, and particularly to make changes with respect to the propellant composition. Furthermore, designers of rocket motors have a great deal of experience with propellant compositions having cast-cured propellant compositions and are less familiar with the characteristics of propellant compositions having thermoplastic binders.
It is believed that high-energy compositions, particularly solid rocket motor propellants, having thermoplastic binders will achieve greater acceptance if they closely approximate the mechanical and burn characteristics of currently used cast-cured propellant compositions. The present invention is particularly directed to propellant compositions which attempt to approximate the mechanical and burn characteristic of poly(butadiene) based cured propellant compositions.
U.S. Pat. Nos. 3,585,9257 and 4,360,643 and European Patent No. 235,741, in general disclose various block polymers, e.g. of butadiene and lactones, and methods of making same, but nowhere suggest using any such block polymer systems as the binder component in high energy composition such as a propellant for a rocket motor.
Polymers derived in the prior art from branched claim lactones such as 6-hydroxy dodecanoic acid lactone (epsilon or &egr;-laurolactone) and 4-hydroxy dodecanoic acid lactone (gamma or &ggr;-laurolactone), and unsubstituted lactones such as 6-hydroxy hexanoic acid lactone (epsilon or &egr;-caprolactone), are not acceptable for the disclosed utility according to the invention because the melting points of these polymers are below that minimally useful, i.e. less than 70° C.
The methods of making the block polymers as disclosed in these three references are materially different from the methods according to the present invention (particularly as set forth in Examples 1-3 to follow). The lithium, sodium and potassium based methods described therein are not applicable to the preparation of low polydispersity, high molecular weight 12-hydroxy dodecanoic acid lactone (hereinafter &lgr;-laurolactone) polymers in high conversion. None utilize a zinc counter ion wherein diethyl zinc reacts with the hydroxyl end group of the butadiene polymer to form an intermediate zinc alkoxide-tipped polybutadiene which functions as the active initiating species, as in the present invention. Similarly none link previously prepared difunctional hydroxyl-terminated polybutadiene blocks with monofunctional poly (&lgr;-laurolactone) blocks using a diisocyanate and a catalyst, as in the present invention.
An earlier parallel effort of applicant with polyoxetanes to form (AB)
n
type materials using a similar method is the subject of U.S. Pat. No. 4,806,613. This patented method for oxetanes, wherein each of the two blocks is separately allowed to react with a difunctional isocyanate to form isocyanate capped blocks which are then linked with butanediol, is quite different from the present invention.
SUMMARY OF THE INVENTION
The object of the present invention is to provide novel thermoplastic elastomers and methods of making same; and chemically uncured high-energy compositions, particularly rocket motor propellants, formed therefrom.
The thermoplastic elastomers are block polymers in which the polymer molecules comprise at least one poly(butadiene) block which is amorphous in the range of ambient temperatures and at least one pair of poly(lactone) blocks, which are crystalline at temperatures up to about 70° C. flanking the polybutadiene block. The lactones from which the poly(lactone) blocks are formed contain between 8 and 18 carbon atoms in the lactone ring with no carbon or heteroatom substituents other than hydrogen on the ring.
The poly(lactone) blocks preferably contain between 10 and 18 carbon atoms in the lactone ring, and most preferably between 10 and 12 carbon atoms. The preferred lactones are 10-hydroxy dodecanoic acid lactone and 12-hydroxy dodecanoic acid lactone (lambda or &lgr;-laurolactone), the latter is most preferred. The derived poly(lactones) are, therefore, linear polyesters without carbon or heteroatom side chains.
According to the present invention two methods of preparing ABA triblock polymers are disclosed. In the first, a zinc counter ion is utilized wherein diethyl zinc reacts with the hydroxyl end group of the hydroxy terminated butadiene polymer to form an intermediate zinc alkoxide-tipped polybutadiene which functions as the active initiating species. The laurolactone polymer grows off the hydroxyl end groups of the butadiene to form the desired ABA block copolymer, producing low polydispersity, high molecular weight &lgr;-laurolactone polymers in high conversion, which characteristics are critically important for the destined end application/utility, i.e. as a binder for high energy propellant compositions. In the second, previously prepared difunctional hydroxyl-terminated polybutadiene blocks are linked with monofunctional poly (&lgr;-laurolactone) blocks using a diisocyanate and a non-metal based catalyst. This technique allows the use of a “building block” approach to the preparation of large numbers of distinct block copolymers from a smaller number of “building blocks” and also circumvents the use of a metal based catalyst in the block polymerization scheme. The poly (&lgr;-laurolactone) is prepared from &lgr;-laurolactone, diethyl zinc and a suitable mono-functional alcohol such as benzyl alcohol.
Also according to the present invention a method of preparing a different class of thermoplastic elastomeric materials with an (AB)
n
structure (as opposed to the ABA structures resulting from the two methods aforementioned) is disclosed wherein butadiene and &lgr;-laurolactone are linked or polymerized. By this method the direct linking of a hydroxyl-terminated poly(butadiene) of functionality 2.0 with a poly(&lgr;-laurolactone) also with a functionality of 2.0 with a difunctional isocyanate occurs. This somewhat different technique parallels an earlier effort of applicant with polyoxe
Hinshaw Jerald C.
Wardle Robert B.
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