Insensitive propellant formulations containing energetic...

Details Insensitive propellant formulations containing energetic... Insensitive propellant formulations containing energetic...

2000-08-04

2003-01-21

Carone, Michael J. (Department: 3641)

Explosive and thermic compositions or charges

Structure or arrangement of component or product

Solid particles dispersed in solid solution or matrix

C149S019500, C149S019600, C525S410000

Reexamination Certificate

active

06508894

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a propellant composition, and particularly to a propellant composition containing copolyurethane thermoplastic elastomers.
BACKGROUND OF THE INVENTION
In the last decade, there has been a significant interest to develop an improved low vulnerability gun propellant (LOVA) formulation for use in insensitive munitions (IM).
A LOVA gun propellant is one which burns properly when intentionally ignited, but which shows low insensitivity towards unplanned external stimuli such as shock or fire. Although most LOVA formulations of the first generation serve well their purposes, they cannot withstand extreme weather conditions where the propellant is subjected to very low temperature, less than −20° C. In cold weather, the first generation of LOVA formulations as well as the conventional gun propellant formulations loose their mechanical integrity as the gun propellant grains become brittle and crack, which can cause overpressures in the gun barrels leading to breech bursts. Moreover, gun cartridges filled with brittle grains are more sensitive to external stimuli. Hence, they can provoke catastrophic accidents as well as erratic ballistics.
A directive of one embodiment of the present invention is to provide propellant compositions which are capable of exhibiting good mechanical behavior under cold weather.
Propellant compositions commonly include energetic copolyurethane thermoplastic elastomer (TPE). Thermoplastic elastomers typically consist of copolymer chains having monomers A and B distributed throughout the chains as ABA or AB, where the A is the hard segment providing the thermoplastic characteristic and B is the soft segment providing the elastomeric behavior to the polymer. Conventionally, the A segment is formed by a crystalline homopolymer and the soft segment is formed by an amorphous homopolymer.
Thermoplastic elastomers of the type ABA are usually obtained by polymerization the soft B segment followed by the addition of the hard A segment, which is crystallisable. To achieve this type of copolymerization, monomers of both types should have similar reactivity to provide a copolymer of controlled structure with suitable adjustable mechanical properties. A good example of this type of technology is the preparation of 3-azidomethyl-3-methyloxetane and 3.3-bis(azidomethyl)oxetane (AMMO/BAMO) energetic thermoplastic elastomer described in U.S. Pat. No. 4,707,540, issued to Manser et al., Nov. 17, 1987 and U.S. Pat. No. 4,952,644, issued to Wardle et al., Aug. 28, 1990. In this energetic thermoplastic elastomer (ETPE), the thermoplastic part is obtained by the crystallization of the BAMO polymer. Manser et al. also described the use of these AMMO/BAMO energetic homopolymers as prepolymers in making thermoset binders for use in propellants. To obtain the thermoset binders, Manser et al. would typically cure the AMMO/BAMO prepolymers with a triol and diisocyanate to form a chemically cross-linked matrix to obtain the desired binder.
In the case of copolymers of the type AB, the thermoplastic elastomers are usually obtained by mixing monomers that have compatible reactive ending groups. U.S. Pat. No. 4,806,613, to Wardle, Feb. 21, 1989, describes such a method of synthesis. Similarly to Manser et al., Wardle also uses BAMO as the crystalline hard segment. In this, both the A and B homopolymers were end capped with toluene diisocyanate (TDI) leaving at each end an unreacted isocyanate. The homopolymers were mixed and joined by using a small chain extender. Alternatively, Wardle used a block linking technique consisting of reacting the B block with phosgene or a diisocyanate followed by the addition of the A block to form the thermoplastic elastomer. Once again, the crystalline homopolymer BAMO which is an expensive starting material is required to form the hard segment of the thermoplastic elastomer. Moreover, this type of thermoplastic elastomer is not recyclable. Hence the use thereof in a gun propellant would produce a propellant that is expensive to make and non-recyclable. Therefore, there exists a need for a gun propellant that is inexpensive and recyclable.
SUMMARY OF THE INVENTION
One object of one embodiment of the present invention is to provide propellant compositions which are useful in cold weather and which incorporate thermoplastic elastomers having copolymer chains with urethane moieties physically bonded by hydrogen bonds to yield the hard segment of the thermoplastic elastomer.
A further object of one embodiment of the present invention is to provide a propellant composition comprising an energetic copolyurethane thermoplastic elastomer, the thermoplastic elastomer including a hard segment generated by the formation of hydrogen bonds between a first urethane group of one linear copolymer chain with a second urethane group of another linear copolymer chain.
Preferably, the amount of energetic copolyurethane thermoplastic elastomer in the propellant composition of the present invention ranges from about 7 to about 15 weight percent, and most preferably, it is in an amount of about 9 weight percent.
Yet another object of one embodiment of the present invention is to provide a propellant composition comprising:
(a) between 70 and 85 weight percent of an explosive crystal;
(b) between 0 and 6 weight percent of an inert binder;
(c) between 7 and 15 weight percent of an energetic copolyurethane thermoplastic elastomer; the thermoplastic elastomer including a member selected from the group comprising:
(i) a hard segment generated by the formation of hydrogen bonds between a first urethane group of one linear copolymer chain with a second urethane group of another linear copolymer chain;
(ii) a linear copolymer chain comprising an A block and a B block, the copolymer chain having the formula:
HO—P—(U—P)n—OH
wherein P is selected from the group consisting of
where the R
1
groups are the same and selected from the group consisting of —CH
2
N
3
and —CH
2
ONO
2
;
R
2
is selected from the group consisting of —OCH
2
CH
2
O—, —OCH
2
CH
2
CH
2
O— and —OCH
2
CH
2
CH
2
CH
2
O— and o and p are each>1; and
where the R
3
groups are the same and selected from the group consisting of —CH
2
N
3
and —CH
2
ONO
2
;
the R
4
groups are —CH
3
;
R
5
selected from the group consisting of —OCH
2
CH
2
O—, —OCH
2
CH
2
O— and —OCH
2
CH
2
CH
2
O—; and q and r are both<1;
U is selected from the group consisting of
and n is 1 to 100;
wherein the A block is provided by the U moieties and the B block is provided by the P moieties.
(iii) a linear copolymer chain comprising an A block and a B block, the copolymer chain having the formula:
HO—P—(U—(C—U)
a
—P)
b
—U—P—OH
wherein P is selected from the group consisting of
where the R
1
groups are the same and selected from the group consisting of —CH
2
N
3
and —CH
2
ONO
2
;
R
2
is selected from the group consisting of —OCH
2
CH
2
O—, —OCH
2
CH
2
CH
2
O— and —OCH
2
CH
2
CH
2
CH
2
O—; and o and p are each>1; and
where the R
3
groups are the same and selected from the group consisting of —CH
2
N
3
and —CH
2
ONO
2
;
the R
4
groups are —CH
3
;
R
5
is selected from the group consisting of —OCH
2
CH
2
O—, —OCH
2
CH
2
CH
2
O— and —OCH
2
CH
2
CH
2
CH
2
O—; and q and r are both>1;
U is selected from the group consisting of
C is selected from the group consisting of
 and
—OCH
2
—(CH
2
)n—CH
2
O— where n is 0 to 8;
a is 1 to 100 and b is 1 to 100;
wherein the A block is provided by the U moieties and the B block is provided by the P moieties.
(iv) a linear copolymer chain comprising an A segment and a B segment, the copolymer chain having the formula:
HO—P—U—(C—U)x—(P—U)y—(C—U)z—P—OH
wherein P is selected from the group consisting of
where the R
1
groups are the same and selected from the group consisting of —CH
2
N
3
and —CH
2
ONO
2
;
R
2
is selected from the group consisting of —OCH
2
CH
2
O—; —OCH
2
CH
2
CH
2
— and —OCH
2
CH
2
CH
2
CH
2
O—; and o and p are each>1;
where R
3
groups are the same and selected from the group consisting of —CH
2
N
3
and —CH
2
ONO
2
;

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