Room temperature cured elastomer

Hydroxy terminated polybutadiene is reacted with naphthyl-potassium and 1omo-2,4-pentadiene in successive steps to form a bis(1,3-pentadienyl ether) derivative. Then the bismaleimide of dimer diamine is added to the polybutadiene derivative whereby a room temperature cure to an elastomer is achieved.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to materials which may be utilized to form 
elastomers at room temperature and to the elastomers thus formed. 
2. Description of the Prior Art 
It is well known to use elastomers as binders for explosives, propellants 
and the like. Literally thousands of elastomers have been disclosed as 
being useful for such purposes. Despite the wide variety of elastomeric 
binders available, those wich have found wide spread use in propellants 
and the like have had one problem in common. That problem is the fact that 
they have only been curable at elevated temperatures. As a result of the 
need for elevated temperature cures, several sub-problems have developed. 
One sub-problem or, in actuality, series of sub-problems stems from the 
fact that an oven is required if cure is to be carried out at an elevated 
temperature. Ovens are expensive. They require space. Elevated temperature 
cures require time. A propellant or the like must be handled in order to 
get it in the out of the oven. Finally, if an oven malfunctions, cure is 
not carried out properly and a batch of prepolymer is wasted. 
More important than the sub-problems related to oven, are a series of 
sub-problems related to the fact that stresses are induced into an 
elastomer when it is cooled to ambient temperature after having been cured 
at an elevated temperature. These stresses often lead to cracking. 
Cracking is especially likely to occur if the elastomer is subjected to 
temperature cycling and such cycling is the rule rather than the 
exception. 
Current theory in stress analysis is that once it is induced, stress is 
never entirely removed. Thus, if an elastomer is cooled below room 
temperature and subsequently raised back to room temperature those 
stresses that are induced by the cooling never completely disappear. 
Since stress is induced when an elastomer is cooled from cure temperature 
to ambient, it would be advantageous if cure could take place at ambient. 
This would eliminate a portion of the life history of a propellant or the 
like during which stress is induced. 
SUMMARY OF THE INVENTION 
According to this invention, the bis(2,4-pentadienyl ether) derivative of 
hydroxy terminated polybutadiene is prepared by reacting hydroxy 
terminated polybutadiene with naphthyl-potassium and 
1-bromo-2,4-pentadiene in successive steps. Then, the bismaleimide of 
dimer diamine is added as a curing agent. Cure takes place at room 
temperature.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The preferred embodiment may be understood from the following specific 
examples. 
EXAMPLE 1 
Preparation of the Bis(1,3-pentadienyl ether) of Hydroxy Terminated 
Polybutadiene 
Degassed hydroxy terminated polybutadiene (40.5 g, 0.029 equivalent) was 
placed in a glass reaction vessel. The system was swept with helium and 
the flask was flamed. Next, 175 ml of pure oxygen-free dimethoxyethane and 
175 ml of purified toluene were added to dissolve the polymer (hydroxy 
terminated polybutadiene). A 0.37 molar solution of naphthyl-potassium in 
dimethoxyethane was added dropwise until the light green color of 
unreacted naphthyl-potassium persisted for at least 5 minutes. A total of 
0.031 equivalents of naphthyl-potassium were used. The reaction time was 
approximately 2.5 hours. 
10.0 g (0.068 equivalent) of 1-bromo-2,4-pentadiene were dissolved in 25 ml 
of pure oxygen-free dimethoxyethane and added to the reaction mixture and 
the mixture was stirred for 3 hours at room temperature and for 1 hour at 
85.degree. C. (The helium atmosphere was maintained.) 
The crude bis(1,3-pentadienyl ether) of hydroxy terminated polybutadiene 
was precipitated from the reaction mixture by adding methanol. It was 
dissolved in benzene and centrifuged to remove potassium bromide. 
Purification was accomplished by repeated precipitation from an ethylene 
dichloride solution using methanol. The derivative was then dried in a 
vacuum at room temperature. The yield was 34.8 g (85.9%). The polymeric 
derivative had a molecular weight of 3800 and contained 2.5 moles of 
conjugated double bonds per mole of polymer. 
EXAMPLE 2 
Pretreatment of Dimer Diamine 
100 g of dimer diamine were dissolved in heptane and washed with aqueous 
sodium chloride solution containing 4.0 g of sodium hydroxide. This formed 
an emulsion which was shaken periodically and allowed to set for 18 hours. 
The organic layer was then washed twice with aqueous sodium chloride and 
ethanol was added to break the emulsion. The resulting mixture was then 
dried over sodium sulfate and in a vacuum to completely remove the 
solvent. 
EXAMPLE 3 
Preparation of the Bismaleimide of Dimer Diamine and Cyclization 
60.0 g (0.2 equivalent) of pretreated dimer diamine were dissolved in 50 ml 
of 1,1,2-trichlorethane and 22.6 g (0.23 mole) of maleic anhydride were 
dissolved in 125 ml of 1,1,2-trichlorethane. The system was swept with 
nitrogen and the dimer diamine solution was added to the maleic anhydride 
solution dropwise, keeping the temperature below 35.degree. C. After the 
addition was complete, stirring was continued, under nitrogen, for 1.0 
hours. This formed the bismaleamic acid. 
4.29 g (0.02 mole) of magnesium acetate tetrahydrate, 49.0 g (0.48 mole) of 
acetic anhydride and 42.5 g (0.42 mole) of triethylamine were added. The 
temperature was rapidly raised to 94.degree. C., held for 1 hour and then 
cooled to room temperature. This cyclized the acid into the bismaleimide. 
The solvent was removed on a rotary evaporator. The crude product was 
dissolved in cyclohexane and washed twice with aqueous sodium chloride. A 
centrifuge was used to break the emulsion. The material was washed with 
aqueous sodium hydroxide solution and then with water until free of base. 
Then it was dried over anhydrous sodium sulfate. The solvent was removed 
and the material was dried in a vacuum. The crude bismaleimide was 
purified by column chromatography over Florisil and eluting with benzene. 
EXAMPLE 4 
Curing the Conjugated Diene Prepolymer Using the Bismaleimide of Dimer 
Diamine 
Enough of the cyclized bismaleimide was used to react with 88 percent of 
the conjugated double bonds; however, this range can be from approximately 
80 percent to 100 percent. 
0.3842 g of the bismaleimide of dimer diamine was added to 1.6612 g of the 
prepolymer, prepared according to Example 1, mixed and poured into a 
silicone mold. After curing for 48 hours at room temperature, the mixture 
had formed a clear elastomer having an elongation greater than 250 
percent. 
The foregoing examples are very specific. It will be apparent to those 
skilled in the art that other similar procedures might be used in lieu of 
those specified. For example, it will be apparent to skilled chemists that 
the cure takes place via a Diels-Alder reaction. Thus, bisdienophiles 
other than the bismaleimide of dimer diamine could be used as the curing 
agent provided they (1) were soluble in the bis(1,3-pentadienyl ether) 
derivative of hydroxy terminated polybutadiene and (2) would react with it 
at room temperature. As another example, reactants other than 
naphthyl-potassium might be used to replace the hydrogen atoms of the 
hydroxy groups of hydroxy terminated polybutadiene with potassium or a 
similar alkali metal in the first step of the preparation of the 
bis(1,3-pentadienyl ether) derivative of hydroxy terminated polybutadiene. 
Also, the bromo group of 1-bromo-2,4-pentadiene might be replacable with a 
similar group such as a chloro group in the second step involved in the 
preparation of the bis(1,3-pentadienyl ether) derivative. Obviously, other 
inert gases could be used in lieu of the helium and nitrogen in the above 
outlines procedures. 
Because of the stability of the carbon to carbon bonds formed during cure, 
the elastomer prepared according to this invention is highly resistant to 
hydrolytic or oxidative degradation. Also, since the cure process involves 
the formation of carbon to carbon bonds, other components such as trace 
metal impurities in the formulation do not have an effect thereon. 
The elastomer is suitable for use as a binder in either explosive 
compositions or propellant compositions.