Thiokol/Polysulphide rubbers

Polysulphide rubbers. Ethylene dichloride and excess of sodium tetrasulphide when heated together give a polymeric polysulphide, Thiokol A, with properties resembling those of rubber ... 

A premix is prepared by mixing the fuel binder (i.e. a polysulphide rubber in the case of the Thiokol propellant) with the necessary curing agents, inert additives, and ballistic modifiers in a double-acting paddle mixer. This mixer is equipped... 

Thiokol Chemical Corp Trenton, NJ, Bulletins on Polysulphide rubbers, Urethanes, and Acrylics. 

Polysulphide rubber, thiol end groups Thiokol LP Thiokol- Morton Polyamides, polychloroprene... 

Rubbers (natural and synthetic) Polyvinyl and cellulose esters Polyhydric alcohol-polybasic acid resins Polysulphide resins (Thiokol A) Polysulphide rubbers Cellophane, polyvinyl alcohol and acetal, and regenerated cellulose 10-0-6 18-0-2 (10-1 3) X 10-1 (10-0-7) X 10-1 (6-3-31) X 10-2 (8-0-0-05) X 10- ... 

The products may be simple linear polymers (as for example Thiokol A), copolymers made using two or more dihalides which are also linear, and branched copolymers in which a small percentage of a trifunctional halide has been used to introduce branch points. Table 15.1 lists some of the high molecular weight polysulphide rubbers that have been made commercially available. 

The early commercial synthetic rubbers created were the polysulphide rubbers now known as Thiokols these rubbers had good oil resistance, unlike natural rubber, but with a very serious drawback which prevented their widespread acceptance, namely their smell. Processing of these materials in factory-size batches proved to be very obnoxious. Acrylonitrile-butadiene copol3nners (nitrile rubbers) were developed by Bayer and were to find eventually worldwide acceptance in many applications requiring oil resistance. In the mid 1930s polychloroprene rubbers became a commercial proposition after early experimental work at Du Pont. These rubbers, intermediate in properties between nitrile and natural rubber, soon found wide acceptance. 

Prepare a saturated solution of sodium sulphide, preferably from the fused technical sodium polysulphide, and saturate it with sulphur the sulphur content should approximate to that of sodium tetrasulphide. To 50 ml. of the saturated sodium tetrasulphide solution contained in a 500 ml. round-bottomed flask provided with a reflux condenser, add 12 -5 ml. of ethylene dichloride, followed by 1 g. of magnesium oxide to act as catalyst. Heat the mixture until the ethylene dichloride commences to reflux and remove the flame. An exothermic reaction sets in and small particles of Thiokol are formed at the interface between the tetrasulphide solution and the ethylene chloride these float to the surface, agglomerate, and then sink to the bottom of the flask. Decant the hquid, and wash the sohd several times with water. Remove the Thiokol with forceps or tongs and test its rubber-like properties (stretching, etc.). 

The value of x in the general polysulphide formula —RS,—, known as the sulphur rank, depends primarily on the value of x in the original sodium polysulphide. This value is an average value since in both the polysulphide and the polymer there is a distribution of values. In practice 2 x 4. Whilst the original polysulphide (Thiokol A) had a sulphur rank of 4 current commercial rubbers have a value of about 2-2-2. 

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