Aliphatic Polysulfides with Multisulfur Links

In commercially significant organic polysulfides with the structural element x is known as the sulfur grade, x is the average number 

Synthesis. Organic polysulfides are manufactured from a,co-dihalogen compounds and sodium polysulfide according to the general equation 

Ethylene dichloride, bis-(jS-chloroethoxy)-methane [bis(2-chloroethyl)-for-mal], bis(2-chloroethyl)-ether, and allyl or benzyl halides are suitable halogen compounds nowadays, mainly bis(2-chloroethyl)-formal is used commercially. Aromatic halogen compounds or vinyl halides are too reactive. The rate of the condensation reaction is increased by ionizing solvents or elevated temperatures. It is not necessary to add the two reaction components in equivalent quantities. In fact, excess Na2S causes —SNa— end groups to be formed these end groups can then undergo a disproportionation reaction  

The situation is therefore similar to that in the synthesis of poly(ethylene terephthalate) by transesterification. Furthermore, the molecular weight can be increased by oxidation of the —SNa end groups in analogy to the cystine-cysteine reaction  

Commercial grades of polysulfides are synthesized by using dichloro-ethylene (Thiokol A of the Thiokol Chemical Corp., sulfur grade 4), bis-(2-chloroethyl)-formalin (Thiokol FA, sulfur grade 2), or a mixture of these two compounds (Thiokol ST, sulfur grade 2.2) as the dihalogen compounds. 

---