AbstractAs thiodiglycol (TG) condenses with itself in the presence of phosphorus pentoxide, sulfuric acid, or potassium hydrogen sulfate at 50–200°, its reaction with di‐ and trihydroxy compounds and with 2‐hydroxyethane‐1‐thiol (MTG) under similar conditions would be expected to give straight‐chain and crosslinked polymers. With certain polyfunctional compounds this has been found to be the case. Some indication of copolymerization was observed with diethylene, trimethylene, and the butylene glycols and with ricinoleic acid, and solid polymers resulted from the interaction of thiodiglycol with tricarballylic acid, 2,2′‐dihydroxydiethyl disulfide (DTG), MTG, and glycerol, respectively. The reactions with the last three hydroxy compounds were studied in detail and the properties of the copolymers produced assessed visually. MTG was found to undergo rapid autocondensation to form brittle solids. Similar polymers were obtained in about 70% yield with small amounts of TG in the reaction mixture; on an increase in the initial TG content, waxy solids, similar to those obtained from TG alone, resulted. As the glycerol content in TG/glycerol mixtures increased up to 40%, the copolymers formed changed from friable gels to brittle solids; any further increase resulted in viscous liquid products only. These results may be attributable to the fact that the reaction is a two‐stage one. TG‐MTG mixtures were reacted with glycerol with a view to improving the tensile strength of the product. This was successful, and the TG‐MTG‐glycerol (50:45:4) mixture, when heated at 154° for 6.5 hr. gave a white, elastic solid, very difficult to cut or break, which could be milled and pressed although tending to swell in benzene and dichlorodiethyl ether. The properties and structures of these new thioplasts made, where possible, from equimolecular quantities of the monomers, are recorded and compared with those of the commercially available Thiokols. Attempts to copolymerize TG with compounds (I), (II), and (III), which contain the reactive 2‐hydroxyethylthio group were unsuccessful.