Ethylene sulfide reacts with isothlocyanates in the presence of triethylamine catalyst at 20°C, to give low-molecular copolymerization products having the general formula [-C(NR)-S-CH2-CH2-S-]n. Their hydrolysis gives a salt of the amine and [-C(O)-S-CH2CH2S-]n. Vacuum-heating the latter gives ethylenedithiocarbonate, and hydrogen peroxide oxidation in formic acid gives ethane disulfonic acid. Treatment of the copolymer from phenyl isothiocyanate and ethylene sulfide with liquid ammonia, amines, or aqueous alkali results in splitting and formation of 2-phenylimino-1,3-dithiolane, while its reaction with ethylene oxide in the presence of triethylamine gives 3-phenyloxazolid-2-one.