Preparation of alkyl mercaptocarboxylate/dialkyl thiodicarboxylate mixture using sulfur and/or water cocatalyst

A method for preparing a poly(oxyalkylene)-polyester-poly(sulfide)-polythiol comprising:

• (1) reacting hydrogen sulfide with an olefinically unsaturated carboxylate of the formula
• CR.sub.2 .dbd.CR--CR.sub.2 --.sub.n CO.sub.2 R'
• wherein R' is an alkyl radical containing 1 to 5 carbon atoms and R is hyrdogen or R', wherein n is zero or an integer having the value of 1, 2 or 3, and wherein the total number of carbon atoms in all of the R and R' groups is 1 to 15 per molecule;
• using an addition catalyst selected from organic and inorganic bases in the presence of a lower alkanol and a cocatalyst consisting essentially of at least one of sulfur and water, wherein the sulfur or water is present in an amount within the range of from 0.0001 to 0.2 part by weight per part by weight unsaturated carboxylate, to produce a mixed ester reaction product;
• reacting the thus-obtained mixed ester reaction product in the presence of a transesterification catalyst with a poly(oxyalkylene)-polyol produced by reacting one or more epoxy-substituted hydrocarbons of the formula ##STR3## wherein R" is H or alkyl with the total number of carbon atoms in the molecule being up to 20 and wherein m is an integer of from 1 to 10, with a polyol of the general formula
• Y(OH).sub.x
• wherein Y is a hydrocarbon moiety having at least two carbon atoms per moiety and a valence equal to the value of x, x being an integer of at least two.