Referring more particularly to the aromatic hydrocarbon-soluble, normally liquid, polysulfide or polydisulfide having terminal --SH groups, dithiol polydisulfides are preferred, these having the formula: ##STR1## where n is from 2-50, preferably from 4-20, and R is an aliphatic radical having from 1-20, preferably from 2-18 carbon atoms.