NEW MATERIAL:A compound shown by the formula (R is substituted or nonsubstituted hydrocarbon bifunctional group; m is 3-1,002 integer).

EXAMPLE: N,N'-Di(γ-butyrolactam)polysulfide.

USE: Useful as a vulcanization agent and/or a vulcanization promoter and further a vulcanization retarder having excellent dispersibility to rubber, vulcanization rate, physical properties of vulcanized rubber, thermal aging resistance, compressive resistance, reversion resistance, bloom resistance and stain resistance.

PREPARATION: N,N'-Di(lactam)disulfide is reacted with sulfur in an amount to give 3-1,002 sulfur atom by theoretically calculating the reaction product in the absence of a solvent to give a compound shown by the formula.