wherein R and R??? are each a monovalent hydrocarbon group with at least three carbon atoms having or not having an ester bond or R and R??? together form a ring and q is an integer of 1 to 3, compounds containing a sulfide structure represented by the formula: R???Sq???R??? wherein R and q are as defined above, and R??? is a bivalent hydrocarbon group having at least three carbon atoms and havin