. . "Stabilizer of the formula (III) A3 --(??? X3)n.(R--Y1 --SOc.crclbar.)n (III) wherein A3 is a hydrocarbon group having a valence of n, ??? X3 is an ammonium cation or a phosphonium cation, R is a monovalent hydrocarbon, n is an integer of 2 to 4, and Y1 is as defined above." . .