PURPOSE: To execute the polymn. of α,β-unsatd. compds. by a base transfer polymn. method by using a sulfonium salt having a specific constitutional formula as a catalyst.

CONSTITUTION: The α,β-unsatd. compds. are polymerized under the base transfer polymn. conditions by using the tris(disubstituted amino)sulfonium perfluoroalkoxide expressed by formula I as the catalyst. In the formula I, R1 to R6 are respectively independently selected and are respectively 1-20C alkyl having at least two α hydrogen atoms or any or all of paired R1 and R2, R3 and R4 as well as R5 and R6 are respectively independently selected and formula II or formula II, where Y is hydrogen or methyl; R and R are respectively independently selected, F, 1-12C perfluoroalkyl, 2-12c perfluoro(alkoxyalkyl), XR or the like, where R is 1-12C perfluoroalkylene or 4-22C perfluorocycloalkylene and X is Cl, Br or I or R and R are together formula IV, where (n) is an integer from 2 to 6.