For example, the compound of formula (2) wherein m=1 can be prepared by reacting a compound of the general formula (5): (R1O)(3-p)(R2)pSi???R3???SH???(5) wherein R1, R2, R3 and p are as defined above, with an alkali alcoholate to form a compound of the general formula (6) (R1O)(3-p)(R2)pSi???R3???SM???(6) wherein R1, R2, R3 and p are as defined above, and M is an alkali metal, and reacting the com