PURPOSE: The reaction of a specific organohydrogenpolysiloxane with a polyoxyalkylene polyether having alkenyloxy groups on the chain terminals gives title polyether giving cured products with high weathering resistance.

CONSTITUTION: The addition reaction between (A) an organohydrogenpolysiloxane of formula I [R1 is monovalent hydrocarbyl, triorganosiloxy; X is halogen, hydrolyzable group; a is 0W2; b is 0W3; m is 0W3 where 1≤a+b≤3] and (B) a polyoxyalkylene polyether having alkenyloxy groups on the chain terminals of formula II or III (R2 is 1W20C divalent hydrocarbyl; R3 is 1W4C divalent hydrocarbyl; Z is H, hydroxyl; n is positive integer) is conducted in the presence of a platinum catalyst to produce the objective polyoxyalkylene polyether.