3 to about 50; R2 and R3 each is different and is an alkyl group of from 1 to 4 carbon atoms and each oxyalkylene radical can be any combination of repeating oxyalkylene units to form block or random copolymers; R4 is the same as R2 or R3 ; R5 is hydrogen or ##STR2## where R7 is hydrogen or an alkyl group of from 1 to 5 carbon atoms and R6 is an divalent alkylene radical of 1 to about 12 carbon a