1 to 22 carbon atoms, and R2 is also such an alkyl group or a group of the formula --(CH2 CH2 O)y H with y being an integer from 1 to 5, and R3 is an alkyl group having 1 to 5 carbon atoms or a group of the formula --(CH2 CH2 O)x H where x is an integer from 1 to 10, and if R2 is an alkyl group having more than 5 carbon atoms, the sum of Y and X is not greater than 10.