Compounds of formula (I) wherein R.sub.1 and R.sub.2 are each independently C.sub.1-C.sub.2 alkyl, and m is 1, 2, 3, 4, or 5 and compositions of formula (II) wherein R.sub.1 and R.sub.2 are each independently C.sub.1-C.sub.4 alkyl, and n is an integer >_0 and wherein the average molar value of n for the total of the compounds of formula (II) in said composition is in the range of (1) to (3) and methods for production thereof. ##STR00001##