SIL represents ##STR4## R3 is selected from the group consisting of hydrogen, alkyl radicals comprising about 1 to about 4 carbon atoms; acyl groups comprising about 2 to about 5 carbon atoms; and oxime groups of the formula --N???CR5 R6, wherein R5 is a monovalent alkyl group comprising about 1 to about 12 carbon atoms and wherein R6 is a monovalent alkyl group comprising about 1 to about 12 carb