Typical compounds of this type are low molecular Weight nonpolymeric ketones having the general formula: R1 where R and R are each aryl radicals, aliphatic resistituted phenyl radicals and particularly when R is a phenyl radical having the formula: wherein R and R are each aryl radicals, aliphatic residues of l to 12 carbon atoms such as alkyl radicals preferably having 1 to 4 carbon atoms or hydr