satisfying a relation of q+r=1 to 30, or ##STR2##wherein R' and R each represent a linear or branched, and saturated or unsaturated aliphatic hydrocarbon group having 8 to 25 carbon atoms or and aryl group and may be the same or different; and s is an integer of 1 to 30.Addition of other chemical ingredients, such as carbon black fibers or ultra fine carbon fibrils, have been reported to provide