hydrogen, or R3 and R4 independently of each other are a member selected from the group consisting of alkyl having 2 to 22 carbon atoms, preferably 12 to 18 carbon atoms, and hydrogen, and x and y independently of each other are an integer from 1 to 16, preferably 8 to 14, with the proviso that the total of the carbon atoms of R1 +R2 or R3 +R4 is from 2 to 26, preferably from 6 to 20, and with th