where R is a straight chain alkyl or alkenyl group of at least 16 carbon atoms, preferably at least 18 carbon atoms, and most preferably at least 20 carbon atoms; or an aralkyl or aralkenyl group of at least 22 carbon atoms, preferably at least 24 carbon atoms and most preferably at least 26 carbon atoms; and n=0-10 (when n=0, the valence of the oxygen atom is completed by H), preferably 1-5 and m