R3 in formula (I) represents ##STR17## or H, or mixtures thereof and R4 represents (CH2 CHO)p H or CH3 When R3 and R4 represent the preferred (CH2 CH2 O)p H group, p is a positive number representing the average degree of ethoxylation, and is preferably from 1 to 10, especially 1.4 to 6, and more preferably from about 1.5 to 4, and most preferably, from 1.5 to 3.0. n and m are integers of from 1 t