The mono-alkenyl polyether is a compound of the formula CH2 ???CH(CH2)x O(CH2 CH2 O)y (CH2 CH3 CHO)z T, or a compound of the formula CH2 ???CH-Q-O(CH2 CH2 O)y (CH2 CH3 CHO)z T. In the formulas, T represents an end group which can be hydrogen; a C1-C10 alkyl group such as methyl, ethyl, propyl, butyl, and decyl; an aryl group such as phenyl; or a C1-C20 acyl group such as acetyl, propionyl, butyryl