wherein R3 is --CH(CH2 OZ1)(CH2 OZ2) or --CH2 {CHOZ1 (CH2 OZ2)}, X is a hydrogen atom or a methyl group, one of Z1 and Z2 is a hydrogen atom and the other is an alkyl group having 4 to 16 carbon atoms or a residual group of an aliphatic acid ester. ##STR2## wherein R1 and R2 are each CH3 --CH2 -- or ##STR3## R3 is .brket open-st.CH2 CH2 O.brket close-st.n H and R4 is .brket open-st.CH2 CH2 O.brket