--(CH2)3 O(CH2 CH2 O)x --R4' wherein x is as defined above, R4' is an alkyl group having 1 to 4 carbon atoms, an acid amido residue represented by the formula: ##STR7## wherein R7 and R8 are as defined above, or an acid amido residue represented by the formula: ##STR8## wherein b is as defined above can be prepared by reacting a siloxanylalkyl ester represented by the formula (II): ##STR9## wherei