The nucleophilic substitution reaction of poly(dichlorophosphazene) with sodium 2-methoxyethoxide and glycine ethyl ester has been studied in detail. Polymers prepared with different methods have been characterized by H-1 NMR, and the results reveal that the addition sequence of the two nucleophilic reagents is an important factor in determining the structure of the resultant polymer. If alkyl ether is added first, the subsequently introduced amino acid ester not only reacts with residual P-Cl but also attacks the alkyl ether side units present by replacing either the whole group or just -OCH3. As a result, a new kind of side group (-OCH2CH2NHCH2COOC2H5) can be detected in the macromolecule. To obtain polymers with desired compositions {poly[(methoxyethoxy)(x)(ethylglycino)(y)-phosphazene]}, the amino acid ester should be introduced initially to react with poly(dichlorophosphazene), and it should be followed by the alkyl ether. © 2005 Wiley Periodicals, Inc.