A series of polyphosphazenes with ester side groups was prepared from a derivative of poly(methyl-phenylphosphazene) that contained alcohol functional groups. The synthesis involved treatment of {[Ph(Me)P = N](2)(Ph[Me(2)C(OH)CH2]P = N)}(n) with acid chlorides, RC(=O)Cl, where R = (CH2)(n)CH3 (n = 2, 4, 6, 8, 10, 12 and 14) in the presence of triethylamine. These new polymers were characterized by H-1, C-13 and P-31 n.m.r. spectroscopy, i.r. spectroscopy, size exclusion chromatography and thermal analysis (d.s.c. and t.g.a.). The systematic dependence of the glass transition temperatures of these new polymers on the number of methylene groups is discussed.