A new postfunctionalization strategy for developing polyphosphazene functionalized with a high density of highly polar molecules was explored, and the moiety loading was up to 0.84 per unit. A polyphosphazene with N,N-dialkyl-substituted aniline as side chains was first synthesized by a direct substituted reaction, and then post azo coupling of p-nitrobenzenediazonium fluoroborate toward the aniline groups afforded functionalized polyphosphazenes with highly polar molecules. The structural characterization was performed with H-1-NMR, IR, and ultraviolet-visible spectroscopy and gel permeation chromatography. (C) 2003 Wiley Periodicals, Inc.