A series of new polyphosphazene polymers were synthesized using three different pendant groups with the goal of probing structure-function relationships between pendant group substitution and polymer swelling/water flux through thin dense films. Formation of polymers with relative degrees of hydrophilicty was probed by varying the stoichiometry of the pendant groups attached to the phosphazene backbone: p-methoxyphenol, 2-(2-methoxyethoxy)ethanol, and o-allylphenol. The polymers in this study were characterized using NMR, thermal methods, and dilute solution light-scattering techniques. These techniques revealed that the polymers were amorphous high polymers (M-w = 10(5)-10(7)) with varying ratios of pendant groups as determined by integration of the H-1- and P-31-NMR spectra. Thin dense film membranes were solution-cast with azo-bis(cydohexane)carbonitrile included in the matrix and crosslinked using thermal initiation.