Lower critical solubility temperature study of alkyl ether based polyphosphazenes

A series of poly[(alkyl ether)phosphazenes] was synthesized and their lower critical solution temperatures (LCST) were examined in water at concentrations from 0.1 to 30.0 wt %. The polymers synthesized were poly[bis(2,3-dimethoxypropanoxy)phosphazene], poly[bis(2,3-bis(2-methoxyethoxy)-propanoxy)phosphazene], poly[bis(2,3-bis(2-(2′-methoxyethoxy)ethoxy)propanoxy)phosphazene], poly[bis-(2,3-bis(2-(2′-(2″-dimethoxyethoxy)ethoxy)ethoxy) phosphazene], and poly[bis(2-(2′-methoxyethoxy)ethoxy)-phosphazene]. All the polymers examined showed LCST behavior. The LCST values were approximately 44.0, 38.0, 49.5, 61.5, and 65.0 °C, respectively. Cross-linked polymer films were examined as hydrogels in water at various temperatures and showed a rapid decrease in volume and weight as the temperature was raised through the LCST. The change in LCST was also examined as a function of increasing ionic strength in the presence of NaCl. A linear decrease in LCST was detected as a function of increasing ionic strength. The enthalpies of phase separation for 5 wt % solutions of the polymers were determined by DSC analysis and were found to be directly related to the LCST for each polymer.