Water Transport Polymers – Structure/Property Relationships of a Series of Phosphazene Polymers

Abstract

A study was undertaken to explore the water passing properties of a series of phosphazene polymers versus the attached pendant group structure. Pendant groups containing different numbers of ethyleneoxy groups were synthetically attached to the backbone of phosphazene polymers. Phosphazene polymers facilitate these types of studies because, during their synthesis, the polymer backbone is formed first and then the desired pendant groups are attached through nucleophilic substitution. For these studies, four polymer series were synthesized and tested for their water passing properties. The polymers contained different amounts of ethyleneoxy units. Two different polymer families were synthesized and compared in this work. The critical difference in the two polymer series is that one contained pendant groups with aromatic rings, in addition to the oligioethyleneoxy moieties, while the other has no aromatic rings in its structure. Polymers with phenyl group-containing pendant groups exhibited poor water permeability if they possessed fewer than six ethyleneoxy units. Polymers with more than six ethyleneoxy units inserted between the phenyl ring (tail) and the polymeric backbone exhibited reasonable water permeability. Two additional series of polymers with mixed pendant groups were synthesized and the water passing properties of the phosphazenes varied in proportion to the hydrophilic to hydrophobic balance induced by each individual pendant group. A final study of polymers with shorter pendant groups demonstrated the effect of pendant group on water permeability. These studies suggest that the polyphosphazenes may be tailored for specific water passing applications.

Keywords:

• polyphosphazenes
• water transport membranes

ACKNOWLEDGEMENTS

Gracious support of this work by the U.S. Department of Energy, under DOE Idaho Operations Office Contract DE-AC07-05ID14517 is hereby acknowledged.