Advanced functional polymer membranes

The importance of phosphorus in polymer chemistry is illustrated by the growth of the broad field of polyphosphazene science. Several hundred high polymers are now known with a phosphorus-nitrogen backbone and combinations or more than 250 different organic side groups. The properties of these polymers depend on both the character of the inorganic backbone and the structure of the organic side groups. This summary reviews the synthesis pathways to these materials, the often-unique structure-property relationships, and challenges for the future expansion of this field.

The expanding field of polyphosphazene high polymers

The dehydration of nitric acid using pervaporation and a nafion perfluorosulfonate/perfluorocarboxylate bilayer membrane

Six different phosphazene polymers have been synthesized with varying ratios of 2-(2-methoxyethoxy)ethanol and diacetone D-glucofuranose to determine how these pendant groups affect the physical, chemical, and thermal characteristics of these terpolymers Diacetone D-glucofuranose serves as the hydrophobic substituent and 2-(2-methoxyethoxy)ethanol is the hydrophilic substituent on the phosphazene backbone Characteristics of the polymers made in this study reflect a blend of the two substituents, ranging from powders to viscous fluids Thermal analysis was used to quantify the thermal stability and water swellability of the polymers Additionally, DSC was employed to determine composition based on the Fox equation Compositions were then verified by integratable proton NMR indicating the validity of the Fox equation for predicting Tg transitions in phosphazene terpolymers Laser light scattering (LLS) revealed that the weight-average molecular weights were in the 107 g mol−1 range with mean square radii between 150 and 200 nm

© 2000 Society of Chemical Industry

Synthesis, characterization and thermal stability of phosphazene terpolymers with 2-(2-methoxyethoxy)ethoxy and diacetone D-glucofuranosyl pendant groups

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 hydrophilicity 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 1 H- and 31 P-NMR spectra. Thin dense film membranes were solution-cast with azo-bis(cyclohexane)carbonitrile included in the matrix and crosslinked using thermal initiation.

Formation of pervaporation membranes from polyphosphazenes having hydrophilic and hydrophobic pendant groups: Synthesis and characterization

Preparation of polymeric membranes with dynamically adjustable separation properties is a new area of research. The approach described herein involves adjusting the permeate pressure of a swollen polymeric membrane to alter its separation properties. For example, during the separation of methylene blue from isopropyl alcohol, pressure on the permeate side was increased such that both methylene blue and alcohol were passed, resulting in no separation. The permeate pressure then was decreased and only colorless isopropyl alcohol passed through the membrane. A subsequent increase in the pressure on the permeate side results in no separation once again demonstrating that the effects were fully reversible. In a mixed dye experiment in isopropyl alcohol, methylene blue and rose bengal were separated with the lower-molecular-weight methylene blue permeating with isopropyl alcohol while the rose bengal was retained in the feed. The new membranes are distinguished by improved control of separation paramet...

R. L. Cowan

Papers

Preparation and characterization of membranes with adjustable separation performance using polyphosphazene membranes