POLYPHOSPHAZENE MEMBRANES - III - SOLID-STATE CHARACTERIZATION AND PROPERTIES OF SULFONATED POLY[BIS(3-METHYLPHENOXY)PHOSPHAZENE]

Poly[bis(3-methylphenoxy)phosphazene] was sulfonated in a solution wit h SO3 and solution-cast into 100-200-mu m-thick membranes from N,N-dim ethylacetamide. The degree of polymer sulfonation was easily controlle d and water-insoluble membranes were fabricated with an ion-exchange c apacity (IEC) as high as 2.1 mmol/g. For water-insoluble polymers, the re was no evidence of polyphosphazene degradation during sulfonation. The glass transition temperature varied from -28 degrees C for the bas e polymer to -10 degrees C for a sulfonated polymer with an IEC of 2.1 mmol/g. The equilibrium water swelling of membranes at 25 degrees C i ncreased from near zero for a 0.04-mmol/g IEC membrane to 900 % when t he IEC was 2.1 mmol/g. When the IEC was < 1.0 mmol/g, SO3 attacked the methylphenoxy side chains at the para position, whereas sulfonation o ccurred at all available aromatic carbons for higher ion-exchange capa cities. Differential scanning calorimetry, wide-angle X-ray diffractio n, and polarized microscopy showed that the base polymer, poly[bis(3-m ethylphenoxy)phosphazene], was semicrystalline. For sulfonated polymer s with a measurable IEC, the 3-dimensional crystal structure vanished but a 2-dimensional ordered phase was retained. (C) 1999 John Wiley & Sons, Inc.