Mixed substituent ether-containing polyphosphazene/poly(bis-phenoxyphosphazene) blends as membranes for CO₂ separation from N₂

Polyphosphazenes gain much of their physical and chemical properties from the substituents attached to the phosphorus atoms in the backbone. Poly(phosphazenes) that have short-chain polyether containing substituents, such as, 2-(2-methoxyethoxy)ethanol, have high CO₂ permeability and selectivity over N₂ as well as resistance to degradation under humidification at 60°C. However, the principal shortcomings of this polymer are the poor mechanical and surface characteristics. Blending of an example of this polyphosphazene (MEEP-80) with poly(bis-phenoxyphosphazene) (PPOP) has yielded more durable materials that have a non-adhesive surface. In this work, the blended polymer membranes were found to have increased CO₂ permeability with higher selectivity over N₂. Thermal analysis and the application of transport models support a structure of the blends that is not either an intimate blend or phase separated bulk structure, but one where PPOP domains retain their crystallinity and are dispersed within an amorphous MEEP-80 phase.