Adverse Effect of Polyelectrolyte Complexation on the CO₂ Permeability of Polyvinylamine Copolymers

Abstract

Polyvinylamine (PVAm) is one of the most studied polymers for facilitated transport membranes (FTMs) in CO 2 separation applications. In this study, poly(N-vinylformamide) (PNVf) was hydrolyzed to prepare a range of PNVf-PVAm copolymer compositions, and the effect of the PVAm fraction on the CO 2 permeability and CO 2 /N 2 selectivity of these polymers was examined. The most permeable film was the polymer containing 52 mol % PVAm units with a CO 2 permeability of 353 Barrer and CO 2 /N 2 selectivity of 96 when tested at 60 °C with humidified 14/86 CO 2 /N 2 mixed gas. Despite containing a higher loading of amines to act as CO 2 carriers, higher PVAm contents yielded significantly lower CO 2 permeability, without a loss of selectivity. This trend was not due to polymer crystallization since none of the PVAm films exhibited crystallinity in X-ray diffraction analysis. The loss of gas permeability at high PVAm content was instead due to strong polyelectrolyte interactions between polymer chains formed when PVAm reacts with CO 2 . Since only the PVAm units are ionized upon reaction with CO 2 , with the PNVf units remaining neutral, the density of these ionic effects increased as PVAm content increased, leading to increased resistance to gas permeation.