Poly(ethylene furanoate) (PEF), the furan-derived analogue to poly(ethylene terephthalate) (PET), can provide a fully biosourced alternative to PET with greatly improved barrier properties and attractive thermal and mechanical properties. The improved barrier for PEF compared to PET is unexpected due to the higher free volume of PEF vs PET. Segmental motions related to penetrant diffusion in both polyesters were studied using dynamic mechanical analysis, 13C–CP/MAS solid-state NMR variable contact-time experiments, and centerband-only detection of exchange (CODEX) measurements. Unlike the active phenyl ring-flipping mechanism in PET, furan ring-flipping is greatly suppressed, thereby reducing β relaxation motions and diffusion in PEF due to the energy penalty associated with the nonlinear axis of ring rotation and ring polarity. Preliminary work also shows similar oxygen solubilities for PEF and PET, thereby proving that the drastic permeability reduction results from a decrease in diffusion coefficient caused by a hindrance in furan ring-flipping.

Transport properties of carbon dioxide in amorphous poly(ethylene furanoate) (PEF) were investigated using complementary pressure-decay sorption and permeation techniques. Detailed measurements for PEF at 35 °C indicate a significant, surprisingly large reduction in carbon dioxide permeability of 19× at 1 atm compared to poly(ethylene terephthalate) (PET), despite both an increase in free volume and carbon dioxide solubility of 1.6× for PEF vs PET. The solubility increase for PEF, which originates from greater interaction between carbon dioxide and the polar furan moiety, is offset by a substantial reduction in diffusivity of 31× compared to PET. Such diffusion reduction for PEF, which is 3× greater than the 9.7× reduction in oxygen diffusivity compared to PET, is thought to originate from a hindrance of polymer ring-flipping motions compared to PET. A possible mechanism for the surprising barrier improvement for carbon dioxide in PEF vs PET is explained herein along with a detailed comparison to oxygen and water transport.

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The modification of cellulose acetate (CA) films via grafting of vinyltrimethoxysilane (VTMS) to −OH groups, with subsequent condensation of hydrolyzed methoxy groups on the silane to form a polymer network is presented. The technique is referred to as GCV-modif ication. The modified material maintains similar H 2 S/CH 4 and CO 2 /CH 4 selectivities compared to the unmodified material; however the pure CO 2 and H 2 S permeabilities are 139 and 165 barrers, respectively, which are more than an order of magnitude higher than the neat polymer. The membranes were tested at feed pressures of up to 700 psia in a ternary 20 vol. %H 2 S/20 vol. % CO 2 /60 vol. % CH 4 mixture. Even under aggressive feed conditions, GCV-modified CA showed comparable selectivities and significantly higher permeabilities. Furthermore, GCVmodified membrane had a lower T g , lower crystallinity, and higher flexibility than neat CA. The higher flexibility is due to the vinyl substituent provided by VTMS, thereby reducing brittleness, which could be helpful in an asymmetric membrane structure.