(401x) Perfluoropolymers and Hydrocarbon Polymer Analogs with Pendant Rings for Gas Separation Membranes

Amorphous glassy perfluoropolymers are
attractive for membrane gas separation, such as He/CH₄ and CO₂/CH₄
separation. These perfluoropolymers often have pendant rings to suppress
crystallinity and achieve high free volume and thus high gas permeability. However,
their applications are hampered by the high cost due to the difficulty in
synthesis. We hypothesize that the pendant rings can be incorporated in
hydrocarbon polymers to achieve similarly superior gas separation properties. In
this study, we design and synthesize hydrocarbon polymers with structures
similar to perfluoropolymers, aiming to elucidate the effect of pendant rings
on gas separation properties. Specifically, we synthesize a perfluoropolymer of
poly(perfluoro-4-methyl-2-methylene-1,3-dioxolane) (PPMMD) and its hydrocarbon
polymer analogue, poly(4-methyl-2-methylene-1,3-dioxolane) (PMMD). These
polymers with pendant rings are thoroughly characterized using FTIR, NMR, GPC,
WAXD, TGA and DSC for physical properties such as molecular weight,
crystallinity, and glass transition temperature. PPMMD shows a H₂
permeability of 236 Barrers and H₂/CO₂ selectivity of 4.1
at 35 ^oC, while the PMMD shows a H₂ permeability of 9.6
Barrers and H₂/CO₂ selectivity of 7.3 at 35 ^oC.
Gas sorption results will be described using the dual mode sorption model. A
series of poly(cyclic ketene acetals) with structures similar to PMMD are
synthesized and characterized for gas separation. This presentation will also discuss
the fractional free volume in these polymers and the use of a free volume model
to describe the gas transport properties in these hydrocarbon polymers and
perfluoropolymer analogs.