Effect of Hexafluoro-2-propanol Substituents in Polymers on Gas Permeability and Fractional Free Volume

Abstract

A series of polymers were synthesized containing hexafluoro-2-propanol (HFP) pendant groups by facile reaction of lithiated polymers with hexafluoroacetone (HFA). The purpose of the study was to evaluate the effect of the HFP group in potential membrane gas separation materials. Dibromobisphenol A polysulfone (PSf-Br2), tetramethylbisphenol A polysulfone (TMPSf), dibromohexafluorobisphenol A polysulfone (6FPSf-Br2), tetramethylhexafluorobisphenol A polysulfone (TM6FPSf), and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) were modified by using n-butyllithium to form lithiated intermediates and then treated with HFA to form the corresponding modified polymers PSf-HFP, TMPSf-HFP, 6FPSf-HFP, TM6FPSf-HFP, and PPO-HFP. Polymers with various degree of substitution per repeat unit of HFP were obtained, depending upon the extent of polymer lithiation and reactivity. PSf-HFP, TM6FPSf-HFP, and PPO-HFP were further derivatized at the hydroxyl group using iodomethane to obtain the respective methylated derivatives (HFM). The polymer structures were characterized by NMR spectroscopy, and thermal properties were investigated by differential scanning calorimetry and thermogravimetric analysis. The gas permeability coefficients of these polymers were measured for the gases He, O2, CO2, and N2. The gas transport properties of PSf-HFP, PSf-HFM, and TMPSf-HFP for He/N2, He/CO2, O2/N2, and CO2/N2 gas pairs were all improved in comparison with PSf and TMPSf. The permeabilities for all gases increased 2-3-fold, while the permselectivities of the four gas pairs increased as well. All the HFP derivatives showed improvements of this magnitude only for the He/CO2 gas pair. † NRCC No. 47860.

Side-chain engineering of ladder-structured polysilsesquioxane membranes for gas separations

“…different alkyl groups, different copolymer ratios, and UV-crosslinking), which is centered at 4.5 Å, is identical due to the high rigidity of double stranded siloxane structure [16,17,24,32]. In general, the inter-chain distance correlates with polymer chain packing, and polymers containing bulky side groups with large inter-chain distance show a low polymer chain packing density or high fractional free volume (FFV) [34][35][36]. The physical properties of LPSQs are listed in Table 1.…”

“…This is due to the quite large interchain distance of the LPSQ membranes. Whereas conventional polymers show an interchain distance ranging from 4 to 7 Å [6,34,55], the inter-chain distance of LPSQ membranes is ca. 1.3 nm, which is within the transition region between solutiondiffusion and Knudsen diffusion-controlled regions [46].…”

Phenyltrimethylammonium Functionalized Polysulfone Anion Exchange Membranes

“…Examples of the functionalization chemistry include sulfonation, 3 bromination, 4 chloromethylation, 5 amidoalkylation, 6 and lithiation. 7−9 Functionalized PSfs have been actively investigated as membrane materials for gas 1,2,10,11 and liquid separation 12 and for fuel cells (FCs). 13−16 For example, sulfonated polysulfones, which have been synthesized by copolymerization with a sulfonated comonomer or by postsulfonation, 13,16 have been widely studied for proton exchange membranes (PEMs) for acidic fuel cells to provide alternatives to established Nafion that has dominated the field.…”

Fluorinated Poly(aryl ether) Containing a 4‐Bromophenyl Pendant Group and its Phosphonated Derivative

“…Bromine in polymers may also be converted readily into various functional groups, such as trimethylsilyl, phosphonate, and many others. [6,7] Bromine-containing polymers are often prepared either by post-bromination or by the polymerization of brominated monomers. [8] Compared with sulfonic acid units, phosphonic acid units are known for their higher chemical and thermal stability and greater ability to retain water.…”