Enhancement in the Gas Permeabilities of Novel Polysulfones with Pendant 4-Trimethylsilyl-α-hydroxylbenzyl Substituents

Abstract

A series of modified polymers with 4-trimethylsilyl-R-hydroxylbenzyl (HBTMS) substituents were made as new materials for membrane gas separation. HBTMS was introduced onto polysulfone (PSf), tetramethylpolysulfone (TMPSf), and hexafluoropolysulfone (6FPSf) by forming lithiated polymer intermediates followed by treatment with an electrophile, p-trimethylsilylbenzaldehyde. The resulting side substituent contains the bulky trimethylsilyl (TMS) groups separated from the polymer chain by an aromatic ring. The polymer structures were characterized by NMR spectroscopy, and thermal properties were investigated by differential scanning calorimetry and thermogravimetry. The permeability coefficients of the resulting polymers PSf-HBTMS, TMPSf-HBTMS, and 6FPSf-HBTMS showed considerable increases over the unmodified polymers. TMPSf-HBTMS showed the greatest improvements in gas transport properties with large increases in both CO 2 and O2 permeabilities of ∼3-fold (72 and 18 Barrers, respectively) compared with TMPSf. In the case of the CO2/N2 gas pair, there was an absence of the typical accompanying tradeoff shown by decreases in permselectivity with increasing permeability. Comparisons of this series of polymers containing the new HBTMS substituent were made with those having other TMS pendant groups.

Preparation and Characterization of Polysulfones Containing Both Hexafluoroisopropylidene and Trimethylsilyl Groups as Gas Separation Membrane Materials

“…The spectral analysis for both of 6FPSf and 6FPSf-Br 2 was reported previously. 36 Figure 1 shows 1 H NMR stacked spectra of three 6FPSf TMS derivatives along with complete assignment for all of the signals. Assignment of the aromatic hydrogen signals is based on the results of simple homonuclear decoupling experiments performed on every proton frequency.…”

“…The distance (δ) from the permeability point (P i vs R ij , where permselectivity R ij ) P i /P j ) to the upper bound line was calculated by the method developed previously. 36 Table 4 lists P, R, and δ values for 6FPSf, TM6FPSf, and their derivatives. The polymer permeability coefficients decrease in the following order: He 4 , which is also the order of increasing kinetic diameters of the gases.…”

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.…”

Revisiting the experimental and theoretical upper bounds of light pure gas selectivity–permeability for polymeric membranes

“…Previous presentations of CO 2 /N 2 upper bounds were made by Shida [6,7],H u [8], Khan [9] and Dai [25]. At the time there was no upper bound for this gas pair defined by Robeson.…”

“…At the time there was no upper bound for this gas pair defined by Robeson. This upper bound was generated by using a slope of −0.34 as would have been predicted by (d N 2 − d CO 2 ) = 0.34 and the most extreme point from Park and Paul [26] as described by Dai et al [25]. Only the Khan upper bound is shown for clarity as the Dai upper bound is essentially co-linear.…”