Gilles P. Robertson

Polymer nanosieve membranes for CO2-capture applications

Microporous organic polymers (MOPs) are of potential significance for gas storage, gas separation and low-dielectric applications. Among many approaches for obtaining such materials, solution-processable MOPs derived from rigid and contorted macromolecular structures are promising because of their excellent mass transport and mass exchange capability. Here we show a class of amorphous MOP, prepared by [2+3] cycloaddition modification of a polymer containing an aromatic nitrile group with an azide compound, showing super-permeable characteristics and outstanding CO(2) separation performance, even under polymer plasticization conditions such as CO(2)/light gas mixtures. This unprecedented result arises from the introduction of tetrazole groups into highly microporous polymeric frameworks, leading to more favourable CO(2) sorption with superior affinity in gas mixtures, and selective CO(2) transport by presorbed CO(2) molecules that limit access by other light gas molecules. This strategy provides a direction in the design of MOP membrane materials for economic CO(2) capture processes.

Properties of SPEEK based PEMs for fuel cell application

Comparative studies of membranes prepared using different solvents, have shown that the casting solvent plays a significant role, affecting their proton conductivity and mechanical strength. It has been found that using DMF strongly decreases the membrane conductivity in comparison with other solvents studied. The 1 H NMR results yield an insight into the mechanism of this effect, evidencing the formation of the strong hydrogen bonding of sulfonic acid groups with DMF. This can explain the large discordances of more than an order of magnitude existing between the conductivity results for sulfonated polyetheretherketone (PEEK) in some previous studies and in this work. It is also found that residual sulphuric acid, which is very difficult to eliminate from highly sulfonated polyetheretherketone (SPEEK), also affects its conductivity and under high temperature treatment, enters into reaction with both DMF and N,N-dimethylacetamide (DMAc), causing their degradation. As discussed in the present contribution, the conductivity measurement technique may also be a reason for discrepancy in the reported conductivity characteristics of SPEEK.

Azide-based Cross-Linking of Polymers of Intrinsic Microporosity (PIMs) for Condensable Gas Separation†

Cross-linked polymers of intrinsic microporosity (PIM)s for gas separation membranes, were prepared by a nitrene reaction from a representative PIM in the presence of two different diazide cross-linkers. The reaction temperature was optimized using TGA. The homogenous membranes were cast from THF solutions of different ratios of PIM to azides. The resulting cross-linked structures of the PIMs membranes were formed at 175 °C after 7.5 h and confirmed by TGA, XPS, FT-IR spectroscopy and gel content analysis. These resulting cross-linked polymeric membranes showed excellent gas separation performance and can be used for O(2) /N(2) and CO(2) /N(2) gas pairs, as well as for condensable gases, such as CO(2) /CH(4) , propylene/propane separation. Most importantly, and differently from typical gas separation membranes derived from glassy polymers, the crosslinked PIMs showed no obvious CO(2) plasticization up to 20 atm pressure of pure CO(2) and CO(2) /CH(4) mixtures.

Poly(aryl ether ketone)s with carboxylic acid groups: synthesis, sulfonation and crosslinking

Carboxylic acid-containing poly(aryl ether ether ketone) (PFEEK–COOH) and poly(aryl ether ether ketone ketone) (PFEEKK–COOH) were synthesized from the monomer 9,9-bis(4-hydroxyphenyl)-fluoren-4-carboxylic acid. The latter polymer, PFEEKK–COOH, was post-sulfonated to yield SPFEEKK–COOH whereby the site and the degree of sulfonation (DS from 0 to 3) could be controlled. The reaction progress and structures of the resulting sulfonated polymers were identified by 1D and 2D NMR techniques. The carboxylic acid group was used as to crosslink SPFEEKK–COOH by reaction with poly(vinyl alcohol) (PVA) to prepare crosslinked membranes. The proton conductivity of a crosslinked SPFEEKK–COOH-1.6/PVA membrane was ∼0.15 S cm−1 at 65 °C, while maintaining acceptable dimensional stability in water. Thermal stability, water uptake and proton conductivity of carboxylated, carboxylated/sulfonated, and crosslinked membranes were investigated.

Copolymers of Intrinsic Microporosity Based on 2,2′,3,3′-Tetrahydroxy-1,1′-dinaphthyl†

A series of new copolymers with high molecular weight and low polydispersity, prepared from tetrahydroxydinaphthyl, tetrahydroxyspirobisindane, and tetrafluoroterephthalonitrile monomers, prevent efficient space packing of the stiff polymer chains and consequently show intrinsic microporosity. One copolymer, DNPIM-33, has an excellent combination of properties with good film-forming characteristics and gas transport performance, and exhibits higher selectivity than the corresponding spirobisindane-based homopolymer PIM-1 for gas pairs, such as O(2) /N(2) , with a corresponding small decrease in permeability. This work demonstrates that significant improvements in properties may be obtained through development of copolymers with intrinsic microporosity (CoPIMs) that extends the spectrum of high-molecular-weight ladder structures of poly(dibenzodioxane)s.

A clustered sulfonated poly(ether sulfone) based on a new fluorene-based bisphenol monomer

A new fluorene-based bisphenol monomer containing two pendant phenyl groups, 9,9-bis(3-phenyl-4-hydroxy)phenyl-fluorene, was readily synthesized in high yield by a one-step reaction from inexpensive starting materials. A series of poly(ether sulfone)s with clustered sulfonic acid groups was prepared for fuel cell applications by polycondensation of the new monomer with bis(4-hydroxyphenyl)sulfone and bis(4-fluorophenyl)sulfone, followed by sulfonation exclusively on the fluorene rings and pendant phenyl rings, using concentrated sulfuric acid at room temperature. The sulfonated polymers gave tough, flexible, and transparent membranes by solvent casting. The ionic exchange capacity (IEC), water-uptake, dimensional stabilities, mechanical properties, thermal and oxidative stabilities as well as proton conductivities and single fuel cell properties of the membranes were investigated. The membranes with high IEC values show high proton transport properties, and their proton conductivities exhibit lower dependence on relative humidity compared with typical aromatic ion exchange membranes. 4-SPES-38 with an IEC value of 2.23 mequiv. g−1 displays comparable fuel cell performance with Nafion 212 under low humidity conditions.

Preparation of Highly fluorinated poly(ether sulfone)s under mild polycondensation conditions using molecular sieves

Highly fluorinated poly(ether sulfone)s were prepared by a modified polycondensation technique, using a molecular sieve dehydrating apparatus in order to efficiently remove water under mild conditions. Consequently, side reactions were minimized, which resulted in the formation of polymers free of microgels. This reaction was also used to introduce pentafluorostyrene moieties into the polymer to provide crosslinking functionalities.

Gas transport and dynamic mechanical behavior in modified polysulfones with trimethylsilyl groups: effect of degree of substitution

Trimethylsilyl (TMS) groups were introduced with controlled degree of substitution (DS) onto the phenylene rings of various polysulfones. The introduction of TMS groups resulted in a marked increase in oxygen permeabilities with small concurrent decreases in oxygen/nitrogen permselectivities. Although TMS groups are bulky, they are highly mobile and are expected to reduce chain packing as evidenced by larger specific volumes and d-spacings with increasing DS. The higher is DS, the greater the reduction in the chain packing that occurs. Dynamic mechanical analyses of sub-glass-transition relaxation, i.e., γ-relaxation behavior, showed that the TMS groups affected the local chain motion. In particular, the motion of unsubstituted phenylene rings increases with DS. Therefore, both the loosened chain packing and the increased local motion by substitution of TMS may result in the increase in the gas permeability.

Modified polysulfone membranes. III. Pervaporation separation of benzene–cyclohexane mixtures through carboxylated polysulfone membranes* †

Membranes prepared from carboxylated polysulfone permeated benzene preferentially from benzene–cyclohexane mixtures by pervaporation. Hydrophilic polysulfones containing carboxyl groups with degrees of substitution (DS) ranging from 0.46 to 1.90 groups per repeating unit were selected for this study. The membrane having a carboxyl group DS of 0.88 showed the best trade-off between flux and permselectivity. The permselectivity towards benzene was 234 at the weight fraction of benzene in feed of 0.1. From pervaporation and sorption experiments, it was evident that permselectivity toward benzene was due to solubility selectivity.

Modified polysulfones 5: synthesis and characterization of tetramethyl polysulfones containing trimethylsilyl groups and their gas transport properties

Polysulfones with rigid backbone structures and silyl-containing substituents were prepared as membrane materials with potentially enhanced gas transport properties. Tetramethylbisphenol-A polysulfone (TMPSf) and tetramethylbiphenol polysulfone (TMPPSf) were made by polycondensation then post-modified to introduce trimethylsilyl (TMS) groups by bromination and lithiation methodology. Substitution of high levels of TMS groups at the ortho-sulfone sites was achieved using direct lithiation followed by addition of a trimethylsilane electrophile. In an approach to increase the overall TMS substitution level as well as introduce these groups on the bisphenol segment, both TMPSf and TMPPSf were cleanly brominated to a degree of substitution (DS) of 2.0 for bromine. While the subsequent lithium–halogen exchange and reaction with TMS electrophile did not give high regioselectivity because of steric hindrance, the overall DS of TMS in the polymers was increased when excess n-butyllithium was used to activate both brominated and ortho-sulfone sites. The polymer structures were characterized by NMR spectroscopy. Their thermal properties as well as O2, N2, CO2 and CH4 gas transport properties were measured. Polymers with a high DS of TMS had very high CO2 and O2 permeabilities and good permselectivities from N2. The permselectivities of CO2/N2 were at or close to the Robeson upper-bound performance line [J. Membr. Sci. 62 (1991) 165].