Cross-linked polyimide membranes

L. Shao, T.-S. Chung, S. H. Goh, and K. P. Pramoda. Transport properties of cross-linked polyimide membranes induced by different generations of diaminobutane (DAB) dendrimers. 7. Membr. ScL, 238(1-2) 153-163, July 2004. 

Physical Properties of Cross-Linked Polyimide Membrane Sample Weight (%) Color... 

Synthesis and Gas Permeability of Hyperbranched and Cross-linked Polyimide Membranes... 

Synthesis and Gas Permeability ofHyperbranchedand Cross-linked Polyimide Membranes 5... 

Synthesis and Cas Permeability ofHyperbranched and Cross-linked Polyimide Membranes 9... 

Synthesis and Gas PermeabilityofHyperbranched and Cross-linked Polyimide Membranes 21... 

Recently, the polymer science field has focused on the role of polymers as membrane materials with precise, well-ordered structures through the development of defined synthesis and analysis of polymers. Among these well-ordered polymers are the hyperbranched polymers (e.g. hyperbranched polyimides). Part of the interest in such polymers is due to the expectation that they could have different properties as compared to common linear polymers. Also, cross-linked polyimides have attracted much attention from researchers, as can be judged by a high number of publications. 

Figures 1.3-1.5 present Robeson diagrams for different gas pairs, in various polyimide membranes. The first examination of these plots shows that the data points for Type II (cross-linked) and Type III (hyperbranched) structures can be found in the whole cloud of the data points including those of linear structures (Type 1). However, the data points for some hyperbranched and cross-linked polyimides are located near the upper bound for O2/N2 pair as shown in Figure 1.3. On the other hand, the majority of the hyperbranched polyimides tend to be located among the common Unear polyimides, as well as that of cross-linked polyimides in the diagram for CO2/N2 pair relationship as shown in Figure 1.4. Finally, the data points for aU three types of the stractures are far from upper bound for the pair CO2/CH4, as seen in Figure 1.5. Apparently, more data are required in order to discuss more specifically the relationship between gas permeation properties and the structure of hyperbranched and cross-linked polymers.

Section I (Novel Membrane Materials and Transport in Them) focuses on the most recent advances in development of new membrane materials and considers the transport parameters and free volume of polymeric and even inorganic membranes. Kanehashi et al. (Chapter 1) present a detailed review of hyperbranched polyimides, which are compared with more common cross-linked polyimides. These polymers with unusual architecture were studied in the hope that they would show weaker tendency to plasticization than conventional linear polymers. However, many representatives of this new class of polymers reveal relatively poor film forming properties due to absence of chain entanglement. Nonetheless, some promising results obtained can show directions of further studies. 

The fabrication of blend membranes is relatively simple compared with that of inorganic flller mixed or cross-linked composite membranes. Bi et al. prepared a series of cross-linked sulfonated poly(arylene ether sulfone)/sulfonated polyimide (cSPAES/SPl) blend membranes by mixing a certain amount of cSPAES and SPI in their triethylamine (TEA) salt forms using m-cresol as a solvent, followed by filtration and casting onto a Petri dish and dried at 80°C for 2 h, 100°C for 2 h, and 120°C for 15 h, respectively, followed by proton exchange with 2 M HCl to obtain the blend hydrocarbon polyelectrolytes. 

According to literary data, the following mixtures of aromatic/aliphatic-aromatic hydrocarbons were separated toluene/ n-hexane, toluene/n-heptane, toluene/n-octane, toluene/f-octane, benzene/w-hexane, benzene/w-heptane, benzene/toluene, and styrene/ethylbenzene [10,82,83,109-129]. As membrane media, various polymers were used polyetherurethane, poly-esterurethane, polyetherimide, sulfonyl-containing polyimide, ionicaUy cross-linked copolymers of methyl, ethyl, n-butyl acrylate with acrilic acid. For example, when a composite polyetherimide-based membrane was used to separate a toluene (50 wt%)/n-octane mixture, the flux Q of 10 kg pm/m h and the separation factor of 70 were achieved [121]. When a composite mebrane based on sulfonyl-containing polyimide was used to separate a toluene (1 wt%)/ -octane mixture, the flux 2 of 1.1 kg pm/m h and the separation factor of 155 were achieved [10]. When a composite membrane based on ionically cross-linked copolymers of methyl, ethyl, w-butyl acrylate with acrilic acid was used to separate toluene (50 wt%)//-octane mixture, the flux Q of 20-1000 kg pm/m h and the separation factor of 2.5-13 were achieved [126,127]. 

Effect of Polyimide DSDA-TrMPD/ODA/DEB Chemical Composition (the Content of Amine Coreagents), Cross-Linking of Polyimide and Addition of Tetracyanoethylene (TCNE) to the Polymer on the Membrane Pervaporation Properties... 

FIGURE 9.28 Dependence of productivity for the mixture (o) and separation factor of benzene/cyclohexane j3p(x) on degree of phosphorylation for phosphorylated and thermally cross-linked BPDA-TrMPD polyimides henzene/cyclohexane, 50/50 wt% mixture, r=343 K, membrane thickness 30-40 p-m. (From analysis of data presented in Semenova, S.I., J. Membr. Sci., 231, 189, 2004. With permission.)... 

Liu, Y. Chung, T.S. Wang, R. Liu, D.F. Chng, M.L. Chemical cross-linking modification of polyimide/poly(ethersulfone) dual layer hollow fiber membranes for gas separation. Industrial Engineering Chemistry Research 2003, 42 (6), 1190-1195. 

Reddy et al., cited by Snape and Nakajima [3], investigated the use of a polyimide ultrafiltration membrane with the skin layer of cross-linked silicone (NTGS 2100), for the removal of chlorophyll and p-carotene from crude sunflower... 

Other membranes, such as sulfonated polyimide [102] or cross-linked sulfonated PVA [103] exhibit a major amoimt, although no quantified, of non-freezable water as compared to Nafion. An interesting behavior was observed in the case of PBl and ABPBI membranes doped with phosphoric acid [104], where the amount of frozen water is 2.2 % for PBI and between 1.1 % and 9.1 % at 100 % relative humidity, much lower than that observed for Nafion under similar conditions. When equilibrated with aqueous methanol, PBI membranes exhibit a maximum of 10 wt% of frozen water, while ABPBI membranes, particularly those prepared by high temperature casting, presented very low percentages of frozen water in all methanol concentrations studied, with a maximum value of 0.6 wt% in methanol 25 w/w%. This result is relevant for the application of ABPBI in DMFC because, the fuel cell start up at low temperatures would not be affected. 

Bi H, Wang J, Chen S, Hu Z, Gao Z, Wang L, et al. Preparation and properties of cross-linked sulfonated poly(arylene ether sulfone)/sulfonated polyimide blend membranes for fuel cell application. J Membr Sci 2010 350(l-2) 109-16. 

FIGURE 11.2 Comparison of FTIR spectra of the cross-linked BTDA-DAPI polyimide membranes at different cross-linker concentrations. 

Wind, J.D., Bickel, C.S., Paul, D.R. and Koros, W.J. 2003a. Sohd-state covalent cross-linking of polyimide membranes for carbon dioxide plasticization reduction. 

Cross-linked (Type II) and hyperbranched (Type III) polyimides can be prepared for the use as gas separation membranes. There are no dendrimers and dendrons known, which would form free-standing membranes. Therefore, we focus on the synthesis of cross-linked (Type n) and hyperbranched (Type III) polyimides. 

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