Fluoropolymer membranes preparation

Yi et al. reported a new type of PVDF membrane prepared by blending two very different polymers, a PVDF fluoropolymer such as Kynar with a sulfonated poly-electrolyte. The new membrane is inexpensive and displayed good performance and durability based on 1,000-h test data. 

To realize the long-term hydrophilicity of the blend polymer membranes, the key point is to improve the stability of the hydrophilic component on the membrane surface and matrix. To this end, amphiphilic polymers have been adopted to replace linear hydrophilic PEG and PVP in membrane preparation. Theoretically, improved interactions among the hydrophobic segments in amphiphilic polymers and the fluoropolymer can improve the compatibility of the blend, and thus enhance the stability of amphiphilic polymer in the membrane matrix. Three kinds of amphiphilic polymers, viz., triblock copolymer of poly(ethylene oxide)-( -poly(propylene oxide)-ft-poly(ethylene oxide) (EPE), comb-like copolymer of polysiloxane with poly(ethylene oxide) and poly(propylene oxide) side chains (ACPS), and the hyperbranched star copolymer of polyester-g-methoxyl poly(ethylene glycol) (HPE-g-MPEG), have been... 

Several recent studies report gas permeation, sorption, and free volume characteristics of these two amorphous fluoropolymers. Nemser and Roman (1991 Nemser, 1993) reported permeability properties of Teflon AF polymer membranes prepared by a melt-press method. Similar to PTMSP, these polymers are permeable to permanent gases. For example, oxygen... 

Like many other fluoropolymers, Nafion is quite resistant to chemical attack, but the presence of its strong perfluorosulfonic acid groups imparts many of its desirable properties as a proton exchange membrane. Fine dispersions (sometimes incorrectly called solutions) can be generated with alcohol/water treatments. Such dispersions are often critical for the generation of the catalyst electrode structure and the MEAs. Films prepared by simply drying these dispersions are often called recast Nafion, and it is often not realized that its morphology and physical behavior are much different from those of the extruded, more crystalline form. 

Since an IPMC functions as a pathway for hydrated cations, its properties will be expected to affect the performance of an IPMC actuator. The membrane materials used in IPMCs have so far been limited to a few commercially available perfluorinated ionic polymers, such as Nafion, and the thickness of the IPMC has also been restricted to the available thickness of the commercial membrane [67]. However, IPMC actuators employing new ionic membranes have now been reported [68]. The membranes are prepared from fluoropolymers grafted with polystyrene sulfonic acid (PSSA). IPMCs assembled with these membranes have been shown to exhibit at least several times larger displacements than the Nafion-based IPMC with similar thickness. 

This chapter presents the preparation and properties of fluorosilicones and some specialty fluoropolymers. The development of various kinds of novel fluorosilicones for membrane-based applications, as well as their fabrication and modification methods, is also described. 

To enhance membrane mechanical and hydro-thermal stability, Jiang et al. prepared a blend of side-chain sulfonated PFCB block copolymer and a PVDF fluoropolymer [129]. The chemical structure of the side-chain sulfonated PFCB ionomer is shown in Scheme 6.32. They evaluated the membrane s fiandamental properties, such as proton conductivity, gas permeability, water uptake, and... 

In their efforts to use various fluoropolymer films to develop PCMs, Scherer and co-workers [51] prepared PVDF-g-PSSA membranes in comparison with their counterparts based on ETFE films. PVDF films were activated from y-radiation (dose of 20 kGy at dose rate of 5.9 kGy h ) at room temperature in air and grafting of styrene with peroxidation method interestingly occurred at 60°C. The influence of the base polymer properties on the grafting behavior was addressed [52], Sulfonation of the grafted films conducted with chlorosulfonic acid/dichloromethane mixture at room temperature. The PEMFC performance of PVDF-based membranes was found to be inferior to their ETFE-based counterparts [52],... 

As a substimte to Nafion impregnation into a fluoropolymer matrix, solution cast films have been prepared from blends of Nafion and vinylidene fluoride-hex-afluoropropylene copolymer [16]. Upon addition of 20 60% vinylidene copolymer, a steep decrease in proton conductivity was observed, from 10 " S cm to 10 -10 S cm , which was accompanied by a significant decrease in methanol permeability. In a more recent paper [27], Si et al. solution cast membranes composed of Nafion and poly(vinylidene fluoride), henceforth denoted as PVDF, where characterized where the PVDF content was varied from 0 to 65 wt%. As expected, the conductivity and methanol permeability decreased with inaeasing PVDF content, with a much more dramatic drop in transport parameters when the PVDF content was >50%. From proton conductivity and methanol permeability data, the relative selectivity can be determined ... 

Chen, J., Septiani, U., Asano, M., Maekawa, Y., Kubota, H., Yoshida, M. (2007b) Comparative study on the preparation and properties of radiation-grafted polymer electrolyte membranes based on fluoropolymer films. J. Appl. Polym. Sd. 103, 1966-1972. 

The first proton-conducting perfluorinated membrane carrying phosphonic acid units was prepared by Kotov et al. [34]. Several co- and ter-fluoropolymers based on tetrafluoroethylene and perfluorovinylenes, such as... 

Some fluoropolymers prepared by DT with iodo-compounds have already been commercialized such as Daiel, Viton, and Technoflon. Such fluoroelastomers may find applications in high technology such as in O-rings, gaskets, hoses, transportation, medical devices, and electronics. The control of the architecture and functionality of the polymer chains makes possible the preparation of peroxide curable fiuoroelastomer with improved properties as well as the development of advanced fluorinated thermoplastic elastomers. Another application of functional fluoropolymers prepared by DT with iodo-compounds is the preparation of membranes for fuel cells. 

Methods of preparation of various functional fluoropolymers suitable for fuel cell applications have been discussed by Ameduri and coworkers [ 120]. They claimed that in spite of the high cost of Nafion and its permeability to methanol, it still remains the fluorinated polymer of choice for the preparation of the proton exchange membranes for PCs. 

Using the optimal conditions for the radical terpolymerization of 4-[(a,/ ,/ -trifluorovinyl)oxy]bromobenzene with the fluoroalkenes, these authors reported the synthesis of new polymer electrolyte membranes based on fluoropolymers incorporating aromatic perfluorovinyl ether sulfonic acids [85,107]. In fact, a novel synthetic route for the preparation of perfluorovinyl ether monomer containing sulfonic functionalities, 4-[(a,, -trifluorovinyl)oxy]benzenesulfonic acid (TFVOBSA), was proposed. This monomer was synthesized in 72% overall yield. Further, the radical (co)- and terpolymerization of 4-[(a,, -trifluorovinyl)oxy] benzenesulfonyl chloride (TFVOBSC) with VDF, HFP, and PMVE (Fig. 2.25)... 

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