Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

PEMs, block copolymer

SuPAES). In common with the previously mentioned PEMs, initial SuPAES materials (see Section 3.3.2.1 for later work on block copolymer derivatives of SuPAES) had a statistical distribution of sulfonic acid groups along the polymer backbone. However, instead of using postsulfonation techniques, sulfonic acid groups were introduced via direction copolymerization that is, suitable sulfonic acid precursor groups were introduced into one of the monomers (13). The advantages of this method are threefold ... [Pg.144]

Block and graft copolymers are composed of significant sequences of different monomer units, normally in a nonstatistical fashion. For block copolymers, these sequences are assembled in a linear fashion whereas in the case of graft copolymers, blocks are grown from or attached to the backbone of another block as branches. In the case of block and graft copolymer PEMs, these sequences may be composed of significantly different chemical units or units that are chemically identical except that one block is sulfonated and the other is not. [Pg.150]

Examples of partially fluorinated block copolymer PEMs. [Pg.154]

There have been few synthetic reports employing these monomers beyond the Ballard work, most likely as a result of presumed high cost and monomer availability. However, the performance and stability demonstrated by these materials in fuel cells may spur further developments in this area. The above-reported copolymers are believed to be random systems both in the chemical composition of the copolymer backbone and with regard to sulfonic acid attachment. Novel methods have been developed for the controlled polymerization of styrene-based monomers to form block copolymers. If one could create block systems with trifluorostyrene monomers, new morphologies and PEM properties with adequate stability in fuel cell systems might be possible, but the mechanical behavior would need to be demonstrated. [Pg.352]

As an extension of the previous work, copolymers based on partially sulfonated ethylene—styrene pseudorandom interpolymers have also been employed instead of the block copolymers (Figure Due to the unique nature of the polymerization catalyst, styrene residues are separated by at least one ethylene residue and the acid groups are distributed randomly along the chain. This material provides an economical and unique counterpoint to the sulfonated SEES PEMs, where the sulfonic acid groups are bunched together in the styrene blocks. Controlling the styrene content in each material provides a route to control the level of sulfonation and resultant ion exchange capacity of the PEM. [Pg.353]

As described previously, Nafion membranes exhibit much higher proton conductivity than any other aliphatic and aromatic PEMs bearing similar ion content due to the special chemical structure and morphology. Partially sul-fonated polystyrene (SPS) and PTFSSA have the same backbone except PTF-SSA possesses a fluoropolymer backbone. The dependence of proton conductivity on EW for SPS at 22 °C [172] and PTFSSA [138] membranes is shown in Fig. 17. The conductivities of the fluorinated block copolymer P(VDF-co-... [Pg.93]

HFP)-fc-SPS [163] and non-fluorinated block copolymers SSEBS [138] and SSIBS [173] are shown in Fig. 18. It can be concluded that fluorous structures generally enhance the conductivity of PEMs. Also, as can be inferred from Fig. 17, fluorous polymers can be prepared with lower EWs without dissolution in water due to the increased hydrophobicity of the backbone. The higher conductivity is most likely due to the decrease in swelHng, the concomitant increase in [H" ], and an increased hydrophihc network. [Pg.94]

In work by Hansen et al., a series of multi-block copolymers based on fluorinated co-SPI was synthesized and its detailed morphological analysis and PEM properties were thoroughly examined [267]. The structure of the multi-block co-SPI is presented in Scheme 3.42. A random variety of co-SPI was prepared to compare their properties. The block length... [Pg.169]

S. Maity, T. Jana, Polybenzimidazole block copolymers for fuel cell synthesis and studies of block length effects on nanophase separation, mechanical properties, and proton conductivity of PEM, ACS Appl. Mater. Interfaces 6 (9)(2014) 6851-6864. [Pg.266]

There have been studies indicating that blends of PBI polymers with pyridine-containing polymers could prove useful in a high-temperature PEM fuel cell. Kallitsis et al. [31] combined commercially supplied w-PBI with an aromatic polyether that contained a pyridine moiety in the main chain (PPyPO) these polymer blends were then soaked in 85% wt PA. Dynamic mechanical analysis of a 75/25 PBl/PPyPO block copolymer showed reasonable mechanical strength and flexibility. The conductivity of this copolymer was not reported, but the conductivity of 85/15 PBI/PPyPO block copolymer was 0.013 S cm at a relatively low PA doping level. Further investigation of these systems is required to prove its utility as a fuel cell membrane. [Pg.404]

Block copolymers combing PBI with other types of macromolecular units have also been developed for superior membrane properties, as shown in Fig. 7.6. Two types of copolymers have been prepared, characterized, and evaluated as fuel cell electrolytes. One is the sulfcmated copolymer containing PBI and snUrmated polymer moieties for low temperature PEMs in both PEM fuel cells and direct methanol fuel cells (DMFCs) [123-126]. The other is the random copolymer containing PBI and poly(imine/ amide) moieties [127, 128]. For the sulfonated PBI copolymers, benzimidazole monomers... [Pg.160]

Mader JA, Btmicewicz BC (2011) Synthesis and properties of segmented block copolymers of functionalised polybenzimidazoles for high-temperature PEM fuel cells. Fuel Cells 11 222—237... [Pg.166]

Water-based PEMs exhibit proton transport mechanisms and mobilities similar to those in liquid electrolytes like hydrochloric acid proton conductivities could reach up to 0.1 S cm in the case of PFSA-type ionomers, and up to 0.5 S cm in the case of block copolymer systems. The temperature range of operation of PEMs stretches from —30°C to 90°C, the lower bound being determined by the freezing point of water, which is suppressed because of the high surface energy of water in nanopores. The upper limit is determined by evaporation of water only a few water-based PEMs have been demonstrated that could maintain a sufficient conductivity above lOO C. [Pg.38]

Asymmetric PEMs with a loosely cross-linked proton conductive layer sandwiched between two primarily hydrophobic layers with limiting methanol swelling have been prepared. A three-component polymer blend (TCB) consisting of poly(4-vinylphenol-co-methacrylate) (PVPMA), poly(butyl methacrylate) (PBM), and acrylic copolymer resin Polaroid B-82 acted as a methanol barrier layer. The proton conductive hydrophilic layer consisted of a random copolymer of 2-hydroxy-2-acrylamido-2-methyl propanesulfonic acid (AMPS) and HEMA, loosely cross-Unked by poly(ethylene glycol) dimethacrylate (PEG-DMA) oligomer. TGA analysis showed that these membranes are thermally stable up to 270 °C. However, their proton conductivity was rather low [172]. Thermoplastic PVDF-SEBS blends compatibUized with MMA block copolymers can be used for solventless fabrication of PEMs [173]. [Pg.33]

The low conductivity of the sulfonated aromatic PEMs at low RH has been attributed to the fact that sulfonated aromatic polymers have fewer connected water domains as well as more phase mixing of the hydrophobic and hydrophilic domains [33], Block copolymers, consisting of covalently bonded chemically dissimilar sequences, exhibit highly periodic microphase-separated structures [34], The characteristic lengths of the structures are determined by the molecular size and are in the 10-100 nm range. Therefore, many research studies have focused on the development of sulfonated multiblock copoly(ether sulfone)s for improving the nanophase-separated structures and proton conductivity under a low RH. [Pg.158]

PMMA is another base material used as PEMs for electrochemical applications, due to its excellent thermal and mechanical stabilities, as well as its ability to significantly increase ion conductivity of PEMs. Mostly PMMA was synthesized as the main component of block copolymers, and another component can be PS and PSSA [45-47]. As one of the most promising aliphatic polymers, PMMA has also been blended with other components like PVDF and Si02 [48-50]. These PEMs prepared... [Pg.453]

Thermal stability is an important property for PEMs, especially in high-temperature systems, and the corresponding characterization is thermogravimetric analysis (TGA). As most of the prepared aliphatic PEMs reported in the literature are block copolymers, graft copolymers, and composites of polymers, with frequently some inorganic materials included, TGA was used to study the differences between PEMs with different compositions [24,37,42,47],... [Pg.463]

As typically observed in the case of non-ionic block and graft copolymers, the immiscibility of the constituent blocks within the copolymers can induce microphase separation beyond even that which normally occurs due to hydrophobic and hydrophilic sites within statistical copolymer PEMs such as Nation. A relatively recent area of PEM research, ionic block and graft copolymers are interesting from the point of view of providing fundamental understanding about the influence of morphology upon proton conduction... [Pg.150]


See other pages where PEMs, block copolymer is mentioned: [Pg.151]    [Pg.152]    [Pg.153]    [Pg.352]    [Pg.284]    [Pg.1094]    [Pg.234]    [Pg.604]    [Pg.606]    [Pg.55]    [Pg.59]    [Pg.78]    [Pg.78]    [Pg.293]    [Pg.87]    [Pg.164]    [Pg.302]    [Pg.302]    [Pg.320]    [Pg.241]    [Pg.590]    [Pg.119]    [Pg.166]    [Pg.25]    [Pg.2779]    [Pg.349]    [Pg.456]    [Pg.594]    [Pg.342]    [Pg.107]    [Pg.150]   
See also in sourсe #XX -- [ Pg.78 ]




SEARCH



PEM

© 2024 chempedia.info