Poly , transport properties

Membranes and Osmosis. Membranes based on PEI can be used for the dehydration of organic solvents such as 2-propanol, methyl ethyl ketone, and toluene (451), and for concentrating seawater (452—454). On exposure to ultrasound waves, aqueous PEI salt solutions and brominated poly(2,6-dimethylphenylene oxide) form stable emulsions from which it is possible to cast membranes in which submicrometer capsules of the salt solution ate embedded (455). The rate of release of the salt solution can be altered by surface—active substances. In membranes, PEI can act as a proton source in the generation of a photocurrent (456). The formation of a PEI coating on ion-exchange membranes modifies the transport properties and results in permanent selectivity of the membrane (457). The electrochemical testing of salts (458) is another possible appHcation of PEI. 

Inspired by good electron transport properties and high PL of PBD and, particularly, a claim by Heeger and co workers [68] of exceptional performance of PBD MEH-PPV mixtures (EL of up to 50% of the PL yield), Bryce and coworkers [697] reported the first poly(PBD) homopolymer (604) and its aza-derivative (605). The device ITO/PEDOT/MEH-PPV 604/A1 showed cT>i" of 0.26%, compared to 0.01% obtained with MEH-PPV alone in an identically prepared device. 

For applications where only mechanical properties are relevant, it is often sufficient to use resins for the filling and we end up with carbon-reinforced polymer structures. Such materials [23] can be soft, like the family of poly-butadiene materials leading to rubber or tires. The transport properties of the carbon fibers lead to some limited improvement of the transport properties of the polymer. If carbon nanotubes with their extensive propensity of percolation are used [24], then a compromise between mechanical reinforcement and improvement of electrical and thermal stability is possible provided one solves the severe challenge of homogeneous mixing of binder and filler phases. For the macroscopic carbon fibers this is less of a problem, in particular when advanced techniques of vacuum infiltration of the fluid resin precursor and suitable chemical functionalization of the carbon fiber are applied. 

Zhang, L., Ma, C. and Mukerjee, S. 2005. Effect of copolymer composition on the oxygen transport properties of sulfonated poly(arylene ether sulfone) and sulfonated poly(sulfide sulfone) PEMs. Journal of the Electrochemical Society 152 A1208-A1216. 

Elabd, Y. A., Napadensky, E., Walker, C. W. and Winey, K. 1. 2006. Transport properties of sulfonated poly(styrene-b-isobutylene-b-sytrene) triblock copolymers at high ion-exchange capacities. Macromolecules 39 399-407. 

Figure 18 shows the temperature dependence of the proton conductivity of Nafion and one variety of a sulfonated poly(arylene ether ketone) (unpublished data from the laboratory of one of the authors). The transport properties of the two materials are typical for these classes of membrane materials, based on perfluorinated and hydrocarbon polymers. This is clear from a compilation of Do, Ch 20, and q data for a variety of membrane materials, including Dow membranes of different equivalent weights, Nafion/Si02 composites ° ° (including unpublished data from the laboratory of one of the authors), cross-linked poly ary lenes, and sulfonated poly-(phenoxyphosphazenes) (Figure 19). The data points all center around the curves for Nafion and S—PEK, indicating essentially universal transport behavior for the two classes of membrane materials (only for S—POP are the transport coefficients somewhat lower, suggesting a more reduced percolation in this particular material). This correlation is also true for the electro-osmotic drag coefficients 7 20 and Amcoh...

Poly- and oligothiophenes are generally p-type (hole-transporting) semiconductors. In thiophene-S,S-dioxide (98AM551 98JOC5497), this modification results in de-aromatization of the thiophene unit and increases the electron affinity and electron-transport properties of the... 

For gas separation membranes, for example, He, O2, and N2 gas transport properties of CA/poly(methyl methacrylate) (PMMA) blends have been measured [108]. This article reported that CA/PMMA blends exhibited phase separation with limited intermiscibility between the components, but they were possibly useful as membrane materials to produce high-purity helium gas streams combined with high helium recovery. 

The preceding structural characteristics dictate the state of polymer (rubbery vs. glassy vs. semicrystalline) which will strongly affect mechanical strength, thermal stability, chemical resistance and transport properties [6]. In most polymeric membranes, the polymer is in an amorphous state. However, some polymers, especially those with flexible chains of regular chemical structure (e.g., polyethylene/PE/, polypropylene/PP/or poly(vinylidene fluoride)/PVDF/), tend to form crystalline... 

Bondar VI, Freeman BD, Pinnau I (2000) Gas transport properties of poly(ether-b-amide) segmented block copolymers. J Polym Sci Part B Polym Phys 38(15) 2051-2062... 

Furthermore, in 2001, Ballard entered an alliance with Victrex to produce two new membrane alternatives. One membrane is based on sulfonated poly(arylether) ketone (a variant of PEEK) supplied by Victrex, which may be better suited to PEMFC fabrication applications. In March 2002, U.S. Patent 6,359,019 was issued to Ballard Power for a graft-polymeric membrane in which one or more trifluorovinylaromatic monomers are radiation graft polymerized to a preformed polymeric base. The strucmres of BAM membranes have been studied by way of small-angle neutron scattering (SANS) [97]. The study of the ionomer peak position suggests the existence of relatively small ionic domains compared to Nalion, despite large water content. Phase separation in the polymer matrix is possibly crucial for the membrane s mechanical and transport properties. 

The transport property of poly(L-glutamic acid) membrane 24) was also photo-controlled by incorporating triphenylmethane leucoderivative, pararosaniline, groups [60]. The pararosaniline groups in the membrane dissociate into ion-pairs upon ultraviolet irradiation, yielding hydroxide ions. 

Photocontrol of the transport property was also studied for poly(L-glutamic acid) membrane with azobenzene-4-sulfonic acid residues [61]. 

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