Aromatic polymers, chemical activity

Wholly aromatic polymers are thought to be one of the more promising routes to high performance PEMs because of their availability, processability, wide variety of chemical compositions, and anticipated stability in the fuel cell environment. Specifically, poly(arylene ether) materials such as poly-(arylene ether ether ketone) (PEEK), poly(arylene ether sulfone), and their derivatives are the focus of many investigations, and the synthesis of these materials has been widely reported.This family of copolymers is attractive for use in PEMs because of their well-known oxidative and hydrolytic stability under harsh conditions and because many different chemical structures, including partially fluorinated materials, are possible, as shown in Figure 8. Introduction of active proton exchange sites to poly-(arylene ether) s has been accomplished by both a polymer postmodification approach and direct co-... 

Aromatic polymers with phosphonated sites directly linked to the main chain have also been prepared by direct polymerization (Scheme 13.2a-d). For example, phosphonated poly(l,3,4-oxadiazole)s have been prepared by direct polycondensation of l,4-dicarbo3y-2-phenyl-phosphonic acid and their dihydrazides in an ionic liquid using triphenyl phosphite as a reaction activator. " The membranes obtained from these polymers were thermally and chemically stable and possessed proton conductivities in the range between 4x10 " and 5x10 mS cm at 100% RH, which is three orders of magnitude lower than the state-of-the-art PFSA membrane Nation . 

Many renewable raw materials contain hydroxyl groups connected to carbon atom and hence can be considered as alcohols. One of the most abundant renewable raw materials is HgnoceUulosic biomass, which is composed of carbohydrate polymers such as cellulose or hemiceUulose, and an aromatic polymer Hgnin. The HgnoceUulose is mainly used in construction materials, as firewood and for production of biofuels, such as biodiesel, ethanol, and hydrogen, which are sustainable alternatives to fossil fuels with reduced CO2 emission. However, modification and effective conversion of biomass to fine chemicals with an added value is an active field of modem research. For instance, partial oxidation of cellulose can lead to significant change in... 

The alternative noncovalent functionalization does not rely on chemical bonds but on weaker Coulomb, van der Waals or n-n interactions to connect CNTs to surface-active molecules such as surfactants, aromatics, biomolecules (e.g. DNA), polyelectrolytes and polymers. In most cases, this approach is used to improve the dispersion properties of CNTs [116], for example via charge repulsion between micelles of sodium dodecylsulfate [65] adsorbed on the CNT surface or a large solvation shell formed by neutral molecule (e.g. polyvinylpyrrolidone) [117] around the CNTs. 

The second synthetic route to PAE containing quinoxaline units involved the reaction of an aromatic dihydroxy quinoxaline or aromatic bis(hydroxy-quinoxaline) with activated aromatic difluoro compounds (Eq. (3)) [15]. The dihydroxy quinoxaline and bis(hydroxyquinoxaline) monomers were readily prepared from the condensation of 1,2-diaminobenzene with 4,4 -dihydroxyben-zil and aromatic bis(o-diamines) with 4-hydroxybenzil, respectively. The Tgs of a series of PAE containing quinoxaline units are presented in Tables 3 and 4. For these polymers, the trend for the Tg is sulfone > carbonyl > terephthaloyl-> isophthaloyl. This trend holds for most polymer families when polymers of similar molecular weights are compared. Several polyphenylquinoxalines of the same chemical structure as those in Table 3 were also prepared by the poly-... 

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