Acid-base polymer systems

For the purposes of this discussion, PEMs are classified in modified Nafion , membranes based on functionalized non-fluorinated backbones and acid-base polymer systems. The prior approaches adopted by researchers and some characteristics of the resultant membranes under each classification are presented in this section. 

In summary, this section demonstrates that there are many kinds of membranes with functionalized non-fluorinated backbones that have been investigated the recent years in order to substitute the expensive Nafion PEM with properties (especially proton conductivity, methanol permeability, and mechanical stability) superior to those of Nafion. The last category of polymeric PEMs is the acid-base polymer systems, which are presented in the following section. 

Savinell and co-workers, [105-107], who have principally studied phosphoric acid doped polybenzimidazole (PBl). Similar systems have been reported by He and co-workers [108], who in addition report the conductivities of PBl based membranes doped with PTA and zirconium hydrogen phosphate [108], Acid-base interactions in entirely polymeric systems have been reported by Kerres and co-workers [102], who prepared and stndied several membranes prepared by blending polymers with acidic (snlfonated-PEEK, sulfonated polyethersulfone) and basic (polybenzimidazole, poly-vinylpyridine) characteristics. Selected acid-base polymer systems are discnssed in the following. 

The literature3 contains some limited work on decaborane-based polymer systems. Typically, most utilize the Lewis acid/base reaction between decaborane (Lewis acid, B10H12) and amines and phosphines (Lewis bases, L) resulting in the formation of complexes (see scheme 2) having the general formulas B10H12L2. For example, the... 

There seems to be no limit to the types of pharmaceutical systems that can be isolated in the amorphous state. In the literature, samples of sugars, acids, bases, polymers, buffers, inorganics, salts, natural products, proteins, and low-molecular-weight APIs have all been reported to exist in an amorphous form. Likewise, pharmaceutical raw materials, intermediates, and final products that include these amorphous materials are widespread and varied (Table 1). 

Additional work is underway to use computational methods to (i) tailor bases to mimic water, perhaps using substituted imidazoles or other proton carriers (ii) understand proton transport in phosphoric acid/basic polymer systems and (iii) augment other experiments on new polymers and additives of various types. 

Chitosan-based nano- and microparticles are widely used for fabrication of controlled dmg release systems. Numerous studies have demonstrated that chitosan and its derivatives (A-trimethyl chitosan, mono-A-carboxymethyl chitosan, etc.) are effective and safe for absorption enhance to improve mucosal (nasal, peroral) delivery of hydrophylic macromolecules, such as peptide and protein dmgs as well as heparins [37,38]. This absorption enhancing effect of chitosan is caused by the opening of intercellular tight junctions, thereby favoring the paracellular transport of macro-molecular dmgs. Recently, a series of successful model chitosan-based polymer systems for mucosal dmg delivery have been reported. Thus, Lim et al. [39] have proposed novel polymer microparticles based on combination of hyaluronic acid and chitosan hydroglutamate... 

Sinclair, R.G. and Gynn, G.M. (1972) Preparation and Evaluation of Glycolic and Lactic Acid-Based Polymers for Implant Devices Used in Management of Maxillofacial Trauma. II, Battelle Memorial Institute, Columbus, OH. Sinclair, R.G. (1973) Slow-release pesticide system. Polymers of lactic and glycolic acids as ecologically beneficial, cost-effective encapsulating materials. Environ. Sci. TechnoL, 7 (10), 955—956. Manninen, M.J. and Pohjonen, T. 

Therefore, the requirement for active management of the PEM water content adds considerable system cost, complexity, and unreliability. Because of this, there is considerable research under way addressing the development of alternative classes of acid-based polymer electrolytes for fuel cells. There are excellent reviews of the progress being made in the development of these alternative polymer electrolytes [22]. 

Along this line, boronic acid-based polymer complexes are sensitive to glucose as a potential insulin delivery system, presumably due to the competitive binding of glucose to boronic acids, which disrupts the boronic acid-diol complex network within the polymer matrix (Scheme 13.5) [157]. In one study, the phenylboronic acid (PBA) moiety was attached to poly(M-vinyl-2-pyrrolidone) (NVP) to form poly(NVP-co-PBA)... 

Viljanmaa M, Sodergard A et al (2002) Lactic acid based polymers as hot melt adhesives for packaging applications. Int J Adhes Adhes 22 219 Welsh J, Higgins J et al (2003) Evaluation of electrically disbonding adhesive properties for use as separation systems. In AIAA 2003-1436 (44th AIAA/ASME/ ASCE/AHS structures, structural dynamics, and materials conference), Norfolk, USA, pp 1-3 Yamada K, Chen T et al (2000) Chitosan based water-resistant adhesive. Analogy to mussel glue. Biomacromolecules 1 252... 

Electrolysis of water has been used for over a century to produce hydrogen and oxygen. The concept of a reversible fuel cell for space applications is based on a combined electrolytic-galvanic fuel cell. Like fuel cells, several different types of electrolyzers and catalysts have been developed, including atmospheric and high-pressure acid-based polymer electrolyzers, alkaline solution systems, and solid oxide-based systems. 

Fig. 23. Representative protecting groups for phenolic and carboxylic acid-based systems, (a) The polymer-based protecting groups are fisted in order of increasing activation energy for acid-catalyzed deprotection, (b) Acid-labile monomeric dissolution inhibitors, a bifunctional system based on protected bisphenol A. (c) Another system that combines the function of dissolution inhibitor and PAG in a single unit.

In choosing a SAM system for surface engineering, there are several options. Silane monolayers on hydroxylated surfaces are an option where transparent or nonconductive systems are needed. However, trichlorosilane compounds are moisture-sensitive and polymeri2e in solution. The resulting polymers contaminate the monolayer surface, which occasionally has to be cleaned mechanically. CarboxyUc acids adsorb on metal oxide, eg, AI2O2, AgO through acid—base interactions. These are not specific therefore, it would be impossible to adsorb a carboxyUc acid selectively in the presence of, for example, a terminal phosphonic acid group. In many studies SAMs of thiolates on Au(lll) are the system of choice. 

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