E. G. Bulycheva

Preparation and Characterization of Sulfonated Polyphenylquinoxalines

Poly(phenylquinoxaline)s.(PPQs) are a family of aromatic condensation polymers known for their outstanding thermal and chemical stability. The pendant phenyl groups and chains isomerism improve the solubility and processing characteristics of these polymers. PPQs have also been shown to possess excellent thermo-oxidative stability and thermohydrolytic stability. This stability makes these polymers candidates for development as proton exchange membranes (PEMs) to be used in fuel cells. In addition to thermohydrolytic stability, PEMs require high protonic conductivity and, in order to achieve this they also require high water uptake. Aromatic condensation polymers do not possess these properties, but ionomers derived from them may. The usual method to derivatiziting these polymers is through sulfonation. In the frames of the present investigation we have carried out sulfonation of two PPQs using an H2SO 4—oleum mixture (4 : 1) as sulfonating agent at 125 3C. As a quinoxaline ring is readily formed in acidic medium synthesis of sulfonated PPQs (SPPQs) was also carried out directly from monomers using an H 2SO4—oleum mixture as solvent, catalyst and as sulfonating agent. Depending on the conditions of the reaction (temperature, duration, and the ratio of components in a sulfonating mixture) the polymers containing 0.2—6.7% S were prepared. SPPQs are soluble in polar organic solvents1 from the solutions of SPPQs high strength films (3 = 80—100 MPa) were cast. On the basis of sulfonated PPQs new cation-exchange membranes were prepared and investigated. Among the cation-exchange membranes developed those of the greatest interest are proton-exchanging membranes for fuel cells. Proton conductivity of the membranes prepared strongly depends on relative humidity and comparable with the conductivity of Nafion 117.

Ionomers of a new type based on sulfonated polyphenylquinoxalines

This communication is devoted to new type iono mers belonging to the class of aromatic ionogenic polymers—sulfonated polyphenylquinoxalines (SPPQ). The interest in SPPQ is due to the fact that the parent polyphenylquinoxalines (PPQ) are promising poly heteroarylenes combining high thermal characteristics and chemical stability with excellent solubility in organic solvents and good film forming properties [7]. Therefore, SPPQ formed upon polymer analogous transformation of PPQ upon sulfonation with a mix ture of sulfuric acid and oleum [8] can be considered as potential effective thermally stable polymeric elec trolytes and as the basis for the production of promis ing thermally stable aromatic ionomers for various applications.

Poly(naphthoylenebenzimidazole)s with Trifluoromethyl and Phenyl Substituents

129 Poly(naphthoylenebenzimidazole)s (PNBIs) is one of the most important classes of thermostable polymers with a combination of unique properties: thermal stability; heat, fire, and chemical resistance; high hydrolytic and radiation stability; etc. [1–3]. However, the application of these polymers is limited by their insolubility in organic solvents and, hence, poor processability. Therefore, attempts have been made in recent years to introduce flexible fragments or bulky substituents into polymeric chains to impart sol ubility to PNBIs [4, 5].

Sulfonated poly(naphthoylenebenzimidazole) and its modification with an alkali metal cation

A method for sulfonation of poly(naphthoylenebenzimidazole) with oleum–sulfuric acid mixture to produce sulfonated poly(naphthoylenebenzimidazole)s (SPNBIs) with different content of–SO3H groups has been developed. SPNBIs containing ≥5% sulfur are soluble in NMP and form stable solutions. It has been revealed that viscosity of SPNBI solutions in NMP increases on decreasing concentration when the content of polar sulfonic groups enhances with sulfonation degree of the initial polymer. Thus, SPNBI shows the polyelectrolyte effect. The substitution of hydrogen atoms in sulfonic groups by an alkali metal ion, potassium, has been conducted by the treatment of SPNBI powders with 5 M KOH aqueous solution under heterogeneous conditions. Potassium salts of SPNBI are insoluble in NMP. The introduction of potassium ions into SPNBI leads to the preparation of ionomers with a thermal stability higher than that of the initial PNBI.

Polynaphthylimides based on isomeric 2,5-bis[(aminophenoxy)phenylen]-1,3,4-oxadiazoles

Polynaphthylimides containing 1,3,4-oxadiazole cycles in main chains of macromolecules are prepared via the interaction of isomeric 2,5-bis[(aminophenoxy)phenyl]-1,3,4-oxadiazoles with dianhydrides of naphthalene-1,4,5,8-tetracarboxylic acid and 1,3-bis(1,8-dicarboxynaphthoyl-4)benzene. These polymers are synthesized through high-temperature polycyclocondensation in N-methylpyrrolidone and molten phenol. The relationships between the solubility and thermal characteristics of polynaphthylimides and their structure are studied, and the optical properties of the polymers are estimated.

Poly(arylene oxides) containing sulfo acid groups: Synthesis, properties, and application

Key advances in the synthesis, characterization, and application of poly(arylene oxides) containing sulfo acid groups in main chains of macromolecules and side substituents are surveyed. The main advantages and drawbacks of various approaches to the synthesis of these polymers, such as postsulfonation of poly(arylene oxides), polycondensation with the use of sulfonated monomers, and transformations of polymers containing reactive groups, are analyzed.

Modification of sulfonated polyphenylquinoxaline by alkali and alkaline earth metal cations

Salts of sulfonated polyphenylquinoxaline (SPPQ) containing alkaline earth metal ions—Mg2+, Ca2+, and Ba2+—were synthesized. The paper considers their solubilities, the properties of solutions, and thermal stability in comparison with analogous characteristics of SPPQ salts with alkali metals. The introduction of alkaline earth metal cations into SPPQ affords soluble polymeric salts having high thermal stability. Solutions of SPPQ salts in N-methylpyrrolidone (N-MP) containing Mg2+, Ca2+, and Ba2+ ions do not exhibit polyelectrolyte properties, unlike solutions of SPPQ salts in which the counterions are Li+, Na+, and K+. Solutions of SPPQ and its salts in N-MP can be converted to water-soluble form by dialysis. This opens up new prospects for using the polymeric salts.

Synthesis of poly(naphthoylenebenzimidazole)s in a green supercritical fluid

250 Poly(heteroarylene)s (PHAs) are of special interest as materials for thermo�, heat�, fire�, and chemical� resistant systems, films, and matrices used for immo� bilization of catalysts, coatings, fibers, etc. [1]. Poly(naphthoylenebenzimidazole)s (PNBIs) are one of the promising classes of PHAs. PNBIs based on six� membered dianhydrides of tetracarboxylic acids are known to be considerably superior in hydrolytic, ther�

Synthesis of new silicon-containing copolybenzimidazoles

19 Polybenzimidazoles (PBIs) are rather promising materials for preparing high temperature (above 100°C) membranes due to their high thermal and mechanical characteristics. Moreover, PBIs doped with strong acids show stable proton conduction at temperatures above 100°C [1–5]. It was noted, however [6, 7], that the doping of PBI with orthophosphoric acid leads to a sharp deteriora tion of the mechanical properties of membranes. One of approaches to stabilize the mechanical strength of polybenzimidazole membranes consists in the preparation of hybrid, in particular polybenzimi dazole–silica, composite systems prior to doping [8–10]. Therefore, we suggested in this work to obtain using sol–gel process new copolybenzimidazole–silica copolymers from organosoluble copolymeric PBIs containing diphenyl ether fragments in the main chain and hydroxy groups in side groups.

Synthesis and properties of ABPPQ for high-temperature proton exchange membrane fuel cells

In this study, the one-pot synthesis of self-polymerizable quinoxaline monomer was developed. 3-(4-hydroxyphenyl)-2-phenyl-6-fluoroquinoxaline and 2-(4-hydroxyphenyl)-3-phenyl-6-fluoroquinoxaline mixture (M1a,b) was synthesized from benzyl 4-hydroxyphenyl ketone and 1,2-diamino-4-fluorobenzene, catalyzed by 1,4-diazabicyclo[2.2.2]octane. Then, an ether-containing AB type polyphenylquinoxaline (ABPPQ) was synthesized successfully from the monomer M1a,b. The ether-containing ABPPQ is organosoluble, and has good proton conductivity at high temperatures after doping with phosphoric acid. It is suitable for use in high-temperature proton exchange membrane fuel cells. Compared to polybenzimidazole (PBI), ABPPQ has higher acid doping level at the same doping time, because it has more sites that can be doped with phosphoric acid in the PPQ’s molecular structure than PBI.