Polycondensation In Polyphosphoric Acid Research Articles

Synthesis and characterization of polybenzimidazole/α-zirconium phosphate composites as proton exchange membrane

To improve the high-temperature performance of proton exchange membranes, the polybenzimidazole (PBI)/α-zirconium phosphate (α-Zr(HPO4)2·nH2O, α-ZrP) proton exchange composite membranes were prepared in this study. PBI polymer containing a large amount of ether units has been synthesized from 3,3′- diaminobenzidine (DAB) and 4,4′-oxybis (benzoic acid) by a direct polycondensation in polyphosphoric acid. The polymer exhibited a good solubility in most polar solvents. Inorganic proton conductor α-ZrP nanoparticles have been obtained using a synthesis route involving separate nucleation and aging steps (SNAS). The effects of α-ZrP doping content on the composite membrane performance were investigated. It was found that the introduction of ZrP improved the thermal stability of the composite membranes. The PBI/ZrP composite membranes exhibited excellent mechanical strength. The composite membrane with 10 wt% ZrP showed the highest proton conductivity of 0.192 S cm−1 at 160°C under anhydrous condition. The proton conducting mechanism of the PBI/ZrP composite membranes was proposed to explain the proton transport phenomena. The experimental results suggested that the PBI/ZrP composite membranes may be a promising polymer electrolyte used in high temperature proton exchange membrane fuel cells (HT-PEMFCs) under anhydrous condition. POLYM. ENG. SCI., 56:622–628, 2016. © 2016 Society of Plastics Engineers

Synthesis and Characterization of Sulfonated Polybenzoxazole for High Temperature Proton Exchange Membranes

Sulfonated Polybenzoxazoles (sPBO) with sulfonation degree ranging from 10% to 30% were synthesized from 4,6-diaminoresorcinol dihydrochloride (DAR), terephthalic acid (TPA), 5-sulfoisophthalic acid monosodium salt (SIPA) by direct polycondensation in polyphosphoric acid (PPA). The structures of sPBOs were verified by FTIR and elemental analysis. The values of inherent viscosity ranged from 2.56 to 1.12 dL/g and decreased with the increasing of sulfonation degree. TGA analysis showed sPBOs were thermal stable up to nearly 250°C. sPBO/PPA polymerization solution were hot pressed directly to form PPA doped sPBO membranes since sPBO was insouble in common solvents. The PPA doping level was about 340%(wt) per gram of sPBOs by theoretical calculations. The tensile strength of PPA doped sPBOs membrances ranged from 9.1 to 3.2 Mpa. At high temperature, sPBO membranes showed excellent proton conductivity. For instance, sPBO membrane with a sulfonation degree of 10% exhibited a proton conductivity of 0.123 S/cm at 170°C.The experimental results indicated sPBO are promising for proton exchange membranes for high temperature proton exchange membranes.

Sulfonated polybenzimidazole/zirconium phosphate composite membranes for high temperature applications

Sulfonated polybenzimidazoles (SPBI) with different sulfonation degrees were prepared from 3,3′,4,4′-amino-diphenyl ether, 5-sulfonated isophthalate sodium and isophthalic acid by direct polycondensation in polyphosphoric acid. Considering the conductivity and oxidative stability of the SPBIs with different sulfonation degrees, the SPBI-10 membrane was optimally selected as base membrane. In order to enhance the proton conductivity, Zirconium phosphate (ZrP) was physically mixed with SPBI-10 to get a serial of composite membranes. The water uptake rises slightly with the increase of ZrP and the phosphoric acid swelling ratio of membranes greatly depends on the concentration of phosphoric acid, dipping time and temperature. At the H3PO4 doping level of 5, the phosphoric acid swelling ratio is up to 15%, and the membranes keep a good mechanical property. Due to the addition of ZrP, the conductivity of SPBI-10-Z3 composite membrane is up to 0.08S/cm at 180 °C, which increases about 20% compared with that of SPBI-10 membrane. This suggests that SPBI/ZrP composite membranes may be a promising polymer electrolyte for high temperature PEMFCs.

Poly(2,5-bibenzimidazole) Membranes: Physico-Chemical Characterization Focused on Fuel Cell Applications

Membranes of Poly(2,5-benzimidazole) (ABPBI), prepared by polycondensation in polyphosphoric acid, were characterized from the fuel cell application point of view: mechanical properties of the membranes for different acid doping levels, thermal stability, permeability for the different gases/vapors susceptible of use in the cell (hydrogen, oxygen, methanol and ethanol), electro-osmotic water drag coefficient, oxidation stability to hydroxyl radicals, phosphoric acid leaching rate and, finally, in-plane membrane conductivity. ABPBI membranes presented an excellent thermal stability, above 500°C in oxygen, suitable mechanical properties for high phosphoric acid doping levels, a low methanol and ethanol limiting permeation currents, and oxygen permeability compared to Nafion membranes, and a low phosphoric acid leaching rate when exposed to water vapor. On the contrary, hydrogen permeation current was higher than that of Nafion, and the chemical stability was very limited. Membrane conductivity achieved 0.07 S cm−1 after equilibration with a humid environment. Fuel cell tests showed reasonable good performances, with a maximum power peak of 170 mW cm−2 for H2/air at 170°C operating under a humidified hydrogen stream, 39.9 mW cm−2 for CH3OH/O2 at 200°C for a methanol/water weight ratio of 1:2, and 31.5 mW cm−2 for CH3CH2OH/O2 at the same conditions than for methanol.

One-pot preparation and continuous spinning of carbon nanotube/poly(p-phenylene benzobisoxazole) copolymer fibers

Poly(p-phenylene benzobisoxazole) (PBO) fibers are some of the strongest organic polymer fibers, however, even stronger fibers can be made using carbon nanotubes (CNTs). In the present study, the copolymerization of functionalized CNTs with PBO was successfully carried out by one-pot in situ polycondensation in polyphosphoric acid. Pristine CNTs were first oxidized to CNT–COOH and then modified by 4,6-diaminoresorcinol (DAR) or PBO trimer (DAR–TA–DAR) to improve the reactivity, solubility, dispersivity, and interfacial adhesion of CNTs in polymer matrix. Functionalized CNTs were further covalently incorporated with PBO through in situ polymerization. The chemical structure and morphology of functionalized CNTs and CNT–PBO copolymers were well characterized for confirming the formation of covalent bond between CNTs and PBO. Moreover, continuous CNT–PBO copolymer fibers have been fabricated using a dry-jet wet-spinning technique. The structure and morphology of CNT–PBO copolymer fibers have been characterized and their mechanical and thermal properties have been investigated. The tensile modulus, tensile strength, and thermal stability of CNT–PBO copolymer fibers have been improved. The improvement in PBO molecular chain packing order, the good dispersion and high alignment of CNTs in the PBO matrix, and the covalent bonding at the CNT–PBO interface have been suggested as the main reasons for the performance improvement of PBO.

Synthesis and characterization of novel polybenzimidazoles containing 4-phenyl phthalazinone moiety

A novel series of homo- and copoly(phthalazinone benzimidazole)s were synthesized from various stoichiometric mixtures of 4-(4-(4-(4-carboxyphenoxy)phenyl)-1-oxophthalazin-2(1H)-yl)benzoic acid ( CPPBC) and isophthalic acid ( IPA) with 3,3′-diaminobenzidine ( DAB) by solution polycondensation in polyphosphoric acid (PPA). The structures of the obtained polymers were characterized by FT-IR and 1H NMR. The obtained polybenzimidazoles were found to be soluble in aprotic polar solvents such as N-methyl-2-pyrolidinone (NMP), N, N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO) and m-cresol, without the addition of inorganic salts. The inherent viscosities of the polybenzimidazoles were in the range of 1.10–2.05 dL/g. All of the polymers show amorphous nature as evaluated by WAXD. These polymers have high glass transition temperatures ( T gs) in the range of 398–408 °C. Thermogravimetric analysis exhibit that these polybenzimidazoles containing 4-phenyl phthalazinone moiety have excellent thermal stability with the temperatures for 5% and 10% weight loss of the polymers ranging from 516 to 594 °C and 560 to 672 °C, respectively.

Structurally isomeric monomers Directed copolymerization of polybenzimidazoles and their properties

Three different series of pyridine based polybenzimidazole (PyPBI) random copolymers consisting of meta-para pyridine linkages were synthesized from various stoichiometric mixtures of meta (2,4; 2,6 and 3,5) and para (2, 5) structure pyridine dicarboxylic acids (PDA) with 3, 3’, 4, 4’- tetra-aminobiphenyl (TAB) by solution polycondensation in polyphosphoric acid (PPA). The influences of the structural isomers of PDA on the PyPBI copolymerization and properties were elucidated by characterizing the resulting copolymers. The solubility of PDA monomers in PPA and the overall monomer concentration in the polymerization were found to be the deciding factors. The higher molecular weight PyPBI were obtained for higher para content copolymers due to the low solubility of para PDA in PPA. The introduction of para structure had enhanced the conjugation along the polymer chain. NMR study showed that the reactivity ratio of para PDA was not identical for all the three sets of PyPBI copolymers, it varied upon the positions of the dicarboxylic acids in the pyridine ring of meta PDAs (structural isomeric effect) with which 2,5 PDA is forming the copolymer. Introduction of para structure and meta PDAs structural isomers affected the thermal stability, flexibility and the photophysical properties of the PyPBI copolymers.

Synthesis and characterization of novel fluorinated polybenzoxazoles derived from 2,5-difluoroterephthalic acid

AbstractA new serious of fluorinated polybenzoxazoles (PBOs) were prepared from 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane together with 2,5- difluoroterephthalic acid (DFTA) and terephthalic acid by the one-pot polycondensation in polyphosphoric acid. The resulting PBOs showed good solubility in many common organic solvents and the thermal stability of PBOs was improved by the introduction of DFTA monomer.

Highly Tough and Highly Transparent Soluble Polybenzoxazoles

Semi-cycloaliphatic (semi-alicyclic) polybenzoxazoles (PBOs) were investigated as candidates for flexible plastic substrates for liquid crystal displays (LCDs). PBOs were prepared by the one-pot polycondensation in polyphosphoric acid (PPA) from 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (BAHP6F) with 1,3- and/or 1,4-cyclohexanedicarboxylic acid (CHDCA). The BAHP6F-based PBOs were soluble in various common organic solvents. In addition, the PBO films showed a relatively a high Tg exceeding 250° C, excellent transparency, and a relatively low value of water absorption ( < 0.5%), simultaneously. The BAHP6F-based PBO films were flexible, but the elongation at break ( Eb ) in the stretching test did not exceed 20%. On the other hand, an ether-containing bis(o-aminophenol), 3,3' -diamino-4,4' -dihydroxydiphenylether (ADPE) exhibited much higher polymerization reactivity with CHDCA than BAHP6F, and as a result led to higher molecular weight PBOs. The ADPE-derived PBO films were relatively tough and showed a very high Eb , which exceeded 50%. However, the values of Tg were lower than those of the BAHP6F-derived PBOs, owing to the presence of the flexible ether linkages in the structure. Copolymerization using BAHP6F and ADPE led to excellent combined properties, namely, high Tg , high transparency, a high degree of toughness, and high solution-processability (solubility). The influence of the PBO preparation routes (one-pot technique or two-step method via thermal cyclization of PBO precursors) on the film transparency and other properties are also discussed. Some of the semi-cycloaliphatic PBOs examined in this work practically attained the target properties required for flexible substrates in LCDs..

Synthesis and Chain-End Modification of a Novel Hyperbranched Polymer Containing Alternating Quinoxaline and Benzoxazole Repeat Units

A new AB2 monomer, 2,3-bis(3-amino-4-hydroxyphenyl)quinoxaline-6-carboxylic acid dihydrochloride, was synthesized in four steps starting from the double condensation of commercially available 3,4-diaminobenzoic acid and 4,4‘-dimethoxybenzil. It underwent facile polycondensation in polyphosphoric acid to afford the corresponding hyperbranched quinoxaline−benzoxazole polymer (PPQ−BO 5) with an intrinsic viscosity of 1.04 dL/g. It was end-capped with 2-thiophenecarboxylic acid, 3,5-dihydroxybenzoic acid, 3-sulfobenzoic acid, 4-sulfobenzoic acid, and 2,3-diphenylquinoxaline-6-carboxylic acid. These hyperbranched polymers displayed an unusual, nonlinear solution viscosity behavior at the concentrations below ∼0.25 g/dL. At these dilute concentrations, both reduced and inherent viscosities decreased precipitously (“inverse polyelectrolyte behavior”). The large numbers of o-aminophenol end groups were further chemically modified to afford hyperbranched PPQ−BO's with various functionalities. Similar to their line...

Regeneration of polycondensation of wholly aromatic poly(azomethine)s with 1,5- or 2,6-substituted naphthalene moiety in main chain

Wholly aromatic poly(azomethine)s with 1,5- or 2,6-substituted naphthalene moiety in the main chains were prepared in aprotic polar solvents or m-cresol under various reaction conditions. In the polymerization of 1,5-diaminonaphthalene with terephthalaldehyde, the polymer that synthesized in (HMPA/DMSO) at room temperature for 24 h by adding 5 wt % of calcium chloride and a very small amount of p-toluenesulfonic acid showed the highest reduced viscosity in all of the polymers from 1,5-diaminonaphthalene. The reduced viscosity of poly(azomethine)s synthesized from 2,6-diaminonaphthalene with 2,6-diformylnaphthalene in m-cresol and with terephthalaldehyde in HMPA/DMSO were ηred = 0.35 and 0.36, respectively. The thermal analysis showed the poly(azomethine)s had high thermal stability and the glass-transition temperatures of these polymers are about 250 °C. The X-ray diffraction showed that they are partially crystalline. They could be polymerized again by second stage polycondensation in polyphosphoric acid. The reduced viscosities of the obtained polymers were about 2–5 times as high as that of the pristine polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1064–1072, 2000

Rigid-rod benzobisthiazole polymer with reactive 2,6-dimethylphenoxy pendent groups

Polycondensation in polyphosphoric acid of 2,5-diamino-1,4-benzenedithiol dihydrochioride with 2-(2,6-dimethylphenoxy)terephthaloyl chloride led to rigid-rod benzobisthiazole polymers with thermally reactive dimethylphenoxy pendants. Soluble polymers with intrinsic viscosities as high as 15.5 dl/g (methanesulphonic acid, 30°C) were obtained. The polymers became insoluble after heat-treatment at approximately 400°C, possibly indicative of a crosslinking reaction between the polymer chains at the pendant sites. Fibres spun from a lyotropic polyphosphoric acid solution and heat treated at 425°C exhibited a tensile modulus of 91 GPa, a tensile strength of 1.10 GPa, and a compressive strength of 400 MPa. Wide-angle X-ray scattering patterns of the polymer fibres indicated that the bulky pendants significantly enhanced the axial registration between the neighbouring rigid-rod polymer backbones.

Multidimensional benzobisoxazole rigid-rod polymers. I. Preparation and characterization

Two- and three-dimensional rigid-rod polymers containing benzobisoxazole structures were prepared through the polycondensation in polyphosphoric acid of 4-[5-amino-6-hydroxybenzoxazol-2-yl]benzoic acid (ABA) with trimesic acid and 1,3,5,7-tetrakis(4-carboxylatophenyl)adamantane, respectively. Thermal properties of the polymers were determined by differential scanning calorimetry, thermogravimetric/mass spectral analysis, and isothermal aging studies. The multidimensional polymers exhibited lower solution viscosities and lower thermooxidative stabilities than the one-dimensional polymer generated by the homopolymerization of ABA under identical reaction conditions. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3451–3456, 1997

Synthesis, processing, and third‐order nonlinear optical properties of benzobisthiazole polymers containing thiophene moieties

AbstractBenzobisthiazole polymers containing mono‐, bi‐, and terthiophene moieties were synthesized through polycondensation in polyphosphoric acid of 2,5‐diamino‐1,4‐benzenedithiol dihydrochloride with thiophene‐2,5‐dicarboxylic acid, 2,2′‐bithiophene‐5,5′‐dicarboxylic acid, and 2,2′:5′,2″‐terthlophene‐5,5″‐dicarboxylic acid, or their corresponding diacid chlorides, respectively. Intrinsic viscosities of up to 8.1 dL/g (methanesulfonic acid, 30°C) were recorded. Polymer structures were verified by elemental analysis and spectroscopic comparison of the polymers with appropriate model compounds. Onset of breakdown under thermogravimetric analysis in air occurred in the 460–590°C range with the benzobisthiazole polymers containing a monothiophene linkage being the most stable. Films suitable for third‐order optical susceptibility measurements could be prepared by extrusion techniques from the benzobisthiazole polymer containing a monothiophene linkage. Degenerate four wave mixing measurements on this film yielded a third order optical susceptibility χ(3) of approximately 4.5 × 10−10 esu. © 1993 John Wiley & Sons, Inc.

Rigid‐Rod benzobisthiazole polymers with reactive fluorene moieties: Synthesis and characterization

AbstractHigh purity 2,7‐fluorenedicarboxylic acid chloride was synthesized in a multistep reaction scheme from 2,7‐dibromofluorene. Subsequent polycondensation in polyphosphoric acid of 2,5‐diamino‐1,4‐benzenedithiol dihydrochloride with terephthaloyl chloride and 2,7‐fluorenedicarboxylic acid chloride led to rigid‐rod benzobisthiazole polymers with reactive fluorene moieties. The proportion of fluorene in the resultant polymers was controlled through reaction stoichiometry. Soluble polymers with intrinsic viscosities as high as 33.7 dL/g (methanesulfonic acid, 30°C) were obtained if the polymerization temperature was not allowed to exceed 165°C. Insoluble, presumably crosslinked polymers were obtained at higher temperature (190–200°C). Thermal characterization of the polymers by differential thermal analysis and thermal gravimetric analysis/mass spectroscopy did not disclose any thermal transition to 450°C. Onset of weight loss in air did not occur until over 550°C.

Poly(P‐benzoquinono)diimidazoles from two‐ring aromatic dicarboxylic acids

AbstractNew poly(p‐benzoquinono)diimidazoles have been synthesized by one‐stage polycondensation in polyphosphoric acid of 2,3,5,6‐tetraamino‐p‐benzoquinone with diphenyl‐4,4′‐dicarboxylic acid, diphenylmethane‐4,4′‐dicarboxylic acid, 4,4′‐oxydibenzoic acid, and 4,4′‐sulfonyldibenzoic acid. The polymers were characterized by infrared and ultraviolet spectral study, viscometric measurements, and thermal analysis. The effects of introducing flexibilizing links such as CH2,O, and SO2 in the backbone of the polymers, on their thermal stability and solubility were studied.

Synthesis and Properties of Pyrrones Containing p-Benzoquinone Units

Abstract Novel pyrrones were synthesized by one-stage polycondensation in polyphosphoric acid of 2,3,5,6-tetraamino-l,4-benzoquinone with pyromellitic anhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, or 3,4,9,10-perylenetetracarboxylic dianhydride. The prepared polymers showed a considerable percentage of imide linkages, so they were heated at 350°C under high vacuum to increase the ring closure to the pyrrone structure. The polymers were insoluble in all common polar aprotic solvents, even in dimethylacetamide-water mixture, after reduction with sodium dithionite, but were slightly soluble in concentrated sulfuric and methanesulfonic acid. The thermal decomposition of the polymers (weight loss 5%) started above 400°C both under nitrogen and in air.

Synthesis and properties of poly(benzoxazines): Poly[6,6?-methylene(4H-3,1-bibenzoxazine) 2,2?-diylphenylenes

A new class of benzoxazine polymers were synthesised from bis(4-amino-3-hydroxymethylphenyl)methane with substituted phthalic acids by solution poly-condensation in polyphosphoric acid. The model compound bis(4H-3,1-benzoxazine)2,2′-p-phenylene was also synthesised. The polymere were characterised by UV and IR spectra, viscosity measurements and thermal analysis.

Syntheses of polyimide copolymers based on N,N′‐(pyromellitoyl)diglycine

AbstractN,N′‐(pyromellitoyl)diglycine (1) was synthesized by reacting pyromellitic anhydride with glycine in polar solvents such as DMAC, NMP, or DMF at 60°C and then refluxed azeotropically with toluene. Among these solvents, it is easy to form DMF‐insoluble salt (1″) in DMF, but this salt can be converted to 1 by treating first with NaHCO3 and then with HCl. Reacting monomer N,N′‐(pyromellitoyl)diaminoacetyl chloride (2) can be obtained by treating with thionyl chloride, and N,N′‐(pyromellitoyl)dimethyl aminoacetate (3) can be obtained by treating 2 with methanol. As 2 reacts with aromatic diamine in polar solvents, such as DMAC, DMF, or NMP, a series of copolypyromellitimide amides (5a–h) can be obtained. These copolymers can be processed by using DMAC + LiCl (5%) as solvent to produce flexible film of good weather resistivity and heat resistivity. Monomer 2 can also react with aromatic dihydrazides in polar solvents to produce copolypyromellitimide hydrazides (6a–c), and 6a–b can be condensated again to produce copolypyromellitimide oxadiazoles (7a–b) in polyphosphoric acid (PPA). Besides, 3 reacts with aromatic tetraamine by carrying out polycondensation in PPA to produce copolypyromellitimide benzimidazole (8). Structures of copolymers mentioned above were identified by comparing IR spectra with those of model compounds. Heat resistivity was measured by the thermogravimetric method, and their solubilities in various solvents were also investigated.

Synthesis and study of polymers prepared from dianhydrides of 3,4,9,10-perylene-1,4,5,8-naphthalene tetracarboxylic acids and aromatic tetra-amines

Low molecular weight products of the condensation of dianhydride of perylene tetracarboxylic acid (DAPTA) with tetra-aminodiphenyl ester (TADPE) and high molecular weight soluble polyaminoamido acids containing alternating naphthalene and perylene units, were obtained in an aprotonic solvent-inorganic salt system. The effect of various factors (LiCl concentration, concentrations of initial components, reaction temperature and dianhydride ratio) on the rate of polycondensation and the molecular weight of polyaminoamido acids was examined. Conditions of cyclization were determined for copolymers. Poly-(aroylene-bis-benzimidazoles) containing alternating perylene and naphthalene units were prepared by high temperature polycondensation in polyphosphoric acid.