Asheesh Singh

Synthesis and characterization of highly fluorinated sulfonated polytriazoles for proton exchange membrane application

A series of polytriazole copolymers (PTFQSH-XX) were synthesized by the click polymerization of 1,1,1,3,3,3-hexafluoro-2,2-bis(4-(prop-2-ynyloxy)phenyl)propane (TF) with a mixture of two diazide monomers: 4,4-bis[3-trifluoromethyl-4(4-azidophenoxy)phenyl]biphenyl (QAZ) and 4,4′-diazido-2,2′-stilbene disulfonic acid disodium salt (“S”). The degree of sulfonation (DS) of the copolymers was controlled by adjusting the mole ratio of “S” to the non-sulfonated diazide (QAZ). The polytriazole copolymers were characterized by FTIR and NMR (1H, 13C and 19F) spectroscopy. The PTFQS-XX membranes were prepared by dissolving the salt form of the copolymers in dimethyl formamide. The physical properties and proton conductivity of the membranes were investigated. The presence of hexafluoroisopropylidene groups in the copolymers contributed to high thermal and oxidative stability and low swelling of the membranes. TEM micrographs of the polytriazole membranes showed a good phase separated morphology with ionic clusters in the range of 3–75 nm. The proton conductivities of the fluorinated membranes were found in the range of 27–136 mS cm−1 at 80 °C in water.

Soluble, optically transparent polyamides with a phosphaphenanthrene skeleton: synthesis, characterization, gas permeation and molecular dynamics simulations

The present study reports the preparation of five new polyamides from a new diamine monomer, 1,1-bis[2′-trifluoromethyl-4′-(4′′-aminophenyl)phenoxy]-1-(6-oxido-6H-dibenz oxaphosphorin-6-yl)ethane, with various aromatic dicarboxylic acids by polycondensation reaction. The polymers were well characterized by different analytical techniques. The polymers were soluble in several organic solvents and showed high thermal stability with 10% weight loss in the temperature range of 345–365 °C in air. Membranes were prepared from these polymers by the solution casting method that showed a tensile strength within the range of 65 to 86 MPa and an elongation at break of 6 to 19% depending on the exact polymer repeat unit structure. The glass transition temperature of the membranes was evaluated by DSC and DMA and the values were within the range of 265–275 °C. The membranes were optically transparent with a cut-off wavelength in the range of 359–396 nm and showed a low dielectric constant. The membranes showed very high gas permeability (PCO2 = 164.7 and PO2 = 59.7 barrer) and offered a good balance of permeability and permselectivity. Molecular dynamics simulations of the polymers were done using an atomistic model that showed good agreement between the size distribution of the free volume and gas transport properties. This study provides an insight into the diffusion behavior of gas molecules in polymer membranes and the results were consistent with the experimentally obtained diffusion behavior.

Gas separation properties of Troeger’s base-bridged polyamides

Abstract A series of new polyamides (PAs) has been prepared from a Troeger base-bridged diamine (TB), 2,8- diamino-4,10-dimethyl-6H,12H-5,11-methanodibenzo[1,5]-diazocine and different commercially available diacid monomers via the conventional polycondensation method. Dense membranes were prepared from the PAs by solution casting and solvent evaporation techniques. The synthesized PAs showed high glass transition temperature (283–290°C), 10% weight loss up to temperature 431°C in air, and tensile strength up to 91 MPa. The PA membranes showed higher permeability than some commercially used glassy polymers (PCO2 up to 109 and PO2 up to 21 Barrer) and permselectivity (PCO2/PCH4 up to 53.7 and PO2/PN2 up to 7.52) in comparison to many other PAs published in the literature.

New sulfonated copoly(triazole imide)s synthesized by a click chemistry reaction with improved oxidative stability

Herein, novel soluble sulfonated copoly(triazole imide)s with different ion exchange capacities were synthesized by a click reaction. The structures of the resulting copoly(triazole imide)s were characterized by FTIR and 1H NMR spectroscopic techniques. These copoly(triazole imide)s were soluble in different organic solvents and formed flexible films with good mechanical properties along with high thermal stabilities. The presence of triazole and flexible moieties contributed towards improving the oxidative stability and swelling properties. The proton conductivities of the copolymers were found to be in the range of 15–98 mS cm−1 at 90 °C in water. Transmission electron microscopy was used to observe the microphase separation of the ionic and hydrophobic domains of the copolymers.

Hexafluoroisopropylidene based sulfonated new copolytriazoles: investigation of proton exchange membrane properties

Abstract A series of novel sulfonated polytriazole copolymers (PTFOSH-XX) was successfully prepared by the click reaction of 4,4′-(perfluoropropane-2,2-diyl)bis((prop-2-ynyloxy)benzene (TF), 4,4′-diazido-2,2′-stilbene disulfonic acid disodium salt (SAZ) and 4,4′-diazidodiphenyl ether (OAZ). The copolymers were characterized by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (NMR) spectroscopy. The copolymers showed high mechanical, thermal and oxidative stability and low swelling. The phase separated morphology of the membranes was confirmed from transmission electron microscopy (TEM). The membranes showed proton conductivity as high as 110 and 122 mS cm−1 at 80 and 90°C, respectively depending on the polymer repeat unit structure.

Synthesis and Characterization of Highly Proton Conducting Sulfonated Polytriazoles

This article describes the synthesis and characterization of highly sulfonated polytriazole copolymers (PTSQSH-I to IV) with IECw values ranging from 2.41 to 3.49 mequiv g–1. The copolymers were synthesized by click reaction between equimolar amount of a dialkyne monomer, potassium 2,5-bis(2-propyn-1-yloxy)benzenesulfonate, and a mixture of two different diazide monomers, 4,4-bis[3′-trifluoromethyl-4′(4-azidobenzoxy)benzyl]biphenyl and 4,4′-diazido-2,2′-stilbene disulfonic acid disodium salt. The copolymers were characterized by Fourier transform infrared and NMR spectroscopy techniques. The membranes were prepared by dissolving the salt form of the copolymers in dimethyl sulfoxide. The copolymers showed high thermal, mechanical, and oxidative stabilities, and the acidified membranes showed very high proton conductivity (43–173 and 132–304 mS cm–1 at 30 and 80 °C, respectively). Transmission electron microscopy images confirmed the formation of well-phase-separated morphology with interconnected hydrophilic domains (20–150 nm).

Fluorinated Polyazoles: Synthesis, Properties, and Applications

Polyazoles are a class of high-strength heterocyclic polymers applied for different high-end applications like fibers, films, coatings, composites, ballistic-protection fabrics, and panel preparation as well as in membrane-based gas separation, pervaporation, and fuel cell applications. Polyazoles can be classified into three broad classes depending on the hetero atoms: polybenzoxazole, polybenzimidazole, and polybenzothiazole. However, their inherent insolubility in common organic solvents restricts their growth in practical applications. Incorporation of the fluorinated moiety in the polymer backbone is one of the important ways to improve the solubility and processability. This chapter deals with the detailed synthesis, properties, and membrane-based applications of these fluorinated high-performance polyazoles.