Styrene grafted ethylene chlorotrifluoroethylene (ECTFE-g-PSSA) protonic membranes: Preparation, characterization, and transport mechanism

Preparation, Modification, and Application of Ethylene-Chlorotrifluoroethylene Copolymer Membranes

Ethylene-chlorotrifluoroethylene (ECTFE) was first commercialized by DuPont in 1974. Its unique chemical structure gives it high heat resistance, mechanical strength, and corrosion resistance. But also due to these properties, it is difficult to prepare a membrane from it by the nonsolvent-induced phase separation (NIPS) method. However, it can be prepared as a microfiltration membrane using the thermally induced phase separation (TIPS) method at certain temperatures and with the selection of suitable solvents, and the use of green solvents is receiving increasing attention from researchers. The surface wettability of ECTFE membranes usually needs to be modified before use to strengthen its performance to meet the application requirements, usually by graft modification and surface oxidation techniques. This paper provides an overview of the structure of ECTFE and its preparation and modification methods, as well as recent advances in its application areas and prospects for the future methods of preparing high-performance ECTFE membranes.

Isothermal and Non-Isothermal Crystallization Kinetics of Poly(ethylene chlorotrifluoroethylene)

The isothermal (IT) and non-isothermal (NIT) crystallization kinetics, morphology, and structure of poly(ethylene chlorotrifluoroethylene) (ECTFE) were investigated via differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide-angle X-ray diffraction (XRD). The Avrami equation could well describe the overall IT crystallization process of ECTFE, and, furthermore, the overall crystallization rate decreased at higher crystallization temperatures (T_c). The equilibrium melting point for ECTFE was found to be 238.66 °C. The activation energies for IT and NIT crystallization were determined as −137.68 and −120.54 kJ/mol, respectively. The Jeziorny model fitted well with the initial stages of NIT melt crystallization, while deviations from linearity in the later stages of the process were due to the collisions of spherulites. Spherulites of ECTFE organized in a hexagonal crystal system were found. The relative crystalline degree of ECTFE under NIT conditions was about 54.55%, and this decreased with the increase in cooling rate. Moreover, the Ozawa and Mo models were suitable for modeling the overall NIT crystallization process of ECTFE.

Crosslinked poly(methyl methacrylate) with perfluorocyclobutyl aryl ether moiety as crosslinking unit: thermally stable polymer with high glass transition temperature

PMMA-based copolymer containing aryl TFVE moieties prepared by copolymerization of MMA and TFVOPMA monomer containing aryl TFVE group and thermal cross-linked by [2π + 2π] cycloaddition reaction of aryl TFVE moieties.

Crosslinked PVA/SSA proton exchange membranes: correlation between physiochemical properties and free volume determined by positron annihilation spectroscopy

Two processes for crosslinking polyvinyl alcohol (PVA) with sulfosuccinic acid (SSA) and thermal crosslinking were used to fabricate a proton exchange membrane (PEM). Such PEMs are used in different fields involving fuel cell applications. The crosslinking reaction between PVA and SSA was confirmed using Fourier-transform infrared (FTIR) spectroscopy. The characterization of the prepared membranes, namely, ion exchange capacity (IEC), thermal analyses, water uptake, and ionic conductivity, was carried out. The IEC of the prepared membranes was found to be between 0.084 and 2.086 mmol g-1, resulting in an essential increase in the ionic conductivity. It was observed that the ionic conductivity was in the range of 0.003-0.023 S cm-1, depending on both temperature and SSA content. From the thermogravimetric analysis (TGA) results, it was revealed that the thermal stability of the crosslinked membranes improved. Moreover, water uptake decreased with increasing SSA content. Positron annihilation lifetime spectroscopy (PALS) was used to study the microstructure of the PVA/SSA membranes and their distribution at different ambient temperatures and relative humidity (RH) values. At room temperature, no significant change was observed in the free-volume holes up to 15 wt% SSA; thereafter, the size of the free-volume holes increased with the SSA content. The PALS results show that at different humidity values, the size of the free-volume holes for crosslinked PVA/SSA membranes is lower than those for Nafion membranes, i.e., the gas permeability for the prepared PVA/SSA membranes is less than that for the Nafion membrane. In addition, a strong correlation between the water uptake, ionic conductivity, tensile strength, and free-volume holes was observed.

A new difluoromethoxyl-containing acrylate monomer for PEG-b-PDFMOEA amphiphilic diblock copolymers

This article reports the first synthesis of a well-defined difluoromethoxyl-containing polyacrylate via ATRP.