Linear Polyethylene with Tunable Surface Properties by Catalytic Copolymerization of Ethylene with <i>N</i>-Vinyl-2-pyrrolidinone and <i>N</i>-Isopropylacrylamide

Linear Polyethylene with Tunable Surface Properties by Catalytic Copolymerization of Ethylene with N-Vinyl-2-pyrrolidinone and N-Isopropylacrylamid

Amphiphilic Polyethylenes Leading to Surfactant-Free Thermoresponsive Nanoparticles

Linear copolymers of ethylene and acrylic acid (PEAA) were prepared by catalytic polymerization of ethylene and tert-butyl acrylate followed by hydrolysis of the ester groups. The copolymers contained COOH groups inserted into the crystalline unit cell with formation of intramolecular hydrogen-bonds, as established on the basis of differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) studies. A solvent-exchange protocol, with no added surfactant, converted a solution in tetrahydrofuran of a PEAA sample containing 12 mol % of acrylic acid (AA) into a colloidally stable aqueous suspension of nanoparticles. Transmission electron microscopy (TEM), dynamic light scattering (DLS), and high sensitivity differential scanning calorimetry (HS-DSC) were used to characterize the nanoparticles. They are single crystals of elongated shape with a polar radius of 49 nm (σ = 15 nm) and an equatorial radius of 9 nm (σ = 3 nm) stabilized in aqueous media via carboxylate groups located preferentially on the particle/water interface. The PEAA (AA: 12 mol %) nanoparticles dispersed in aqueous media exhibited a remarkable reversible thermoresponsive behavior upon heating/cooling from 25 to 80 °C

Kinetic and Mechanistic Aspects of Ethylene and Acrylates Catalytic Copolymerization in Solution and in Emulsion

Ethylene was copolymerized with acrylates in solution and in emulsion using sulfonated arylphosphine Pd-based catalysts. The copolymerization of C2H4 and methyl acrylate in toluene was slowed by the σ-coordination of the acrylate on Pd. The substitution of pyridine by itself was shown to proceed via an associative mechanism with activation parameters ΔH‡ = 16.8 kJ/mol and ΔS‡ = −98 J mol−1 K−1 whereas the activation parameters for the substitution of pyridine by methyl acrylate were found to be ΔH‡ = 18.1 kJ/mol and ΔS‡ = −87 J mol−1 K−1. Using these Pd-based catalysts in an emulsion polymerization process, latexes of copolymers of ethylene with various acrylates having particle diameters ∼200 nm were obtained for the first time. Their solid contents did not exceed 5% because of the low activity of the catalyst resulting from the coordination of water and from the slow decomposition of the active site by water

Influence of the Polymer Precursor Structure on the Porosity of Carbon Nanofibers: Application as Electrode in High-Temperature Proton Exchange Membrane Fuel Cells

Polyacrylonitrile and polyheteroarylenes, such as polybenzimidazole (PBI) and a polymer of intrinsic microporosity (PIM-1), have been employed to prepare nanoporous electrospun carbon nanofiber (CNF)-based materials for high-temperature proton-exchange (or polymer-electrolyte) membrane (HT-PEM) fuel cells. The nanoporous CNF mats are obtained by Nanospider (needle-free) electrospinning method from polymer solution followed by pyrolysis at 1500 °C to form nanoporous electrospun polymer nanofiber self-supporting mats with micropores (D D 2–50 nm). The nanoporous CNF samples are extensively characterized by N2 and CO2 adsorption applying the BET, BJH, Dubinin–Radushkevich (DR), NLDFT, and GCMC methods, CO2 uptake, Raman spectroscopy, elemental analysis, electrical conductivity, electron microscopy, and XPS. The role of the polymer precursor on the obtained values of specific surface area (SSA) and volume for micro- and mesopores is presented and discussed. The PBI-based CNF material reaches a micropore SSA of 919 m2 g–1 and CO2 uptake of 4.0 mmol g–1 derived from CO2 adsorption (273 K) data, and a micropore SSA of 873 m2 g–1 according to the t-method derived from N2 adsorption data. Close values confirm higher accessibility of micropores compared with the case of PIM-based CNF, where the micropore SSA values derived from CO2 and N2 adsorption data are different and indicate the partial inaccessibility of micropores for low-temperature nitrogen adsorption (77 K). Platinum-decorated CNF mats are successfully tested as electrodes for HT-PEM fuel cells, showing the feasibility of using the mats as cathodes; nevertheless, further optimization is required. For CNF anodes, the HT-PEM fuel cell performance reaches 0.69 V at 0.2 A cm–2 and 0.53 W cm–2 at 1.4 A cm–2 which permits the use of the Pt/CNF mats as anodes