Membranes for the Capture and Screening of Waterborne Plutonium Based on a Novel Pu-Extractive Copolymer Additive

This contribution describes the fabrication of plutonium-adsorptive membranes by non-solvent induced phase separation. The dope solution comprised poly(vinylidene fluoride) (PVDF) and a Pu-extractive copolymer additive of PVDF-g-poly(ethylene glycol methacrylate phosphate) (EGMP) in dimethylformamide (DMF). The effects of casting conditions on membrane permeability were determined for PVDF membranes prepared with 10 wt% PVDF-g-EGMP. Direct-flow filtration and alpha spectrometry showed that membranes containing the graft copolymer could recover Pu up to 59.9 ± 3.0% from deionized water and 19.3 ± 3.5% from synthetic seawater after filtering 10 mL of 0.5 Bq/mL 238Pu. SEM-EDS analysis indicated that the graft copolymer was distributed evenly throughout the entire depth of the copolymer membranes, likely attributing to the tailing observed in the alpha spectra for 238Pu. Despite the reduction in resolution, the membranes exhibited high Pu uptake at the conditions tested, and new membrane designs that promote copolymer surface migration are expected to improve alpha spectrometry peak energy resolutions. Findings from this study also can be used to guide the development of extractive membranes for chromatographic separation of actinides from contaminated groundwater sources.

Liquid-liquid phase separated microdomains of an amphiphilic graft copolymer in a surfactant-rich medium

The liquid-liquid phase separation (LLPS) of amphiphilic thermoresponsive copolymers can lead to the formation of micron-sized domains, known as simple coacervates. Due to their potential to confine active principles, these copolymer-rich droplets have gained interest as encapsulating agents. Understanding and controlling the conditions inducing this LLPS is therefore essential for applicative purposes and requires thorough fundamental studies on self-coacervation. In this work, we investigate the LLPS of a comb-like graft copolymer (PEG-g-PVAc) consisting of a poly(ethylene glycol) backbone (6 kDa) with 2-3 grafted poly(vinyl acetate) chains, and a PEG/PVAc weight ratio of 40/60. Specifically, we report the effect of various water-soluble additives on its phase separation behavior. Kosmotropes and non-ionic surfactants were found to decrease the phase separation temperature of the copolymer, while chaotropes and, above all, ionic surfactants increased it. We then focus on the phase behavior of PEG-g-PVAc in the presence of sodium citrate and a C14-15 E7 non-ionic surfactant (N45-7), defining the compositional range for the generation of LLPS microdomains at room temperature and monitoring their formation with fluorescence confocal microscopy. Finally, we determine the composition of the microdomains through confocal Raman microscopy, demonstrating the presence of PEG-g-PVAc, N45-7, and water. These results expand our knowledge on polymeric self-coacervation, clarifying the optimal conditions and composition needed to obtain LLPS microdomains with encapsulation potential at room temperature in surfactant-rich formulations.

Thermoresponsive Molecular Brushes with a Rigid-Chain Aromatic Polyester Backbone and Poly-2-alkyl-2-oxazoline Side Chains

A new polycondensation aromatic rigid-chain polyester macroinitiator was synthesized and used to graft linear poly-2-ethyl-2-oxazoline as well as poly-2-isopropyl-2-oxazoline by cationic polymerization. The prepared copolymers and the macroinitiator were characterized by NMR, GPC, AFM, turbidimetry, static, and dynamic light scattering. The molar masses of the polyester main chain and the grafted copolymers with poly-2-ethyl-2-oxazoline and poly-2-isopropyl-2-oxazoline side chains were 26,500, 208,000, and 67,900, respectively. The molar masses of the side chains of poly-2-ethyl-2-oxazoline and poly-2-isopropyl-2-oxazoline and their grafting densities were 7400 and 3400 and 0.53 and 0.27, respectively. In chloroform, the copolymers conformation can be considered as a cylinder wormlike chain, the diameter of which depends on the side chain length. In water at low temperatures, the macromolecules of the poly-2-ethyl-2-oxazoline copolymer assume a wormlike conformation because their backbones are well shielded by side chains, whereas the copolymer with short side chains and low grafting density strongly aggregates, which was visualized by AFM. The phase separation temperatures of the copolymers were lower than those of linear analogs of the side chains and decreased with the concentration for both samples. The LCST were estimated to be around 45 °C for the poly-2-ethyl-2-oxazoline graft copolymer, and below 20 °C for the poly-2-isopropyl-2-oxazoline graft copolymer.

Graft Copolymerization of Methyl Methacrylate and Vinyltriethoxysilane onto Natural Rubber

Preparation and characterization of natural rubber grafted with methyl methacrylate (MMA) and vinytriethoxysilane (VTES) were performed in the present work. Graft copolymerization of methyl methacryate was carried out in latex stage, and VTES was added during the graft copolymerization of MMA. FTIR and NMR spectroscopy were used to investigate the structure of graft copolymer and determination of conversion and grafting efficiency of MMA. It confirmed that the poly(methyl methacrylate) (PMMA) and silica particles (PVTES) were successfully formed in NR-graft-PMMA-PVTES graft copolymer. Conversions of MMA were about 90-100%; however, MMA grafting efficiency decreased as the MMA concentrations increased. Tensile property of NR-graft-PMMA-PVTES was found to improve compared with that of pure NR.

Analysis of the Anti-Corrosion Performance of Dextrin and Its Graft Copolymer on J55 Steel in Acid Solution

This paper studies the corrosion inhibition performance and mechanism of dextrin (Dxt) and its graft copolymer with caprolactam (Dxt-g-CPL) on J55 steel in 1 M HCl solution. Caprolactam is grafted and copolymerized with dextrin by a chemical synthesis method, to obtain a dextrin graft copolymer corrosion inhibitor. The composition of the synthesized graft copolymer was characterized by FTIR to identify whether the grafting was successful. Through weightlessness, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curve (TAFEL), scanning electrochemical microscope (SECM), scanning electron microscope (SEM), and contact angle experiments, the graft copolymer to J55 steel in 1 M HCl solution and the corrosion inhibition performance were evaluated. Moreover, we discuss its corrosion inhibition mechanism. The dextrin graft copolymer has good corrosion inhibition performance for J55 in 1 M HCl solution. When the concentration of the corrosion inhibitor increases, the corrosion inhibition efficiency will also increase. At a certain concentration, when the temperature rises, the corrosion inhibition efficiency will gradually decrease. When the concentration is 300 mg/L, it has a better corrosion inhibition effect, and the corrosion inhibition efficiency is 82.38%. Potential polarization studies have shown that Dxt-g-CPL is a mixed corrosion inhibitor, which inhibits both the cathode and the anode of the electrode reaction. SEM, SECM, and contact angle analysis results show that Dxt-g-CPL can significantly inhibit corrosion. Compared with Dxt, Dxt-g-CPL has a better inhibitory effect.