Selective and Controlled Grafting from PVDF-Based Materials by Oxygen-Tolerant Green-Light-Mediated ATRP.

Poly(vinylidene fluoride) (PVDF) shows excellent chemical and thermal resistance and displays high dielectric strength and unique piezoelectricity, which are enabling for applications in membranes, electric insulators, sensors, or power generators. However, its low polarity and lack of functional groups limit wider applications. While inert, PVDF has been modified by grafting polymer chains by atom transfer radical polymerization (ATRP), albeit via an unclear mechanism, given the strong C-F bonds. Herein, we applied eosin Y and green-light-mediated ATRP to modify PVDF-based materials. The method gave nearly quantitative (meth)acrylate monomer conversions within 2 h without deoxygenation and without the formation of unattached homopolymers, as confirmed by control experiments and DOSY NMR measurements. The gamma distribution model that accounts for broadly dispersed polymers in DOSY experiments was essential and serves as a powerful tool for the analysis of PVDF. The NMR analysis of poly(methyl acrylate) graft chain-ends on PVDF-CTFE (statistical copolymer with chlorotrifluoroethylene) was carried out successfully for the first time and showed up to 23 grafts per PVDF-CTFE chain. The grafting density was tunable depending on the solvent composition and light intensity during the grafting. The initiation proceeded either from the C-Cl sites of PVDF-CTFE or via unsaturations in the PVDF backbones. The dehydrofluorinated PVDF was 20 times more active than saturated PVDF during the grafting. The method was successfully applied to modify PVDF, PVDF-HFP, and Viton A401C. The obtained PVDF-CTFE-g-PnBMA materials were investigated in more detail. They featured slightly lower crystallinity than PVDF-CTFE (12-18 vs 24.3%) and had greatly improved mechanical performance: Young's moduli of up to 488 MPa, ductility of 316%, and toughness of 46 × 106 J/m3.

A Straightforward Method for the Generation of Hyperpolarized Orthohydrogen with a Partially Negative Line.

The hydrogen molecule, which exists in two spin isomers (ortho- and parahydrogen), is a highly studied system due to its fundamental properties and practical applications. Parahydrogen is used for Nuclear Magnetic Resonance signal enhancement, which is hyperpolarization of other molecules, including biorelevant ones. Hyperpolarization can be achieved by using Signal Amplification by Reversible Exchange (SABRE). SABRE can also convert parahydrogen into orthohydrogen, and surprisingly, in some cases, it has been discovered that orthohydrogen's resonance has the Partially Negative Line (PNL) pattern. Here, an approach for obtaining orthohydrogen with a PNL signal is presented for two catalysts: Ir-IMes, and Ir-IMesBn. The type of solvent in which SABRE is conducted is crucial for the observation of PNL. Specifically, a PNL signal can be easily generated in benzene using both catalysts, but it is more intense for Ir-IMesBn. In acetone, PNL is observed only for Ir-IMesBn. In methanol, no PNL is detected. The PNL effect is only detectable during the initial steps of pre-catalyst activation, and disappears as the activation process progresses. We have proposed a working hypothesis that explains our results. The presented data may facilitate the further investigation of PNL and its applications in material science and catalysis.