Enhancing the Anhydrous Proton Conductivity of Boronic and Phosphonic Acid Functional Copolymers by Grafting With Flexible Spacers

Polymers comprised of phosphonic acid units are generally preferred for proton conducting membranes due to their high proton conductivity in humidified and anhydrous state. Polymers based on 4-vinylbenzene boronic acid and diisopropyl-p-vinylbenzyl phosphonate were synthesized and the phosphonate group was hydrolyzed. Boronic acid groups were grafted with polyethyleneglycol methyl ether (PEGME) to produce more flexible copolymers. The copolymerization and grafting reactions were verified by Fourier Transform infrared spectroscopy, thermogravimetric analysis and differential scanning calorimetry (DSC). The P content of the samples was analyzed with SEM–EDS. Thermograms indicate that the copolymers are thermally stable to 200 °C. In addition, grafting resulted in the inhibition of condensation of the acidic units. DSC results show that after grafting the copolymers have distinct melting temperatures corresponding to PEGME units, which are bound to the polymer. The ion exchange capacity and cyclic voltammetry of the copolymers results were measured. The proton conductivity of the copolymers was investigated in the anhydrous state. Although the copolymers have low proton conductivity (<10^?10 S/cm), they reached a value of 1.6 × 10^?6 S/cm after grafting with PEGME units. This demonstrated that the presence of flexible side units increased the proton conductivity at least five orders of magnitude. This idea can be used for designing the novel membranes for fuel cells.     

Regioselective Alkylations of Cyclic 1,3-Diketones via Metalated Dimethylhydrazones

Cyclic 1,3- diketones 1 are transformed into their 2,2-dimethylhydrazones 2 , which can be alkylated regio-selectively at different positions after mono-, di-, tri-, and tetrametalation. Monometalated C-2 unsubstituted hydrazones afford C-2 and N-alkylation, monometalated C-2 substituted hydrazones afford only C-2 alkylation. The regioselectivity of the alkylation of the polymetalated hydrazones follows Hauser's rule according to the sequence: NH- > C-4 Ha > C-5 > C-4 Hb. Hydrolysis of the product hydrazones 3–5 afforded mono- and polyalkylated 1,3- diketones 7 in good yields.     

Molecular Dynamics of Drying-Induced Structural Transformations in a Single Nanocellulose

Nanocellulose is attracting attention in the field of materials science as a sustainable building block. Nanocellulose-based materials, such as films, membranes, and foams, are fabricated by drying colloidal dispersions. However, little is known about how the structure of a single nanocellulose changes during the complex drying process. Here, all-atom molecular dynamics simulations and atomic force microscopy is used to investigate the structural dynamics of single nanocellulose during drying. It is found that the twist morphology of the nanocellulose became localized along the fibril axis during the final stage of the drying process. Moreover, it is shown that conformational changes at C6 hydroxymethyl groups and glycoside bond is accompanied by the twist localization, indicating that the increase in the crystallinity occurred in the process. It is expected that the results will provide molecular insights into nanocellulose structures in material processing, which is helpful for the design of materials with advanced functionalities.