SYNTHESIS OF 3,3´-(1,4-PHENYLENE)BIS(1-(4-R-PHENYL)-5-PHENYL-5,6-DIHYDRO-1,2,4,5-TETRAZINIUM) PERCHLORATES

A series of 3,3'-(1,4-phenylene)bis(1-4-R-phenyl)-5-phenyl-5,6-dihydro-1,2,4,5-tetrazinium) perchlorates containing hydrogen, methyl, bromio, methoxy, acetyl and nitro groups (R = H, Me, Br, OMe, COMe, NO2) as substituents were obtained as a result of a three-stage synthesis from terephthalic aldehyde. The synthesis of tetrazinium salts was carried out by reaction of the corresponding formazans with formalin in the presence of perchloric acid in dioxane. Formazans were obtained by reaction of terephthalic aldehyde phenylhydrazone with arenediazonium tosylates in a mixture of DMF and pyridine. The usage of arenediazonium tosylates made it possible to extremely simplify the segregation and purification of formazans. The phenylhydrazone was synthesized according to the standard procedure from terephthalic aldehyde and phenylhydrazine/hydrochloric acid in aqueous dioxane. The formazans and tetrazinium perchlorates were isolated in individual state and characterized by elemental analysis, IR, UV, 1H and 13C NMR spectroscopy data. The process of electrochemical reduction of tetrazinium perchlorates was studied using the method of cyclic voltammetry (CV). Thus, the CV curves of all salts in the cathode region contain two one-electron reduction peaks, which are related to the sequential formation of a radical cation and a biradical. It was found that electron-donating substituents (R = Me, OMe) in the aromatic ring at position 1 facilitate the reduction of tetrazinium cation, while electron-withdrawing substituents (R = COMe, NO2) hinder this process. On this basis, it was suggested that the corresponding bis-verdazyl radicals should be easily formed in the presence of electron-donating substituents in the aromatic ring at position 1. Thus, 3,3´-(1,4-phenylene)bis(1-(4-R-phenyl)-5-phenyl-5,6-dihydro-1,2,4,5-tetrazinium-1) perchlorates are perspective precursors of symmetric biradical systems based on verdazyl radicals.

Design of Azomethine Diols for Efficient Self-Healing of Strong Polyurethane Elastomers

Azomethine diols (AMDs) were synthesized by condensation between a terephthalic aldehyde, polyether diamine, and ethanol amine. The synthesized AMDs were employed to introduce azomethine groups into the backbones of polyurethane elastomers (PUEs). Different AMDs were designed to control the concentration and distribution of azomethine groups in PUEs. In this study, we explored the intrinsic self-healing of AMD-based PUEs by azomethine metathesis. Particularly, the effects of the concentration and distribution of the azomethine groups on the AMD-based PUEs were considered. Consequently, as the azomethine group concentration increased and the distribution became denser, the self-healing properties improved. With AMD3-40, the self-healing efficiency reached 86% at 130 °C after 30 min. This represents a 150% improvement over the control PUE. Additionally, as the AMD content increased, the mechanical properties improved. With AMD3-40, the tensile strength reached 50 MPa. Therefore, we concluded that the self-healing and mechanical properties of PUEs can potentially be tailored for applications by adjusting the concentration and design of AMD structure for PUEs.

Synthesis and photophysical study of new blue fluorescent poly(azomethine-1,3,4-oxadiazole)s containing dimethylamino groups

New aromatic polyazomethines were synthesized by polycondensation reaction of a diamine containing 1,3,4-oxadiazole ring, namely, 4,4′-diamino-4″-[2-(4-phenoxy)-5-(4-dimethylaminophenyl)-1,3,4-oxadiazole)]triphenylmethane, with terephthalic aldehyde or bis(4-formylphenoxyphenyl)fluorene, by using N-methyl-2-pyrrolidinone (NMP) as solvent. The polymers were easily soluble in polar solvents, such as NMP, N, N-dimethylacetamide, or chloroform, and showed high thermal stability with the initial decomposition temperature above 415°C and the temperature of 10% weight loss in the range of 450–460°C. They exhibited high char yield at 800°C in the range of 52–56%. Optical properties were studied by absorption and photoluminescence spectra. In solution, the polymers presented two absorption maxima in the ranges 273–278 and 330–346 nm and emitted violet-blue light in the range of 413–468 nm, depending on the solvent polarity. The Stokes shift and emission quantum yield values depend on the polymer structure and solvent polarity. The emission intensity in NMP solution was enhanced upon increasing the HCl concentration, while the absorption spectral profile was slightly influenced.

POSS-based meso-/macroporous covalent networks: supporting and stabilizing Pd for Suzuki–Miyaura reaction at room temperature

Porous covalent organic networks synthesized by Schiff base chemistry reaction of POSS and terephthalic aldehyde could serve as both supports and stabilizers for Pd catalyst, which exhibited excellent performances for Suzuki-Miyaura reactions.