Supramolecular Association of Hydrogen-bonded Polybutadienes Functionalized with Ureidopyrimidone

Ureidopyrimidone (UPy) is a well-known self-complementary quadruple hydrogen bonding unit, extensively applied in the preparation of supramolecular polymers with enhanced physical properties. The property enhancement is assigned partly to linear chain extension and fibrillar nanophase separation due to secondary hydrogen bonding by urethane and urea linker, though a clear distinctive structure property relationship has not be reported. In this work, two distinct sets of UPy functional polymers, a series of monochelic polybutadienes (PBd) and telechelic polybutadienes, were synthesized and analyzed by solution and bulk characterization techniques to probe the role of polymer chain mobility and polarity on the UPy chain-end association. ω [omega]-UPy terminated polybutadiene was semi-solid waxy material, indicating association beyond dimers. Solution studies indicate the presence of star-like micelles that are in equilibrium with dimers. These aggregated micellar clusters have distinct endothermic transitions in differential scanning calorimetry (DSC). Atomic force microscopy (AFM) studies show an evidence of micellar-clusters forming associated parallel line-like structures on a mica surface with the well-defined order. A series of α [alpha], ω [omega]-di-UPy terminated polybutadienes and hydrogenated polybutadienes were synthesized, and their properties was evaluated as a function of 1,2-vinyl content. Telechelic UPy-PBd differs strongly in their physical properties, PBd with low Tg [glass transition temperature] (-90 °C) forms semi-solid and brittle material, whereas PBd with moderate Tg (-45 °C) gave strong thermoplastic elastomer. AFM images give parallel association of micellar clusters. Dynamics of micellar-cluster associated UPy domains with unassociated chain extended dimers lead to gelation at specific temperature depending on the characteristics of the linker precursor oligomers. Supramolecular gel transition temperature (Tsg) was identified in rheological studies on various UPy telechelics. In addition, polystyrene and poly(n-butylacrylate) UPy telechelics were also prepared by copper (I) catalyzed alkyne azide coupling (CuAAC) “click” reaction. The triazole linker in these polymers interferes with the UPy association and reduces the size of the hydrogen bonded UPy aggregates, which was found to improve the physical property of the supramolecular polymers. An attempt was made to examine the role of polymer chain mobility and its polarity was used to correlate structure and property with reference to room temperature

A simple and efficient approach to the synthesis of 2-substituted benzimidazole via sp3 C–H functionalization

A facile and novel approach to the synthesis of 2-substituted benzimidazole was developed via a tandem reaction following sp3 C–H functionalization. Here we report a simple, efficient and tandem oxidative dehydrative coupling reaction of N-benzylbezene-1,2-diamine in the presence of oxidant tert-butyl hydroperoxide (TBHP) in solvent acetonitrile to give substituted benzimidazole

Synthesis and antifungal activity of 1, 5-diaryl pyrazole substituted thiazole derivatives

918-923Series of eight derivatives of 5-bistrifluoromethyl phenyl pyrazole substituted thiazole have been prepared and characterized by 1H and 13C NMR, and mass spectrometry. All the synthesized derivatives have been screened for antifungal activity against four fungal pathogens such as Candida albicans, Aspergillus flavus, Aspergillus fumigatus and Aspergillus niger using broth microdilution method. Active compounds have also been screened for MIC (minimum inhibitory concentration) and MFC (minimum fungicidal concentration). Three compounds 8b, 8f and 8h are found to be equi-potent with standard drug actidione, against Candida albicans and Aspergillus flavus strains

Synthesis and Characterization of Comb and Centipede Multigraft Copolymers P<i>n</i>BA‑<i>g</i>‑PS with High Molecular Weight Using Miniemulsion Polymerization

Comb and centipede multigraft copolymers, poly­(<i>n</i>-butyl acrylate)-<i>g</i>-polystyrene (P<i>n</i>BA-<i>g</i>-PS) with P<i>n</i>BA backbones and PS side chains, were synthesized via high-vacuum anionic polymerization and miniemulsion polymerization. Single-tailed and double-tailed PS macromonomers were synthesized by anionic polymerization and Steglich esterification. Subsequently, the copolymerization of each macromonomer and <i>n</i>BA was carried out in miniemulsion, and multigraft copolymers were obtained. The latex particles of multigraft copolymers were characterized using dynamic light scattering. The molecular weights of macromonomers and multigraft copolymers were analyzed by size exclusion chromatography. Moreover, the molecular weights and structures of macromonomers were investigated by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and ¹H nuclear magnetic resonance spectroscopy. The weight contents of PS in comb and centipede multigraft copolymers were calculated by ¹H nuclear magnetic resonance spectroscopy. The thermal properties of multigraft copolymers were characterized by thermogravimetric analysis and differential scanning calorimetry. The microphase separation of multigraft copolymers was observed by atomic force microscopy and transmission electronic microscopy. Rheological measurements showed that comb and centipede multigraft copolymers have elastic properties when the weight content of PS side chains is 26–32 wt %. Centipede multigraft copolymers possess better elastic properties than comb multigraft copolymers with the similar weight content of PS. These findings are similar to previous results on poly­(isoprene-<i>g</i>-polystyrene) comb and centipede copolymers made by anionic polymerization