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Herein, novel isomeric diamines containing semi-N-methyl substituted bisbenzimidazole and derived polyimides (PIs) were successfully synthesized. Experimental data showed that the obtained PIs exhibited outstanding heat resistance and dimensional stability, including 5 % thermal weight loss temperature (Td5 %) of 547 ~ 557 °C, high glass transition temperature (Tg) of 407 ~ 423 °C, and low coefficient of thermal expansion (CTE) of 2.2 ~ 17.6 ppm/°C. The influence of molecular structure of isomeric diamines, including para and ortho substituted N-methyl, on the molecular packing and properties of polymer was discussed. As a result, the novel PIs showed lower CTE than traditional PABZ (5-amino-2-(4-aminobenzene)-benzimidazole) based PIs without bringing high water absorption. These high-performance PI films with matching CTE of copper have potential applications in flexible display substrates and printed circuit boards. [ABSTRACT FROM AUTHOR]

Eight compounds, including one sphingolipid ( 1), two flavonoids ( 2, 3), four sterols ( 4-7), and one amino acid ( 8), had been isolated and purified from Amaranthus retroflexus L. Their structures were elucidated on the basis of spectroscopic analyses, including 1D and 2D NMR and ESI-MS. Among them, 1-O- β-D-glucopyranosyl-(2S,3R,4R,8E)-2-[(2′R)-2′-hydroxytetracosanoylamino]-1,3,4-octadecanetriol-8-ene ( 1) was identified as a new compound, and α-spinasteryl-3-O- β-D-glucopyranoside ( 4), 3 β,12 β,20(S)-trihydroxydammar-24-ene-6-O- β-D-glucopyranoside ( 6), and 2 β,3 β-dihydroxy-30-norolean-12,20(29)-diene-23,28-dioic acid 28-O- β-D-glucopyranosyl ester ( 7) were isolated from this plant for the first time. This is the first more comprehensive report on chemical compositions of Amaranthus retroflexus L. [ABSTRACT FROM AUTHOR]

As the continuous development of aerospace and outer space exploration, high-performance thermal insulation materials with high-temperature resistance and attractive mechanical properties have always been a fascinating topic of research to protect human body or components from extreme environments. In this research, hydrophobic silicon dioxide (SiO2) nanoparticles as molecular skeleton enhancers and heat transfer inhibitors are introduced in crosslinked polyimide (PI) aerogels with rigid molecular structure to maintain the stable nanoporous network structure. The density, shrinkage, porosity, specific surface area and pore size distribution of PI/SiO2 composite aerogels can be adjusted by the addition of SiO2 nanoparticles, so as to improve the comprehensive performances. The excellent thermal stability and mechanical properties of PI/SiO2 composite aerogels with super-high working temperature of over 550 °C and high modulus of compression and tension (compression Young’s modulus of 37.75 MPa and tensile modulus of 237.1 MPa) ensure their use as a structural component. The charming thermal conductivity (29.7 mWm−1 K−1) and excellent flame resistance make them a candidate for high-performance thermal insulation materials.Graphical abstract: As the continuous development of aerospace and outer space exploration, high-performance thermal insulation materials with high-temperature resistance and attractive mechanical properties have always been a fascinating topic of research to protect human body or components from extreme environments. In this research, hydrophobic silicon dioxide (SiO2) nanoparticles as molecular skeleton enhancers and heat transfer inhibitors are introduced in crosslinked polyimide (PI) aerogels with rigid molecular structure to maintain the stable nanoporous network structure. The density, shrinkage, porosity, specific surface area and pore size distribution of PI/SiO2 composite aerogels can be adjusted by the addition of SiO2 nanoparticles, so as to improve the comprehensive performances. The excellent thermal stability and mechanical properties of PI/SiO2 composite aerogels with super-high working temperature of over 550 °C and high modulus of compression and tension (compression Young’s modulus of 37.75 MPa and tensile modulus of 237.1 MPa) ensure their use as a structural component. The charming thermal conductivity (29.7 mWm−1 K−1) and excellent flame resistance make them a candidate for high-performance thermal insulation materials. [ABSTRACT FROM AUTHOR]

Herein, novel isomeric diamines containing semi-N-methyl substituted bisbenzimidazole and derived polyimides (PIs) were successfully synthesized. Experimental data showed that the obtained PIs exhibited outstanding heat resistance and dimensional stability, including 5 % thermal weight loss temperature (Td5 %) of 547 ~ 557 °C, high glass transition temperature (Tg) of 407 ~ 423 °C, and low coefficient of thermal expansion (CTE) of 2.2 ~ 17.6 ppm/°C. The influence of molecular structure of isomeric diamines, including para and ortho substituted N-methyl, on the molecular packing and properties of polymer was discussed. As a result, the novel PIs showed lower CTE than traditional PABZ (5-amino-2-(4-aminobenzene)-benzimidazole) based PIs without bringing high water absorption. These high-performance PI films with matching CTE of copper have potential applications in flexible display substrates and printed circuit boards. [ABSTRACT FROM AUTHOR]