Heng Zhou

Addition-curable phthalonitrile-functionalized novolac resin

A novel addition-curable novolac resin with phthalonitrile groups (PN) was successfully synthesized by a simple nucleophilic substitution reaction between the novolac resin and 4-nitrophthalonitrile. The final product was characterized with gel permeation chromatography (GPC), Fourier transform infrared (FT-IR) spectrometry, and proton nuclear magnetic resonance (1H-NMR) spectroscopy. Processing capability and cure behavior of PN resin was investigated by rheometer and differential scanning calorimetry (DSC), respectively. Rheometric studies showed PN resin possessed a broad processing window between 140 and 225°C with a low viscosity from 0.4 to 4 Pa.s. DSC results showed PN resin can be cured at about 220°C via thermal polymerization of phthalonitrile groups. An ultrahigh curing temperature (such as 375°C) that was typical for the other phthalonitrile functional prepolymers was not necessary for this resin and 250°C was used as a maximum post-cure temperature to achieve the desired properties. Thermogravimetric analysis (TGA) showed T 5 % (temperature of 5% weight loss) of the final cured products in nitrogen was 448.7°C, and the char yield was 70.29% at 900°C. Furthermore, T 5% of cured PN resin in air was 455.2°C, and the char yield in air was 34.48% at 700°C,revealing that the cured resin possessed excellent thermo-oxidative stability. Dynamic mechanical analysis (DMA) showed the inflection point of tan δ was 371.9°C. The excellent processability and thermal stabilities proved PN resin as a promising candidate for advanced composite matrices.

Synthesis, characterization and immobilization of N-doped TiO2 catalysts by a reformed polymeric precursor method

A novel synthetic method to prepare N-doped TiO2 catalysts was studied, by which a stable and homogeneous liquid polymeric precursor was produced, thus the catalysts can be loaded on suitable substrates, making catalysts facilely separated from waste water. The doping ratios and annealing temperatures were optimized by testing photodegradation of the products to methyl orange. To improve the Brunauer–Emmett–Teller surface areas of the catalyst, PEG was grafted to the structure of precursor polymer, by which an increase of 55% in BET surface areas and 20% in the photodegradation efficiencies was achieved. The crystalline phase was measured by X-ray diffraction and structural parameters were calculated by Xpert Highscores. FESEM and HRTEM pictures showed that the average particle size of the nitrogen doped and PEG modified catalyst reached to only 5 nm. X-ray photoelectron spectroscopy showed that nitrogen dope mode was interstitial. Using quartz fabrics as substrate, the loaded catalysts were facilely recycled and reused by 15 times without decay in photodegradation efficiency.

Toughness reinforcement of bismaleimide resin using functionalized carbon nanotubes

Carbon nanotubes (CNTs) with various functionalization states were used to toughen bismaleimide resin. Differential scanning calorimeter and rheometric measurements were conducted to monitor the processability of the hybrid systems. The toughness of the corresponding composites was investigated by Charpy impact and flexural tests, while the thermal properties were obtained from dynamic mechanical and thermogravimetric analyses. The results showed that the loading and functionalization state of the CNTs in the resin matrix had a great influence on the mechanical performance and glass transition temperature, but less influence on thermal decomposition temperature of the composites. These phenomena could be attributed to the differences in dispersion state, interfacial adhesion, and interfacial compatibility of CNTs in the resin matrix. Compared with the pure resin, composites containing 0.50 wt% diaminodiphenylmethane-treated CNTs showed 60% improvement in impact strength and 100% improvement in flexural toughness while preserving their thermal properties.

Evolution of the formation of a covalent triazine-based framework catalyzed by p-toluenesulfonic acid monohydrate

A porous covalent triazine-based framework (CTF) was prepared by a two-step strategy, where p-toluenesulfonic acid monohydrate (TsOH·H2O) was used as a catalyst. The porosity and gas storage capacity of the as-obtained framework was evaluated. In addition, the evolution of the chemical structure during the two stages was studied. Crystallite size was calculated to study the formation of the framework; the evolution of internal porosity has been discussed based on the results obtained. In the first step, a triazine-based polymer was formed at relatively low temperatures, and limited crystallites were developed. However, in the second step, a treatment at higher temperatures performed in an open system resulted in the purification of the chemical structure; furthermore, CTF lamellae with an improved ordered stacking developed, resulting in a dramatic increase in internal porosity.