The Performance and Synthesis of Alkynyl-Functionalized Benzoxazine Containing Phthalide Side Groups and Cyano Groups with Different Molecular Weights

Benzoxazine resins are widely employed in a variety of applications due to their exceptional heat resistance and treatment properties. However, traditional benzoxazine resins still confront hurdles in today's engineering applications, such as their inability to provide long-term service in high-temperature settings and their inadequate toughness. In this study, four alkyne-functionalized benzoxazines with phthalide side groups and cyano groups of varying molecular weights were produced. Fourier transform infrared spectroscopy (FT-IR) and hydrogen nuclear magnetic resonance spectroscopy (1H-NMR) were used to characterize the resin structure, and differential scanning calorimetry (DSC) was used to investigate the thermal curing kinetics at different warming rates. The apparent activation energy was 116.9 kJ/mol. In-situ FT-IR was used to investigate the cure mechanism. Dynamic mechanical analysis (DMA) was used to evaluate the gelation time of BOZ series resins at various temperatures, and the curing process was designed by combining the results with DSC. The Tg of the composites made using BOZ-1N21 as the matrix was 336 °C, which was much higher than the Tg of the BP-a resin made with aniline, phenolphthalein, and formaldehyde (Tg = 251 °C). As a result, the resin system is expected to be employed in applications requiring high-temperature resistance and toughness.

Curing behavior and properties of ultra-high temperature resistant RTM bismaleimide resin

The properties of a RTM bismaleimide resin with low viscosity and ultra-high temperature resistance were systematically investigated, including its curing kinetics and rheological properties, and the thermal and mechanical properties of its cured resins. The thermal curing kinetics was investigated by differential scanning calorimetry (DSC) method with multiple heating rates. DSC curves display a cure regime in the temperature range of 150∼300°C and the exothermic peaks shift from 194°C to 231°C with heating rate. The apparent activation energy of curing reaction is calculated as 78.2 kJ/mol. The rheological properties were studied in terms of the changes of the non-isothermal and isothermal viscosity tested using a rotary viscometer. The test results show that the RTM resin has a wide molding temperature window from 90°C to 200°C and long molding time at 110°C for 275 min with a flow viscosity less than 1000 mPas. Dual-Arrhenius model was established to predict the viscosity characteristics at different constant temperatures, showing a good agreement with the experimental data. Four curing cycles were designed to obtain cured networks with different microstructures, and the thermal and mechanical properties of the cured resins suffered from various curing cycles were characterized by dynamic mechanical analysis (DMA) and universal material testing machine. The results exhibit that the cured product has a ultra-high glass transition temperature of 373.5°C and larger flexural strength of 145.4 MPa after post-curing at 250°C for 10 h.