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ABSTRACT: The dynamic and mechanical properties of the three thermoplastic polyimides—crystallizable polyimide BPDA‐P3 and amorphous polyimides ODPA‐P3 and aBPDA‐P3—have been simulated using the atomistic molecular dynamics technique. The three simulated polyimides differ in the chemical structure of their corresponding dianhydride fragments. Analyzing the local orientational mobility of different phenylene rings, it has been established that the increase of the glass‐transition temperature (Tg) in the ordered set T g aBPDA − P 3 > T g BPDA − P 3 > T g ODPA − P 3 is caused by the slowing down of the phthalimide rings relaxation in the corresponding dianhydride fragments. It has been observed that rather poor mechanical characteristics upon aBPDA‐P3 stretching in the strain‐hardening regime are also due to the low orientational mobility of the phthalimide rings. The correlation between the dynamic fragility and the polyimides strain‐hardening moduli has been observed; the increase of the dynamic fragility leads to the increase of the strain‐hardening modulus. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 375–382 [ABSTRACT FROM AUTHOR]

A phenylethynyl-terminated reactive diluent [Card-4-phenylethynylphthalic anhydride (PEPA)], which contained fluorenyl cardo structures, was successfully synthesized and used as a modifier for flexible phenylethynyl-terminated imide oligomer (PEI-PEPA). The chemical structure, crosslink characterization, molecular weights, and thermal properties of the products were characterized. The imide systems with addition of 10, 20, 30, and 40 wt% Card-PEPA to PEI-PEPA (PEI-PEPA-Card) and their cured resin systems were prepared. The thermal curing behaviors of imide systems at different heating rates were analyzed by using differential scanning calorimetry. Thermal properties such as glass transition temperature ( Tg) and char yield at 800°C of the resultant resin systems were studied by differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The rheological properties were also investigated using a dynamic rheometry. These properties were found to be outstanding compared with pure PEI-PEPA. The uncured imide systems exhibited lower Tg and lower isothermal viscosity with addition of Card-PEPA. Furthermore, the Tg and char yield of the cured resin systems increased with addition of Card-PEPA. The cured resin systems containing 40 wt% Card-PEPA exhibited the highest Tg of 359°C and char yield at 800°C of 66.5%. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]