Two novel acetylene-terminated isoimide oligomers and their corresponding imide oligomers have been synthesized by using trifluoroacetic anhydride or acetic anhydride as dehydrating agent, respectively. Their main structure was confirmed by Fourier transform infrared spectroscopy (FTIR). The isoimide oligomers were amorphous and showed excellent solublility in many common solvents, such as acetone and tetrahydeofuran, whereas the imide oligomers cannot dissolve in them. Differential scanning calorimetry and rheometer were used to study crosslinking behavior and processability of these oligomers. The isoimide oligomers exhibited considerably wider processing window and lower viscosity compared with imide ones. As expected, the isoimide form could be converted to imide form through thermal treatment, which could be demonstrated by FTIR. After the oligomers were cured, the polyisoimides showed similar properties compared with corresponding polyimides. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

A novel diamine, 1,4-bis [3-oxy-(N-aminophthalimide)] benzene (BOAPIB), was synthesized from 1,4-bis [3-oxy-(N-phenylphthalimide)] benzene and hydrazine. Its structure was determined via IR, ¹H NMR, and elemental analysis. A series of five-member ring, hydrazine-based polyimides were prepared from this diamine and various aromatic dianhydrides via one-step polycondensation in p-chlorophenol. The inherent viscosities of these polyimides were in the range of 0.17–0.61 dL/g. These polymers were soluble in polar aprotic solvents and phenols at room temperature. Thermogravimetric analysis (TGA) showed that the 5% weight-loss temperatures of the polyimides were near 450°C in air and 500°C in nitrogen. Dynamic mechanical thermal analysis (DMTA) indicated that the glass-transition temperatures (T_gs) of these polymers were in the range of 265–360°C. The wide-angle X-ray diffraction showed that all the polyimides were amorphous. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

In the past decades, 4-phenylethynyl phthalic anhydride (4-PEPA) has been the most important endcapper used for thermoset polyimide. As the isomer of4-PEPA, 3-phenylethynyl phthalic anhydride (3-PEPA) has attracted our interest. In this article, 3-PEPA was synthesized and a comparative study with 4-PEPA on curing temperature, curing rate, thermal and mechanical properties of oligomers and cured polymers was presented. The new phenylethynyl endcapped model compound, N-phenyl-3-phenylethynyl phthalimide, was synthesized and characterized. The molecular structure of model compound was determined via single-crystal X-ray diffraction and the thermal curing process was investigated by Fourier transform infrared. Differential scanning calorimetry clearly showed that the model compound from 3-PEPA had about 20 °C higher curing onset and peak temperature than the 4-PEPA analog. This result was further proved by the dynamic rheological analysis that the temperature of minimum viscosity for oligomers end-capped with 3-PEPA was above 20 °C higher than that of the corresponding 4-PEPA endcapped oligomers with the same calculated number average molecular weight. The cured polymer from 3-PEPA displayed slightly higher thermal oxidative stability than those from 4-PEPA by thermogravimetric analysis. The thermal curing kinetics of 3-PEPA endcapped oligomer (OI-5) and 4-PEPA endcapped oligomer (OI-6) fitted a first-order rate law quite well and revealed a similar rate acceleration trend. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4227–4235, 2008