Thermosetting resins prepared from the reactions of diaminomaleonitrile with 4,4′-bismaleimidediphenylmethane and electrical conductivity measurements of the resulting materials following pyrolysis

Abstract

A new series of thermosetting resins were prepared from the reaction of diaminomaleonitrile (DAM) with 4,4′-bismaleimidediphenylmethane (BM) under various molar ratios. The resins were characterized by FT-IR, DTA, TGA and TMA. They had a complex network structure depending on their composition. The DTA studies revealed that their crosslinking started at about 40 °C below the temperature required for crosslinking of BM. Their thermal stability was correlated with their composition and the curing conditions. The cured resins obtained upon curing at 300 °C for 60 h were remarkably more thermally stable than BM which cured itself under the same conditions. They were stable up to 326–377 °C and afforded an anaerobic char yield of 56–72% at 800 °C. Prior to pyrolysis, most of the resins were of amorphous structure, and behaved electrically, at room temperature, as insulators. A decrease of the electrical resistivity was observed with increasing pyrolysis temperature. All resulting conductive materials were of amorphous structure as revealed by their X-ray diffraction profiles. The temperature dependence of the electrical resistivity was measured in the temperature range −173–327 °C (100–600K) for all pyrolysed materials. The results suggest semiconducting properties. The thermally activated conduction model, as well as the variable range hopping model, were applied in order to interpret the experimental data. The observed electrical conductivity seems to be thermally activated and could be associated with intermolecular and intramolecular hopping conduction processes. The activation energies for the intermolecular process ranges from 0.249 to 0.018 and 0.387 to 0.059 eV for the intramolecular process depending on the pyrolysis temperature. The electrical behaviour of all conductive materials could be easily controlled from insulating to semiconducting by controlling both the pyrolysis temperature and duration. The highest electrical conductivity of 1.98 × 10 1 S cm −1 was observed for a conductive material pyrolysed at 800 °C for 40 h.