Synthesis and Thermal Properties of Bismaleimides with Mesogen Aromatic Amide-Ester and Flexible Polymethylenic Group

Four bismaleimides with mesogen amideester aromatic and flexible polymethylenic group variable length (8 = n = 11) were synthesized in two stages, producing yields exceeding 80%. These bismaleimides (BMIs) were obtained after several purifications by dissolutionprecipitation in dimethylformamidemethanol (1/4) with over 94% purity (high-performance liquid chromatography). These pure BMIs were characterized by nuclear magnetic resonance, Fourier transform infrared spectroscopy, and elemental analysis and studied by differential scanning calorimetry, thermogravimetric analysis, polarized light microscopy, and X-ray diffraction. Solubilities and thermal properties show effects of parity. The even BMIs are more difficult to solubilize than the odd BMI. The melting points of the even BMI (approximately, 220 degrees C) are far higher than those of odd BMI (approximately, 160 degrees C). Crosslinking temperatures of even BMI are close to 230 degrees C, whereas odd BMI crosslinking temperatures are higher (approximately, 250 degrees C). Even BMIs give rise to a liquid crystal state upon melting. Under the same conditions, odd BMIs give rise to an amorphous state; however, after crosslinking, the four bismaleimides give rise to an ordered liquid crystal state of smectic type. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013