Synthesis, characterization, and gelation and development of liquid crystalline order during isothermal cure of rigid rod epoxy

The liquid crystalline thermoset monomers 4,4′-diglycidyloxy-α-methylstilbene (DOMS) and D2A1 that resulted from reaction between DOMS and aniline were synthesized. The monomers were characterized with cross-polarized optical microscopy, differential scanning calorimetry (DSC) and dynamic thermogravimetric analysis (TGA). DOMS showed monotropic liquid crystalline mesophase and D2A1 showed smectic phase even at room temperature and turned into nematic then cleared upon heating.; DOMS was cured with sulfanilamide (SAA) and D2A1 was cured with catalytic curing agent, 1-methyl imidazole (MI). Thermal stability tests of DOMS-SAA, D2A1-MI and commercial nonliquid crystalline epoxy, diglycidyl ether of bisphenol A (DGEBA) SAA system via dynamic TGA shows that the factor that most influences thermal stability is the molecular structure of the material itself rather than liquid crystalline phases. The %conversion data were determined from dynamic DSC scan to examine the applicability of Flory's gelation theory. The results reveal that even though the amount of reaction that occurs in the liquid crystalline phase is different at different cure temperatures, the isoconversion theory of gelation fits quite well. The actual average value of the conversion at the gel point is 0.677, which is slightly higher than the calculated theoretical value of 0.577 because of the failed assumptions of this theory. That is, there might be reactivity differences among the same types of functional groups and intramolecular connections are possible.; The phase transitions do not show isoconversion behavior in contrast to gelation. Instead, the conversion where phase changes from isotropic to a liquid crystalline phase tends to increase with temperature because the critical length of the molecules needed for the liquid crystallinity increases with temperature.