Many factors affect the formation of lyotropic liquid crystals (LLCs) in the poly(p-phenylene terephthamide) (PPTA)/H2SO4 system. In this systematic work, we prove that the hydrogen bonding between PPTA and H2SO4 plays a very important role for the LLC formation by using a combination of several characterization methods. Texture features and transition temperatures of different phases owing to hydrogen bonding in the PPTA/H2SO4 system were obtained by using polarized light microscopy and differential scanning calorimetry. C-13 NMR and FTIR spectroscopy were applied to investigate the chemical structures in different phases, especially the hydrogen bonding between PPTA and H2SO4 . The effect of molecular weight on phase transition was also examined. Moreover, guest compounds such as H2O, CH3SO3H, and carbon nanotube added will destroy the hydrogen-bonding network in the PPTA/ H2SO4 system, resulting in different phase behaviors. All these results demonstrate that hydrogen bonding between PPTA and H2SO4 is the key factor for the highly ordered arrangement of polymer chains in the LLC state that is a nematic phase. (C) 2018 Elsevier Ltd. All rights reserved.