Abstract
The curing behaviour of the composition of a liquid-crystalline diepoxy monomer (LCEM) with the central triaromatic mesogenic group was studied using differential scanning calorimetry, conventional DSC and temperature-modulated TMDSC and nuclear magnetic resonance 1H-NMR spectroscopy. The stoichiometric amount of primary aromatic diamine, 4,4′-diaminodiphenylmethane (DDM), was used as a curing agent. TMDSC TOPEM® allowed the separation of the thermal effects related to reversible processes (e.g. phase transitions) from irreversible processes (cross-linking reaction) and determining that irreversible curing reaction occurs at the same time as reversible transition of the LCEM from crystal to the liquid-crystalline nematic phase. Additionally, 1H-NMR analysis of the LCEM/DDM mixture preheated to a temperature from the temperature range of complex thermal changes was conducted. The obtained spectrum clearly showed the presence of partially cured products in the investigated samples and additionally proved that during the endothermic phase transition of the LCEM monomer an exothermic cross-linking reaction was occurring.
Highlights
Liquid-crystalline (LC) compounds have been known for over 100 years, since they were discovered by Friedrich Reinitzer at the end of the 19th century [1]
temperature-modulated DSC (TMDSC) TOPEMÒ allowed the separation of the thermal effects related to reversible processes from irreversible processes and determining that irreversible curing reaction occurs at the same time as reversible transition of the liquid-crystalline diepoxy monomer (LCEM) from crystal to the liquid-crystalline nematic phase
Analysis of the reactivity of LCEM/DDM compositions by the DSC method showed that in the course of heating on the DSC curve some deformation of the endothermic transition peak of the monomer from the crystalline (Cr2?N) to the liquid-crystalline phase above 130 °C presented itself, what indicates that some more complex process than phase transition is occurring in mentioned temperature and it calls for a deeper investigation
Summary
Liquid-crystalline (LC) compounds have been known for over 100 years, since they were discovered by Friedrich Reinitzer at the end of the 19th century [1]. The conventional DSC analysis showed that there is a deformation in the liquid-crystalline transition of LC monomer (i.e. from crystal to liquidcrystalline phase transition) during heating of the analysed composition, which suggested that the partial exothermic cross-linking reaction with epoxy groups’ involvement takes place simultaneously with the endothermic phase transition of liquid-crystalline epoxy monomer (LCEM). In this paper, this hypothesis was confirmed based on the TMDSC and 1H-NMR results. Deuterated solvents such as DMSO-d6 and CD2Cl2, with deuterium isotope
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