Isothermal Curing of Acetylene Functionalized Liquid Crystalline Thermoset Monomers

To investigate the effects of molecular architecture on the liquid crystalline phases and times to gelation during isothermal curing, two homologous series of acetylene functionalized thermotropic liquid crystalline monomers were synthesized and examined. New liquid crystalline phase−time−temperature−physical transformation diagrams (LCPTTT) were constructed for four of the monomers and illustrate that the monomers change from nematic liquids to isotropic or biphasic gels during isothermal curing. However, reemergence of an ordered phase occurred if the monomers were cured at low enough temperature. The critical temperature for ordered phase retention in the final vitrified material is inversely proportional to the length of the terminal flexible chain. The time to gelation for a single set of isothermal cure conditions did show an increase in gel times with increasing chain length; however, an odd−even effect was seen in both series rather than a linear increase.