Isothermal Curing of Acetylene Functionalized Liquid Crystalline Thermoset Monomers

Abstract

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-timetemperature-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.

Influence of liquid crystalline ordering on the properties of selected cured nematic epoxy materials

“…In other studies it has been generally found that reaction kinetics is enhanced in more ordered phases (Guymon and Bowman, 1997;Liu et al, 1997;Mormann and Brocher, 1999) and that the network formation tends to stabilize more ordered phases (Lin et al, 1997;Shiota and Ober, 1997). However, there are also examples in which the network formation destabilizes the liquid crystalline phase (Gavrin and Douglas, 2001;Osada et al, 1996). The research works also suggest that the final properties of a liquid crystalline polymer network are affected not only by the structure of the reagents and the density of the cross-linking bonds (Amendola et al, 1996) but also by the degree of molecular order in the course of the reaction (Davis and Mitchell, 1996;Hirn et al, 1996).…”

All‐aromatic liquid crystal thermosets: New high‐performance materials for structural applications

“…Curing of the reactive monomers in the presence of a magnetic field resulted in well-oriented triazine networks with low values of the CTE (17 ppm/uC) in the direction of the applied field. Gavrin et al functionalized their liquid crystal monomers with acetylene and phenylethynyl moieties, and observed low viscous nematic melts upon heating [16,17]. Unfortunately, very limited mechanical and physical properties of the crosslinked thermosets were reported.…”

New liquid crystals and liquid crystalline thermosets based on wholly aromatic rigid-rod mesogens

“…Typical rigid-rod thermosets consist of reactive endgroups such as maleimide and nadimide attached directly to rigid-rod components such as biphenyl, phenyl benzoate, methyl stilbene or naphthyl structures. 6,7,12,[15][16][17][18][19] Various synthetic pathways for the preparation of LCTs have been described. Of these pathways, Hoyt et al 6,7 have investigated the thermal polymerization of maleimides and nadimides, i.e., both rigid-rod ester and rigid-rod amide monomers end-capped with maleimide, nadimide, and methylnadimide crosslinking functionalities.…”