Synthesis of functional liquid crystalline polymers for exfoliated clay nanocomposites

Abstract

The incorporation of nanoparticles like nanoclays into liquid crystalline polymers (LCPs) represents an effective pathway toward further improving their intrinsic properties and thus broadening their scope of high-performance applications. The underlying mechanism lies in that nanoclays may have strong interactions with mesogenic units of LCPs leading to the synergetic effects of two unique systems, which substantially depend on whether nanoclays can be well dispersed in the LCPs. However, it remains a great challenge to intercalate conventional LCP molecules into the clay gallery, not to mention exfoliation, because of the molecular rigidity of LCPs. This book chapter reviews the recent advances in the fundamental understanding of exfoliation mechanism of nanoclays in LCPs in the literature, with an emphasis on the design and synthesis of a series of functional LCPs having pyridyl, azopyridine or terpyridine groups, which can form strong specific interactions with nanoclays in such a way that nanoclays can be well dispersed in the LCPs. Specifically, the hydrogen bonding between pendent pyridyl groups or side-chain azopyridine groups in a LCP and the hydroxyl groups in a surfactant residing at the surface of an organoclay resulted in high degree of dispersion of nanoclays in the polymer matrix. Furthermore, the Coulombic interactions between the negatively charged clay surface and the positively charged ruthenium ion center located in the side-chain of a LCP led to the exfoliation of natural clay in LCPs without the necessity to treat pristine clay with surfactants. The rheological behaviors of these complex fluids were also elaborated on, and the rheological measurements were demonstrated to be a useful technique for detecting the dispersion characteristics of LCP/clay nanocomposites.