Liquid Crystalline Epoxy Resins

Abstract

The idea of developing crosslinked liquid crystalline (LC) networks was proposed by Nobel laureate, Pierre-Gilles de Gennes in 1969 (Gennes and Prost 1995). Subsequent efforts in this area resulted in a group of materials known as liquid crystalline thermosets (LCTs), which combines the outstanding properties of both liquid crystals and crosslinked thermosets (Shiota and Ober 1997a; Douglas 2002; Barclay and Ober 1993). A great number of LCTs have been synthesized using a variety of monomers, including epoxy (Carfagna et al. 1997; Giamberini et al. 1995; Mallon and Adams 1993), acrylate (Hikmet and Broer 1991; Hikmet et al. 1992; Litt et al. 1993; Holter et al. 1996), maleimide (Hoyt and Benicewicz 1990a, b), and cyanate ester (Mormann and Zimmermann 1995, 1996; Barclay et al. 1992a; Mormann and Kuckertz 1998). These materials exhibit properties that transcend their amorphous counterparts because of a polydomain structure. Among all the LCTs synthesized, liquid crystalline epoxy resins (LCERs) have received the most attention because of their diverse applications, such as microelectronics packaging materials, optical wave guides, adhesives, color filters, and structural materials. LCERs are generally formed upon curing of low molecular weight, rigid rod epoxy monomers with amines or anhydrides, resulting in the retention of a LC phase by the three dimensional crosslinking networks. Early investigation of LCERs focused on molecular architecture of the epoxy monomers and the related LC phase transition. Subsequent work involves studies on cure kinetics, phase evolution, molecular orientation and thermomechanical characterization of the LCERs. More recently, there have been efforts on fabrication of composites and nanocomposites using LCERs.