Epoxy liquid-crystalline thermoset curing

Liquid crystalline thermoset system 1. Liquid crystalline thermoset prepolymer dihydroxy methylstilbene epoxy (Mn, 3600) 2. Curing agent 4,4 -methylene dianiline ... 

Liquid crystals exhibit a partially ordered state (anisotropic) which falls in-between the completely ordered solid state and completely disordered liquid state. It is sometimes referred to as the fourth state of matter . In recent years, interest in liquid crystalline thermosets (especially liquid crystalline epoxy) has increased tremendously [33-44]. If the liquid crystal epoxy is cured in the mesophase, the liquid crystalline superstructure is fixed permanently in the polymer network, even at higher temperature. Liquid crystal epoxies are prepared using a liquid crystal monomer [33-38] or by chemical modification of epoxy resin [43] which incorporates liquid crystal unit in the epoxy structure. Liquid crystalline epoxy resins with different types of mesogen such as benzaldehyde azine [33], binaphthyl ether [34, 35], phenyl ester [36, 37] and azomethine ethers [38, 39] have been reported. Depending on the chemical nature of the mesogen, the related epoxies display a wide range of thermomechanical properties. The resins can be cured chemically with an acid or amine [40, 41] or by photochemical curing in the presence of a photo-initiator [3]. Broer and co-workers [42] demonstrated the fabrication of uniaxially oriented nematic networks from a diepoxy monomer in the presence of a photo-initiator. 

Keywords Liquid crystalline thermosets, liquid crystalline epoxy resins, curing reactions, mechanical properties, thermal properties... 

Balamumgan R, Kannan P (2010) 1,3,4-Oxadiazole epoxy resin-based liquid crystalline thermosets and their cure kinetics. J Mater Sci 45 1321-1327... 

Castell P, Sena A, Galia M (2004) Liquid-crystalline thermosets from liquid-crystalline epoxy resins containing bisazomethinebiphenylene the central core copolymerization with a nonmesomorphic epoxy resin. J Polym Sci Polym Chem 42 3631-3643 Chtm S, Hsu SH, Wu MC, Su WF (2011) Kinetics studies on the accelerated curing of liquid crystalline epoxy resin/multiwalled carbon nanotube nanocomposites. J Polym Sci Polym Phys 49 301-309... 

Liquid Crystalline Epoxy Resins can be cured in different ordered states depending on the curing agent used. With aromatic amines the thermoset is crosslinked in a nematic structure. No isotropization temperature can be detected. The reaction can be monitored by means of DSC analysis. A double peak exotherm indicates that the crosslinking reaction forms a liquid crystalline resin. Kinetic models can be applied to separate the contributions of the different reactions. 

Giambtaini M, Amendola E, Carfagna C (1997) Lightly crosslinked liquid crystalline epoxy resins the effect of rigid-rod length and applied stress on the state of order of the cured thermoset. Mataomol Chem Phys 198 3185—3196 Grebowicz JS (1996) On the formation of liquid crystalline texture in epoxy resins. Macromol... 

Shiota A, Ober CK (1996) Synthesis and curing of novel LC twin epoxy monomers Jot liquid crystal thermosets. J Polym Sci Polym Chem 34 1291-1303 Shiota A, Ober CK (1997) Analysis of smectic structure formation in liquid crystalline thennosets. 

---