Liquid crystalline thermoset

Functionalized LCP may be used as comonomers in thermoset formulations. Upon cure, liquid-crystalline thermosets (LCT) are obtained, with a morphology characterized by the presence of liquid-crystalline dispersed domains. 

HOYTETAL. Rigid Rod Molecules as Liquid-Crystalline Thermosets... 

Mormann, W. Liquid crystalline thermosets. Trends Polym. Sci. 1995, i, 255-261. 

As discussed earlier, while the scale of the fillers is substantially different, nanocomposite materials concepts and technology are very similar to those of conventional composite materials. This is clearly demonstrated in the case of new thermosets for nonlinear optical (NLO) applications, " " where nanocomposite of liquid crystalline thermosets, IPNs, and simple filled thermosets are evaluated. Tripathy et al. discussed four different ways to prepare nonlinear optical polymers. (1) The polymer matrix is doped with NLO moieties in a guest/host system (2) In side-chain polymer systems, NLO polymers with active moieties are covalently bonded as pendant groups (3) In the main chain polymer, the chromo-phores are incorporated as parts of the main polymer backbone to enhance the temporal stability of the NLO properties and (4) Stability of the optical noninearity in sol-gel-based thermosets is related to... 

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

Liquid crystalline thermoset epoxy prepolymer Not applicable Nematic to isotropic 176... 

Qin, H. Mather, P.T. Optical rheology of new liquid crystalline thermosets (lets) influence of shear on disclination texture. Mat. Res. Soc. Symp. Proc. 2002, 709, CC8.4.1-7. 

Figure 10.2 Non-equilibrium phase diagram describing the behavior of liquid crystalline thermosets (adapted from Reference [29]).

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. 

Liquid crystalline thermosets (LCT) with a rigid rod-like mesogenic group capped firom both ends by reactive fimctional groups can be used as matrices for production of advanced composites, coatings or adhesives (1, 2). hi this case ordering of the chains of the final network polymer is the only way to improve its physical and mechanical properties. 

In recent years liquid crystalline thermosetting polymers have been the object of extensive research and patent activity (1-8). The interest in these materials lies in their challenging theoretical implications and in the noticeable potential applications. Highly crosslinked liquid crystalline thermosets turned out to be promising candidates for thin film applications in electronic packaging and as matrix materials for advanced composites due to their superior mechanical properties and heat resistance (4-6) on the other hand, lightly crosslinked networks can be easily oriented by mechanical stress and this results in a change of their optical properties (9). Applications as... 

Cross-linked polymeric liquid crystals offer a wide variety of unique and in-tere.sting properties. Because of the interaction between the mesogens and the network backbone in liquid crystal elastomers, mechanical deformations can align the director, and these materials are piezoelectric. Industrial applications of liquid crystalline thermosets are driven by additional properties such as toughness, a tunable coefficient of thermal expansion, ferroelectricity, and nonlinear optical properties. Reviews on this topic are given by Barclay and Ober [4] and by Warner and Terentjev [5]. 

Rigid-rod polymers are often liquid crystalline polymers classified as lyotropic, such as the aramid Kevlar (DuPont), or thermotropic liquid crystalline polymers, such as Vectran (Celanese) (see Polyamides, Aromatic Liquid Crystalline Polymers, Main-Chain Liquid Crystalline Thermosets). 

LIQUID CRYSTALLINE THERMOSETS. See Volume 3. LITERATURE OF POLYMERS. See Information Retrieval. LITHOGRAPHIC RESISTS. See Volume 6. 

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