Liquid-crystalline thermosetting polymers

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... 

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 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. 

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. 

Mormann, W. (1998). Liquid crystalline thermoset networks by step polymerization of cyanates and epoxides. Wiley Polym. Networks Group Rev. Ser., 1 347. 

Balamumgan R, Kannan P (2009) Synthesis and properties of a liquid crystalline thermoset epoxy resin containing 1,3,4-oxadiazole groups. High Perform Polym 21 251-264... 

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... 

Mormann W, Broche M, Schwarz P (1997) Mesogenic azomethine based diepoxides— monomers for the synthesis of liquid crystal thermoset networks. Macromol Chem Phys 198 3615-3626 Mossety-Leszczak B, Wlodarska M (2011) Liquid crystallinity in polymers—liquid crystalline epoxy resins. In Iwan A, Schab-Balcerzak E (eds) Liquid crystalline organic compounds and polymers as materials of the XXI century from synthesis to applications. Transworld Research Network, Kerala... 

Liquid-crystalline polymers (LCP) can be used in thermoset systems as initially miscible modifiers that phase-separate during cure. 

Block copolymers, polymer blends, polymers at interfaces, liquid crystalline polymers, polymers with novel optical and electronic properties, cross-linked polymers (including elastomers and thermosets), and biocompatible polymers are all areas of active research that are beyond the scope of this chapter. 

The field of thermoset polymers is an area of polymer science that has not yet been widely integrated with liquid crystal polymer research. It is interesting to note that Finkelmann et al. (5) reported on the formation of crosslinked elastomeric liquid crystalline networks in 1981. Although the general concept of a... 

Barclay, C.G. McNamee, S.G. Ober, C.K. Papathomas, K.I. Wang, D.W. Liquid crystalline epoxy thermosets mechanical and magnetic alignment. J. Polym. Sci. Polym. Chem. 1992, 30, 1845-1853. 

Polymeric nanocomposites are a class of relatively new materials with ample potential applications. Products with commercial applications appeared during the last decade [1], and much industrial and academic interest has been created. Reports on the manufacture of nanocomposites include those made with polyamides [2-5], polyolefins [6-9], polystyrene (PS) and PS copolymers [10, 11], ethylene vinyl alcohol [12-15], acrylics [16-18], polyesters [19, 20], polycarbonate [21, 22], liquid crystalline polymers [8, 23-25], fluoropolymers [26-28], thermoset resins [29-31], polyurethanes [32-37], ethylene-propylene oxide [38], vinyl carbazole [39, 40], polydiacethylene [41], and polyimides (Pis) [42], among others. 

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