Combined liquid crystal polymers

Figure 5.3. A general template for combined liquid crystal polymers.

Liquid crystal polymers (LCP) are a recent arrival on the plastics materials scene. They have outstanding dimensional stability, high strength, stiffness, toughness and chemical resistance all combined with ease of processing. LCPs are based on thermoplastic aromatic polyesters and they have a highly ordered structure even in the molten state. When these materials are subjected to stress the molecular chains slide over one another but the ordered structure is retained. It is the retention of the highly crystalline structure which imparts the exceptional properties to LCPs. 

Electro-optic materials can be made using liquid crystal polymer combinations. In these applications, termed polymer-stabilized liquid crystals [83,86], the hquid crystal is not removed after polymerization of the monomer and the resulting polymer network stabilizes the liquid crystal orientation. 

To produce novel LC phase behavior and properties, a variety of polymer/LC composites have been developed. These include systems which employ liquid crystal polymers (5), phase separation of LC droplets in polymer dispersed liquid crystals (PDLCs) (4), incorporating both nematic (5,6) and ferroelectric liquid crystals (6-10). Polymer/LC gels have also been studied which are formed by the polymerization of small amounts of monomer solutes in a liquid crystalline solvent (11). The polymer/LC gel systems are of particular interest, rendering bistable chiral nematic devices (12) and polymer stabilized ferroelectric liquid crystals (PSFLCs) (1,13), which combine fast electro-optic response (14) with the increased mechanical stabilization imparted by the polymer (75). 

RPs that combine two different materials (plastic matrix and reinforcement) are a separate major and important segment in the plastic industry. They are also called plastic composites and composites. There are also self-reinforcing plastics such as liquid crystal polymers (Chapter 1) and others.301 It is a fact that RPs have not come near to realizing their great potential in a multitude of applications usually due to cost limitations that particularly involves the use of expensive fiber reinforcements (carbon, graphite, silica, etc.).1 Information on thermoplastic and thermoset plastic RPs are reviewed in Chapter 15. 

Xvdar Solvay Advanced. TM for liquid crystal polymer glass/mineral combination product. 

Similarly, at T > coalescence of semicrystalline dispersed domains combined with stress-induced crystallization leads to formation of long fibers. This effect has been explored for the performance improvement of blends comprising liquid crystal polymers, LCP [La Mantia, 1993]. 

Thermotropic liquid crystal polymers (LCI ) are of considerable current interest, because of their theoretical and technological aspects [1-3]. Evidently, a new class of polymers has been developed, combining anisotropic physical properties of the liquid crystalline state with diaracteristic polymer features. This unique combination promises new and interesting material properties with potential ai lications, for example in the field of high modulus fibers [4], storage technology, or non-linear optics [5]. 

Copolymerization reactions can use many other combinations, but one interesting reaction involves the modification of poly(ethylene terephthalate) by reacting the preformed polymer with -acetoxybenzoic acid. This has the effect of introducing a mesogenic unit to the structure at the points where the two units combine, producing a thermotropic liquid crystal polymer with a flexible spacer. 

Liquid crystal polymers (LCPs) were introduced over the last three decades. In the liquid state, either as a solution (lyotropic) or a melt (thermotropic), they lie between the boundaries of solid crystals and isotropic liquids. This polymeric state is also referred to as a mesomorphic structure, or a mesophase, a combined term adopted from the Greek language (mesos = intermediate morphe = form). This state does not meet all the criteria of a true solid or a true liquid, but it has characteristics similar to both a solid and a liquid. For instance, the anisotropic optical properties of LC polymeric fluids are like those of crystalline solids, but their molecules are free to move as in liquids. 

High barrier plastic containers are currently made from multiple layers of a relatively thick economical polymer such as polyethylene terephthalate (PET) or polyethylene, combined with a thin layer of a barrier polymer such as ethylene vinyl alcohol (EVOH). In a similar way, multilayer barrier containers can be made with a thin layer of liquid crystal polymer (LCP), as an excellent barrier to oxygen, water vapor, and other gases. 

Liquid crystals, polymers and liquid crystalline polymers are soft condensed matter systems of major technological and scientific interest. In liquid crystals the orientational order of the constituent molecules is associated with a reduced or absent translational order. This gives liquid crystalline systems a combination of fluidity (liquid-like properties) and anisotropic electro optic properties, similar to those of a crystal. Orientational order can be controlled easily by the application of external fields, leading to the spatial switching of bulk properties in response to external stimuli. This provides the basis for a wide range of technological applications, including displays, optical switches, adaptive optics for telescopes and many other electro-optical devices. 

A great maity SCLCPs have been synthesised because of the combination of the vast number of mesogenic core nnits available from stmctuie-property relationship evaluation of low molar mass liquid crystals and the maity different backbone (BB) types possible e.g., siloxanes, acrylates, methacrylates, ethylenes, epoxides). Additionally, as shown in Figure 5.4, homopolymers (5.4a), SC copolymers (5.4b), BB copolymers (5.4c), and SC/BB copolymers (5.4d) considerably extend the scope of known and potential liquid crystal polymers. 

Some types of liquid crystal displays combine liquid crystal material and polymer material in a single device. The first of these involves micrometre sized droplets of nematic hqnid crystal in a solid, isotropic polymer matrix. There are two requirements on the polymer for this device to work. First, the index of refraction of the polymer, n must... 

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