Engineering with liquid-crystalline polymers

Novel Composites from Blends of Amorphous and Semicrystalline Engineering Thermoplastics with Liquid-Crystalline Polymers... 

Engineering polymers sueh as polyethylene, polypropylene, polystyrene, and polyvinyl ehloride ean be reinforced with liquid crystalline polymers. The stronger, less thermally expansive Uquid... 

Essentially, then, no new, large-volume, highly profitable fibers have been developed since the mid-1950s. Instead, the existing ones have become commodities with all the economic impact thereby implied. No major chemical engineering processes have been added, although the previously described ones have been modified to allow for spinning of liquid crystalline polymers or the formation of gel spun fibers. Research activity has been reduced and centered essentially on modifications of fiber size, shape, and properties, and many variants now are successfully marketed. Production volumes have increased enormously for nylon, polyester, and polyolefin. 

Specific blends, which could offer an interesting combination of properties with proper com-patibilization, include PPS/PSE, PEl/PPS, PA/PSE, PA/PEI, and PC/PPS. Patent activity has been noted for most of these blend combinations as well as other selected blends involving engineering polymers as noted in Table 17.3. A number of recent patent and published papers have discussed blends of engineering polymers with various specialty polymers including high temperature polymers, liquid crystalline polymers (LCP s), conductive polymers, and as matrix materials for molecular composites. These will be discussed in the following sections. 

This article is reprinted with permission from C. Pugh, A. Kiste, Progress in Polymer Science, Vol. 22 Molecular Engineering of Side-Chain Liquid Crystalline Polymers by Living Polymerization, (1997), Elsevier Science Ltd., Oxford, England. 

WITH the easy-processing properties in the liquid crystalline phase, main-chain TLCPs have been widely used as high-strength fiber, fiber reinforcement, in situ reinforcement additive, and injection molded articles, etc, [ 1 -4]. The successful applications are quite dependent on the adhesion at interface of the liquid crystalline polymer and the conventional engineering resin, which is indeed affected by surface tension and/or interfacial tension between the two phases [1-2],... 

In spite of the promising performances of the liquid-crystalline polymers, their use is limited to few practical application. This is due to the high pronounced anisotropy of orientation and properties of LCP processed in the pure state. The apparent contraddiction can be avercome by blending the mesomorphous polymer with ordinary engineering thermoplastics. 

A history of the industrial development of thermotropic polymers would not be complete without a brief review of preceding technology, that is, the discoveries and developments made in lyotropic polymers. Thus, the timeline of milestones in liquid crystalline polymers proceeds from the initial observation of small molecule liquid crystallinity to the discovery of lyotropic and thermotropic high performance polymers and on through to the recent commercialization of thermotropic polyesters with the introduction of the Vectra (Celanese Corporation) and Xydar (Dartco Manufacturing) families of engineering resins. 

Although it is diffucult to homopolymerize MAH it can be easily copolymerized with numerous vinyl monomers. Such copolymers have achieved technical importance as coatings, glues, adhesives, thickeners, resins, and engineering plastics. In recent literature these polymers were also investigated as side-chain liquid-crystalline polymers [965], ArF-or 193nm-photoresists [966-972]. 

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