Polymers, liquid crystalline types

Many engineering thermoplastics (e.g., polysulfone, polycarbonate, etc.) have limited utility in applications that require exposure to chemical environments. Environmental stress cracking [13] occurs when a stressed polymer is exposed to solvents. Poly(aryl ether phenylquin-oxalines) [27] and poly(aryl ether benzoxazoles) [60] show poor resistance to environmental stress cracking in the presence of acetone, chloroform, etc. This is expected because these structures are amorphous, and there is no crystallinity or liquid crystalline type structure to give solvent resistance. Thus, these materials may have limited utility in processes or applications that require multiple solvent coatings or exposures, whereas acetylene terminated polyaryl ethers [13] exhibit excellent processability, high adhesive properties, and good resistance to hydraulic fluid. 

Another natural polymer that needs a fresh look into its structure and properties is bitumen [123], also called asphaltines, that are used in highway construction. Although a petroleum by-product, it is a naturally existing polymer. It primarily consists of polynuclear aromatic and cyclocaliphatic ring systems and possesses a lamellar-type structure. It is a potential material that requires more study, and high-performance materials such as liquid crystalline polymer (LCP) could be made from it. 

Finkelmann et al. 256 274,2781 have also investigated the synthesis and the characteristics of siloxane based, crosslinked, liquid crystalline polymers. This new type of materials displays both liquid crystallinity and rubber elasticity. The synthesis of these networks is achieved by the hydrosilation of dimethylsiloxane-(hydrogen, methyl)siloxane copolymers and vinyl terminated mesogenic molecules in the presence of low molecular weight a,co-vinyl terminated dimethylsiloxane crosslinking agents156 ... 

In contrast to the substituted PPO s, It Is theoretically possible to obtain the same substituted PECH s by homopolymerization of the corresponding mesogenic oxirane, or by its copolymerization with epichlorohydrin. We have attempted these polymerizations in order to better interpret the thermal behavior of the more complicated copolymers that we have obtained by polymer analogous reactions. Homopolymerization would be instructive because the incorporation of nonmesogenic units into liquid crystalline homopolymers doesn t as a rule change the type of mesophase obtained (5). 

The SD is a phase separation process usually occurring in systems consisting of more than two components such as in solutions or blends. However, in the present case the system employed is composed of one component of pure PET. In this case, what triggers such an SD type phase separation Doi et al. [24, 25] proposed a dynamic theory for the isotropic-nematic phase transition for liquid crystalline polymers in which they showed that the orientation process... 

Dendritic polymers are most often reported to be amorphous, which can be anticipated from their highly branched architecture. However, some exceptions are presented in the literature. Percec et al. [34,35] reported on liquid crystalline (LC) hyperbranched polymers where the LC-phase was achieved by conformational isomerism. Various repeat units of A2B type have been used where a flex-... 

If one follows the solution viscosity in concentrated sulfuric acid with increasing polymer concentration, then one observes first a rise, afterwards, however, an abrupt decrease (about 5 to 15%, depending on the type of polymers and the experimental conditions). This transition is identical with the transformation of an optical isotropic to an optical anisotropic liquid crystalline solution with nematic behavior. Such solutions in the state of rest are weakly clouded and become opalescent when they are stirred they show birefringence, i.e., they depolarize linear polarized light. The two phases, formed at the critical concentration, can be separated by centrifugation to an isotropic and an anisotropic phase. A high amount of anisotropic phase is desirable for the fiber properties. This can be obtained by variation of the molecular weight, the solvent, the temperature, and the polymer concentration. 

The methods that have been examined for producing polarised EL include the use of liquid crystalline chiral oligomers and polymers. - Promising results have been obtained using conjugated polymers where fluorene makes up the backbone, e.g. (5.6), which was synthesised from the dibromo monomer via Yamamoto coupling. These types of material exhibit LC behaviour at transition temperatures of 100-200 °C, and produce blue polarised EL (425 nm) from thin flhns. °... 

G.3.3.3 Liquid Crystal Displays (LCDs). Liquid crystalline polymers, first intro-dnced in Section 1.3.6.3, are ntilized for a different type of computer and television display, the liquid crystal display (LCD). Most of today s laptop computers and handheld devices ntilize color flat panel displays where the light transmission from the... 

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