Thermotropic aromatic copolyesters with

THERMOTROPIC AROMATIC COPOLYESTERS WITH CYCLOALIPHATIC UNITS 81 Characterization... 

Main Chain LC Polymers. New thermotropic copolyesters with either random or ordered mesogenic sequences have been reported with a wide range of mesophase behaviors. Recent developments in this field have included the use of naphthalene, stilbene and related structures in addition to the traditional phenylene groups to produce the required rigid main chain, and these are described in chapters by Jin, Jackson and Morris, and Skovby et al. Efforts have been undertaken to control transition temperatures and solubility through the use of either substituents or changes in the monomer sequence distribution. Successful application of these efforts have led to the commercialization of several thermotropic aromatic copolyesters (23.24). 

In the late 1980s, new fully aromatic polyester fibers were iatroduced for use ia composites and stmctural materials (18,19). In general, these materials are thermotropic Hquid crystal polymers that are melt-processible to give fibers with tensile properties and temperature resistance considerably higher than conventional polyester textile fibers. Vectran (Hoechst-Celanese and Kuraray) is a thermotropic Hquid crystal aromatic copolyester fiber composed of -hydroxyben2oic acid [99-96-7] and 6-hydroxy-2-naphthoic acid. Other fully aromatic polyester fiber composites have been iatroduced under various tradenames (19). 

Although studies concerning main chain liquid crystalline polymers were originated by Onsager (la) and Ishihara (lb) in the late 1940 s, extensive work in this field did not really begin until the early 1970 s. Jackson and Kuhfuss (2) reported the first thermotropic polyester by modifying polyethylene terephthalate with various amounts of p-hydroxybenzoic acid (HBA). They found that the copolyester with HBA content of at least 35 mole % have opaque melts. Subsequent studies in the area of aromatic polyesters by various authors resulted in a large number of patents and publication. (3.) These polymers were all derived from unsubstituted and... 

In this article, in connection with our previous endeavor, we would like to report synthesis and properties of new copolyesters having ordered comonomer sequences consisting of mesogenic units and polymethylene spacers, i.e., thermotropic aromatic-aliphatic copolyesters having sequentially ordered structures ... 

In yet another classification, they can be broadly classified into three classes namely Aromatic polyamides or Aramides like Kevler, Twaron, etc., Aromatic heterocyclic and Aromatic copolyesters (Pegoretti and Traina 2009). Aromatic heterocyclic LCPs are kind of lyotropic liquid crystal containing wholly aromatic molecular framework with fused heterocyclic ring along the main chain. Aromatic copolyesters exhibit thermotropic behavior and are characterized by high... 

Aromatic copolyesters which are sufficiently rigid to form a nematic mesophase upon heating (e.g. 4 and 5) also give HSHM fibres, but major industrial exploitation awaits improved competitiveness with established fibres. Exceptionally high strength values have been reported for fibres made from thermotropic nematogenic poly(azomethine)s (e,g, 6) but these materials seem to suffer from a poor hydrolytic stability. ... 

Among the many different classes of thermotropic polymers, only a limited number of polyesters based on aromatic ester type mesogenic units have been studied by rheological methods, beginning with the publication by Jackson and Kuhfuss of their work on the p-oxybenzoate modified polyethylene terephthalate, PET, copolymers. They prepared a series of copolyesters of p-hydroxybenzoic acid, HBA, and PET and measured the apparent melt viscosity of the copolymers as a function of their composition by use of a capillary rheometer. On inclusion of low levels of HBA into PET, the melt viscosity increased because of partial replacement of the more... 

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