Copolyesters thermotropic type

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... 

Figure 5.3. Representative structures of three types of thermotropic copolyesters.

Hierarchical systems were introduced in section 9.5. It is possible to treat these systems quantitatively [58,64,65]. George and Porter [64], for example, have mixed a monomolecular liquid crystal (MLC), i.e. a low molar mass molecule, with a thermotropic copolyester of the Kuhfuss and Jackson type [10]. They found that it was possible to describe the melting behavior of their system with reasonable accuracy by equation (9.9), although that has been derived by Flory [66] for... 

This scheme of phase and relaxational transitions in this representative thermotropic LC copolyester provides an adequate description of the experimental evidence obtained. The validity of this scheme and the universal character of the transitions described for other copolyester where all monomeric units have the same lengths, can be shown for the whole family of thermotropic LC copolyesters by comparing the temperature behavior of CPE-1 with other polymers of this type. 

A type of aromatic-aliphatic liquid crystalline copolyesters has been synthesized from 2-chlorohydroquinone, 1,4-CHDM and terephthaloyl chloride (Figure 6.14). The CHDM units act in these copolyesters as flexible spacers providing the necessary chain mobility to be thermotropic. The structure and thermal behavior of these copolyesters were characterized by hot-stage polarized light microscopy, SEM, FTIR, NMR, DSC and TGA (57). It has been reported that they are insoluble in common solvents and may form mesophases at temperatures near the melting temperature of PET (58). 

The commercial polymers used in the study are characterized in Table 1. The polypropylenes PP1-PP5 were homopolymers exhibiting different melt viscosities (see Fig. 1) supplied by Neste Chemicals. Liquid-crystalline polymer 1 (LCPl) (Vectra A950 by Hoechst Celanese) is a totally aromatic polyester-type thermotropic main-chain LCP copolymer based on p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA). Liquid-crystalline polymer 2 (LCP2) (Rodrun LC-3000 by Unitika Ltd) is a more flexible thermotropic main-chain LCP copolyester consisting of 60%... 

Liquid crystal copolyesters have been synthesized [50-56] on the basis of -acetoxybenzoic acid, acetoxybisphenol, terephthalic acid and m-acetoxy-benzoic acid by means of polycondensation in melt. All the copolyesters are thermotropic and form nematic phase. The types of LQPs of -oxybenzoic acid are given in Table 3.2. 

A great many aromatic polyesters and copolyesters which show thermotropic behaviour have now been reported, particularly in the patent literature. The copolyesters may contain either combinations of different types of mesogenic units or combinations of mesogenic and non-mesogenic (non-linear) units. The structures of many of the different types of monomers used to form liquid crystal aromatic polyesters and copolyesters are shown in Table 3. ... 

The thermotropic polymers used in these studies are all random copolyesters. As has previously been documented for other types of polymers, the presence of aromatic rings and/or conjugated bonds, and the absence of CH2—CH2 and ether linkages yield materials most resistant to beam damage (by processes such as chain scission and cross-linking). The family of thermotropic copolyesters most extensively studied here comprises the following randomly sequenced segments ... 

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