Copolyester LCPs

In this research, commercially available PHB/PET copolyester LCP, PEN and PET were mechanically blended to form the LC phase of the blends. The critical composition of PHB in the PEN and PET forming an LC ternary blend was investigated, and the miscibility and thermal behavior were studied using thermal analysis. The PHB content in the ternary blend was controlled by the amount of PHB/PET copolyester, as a high-molecular-weight PHB homopolyester does... 

The first thermotropic LCPs were reported in the mid-1970 s by Roviello and Sirigu (15) and Jackson and Kuhfuss (16). Since then, a large number of LCPs have been reported an excellent, though now dated, review of main-chain (i.e., the mesogen is in the polymer backbone) thermotropic LCPs was published by Ober et al. (17). In the 1980 s, several thermotropic aromatic copolyester LCPs were commercialized. 

Various liquid crystalline copolyesters (LCP s) were used depending on the particular thermoplastic matrix which was selected. In this work three high performance matrices were used polyether-... 

A forced mixture of PET with a liquid-crystalline copolyester (LCP) of ethylene terephthalate and... 

An equally important observation for the above copolyester LCPs is that the ordered arrangement of polymeric mesophases in the melt is retained upon cooling, which is manifested in greatly improved mechanical properties (see Figure 5.5b). The liquid crystalline behavior is therefore advantageous from the standpoint of both processing and properties. Thermotropic liquid crystal copolyesters of structures similar to (I) are now available commercially. 

Materials. As a matrix polymer, polyetherimide (PEI) Ultem KXX) of General Electric and polyphenylenesulfide (PPS) Ryton GR-02 of Phillips Petroleum were used. The reinforcing component was thermotropic liquid crystalline copolyester (LCP) Vectra B950 of Hoechst-Celanese. The chemical structures of PEI and LCP are presented in Figure 1. 

Some liquid ciystalline copolyesters (LCP) derived from dihydroxydiphenylacetate, acetobenzoic acid, isophthtalic and terephthtalic acids with various proportions of the latter two comonomers were investigated. The LCP thermal stability and the degradation behavior under processing temperatures were studied. The kinetics of loss in weight, the oxygen uptake as well as the oxidation product evolution were studied. On the basis of the data obtained a mechanism for the LCP high-temperamre thermal oxidation, relative to such for other polyheteroaiylenes was proposed. 

Liquid-crystal aromatic copolyesters (LCP) were studied. They were derived from dioxydiphenyl diacetate, acetoxybenzoic, iso- and terephthalic acids (IPA and TPA, respectively) 100/0, 75/25, 50/50, 25/75, 0/100. 

This polyester class comprises amorphous high-Tg copolyesters, known as amorphous polyarylates, and semicrystalline polyesters that often exhibit anisotropic hquid crystalline (LC) melts. Liquid crystalline polyesters are often termed as polyester LCPs. 

Polarized optical photographs of the blends are shown in Figure 20.3. The spherical LCP domains are irregularly dispersed in the PEN and PET phases below 20 mol % PHB content (Figure 20.3(a)). The results observed from 30 mol % PHB reveal a continuous co-existence of the PHB phase and the PEN/PET matrix in the blended polymers (Figure 20.3(b)). However, the blend with 40 mol % PHB shows a nematic LC phase. This result is similar to that found for the copolyesters synthesized by Chen and Zachmann [26], who found... 

Most of the work to date concerns the area with the greatest potential for commercial exploitation, the blending of LCPs with conventional polymers. While a few studies of solution blending with Kevlar do exist [57-61], most of the work has centered on melt blending thermotropic copolyesters (Vectra, Xydar) with engineering thermoplastics (PET, PC, PEI, etc.). For convenience, this work may be separated into three blend regions based on LCP content, namely ... 

Mechanical studies have also been performed on another non-LCP system -copolyesters of PET and PEN, where both copolymer units having flexible chain segments and lack a liquid-crystalline behaviour (Santa Cruz et al, 1992). The whole range of PET/PEN copolymers can therefore be prepared in the amorphous state. 

The melt viscosity of LCPs is sensitive to thermal and mechanical histories. Quite often, instrumental influences are important in the value of viscosity measured. For example, the viscosity of HBA/HNA copolyesters are dependent on the die diameter in capillary flow (59). LCP melts or solutions are very efficiently oriented in extensional flows, and as a result, the influence of the extensional stresses at the entrance to a capillary influence the shear flow in the capillary to a much greater extent than is usually found with non-LC polymers. 

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