HBA/PET copolyester

Figure 4.6 Semilogarithmic plot of MFI versus T for HBA/PET copolyester using data from Refs. 42, 85, and 86. (Reprinted from Ref. 38 with kind permission from Elsevier Science S.A., Lausanne, Switzerland.)...

Figure 9.6 DSC thermograms for compression-molded 60/40 HBA/PET copolyester specimens during (a) the heating cycle and (b) the cooling cycle at a rate of 20°C/min, where curve (1) is for the first heating or cooling cycle, curve (2) is for the second heating or coofing cycle, and curve (3) is for the third heating or cooling cycle.

Boyd and his co-workers extended their earlier studies of the PET homopolymeron HBA/PET copolyesters, being primarily interested... 

The HBA/HNA system provides a more suitable system for study, since it is prepared by melt polymerization of the two monomers and is far more stable at elevated temperatures compared to the PHBA/PET. The HBA/HNA copolymers are soluble in pentafluorophenol permitting use of NMR techniques to characterize diad sequences. In Fig. 13b,c the 13CNMR spectrum of the carboxyl carbon region of the HBA/HNA copolyesters of the 73/27 and 48/52 systems is shown [34]. Also shown in Fig. 13a,d are the spectra of 13C enriched HBA and HNA containing copolymers permitting unique identification of the diad sequences. As a result of this technique it was possible to determine the reactivity ratios of the two monomers by analyzing the 50/50 copolymer after polymerization to a molar mass value of 2000 [35]. Examination of the copolymer by 13C NMR showed the same ratio of monomers as in the starting... 

Type-2 copolyesters were synthesized by melt polycondensation of 4-acetoxybenzoic acid (HBA) and 6-acetoxy-2-naphthoic acid (HNA) (Calundann, 1979). While the 4-acetoxybenzoic acid tends to form P(HBA) blocks in certain cases such as in the copolymers of HBA/BP/TA/IA discussed in the previous section, and in HBA/PET copolymers to be discussed in the next section, a random distribution is readily achieved in HBA/HNA copolymers because the two monomers have about the same reactivity toward copolymerization. As shown in Figure 5.3, the 2,6-naphthalene... 

One significant result of the nonuniform distribution of PET and HBA segments in the copolyester chains is the low HDT as shown in Table 5.10. The HDT for the copolymer containing 60 mol-% HBA (PET/60-HBA) was only 64 °C which was about the same as that of PET. Obviously this low value was attributed to the presence of PET-rich phase. Another result is the presence of highly melting particles which may come out unmelted during process leading to structural defects and lower properties. 

HBA/PET 80/20 a liquid crystalline copolyester composed of 80 mole percent p-hydroxy-benzoic acid [HBA] and 20 mole percent PET. 

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... 

Table 5.10. Properties of injection-molded PET/HBA copolyesters with varied HBA mol-%. ...

The melt-processibility, superb mechanical property, and the relatively low cost of production make the liquid crystalline PET/HBA copolyesters very attractive. However because of the tendency toward homopolymerization of the acyl ester of 4-hydroxybenzoic acid to form... 

Skin/core morphologies are common in blends of LCP s and thermoplastic polymers and they play a significant role in defining the properties of both extruded and injection molded samples. Usually, LCP s in the skin have a higher degree of orientation than in the core when the blends are extruded or injection molded (Husman et al. 1980 Hedmark et al. 1989 Lee 1988). Baird et al. (Baird and Mehta 1989 Baird and Sukhadia 1993) observed a skin/core morphology in blends of PA 66 with HBA/HNA and 40 PET/60 PHB and 20 PET/80 HBA copolyesters. More LCP fibers were present in the skin than in the core for both systems. Isayev and Swaninathan (1994) also reported shell-core structure in the fracture surfaces of injection molded blends of HNA/HBA liquid crystalline copolyesters and poly (etherimide). 

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