PET /HBA

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... 

Type - 3 polyesters were synthesized by copolymerization of 4-acetoxybenzoic acid (HBA) and PET. The properties of PET/HBA copolymers with varied composition are tabulated in Table 8.6. It was found that the reaction mixture become turbid for HBA composition higher than 35%, this was due to liquid crystalline nature of copolymer. It can be observed from the table that non-liquid crystalline PET / 30-HBA is stronger than that of compositions with liquid crystalline nature. Low production cost of PET/HBA with good mechanical properties and processability made it very attractive. However, because of the tendency toward homopolymerization of the acyl ester of 4-hydroxybenzoic acid to form poly(4-oxybenzoyl)... 

PSF LCP PSF-LCP (AB) BCP LCP = PET/HBA (hydroxyben-zoic acid) mechanical property and cyrofractured surfaces showed evidence of compatibUization 238... 

The effect of the small amount of copolymerized units seems to improve the mobility of the polymer chains, and its consequent high crystallinity. We also found these same effects of small amounts in the copolymerization of HBA/PET-type LCPs [34],... 

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... 

It has been found by Baird and others [74-77] that the presence of LCP may accelerate and presumably direct the crystallization of conventional polymers (PET, etc.). Porter [76] has shown that, by blending biphasic polymers such as the PET-poly HBA copolymers, miscibility may be achieved between the conventional phase of the biphasic polymer with another conventional polymer that component is miscible with, i.e., X7-G/PBT. The latter phenomena may offer direction in the search for useful compatibilizing agents for LCP/conven-tional polymer systems. 

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... 

Jerman and Baird recently conducted rheological studies on the same copolymers using an Instron capillary rheometer. They also measured die swell and entrance pressures. They observed that the viscosity of the 60 mole % HBA/PET copolymer was two orders of magnitude lower than that of PET when compared at the same temperature of 285 °C, which is similar to the results reported earlier by Jackson and Kuhfuss Die swell of the copolymers was highly temperature dependent. In general,... 

DeMeuse and Jaffe. In another chapter, Brostow et al. discuss the phase behavior of binary and ternary mixtures containing an LCP component. The kinetics of thermally induced phase separation of an HBA/PET LCP blended with poly(ether imide) are described by Zheng and Kyu. 

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. 

The high tendency to homopolymerization of the 4-acetoxybenzoic acid relative to transesterification is responsible for the nonuniform distribution. In order to obtain copolymers with HBA units randomly distributed along the chains, the monomer 4-acetoxybenzoic acid may be added in portions rather than in a singla batch. Unitika (Suenaga and Okada, 1989) advanced the production process so that the HBA and PET moieties are uniformly distributed in the copolymers. With the advanced process the resins ( Rodrun LC-5000 ) showed almost 100% solubility in a hot (150 °C-160 °C) 50/50 mixed solvent of tetrachloroethane and phenol, while that produced by the old (Jackson and Kuhfuss, 1973) method has an insoluble residue of about 30 wt-%. The 13C-NMR spectra also showed that... 

Extrusion temp. °C PET/60 HBA Draw-down ratio (Vo = 1.02 m/min) Modulus GPa Strength MPa PET/80 HBA Draw-down ratio (Vo = 1.06 m/min) Modulus GPa Strength MPa... 

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

Melt spun fibers of copoly(HBA/DHN/TPA) were obtained from Celanese Research Company for three monomer mole ratios 60/20/20, 50/25/25, and 40/30/30. These copolymers had been prepared by melt copolymerization of the three monomers (using the acetoxy derivatives of HBA and DHN) as described by Calundann [9]. Melt spun fibers of HBA-modified PET were supplied by Tennessee Eastman Company, and contained 60 and 80 mole % HBA. These had been synthesized from PET and 4-acetoxy-benzoic acid by transesterification in the melt, as described by Jackson and Kuhfuss [10]. 

In addition, at high temperature, the polymer adopts a third, more open hexagonal structure [5], and the fiber diagram of this form shows all the reflections given by the copolymer. We can conclude that the fibers of HBA-modified PET (at high HBA content) contain ordered regions that have the same basic structure as the high temperature form of homopoly(HBA). 

---