Poly , Vectra

Poly(p-phenylene terephthalamide (Kevlar) (b) copolyester of p-hydroxybenzoic acid and biphenylene terephthalate (Xydar) (c) copolyester of p-hydroxybenzoic acid and 2,6-hydroxynaphthoic acid (Vectra). 

It should also be mentioned that a combination of ester and amide linkages was frequently used to prepare thermotropic LC polyesteramides. Frequently, the inexpensive p-aminophenol is incorporated. For example, the Vectra B series is a poly(naph-thoate-aminophenolterephthalate) derived from 6-hydroxy-2-naphthoic acid (HNA), p-aminophenol, and terephthalic acid [14]. It is obvious that only a limited amount of p-aminophenol can be incorporated in order to maintain thermotropic liquid crystalline behavior. The amide linkage enhances the intermolecular interactions via hydrogen bridges and improves the solid state properties of the material. 

Both conventional and liquid-crystal polymers can be processed by melt spinning. The principal requirement is that the polymer must not degrade before becoming molten. Examples are nylon-6, nylon-6,6 and poly(ethylene terephthalate) ( polyester , terylene , or dacron ) for conventional polymers and the Vectra series (see section 12.4.3) among the thermotropic liquid-crystal polymers. 

Suppliers and commercial grades are shown in Table 16.7. Monomers and structural units used in commercial available LCPs have been sununarized in the literature. Vectra types are random copoly(ester)s based on HBA and 2-hydroxy-6-naphthoic acid or copoly(ester amide)s based on 4-aminophenol and TPA. Xydar types are fully aromatic poly(ester)s based on HBA, BP, and TPA. Neat poly(ethylene terephthalate), is not a LCP. However, by the introduction of HBA it becomes a LCP. The ethylene groups act as flexible spacers that reduce the nematic transition temperature. Commercial available types of this kind are X7G and Rodrun types. Tradenames appearing in the references are shown in Table 16.8. 

Gopakumar et al. [10] reported the in situ compatibilization of poly(phenylene sulfide) (PPS)/wholly aromatic thermotropic liquid crystalline polymer (TLCP) Vectra A950 blends by reactive extrusion. The authors prepared the in situ compatibilized PPS/TLCP blends in a twin-screw extruder by reactive blending of PPS and TLCP in the presence of dicarboxyl-terminated poly(phenylene sulfide) (DCTPPS). Block copolymer was formed during reactive blending, by transesterification reaction between carboxyl... 

Izod impact strength is very important characteristic of the engineering plastics.The izod impact strength(notched,J/m) of injection molded test pieces was 92 J/m which was lower than , but higher than those of poly(butylene terephthalate) and glass fiber reinforced . 

Figure 10.9 Polarized photomicrograph of oriented Vectra A950 (poly (hydroxybenzoic acid-co-hydroxy naphthoic acid)). The arrow indicates the shear direction.

The relaxation behavior of nematic, longitudinal PLCs is greatly complicated by their multiphase character. The presence of both crystallites and a coexisting isotropic component has been reported [32]. Vectra A (poly(p-hydroxybenzoic acid-co-2,6-hydroxynaphthoic acid)), currently one of the more widely used and studied commercial polymers, exhibits, despite that fact that it is a statistical copolymer, a sizeable amount (10-60%) of crystallinity, either of the non-periodic layer type [121] or of a truly statistical type according to the model of Biswas and Blackwell [122]. It has become clear that the relaxation of oriented Vectra is to a substantial degree controlled by the thermal behavior of its tiny crystallites. 

Samples of oriented Vectra A950 (poly(hydroxy-benzoic acid (73%) -co-hydroxy-naphthotic acid (27%))), obtained from the surface skin of injection molded specimens, were annealed at different temperatures and the order parameter was assessed by IR spectroscopy and X-ray scattering in a recent study of Wiberg and Gedde [127]. They found... 

Poly(oxybenzoate-co-oxynaphthoate). Figure 2.64 represents an even more complicated polymer system. In this case the macromolecule is the random copolymer poly(oxybenzoate-co-oxynaphthoate), a high-strength material (Vectra ). 

Random copolymerization is an effective way to disturb the regular molecular structure of the polymer chain. The lack of periodicity along the chain inhibits crystallization and, thus, reduces the crystal size and perfection and depresses Tm. If the chosen comonomer is essentially linear, losses of chain mesogenicity can be minimized. This approach has been followed in designing thermotropic copolyesters, such as Vectra A by Celanese (now Ticona), which continues to enjoy commercial success. Vectra A is the copolyester of p-acetoxybenzoic acid (ABA) and 2,6-acetoxynaphthoic acid (ANA) with a mole ratio of 73/27. The melting point of this LCP is around 280°C, which is much lower than the melting points of the either poly (ABA) or poly (ANA) [6]. 

Differential scanning calorimetry was used to study the non-isothermal crystallization behavior of blends of poly(phenylene sulfide) (PPS) with the thermotropic liquid-crystalline copoly(ester amide) Vectra-B950 (VB) [126], The PPS crystallization temperature and the crystallization rate coefficient increased significantly when 2-50% VB was added. The Ozawa equation was shown to be valid for neat PPS as well as for the blends. The values of the Avrami exponents matched well against those determined previously using isothermal analysis, and they are independent of the concentration of VB. 

Many thanks are given to the Tennessee Eastman Corporation for the donation of the p(ET/HBA) copolymers, poly(ethyleneterephthalate-hydroxybenzoic acid), and to the Hoechst-Celanese Corporation for donation of the Vectra polymer RD-501 p(HBA/HNA/TA/HQ), poly(hydroxybenzoic acid-r-hydroxynaphthoic acid-r-terephthalic acid-r-hydroquinone). 

Four thermoplastic polymers polypropylene (PP), polycarbonate (PC), poly(ethylaie terephthalate) (PET), and nylon-6 (NY), and four LCPs Vectra A-900 (VA), Vectra B-950 (VB), SBH 1 1 2 (SBH), and SBHN 1 1 3 5 (SBHN) were used. The source and some of the characteristics of the polymers, as well as the compositions of the LCPs, are shown in Table 1. 

Thermotropic aromatic copolyester fibers are produced by melt spinning since the combination of an aromatic backbone and flexible segments results in an LCP which can be melt processed. Copolyesters, such as p-hydroxybenzoic add (PHBA) modified poly(ethylene terephthalate) (PET), 60/40 PHBA/PET (X7G) polymers, have been produced by the Tennessee Eastman Company [425-427]. Other melt processable nematic thermotropic LCPs (TLCP), based on combinations of 2,6-naphthalene dicarboxylic add (NDA), 2,6-dihydroxynaphthalene (DHN) and 6-hydroxy-2-naphthoic acid (HNA), and referred to as Vectra LCP resins, have been conunercialized (trademark by Hoechst Celanese Corporation [406]). 

Thermotropic aromatic copolyesters i.e. polyObenzoate-naphthoate) and poly(naphthoate-aminophenol terephthalate) Vectra Vectran Hoechst Celanese Hoechst Celanese Fabricated parts, interconnects, connectors Fibers in sporting goods, sailcloth, bow strings. Films for printed circuit boards... 

Type-1 polyester is made up of 1, 4-biphenylene moieties with an approaximate heat-deflection temperature (HDT) of 300°C under a load of 18.6 kg/cm. The representative product is named as "Xydar". Type - 2 polyester is made up of 2, 6-naphthalene moiety with an approximate HDT of 210°C under a load of 18.6 kg/cm. The representative product name of type 2 is "Vectra". While Type-3 polyester is made up p-hydroxybenzoic acid (HBA) modified poly (ethylene terephthalate) i.e combination of moieties of HBA and PET usually with 70/30 proportion. The representative product name of type -3 is "Rodrun". 

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