Vectra polymers

Aromatic polyesters were particularly good candidates for this new field of thermotropic main-chain polymers, since the relatively low energy of association of the ester groups led to low inter-chain forces. Further research led to the discovery that incorporation of 2,6-naphthylene or of 4,4 -biphenylyl groups, in addition to p-phenylene groups, as components of aromatic polyesters, introduced a useful new degree of randomness. Particularly useful, and the basis of the commercial products Vectra (polymer) and Vectran (fibre) from Hoechst-Celanese and Kuraray, are the copolymers formed by polymerisation of mixtures of p-acetoxybenzoic acid and 6-acetoxy-2-naphthoic acid. Within a range of... 

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). 

Further research led to the finding that incorporation of 2,6-naphthyleneorof4,4 -biphenylylgroups,inadditiontop-phenylene groups, as components of aromatic polyesters, introduced a new degree of randomness. The commercial products Vectra (polymer) and... 

Chemical Resistance of LGPs. Ceitain liquid crystal polymers (eg, Vectra) have extremely high chemical resistance to a variety of aggressive chemicals and solvents. Table 18 shows the chemical stabiUty of Vectra test-bars to various agents (244). 

These LCT materials have very high tensile and flexural strength, and excellent mechanical and chemical resistance properties. Some commercial LCT are Vectra (Hoechst-Celanese) and Xydar (Amoco). Du Pont, ICI, GE, and Dow Chemical are also suppHers. Their appHcation in electronic embedding is stiU. in its infancy because of the high temperature processing requirement. Nevertheless, this class of thermoplastic polymers will play an important role in electronic embedding. 

Yet another recent development has been the alloying of polycarbonates with liquid crystal polymers such as Vectra (see Section 25.8.1). These alloys are notable for their very good flow properties and higher strength and rigidity than conventional bisphenol A polycarbonates. 

Polymers based on these structures became available as Victrex SRP (ICI), Vectra (Hoechst) and Xydar (Amoco). It is reported that the Vectra materials are based on p-hydroxybenzoic acid and hydroxynaphthoic acid monomers, whilst Xydar is based on terephthalic acid, p-hydroxybenzoic acid and pp -dihydrox-ybiphenyl. Whilst properties vary between grades, in general they possess the following outstanding properties ... 

The polymers studied and the experimental procedure were described in the last section. The samples were made of the same PC-TLCP composite and the pure TLCP Vectra A950, respectively. To study the influence of sample forms and geometries on mechanical constants, plate samples (80 x 80 x 2 mm-) were also injection molded with a film gate. Tensile samples were then cut from the plate in the longitudinal (//) and transverse... 

Aromatic polyesters that do not contain any flexible structural units are often nonmeltable or extremely high melting polymers that cannot be processed. Copolymerization is a way to obtain processable wholly aromatic polyesters The Tm versus copolyester composition curve is a U-shaped curve exhibiting a minimum that is generally well below the Tm of corresponding homopolymers. Liquid crystalline aromatic polyesters, for instance, are usually copolymers.72 An example is Ticona s Vectra, a random copolyester containing 4-oxybenzoyl and 6-oxy-2-naphthoyl units in ca. 70 30 mol ratio. This copolymer melts at ca. 

Injection molded thermoplastic bipolar plates made of Vectra LCP (liquid crystal polymer) and Fortron PPS fabricated by Ticona Engineering Polymers, (http //www.ticona.com/redesign/ index/markets/innovation/fuel cell.htm Ticona Engineering Polymers. 2008 accessed March 2008.)... 

Precision parts, electric connectors Vectra Zylon Twaron Liquid crystalline polymers DuPont, USA Toyobo, Japan Akzo, Netherlands... 

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 ... 

An example of such behaviour is shown in Fig. 15.46 for Vectra A900, which is a copolymer consisting of 73 mol% HBA (1,4-hydroxy benzoic acid) and 27 mol% HNA (2,6-hydroxy naphthoic acid) (Langelaan and Gotsis, 1996). In this figure, Regions I and III are undoubtedly present, but Region II is very narrow, if indeed it exists for this polymer,... 

Another peculiar property of LCPs is shown in Fig. 15.47, where the transient behaviour of the shear stress after start up of steady shear flow is shown for Vectra A900 at 290 °C at two shear rates. We will come back to this behaviour in Chap. 16 for lyotropic systems where this behaviour is quite common and in contradistinction to the transient behaviour of conventional polymers, as presented in Fig. 15.9. This damped oscillatory behaviour is also found for simple rheological models as the Jeffreys model (Te Nijenhuis 2005) and according to Burghardt and Fuller, it is explicable by the classic Leslie-Ericksen theory for the flow of liquid crystals, which tumble, rather than align, in shear flow. Moreover, it is extra complicated due to the interaction between the tumbling of the molecules and the evolving defect density (polynomial structure) of the LCP, which become finer, at start up, or coarser, after cessation of flow. 

Figure 11.2 Chemical structures of some well-studied LCPs. The top four structures are usually used as lyotropic polymers, and the bottom two are thermotropes. Estimates of the persistence lengths (Xp) and effective diameters (d) of these molecules are (Xp, d) = (12,1.04) nm for HPC, (90, 1.5) nm for PBLG. 129.0.6) nm for PPTA. (20.0.6) nm for PBZT. (12.0.6) nm for Vectra A. and (6.0.5) nm for OQO(phenylsulfonyl)10. These values, listed in Baek et al. (1994), Brelsford and Krigbaum (1991), and Farmer et al. (1993), are both solvent- and temperature-dependent, and thus should be used with caution. (From Donald and Windle 1992, with permission from Cambridge University Press.)...

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