Vectra, aromatic polyester

PEN). This article also covers the increasingly commercially important high performance Hquid crystalline all-aromatic polyesters, eg, Vectra [70679-92-4], [82538-13-4] andXydar [31072-56-7]. 

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. 

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... 

A second range of LCPs were introduced by Hoechst Celanese under the trade name Vectra. Vectra is an aromatic polyester condensate derived from 2,6-dihydroxynaphthalene. Its main advantages are its fast cycling and ease of processing, the melt temperature for both injection and extrusion grades being typically about 285°C. 

The most common form is the nematic, a bimdle of parallel, long, rodlike molecules. Additional cooling to the primary transition temperature, T leads to solidification into a solid crystalline phase (small crystallites). In the region between Tj and T , a liquid of very low viscosity prevails, in contrast to the high melt viscosity. The aromatic polyesters have high heat distortion temperatures (HDT). Vectra, composed of para-hydroxy-benzoic acid (PHBA) and para-hydroxy-naphtoic acid (PHNA), has an HDT of 180 C-240 C. Xy-dar, composed of PHBA, tera-phthalic acid and biphenol, has an even higher HDT of 260 C-350 C. 

Results are presented of an investigation of the use of linear-temp, controlled pyrolysis with subsequent analysis of the pyrolysates (volatiles and residues) by 18V electron-impact mass spectrometry and FTIR spectrometry to provide information on the thermal degradation mechanisms of aromatic polyesters, in particular polyhydroxybenzoic acid and oxybenzoate-oxynaphthoate copolymer (Vectra). 13 refs. 

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... 

The commercial polymers used in the study are characterized in Table 1. The polypropylenes PP1-PP5 were homopolymers exhibiting different melt viscosities (see Fig. 1) supplied by Neste Chemicals. Liquid-crystalline polymer 1 (LCPl) (Vectra A950 by Hoechst Celanese) is a totally aromatic polyester-type thermotropic main-chain LCP copolymer based on p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA). Liquid-crystalline polymer 2 (LCP2) (Rodrun LC-3000 by Unitika Ltd) is a more flexible thermotropic main-chain LCP copolyester consisting of 60%... 

In late 1985 Hoechst Celanese commercialized a family of LCPs under the trademark Vectra. Based on hydroxybenzoic acid and naphthalene derivatives, like Xydar , Vectra LCP exhibits a nematic structure. Although Xydar and Vectra are classified genetically as wholly aromatic polyesters with similar basic structures, it is important to note that many of the characteristics of the LCP polymer systems vary significantly with their chemical compositions. Other companies that are commercially active include Sumitomo Chemical, Mitsubishi Chemical, Ueto and Unitika. 

Vectra based on aromatic polyesters (Calundann 1980) respectively. Molecular structure of aromatic polyester based liquid crystalline polymer, Vectra is represented in Fig. 13.1. 

Liquid crystal polymer Aromatic polyester LCP Xydar, Zenite, Vectra... 

Liquid crystalline aromatic polyamides were the first chemical class to be commercialised. The best known example is Kevlar fibre which is spun from liquid crystalline solution to obtain the benefit of the high orientation present in the nematic phase. Subsequently, melt-processable main-chain polyesters were developed and brought to the market (Amoco with Xydar, Hoechst-Celanese with Vectra). 

Most LC polymers in the market are linear, highly aromatic thermotropic polyesters. They combine chemical stability with chain rigidity and retain dimensional stability (remain as glasses) up to 200°C or 300°C and are also very chemically stable (resistant to oxidation). These types of PLCs, such as the commercial Vectra and Xydar, are usually processed in the melt state with conventional fabrication techniques such as extrusion and molding (see Chapter 14). A major advantage of such polymers is that they can be melt processed and form extranely precise molded structures that do not shrink on cooling. They have been used in molded parts for microelectronics and in mounting brackets for optical communications. 

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