P-Phenylene group

The successful development of polyfethylene terephthalate) fibres such as Dacron and Terylene stimulated extensive research into other polymers containing p-phenylene groups in the main chain. This led to not only the now well-established polycarbonates (see Chapter 20) but also to a wide range of other materials. These include the aromatic polyamides (already considered in Chapter 18), the polyphenylene ethers, the polyphenylene sulphides, the polysulphones and a range of linear aromatic polyesters. 

The common feature of the p-phenylene group stiffens the polymer backbone so that the polymers have higher TgS than similar polymers which lack the aromatic group. As a consequence the aromatic polymers tend to have high heat deformation temperatures, are rigid at room temperature and frequently require high processing temperatures. 

Table 21.1 Comparison of properties of unfilled grades of thermoplastics containing p-phenylene groups...

Polymers containing p-phenylene groups and other ring structures. 

Linear Polymers with p-Phenylene Groups and Other Ring Structures... 

Conducting polymers with p-phenylene groups in the backbone can be generated by the metathetical reaction shown in Eq. 14.1. Doping of these polymers with acceptors such as h. Bra, or AsFs increases the conductivity to ca. lO " cm. ... 

Now let us consider some reference skeletal group Go. For convenience, we shall choose as the reference skeletal group the p-phenylene group. We define... 

Figure 5. Structure of closo-/ (lr2BkH2)(C6HItPPh2)2(CO)3(PPhs)] with the T -phenyl groups omitted (apart from their ipso C atoms), but with the two ortho-cycloboro-nated P-phenylene groups retained (6),...

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... 

Frequently occurring combinations of p-phenylene groups with other, mostly functional groups, are given - with their Yg increments - in Table 6.3. 

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