Properties and structure of polysulphones

All of the commercial polymers are linear and although most have regular structures they are all, at least for practical intents and purposes, amorphous. The high in-chain aromaticity leads to high values of the Tg, the Amoco product Udel having a Tg of about 190°C whilst the ICI polymer has an even higher value of about 230°C. The Amoco materials have a condary transition at -100°C and that of the ICI polymer is -70°C. Typical values are about 23 000. 

Within these temperature ranges the polymers are, like the polycarbonates, tough. Because of the stiff chain and the resultant high Tg, processing temperatures need to be above 300°C. 

Although the structure is polar much of the polarity is frozen in at normal service temperatures. In such conditions electrical insulation properties are quite good even at high frequencies. As with many aromatic polymers, tracking resistance leaves something to be desired. 

The commercial polymers are generally resistant to aqueous acids and alkalis although they are attacked by concentrated sulphuric acid. As might be expected of a highly polar polymer it is not dissolved by aliphatic hydrocarbons but solvents include dimethyl formamide and dimethyl acetamide. 

The differences between the main types of polysulphone are quite small. The polyethersulphones (Type III in Table 21.3) have markedly better creep resistance at elevated temperatures, e.g. 150°C, significantly higher heat distortion temperatures and marginally superior room temperature mechanical properties than the Type II materials. They also exhibit higher water absorption, dielectric constant and specific gravity. 

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The materials examined were high and low density polyethylene, silvered fluorinated ethylene propylene teflon blanket material, polysulphone matrix resin/graphite fibre reinforced composites, poly(methyl methacrylate) and silicones [326, 450,1326, 2314]. Long term exposed polymeric samples show loss of surface integrity and surface erosion. The radiation combines with atomic oxygen to initiate chain scission and crosslinking, both of which greatly affect the polymers structural properties. 

Three basic types of aromatic polysulphone are produced commercially (Fig. 12.IB, C and D). These products differ only slightly in molecular structure and have similar properties but, nevertheless, it has become common practice to differentiate between them by use of the designations shown. This differentiation is not justified on the basis of chemical structure since all of the products may be described as polysulphones, polyarylsulphones or polyethersulphones. 

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