Polysulphonates aromatic

As the author pointed out in the first edition of this book, the likelihood of discovering new important general purpose materials was remote but special purpose materials could be expected to continue to be introduced. To date this prediction has proved correct and the 1960s saw the introduction of the polysulphones, the PPO-type materials, aromatic polyesters and polyamides, the ionomers and so on. In the 1970s the new plastics were even more specialised in their uses. On the other hand in the related fields of rubbers and fibres important new materials appeared, such as the aramid fibres and the various thermoplastic rubbers. Indeed the division between rubbers and plastics became more difficult to draw, with rubbery materials being handled on standard thermoplastics-processing equipment. 

To enhance the resistance to heat softening his-phenol A is substituted by a stiffer molecule. Conventional bis-phenol A polycarbonates have lower heat distortion temperatures (deflection temperatures under load) than some of the somewhat newer aromatic thermoplastics described in the next chapter, such as the polysulphones. In 1979 a polycarbonate in which the bis-phenol A was replaced by tetramethylbis-phenol A was test marketed. This material had a Vicat softening point of 196 C, excellent resistance to hydrolysis, excellent resistance to tracking and a low density of about l.lg/cm-. Such improvements were obtained at the expense of impact strength and resistance to stress cracking. 

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. 

Although it is somewhat of an oversimplification, the polysulphones are best considered as a group of materials similar to the aromatic polycarbonates but which are able to withstand more rigorous conditions of use. Because of their higher price they are only considered when polycarbonates or other cheaper polymers are unsuitable. 

The simplest aromatic polysulphone, poly-(p-phenylene sulphone) (formula I of Table 21.3) does not show thermoplastic behaviour, melting with decomposition above 500°C. Hence in order to obtain a material capable of being processed on conventional equipment the polymer chain is made more flexible by incorporating ether links into the backbone. 

A consequence of the reaction is that it is possible to produce a range of polymers by reacting bisphenates with appropriately activated aromatic dihalides. In the case when the dihalide is activated by the presence of a sulphone —SO,— group the polymers may be referred to as polysulphones. The Amoco materials are prepared in this way. 

The polysulphones tend to be used in applications when requirements cannot quite be met by the much cheaper polycarbonates and possibly aromatic polyethers. In many of the fields of use they have replaced or are replacing ceramics, metals and thermosetting plastics rather than other thermoplastics. 

As with the polysulphones, the deactivated aromatic nature of the polymer leads to a high degree of oxidative stability, with an indicated UL Temperature Index in excess of 250°C for PEEKK. The only other melt-processable polymers in the same league are poly(phenylene sulphides) and certain liquid crystal polyesters (see Chapter 25). 

It has already been shown (e.g. Chapters 20 and 21) that the insertion of a p-phenylene into the main chain of a linear polymer increased the chain stiffness and raised the heat distortion temperature. In many instances it also improved the resistance to thermal degradation. One of the first polymers to exploit this concept commercially was poly(ethylene terephthalate) but it was developed more with the polycarbonates, polysulphone, poly(phenylene sulphides) and aromatic polyketones. 

The first secondary transition below Tg, the so called fj-relaxation, is practically important. This became evident after Struik s (1978) finding that polymers are brittle below Tp and establish creep and ductile fracture between Tp and Tg. The p-relaxation is characteristic for each individual polymer, since it is connected with the start of free movements of special short sections of the polymer chain. In view of more recent data of Tp Boyer s relation, Eq. (6.29), is very approximate and fails completely for amorphous polymers with high Tg s (e.g. aromatic polycarbonates and polysulphones). Some rules of thumb may be given for a closer approximation. 

Some polymers show discoloration as well as reduction of the mechanical properties (e.g. aromatic polyesters, aromatic polyamides, polycarbonate, polyurethanes, poly (phenylene oxide, polysulphone), others show only a deterioration of the mechanical properties (polypropylene, cotton) or mainly yellowing (wool, poly(vinyl chloride)). This degradation may be less pronounced when an ultraviolet absorber is incorporated into the polymer. The role of the UV-absorbers (usually o-hydroxybenzophenones or o-hydroxyphenylbenzotriazoles) is to absorb the radiation in the 300-400 nm region and dissipate the energy in a manner harmless to the material to be protected. UV-protection of polymers can be well achieved by the use of additives (e.g. nickel chelates) that, by a transfer of excitation energy, are capable of quenching electronically excited states of impurities (e.g. carbonyl groups) present in the polymer (e.g. polypropylene). 

Polymers with an aromatic group in the main chain, however, such as polysulphones, polycarbonates and poly(phenylene oxides) proved to be intermediate in their smoke generation, possibly due to their considerable charring tendency. Also the unexpected drop in smoke density observed when poly(vinyl chloride) is partially chlorinated may be attributed to the high char yield. Einhom et al. (1968) concluded that smoke development decreases with increasing amount of chlorine- and phosphorus-containing additives, and with increasing cross-link density. 

A detailed study of the same aromatic polysulphone (PS) has been reported by Davis [296]. The gas composition does not change with the time of heating. Volatile liquid and solid products have been separated and identified by gas chromatography and mass spectrometry the results are given in Table 24. After three hours heating, a gel is formed. The amount of gel is not affected by the presence of the volatile pyrolysis products. If the theory of Charlesby-Pinner is applied to the gel formation data, a straight line with a positive intercept of 0.35 is obtained. This means that chain scission also occurs. The rate of S02 evolution is in agreement with the results of Levy and Ambrose [297] on the pyrolysis... 

The radiolysis of polycarbonate presents similarities to that of aromatic polysulphones [383, 384]. It undergoes main-chain scission with a G value of 0.09 under vacuum and 0.14 in an oxygen atmosphere. The gases evolved are carbon monoxide, carbon dioxide, hydrogen and methane. The G values are, respectively, 3.6 x 10 1,1.9 x 10 1, 1.3 x 10 2 and 1.3 x 10-3. Since G(CO + C02) is larger than the G value for chain scission, cage recombination of the macroradicals is supposed to occur. 

Aromatic polysulphones retain their mechanical properties after absorption of 108 rad. 

For aromatic compounds, that are activated towards electrophilic aromatic substitution, the reaction is easily carried out at room temperature. With highly activated aromatic compounds, di-, tri- or even polysulphonation products may be formed. In such cases, an inert solvent such as chloroform or carbon tetrachloride is used if the monosulphonation product is the one required. 

Polysulphones The polysulphone family of polysulphone (PSU) and polyether sulphone (PES) is a TP based on sulphone derivatives, aiming at high heat-stability. PSU originated in the discovery of a method of producing high molecular weight aromatic polyethers. 

Routes to aromatic polysulphones were discovered independently and almost simultaneously in the early 1960 s in the laboratories of the 3H Corporation (3) and Union Carbide Corporation (6) in the USA and at the Plastics Division of ICI in the UK (4). All three companies have since commercialised their disciveries. In 1963 Union Carbide introduced Udel Polysulfone which is rated to have a continuous use tmp-... 

The toughness of the polysulphones is very depend it on structure (10) and is easily spoilt by the inclusion of bulky side groups or by departing substantially from all para-orientation of groups forming the links between aromatic rings (Fig 2). 

Membranes from various manufacturers A, Hollosep-cellulose triacetate hollow fibre membrane (Toyobo) B, sulphonated polysulphone composite hollow fibre membrane (Albane International) C, BlO-aromatic polyamide hollow fibre membrane (Du Pont) D, PEC-1000-composite flat-sheet membrane (foray) E, NS-200-composite polyfurfuryl alcohol membrane F, FT-30-composite polyamide flat-sheet membrane (Film Tec/Dow) G,... 

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