Polysulfones

Polysulfones are both aliphatic and aromatic polymers that are resistant to high temperatures and are very stable. 

Typically, polysulfones are prepared by the reaction of disodium bisphenol A with 4,4 -dichlorodiphenylsulfone. 

Their resistance to autoclave sterilization makes them useful for medical instruments and trays. Other uses are microwave cookware, coffee decanters, and corrosion-resistant piping. 

Polysulfones are a group of polymers that are also heat resistant and thermally stable. A typical repeat unit of a poly sulfone is shown below (Fig. 2.36). These are a special group of polyethers (the ether linkage connects the polymeric chain). 

Other polyethers such as poly(phenylene oxide) are prepared by oxidation reactions using a transition metal complexes containing metal ions such as Cu (see Eq. 2.64). 

Meanwhile, most commercial polysulfones (PSU) and poly(ether sulfone)s (PES) are obtained from conversion of suitable aromatic dihalides with bisphenols by nucleophiUc displacement polycondensation (Fig. 19B). Generally, 4,4 -dichlorodiphenyl suUbne (DCDPS) is reacted with alkali salts of bisphenols [92,93]. The reaction is carried out in solution using hT-methyl-2-pyrrolidone (NMP), N,N-dimethyl acetamide (DMAc), or dimethyl sulfoxide (DMSO) as the solvent. Occasionally, the more reactive, but also more expensive, 4,4 -difluorodiphenyl sulfone might be used for experimental purposes. Usually, the electronegativity of the sulfone Unkage is sufficient to increase the reactivity of the aromatic chloride in DCDPS (Fig. 19). 

Alternatively, the bistrimethylsilyl ethers of the bisphenols can be used instead of the alkali salts. This approach has the advantage, since the formation of water and, thus, the risk of a hydrolytic cleavage of C-F bonds is avoided. Furthermore, the purification of the silylated bisphenols can be achieved by simple vacuum distillation. The use of silylated bisphenols also aUows for the preparation of poly(arylene ether)s in the melt (T 130-300 °C) in the presence of catalytic amounts of CsF or KF, thus, avoiding the removal of large amounts of inorganic salts and solvents [94-96] (Fig. 19C). 

Polysulfones (PSU) and poly(ether sulfone)s (PES) have been widely used as membrane materials for ultrafiltration, pervaporation [97-99], or electrodialysis [100], due to their chemical und thermd stability, high glass transition temperature (Tg), which is in the range of 180 °C to values well above 200 °C, as well as their good film-forming properties and solubility in dipolar aprotic solvents, such as NMP, DMAc, or DMSO. 

Besides the classical polyethersulfone (Fig. 19A) derived from the reaction of 4,4 -dihalodiphenyl sulfone and 4,4 -hydroxydiphenyl sulfone or self-condensation of 4-halo-4 -hydroxydiphenyl sulfone and polysulfone (Fig. 19B) derived from the reaction of bisphenol A (2,2-his-(4-hydroxy-phenyl) propane) and 4,4 -dihalodiphenyl sulfone, a large number of polysulfones have been either conunercialized or prepared for research purpose by variation of the bisphenol moieties. 

Industrially important sulfur-containing polymers are polysulfones and polysulfides. The materials differ considerably in properties and in use. 

These materials are an important group of engineering plastics. Aliphatic polysulfones were first synthesized at the end of the last century. That synthesis was based on reactions of SO2 with olefins  

Aliphatic sulfones, however, lack good thermal stability and are not commercially important. Aromatic sulfones, on the other hand, have many desirable physical properties. They are clear, rigid, tpugh materials, with a high value of 7g. Several aromatic sulfones are prepared commercially. 

The original preparation of aromatic polysulfones was described in 1958. This was followed by investigations of many different structures of polysulfones. One current commercial material is a condensation product of 2,2 -bis(hydroxyphenyl) propane with 4,4 -bis(chlorophenyl) sulfone. It fohns by a ) llliamson synthesis, because the reactivity of the halogens is enhanced by the sulfone groups  

The condensation takes place at 160 °C in an inert atmosphere and in some suitable solvents, like chlorobenzene. Commercially, polymers are available in molecular weight ranges from 20,000-40,000. Much higher molecular weight materials, however, form readily. This polymer is tough and high melting. 

7 Step-Growth Polymerization and Step-Growth Polymers 

A polysulfone is characterized by the presence of the sulfone group as part of its repeating unit. Polysulfones may be aUphatic or aromatic. AUphatic polysulfones (R and are alkyl groups) were synthesized by radical-induced copolymerization of olefins and sulfur dioxide and characterized many years ago. However, they never demonstrated significant practical utiUty due to their relatively unattractive physical properties, not withstanding the low cost of their raw materials (1,2). The polysulfones discussed in this article are those based on an aromatic backbone stmcture. The term polysulfones is used almost exclusively to denote aromatic polysulfones. 

The diphenylsulfone group is suppHed to the repeat unit of aU polysulfones by DCDPS the differentiating species between various polysulfones comes from the choice of bisphenol. There are three commercially important polysulfones referred to genericaHy by the common names polysulfone (PSF), polyethersulfone (PES), and polyphenylsulfone (PPSF). The repeat units of these polymers are shown in Table 1. 

PES repeat unit stmcture can alternatively be drawn as Victrex polyethersulfone [25667 2-9]. 

Nucleophilic Substitution Route. Commercial synthesis of poly(arylethersulfone)s is accompHshed almost exclusively via the nucleophilic substitution polycondensation route. This synthesis route, discovered at Union Carbide in the early 1960s (3,4), involves reaction of the bisphenol of choice with 4,4 -dichlorodiphenylsulfone in a dipolar aprotic solvent in the presence of an alkaUbase. Examples of dipolar aprotic solvents include A/-methyl-2-pyrrohdinone (NMP), dimethyl acetamide (DMAc), sulfolane, and dimethyl sulfoxide (DMSO). Examples of suitable bases are sodium hydroxide, potassium hydroxide, and potassium carbonate. In the case of polysulfone (PSE) synthesis, the reaction is a two-step process in which the dialkah metal salt of bisphenol A (1) is first formed in situ from bisphenol A [80-05-7] by reaction with the base (eg, two molar equivalents of NaOH), 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

In addition to sulfone, phenyl units, and ether moieties, the main backbone of polysulfones can contain a number of other connecting units. The most notable such connecting group is the isopropylidene linkage which is part of the repeat unit of the well-known bisphenol A-based polysulfone. It is difficult to clearly describe the chemical makeup of polysulfones without reference to the chemistry used to synthesize them. There are several routes for the synthesis of polysulfones, but the one which has proved to be most practical and versatile over the years is by aromatic nucleophilic substitution. This polycondensation route is based on reaction of essentially equimolar quantities of 4,4,-dihalodiphenylsulfone (usually dichlorodiphenylsulfone (DCDPS)) with a bisphenol in the presence of base thereby forming the aromatic ether bonds and eliminating an alkali salt as a by-product. This route is employed almost exclusively for the manufacture of polysulfones on a commercial scale. 

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- 

ACS Symposium Series American Chemical Society Washington, DC, 1974. 

A priori, there are two possibilities for synthesising the polyarylene sulphones. Either a polyether synthesis could be used to join up the aryl sulphone intermediates with ether linkages or a polysulphonylation process employed to link up aryl ethers. In practice either method can be used and will give polymers of hi molecular wei t provided that the intermediates are selected tfithin certain structuiml limitations and the reactim conditions are closdy controlled. The methods are quite different chemically and a polymer structiire made by one route cannot usually be made by the other, althou some structures can be made by either process. 

Polyetherification - A poLyether qrnthesis according to equation. A) was first described by Union Carbide Corporation (6). In this process ether bonds 

The following mechanism for the thermal degradation of PSF is suggested on the basis of the available experimental data. C-S bond scission is the primary process, followed by elimination of sulfnr dioxide and the formation of two phenyl radicals, which add to the phenylene rings of the chain [16]  

Subsequently, the degradation may proceed in two directions namely abstraction of an hydrogen atom from the cyclohexadienyl-type radical and cleavage of the Ar-O bond  

Both these reactions cause the crosslinking of polymer chains. 

Numerous ways to evaluate the degradation behaviour of polyarylene sulfones are reported in the literature. Danilina and co-workers [17] used infrared (IR) analysis for the pyrolysates of PES and PSF along with a change in the absorption peaks after two hours at 470 °C, they showed the formation of sulfur dioxide and phenol from the scission of sulfone and ether linkages. Crossland and co-workers [18] reported the results of TGA and Py-MS in the evaluation of the pyrolysis mechanism and pyrolysates of various PSF main-chain scission and hydrogen abstraction were indicated. However, the relative stability of the different PSF could not be postulated 

The major mechanisms in the pyrolysis of PES were shown to be main chain random scission and carbonisation in the one-stage reaction region for the release of sulfur dioxide from the sulfone group and phenol from the ether group. The stability of the sulfone group was more fragile than that of the ether group as shown in Equation 6.13  

Polysulfone is a thermoplastic copolymer of the sodium salt of bis-phenol A and p,/7 -dichlorodiphenyl sulfone  

Polyaryl sulfones can be produced by Friedel-Crafts type reactions 

It can be polymerized at — 80°C to high-molecular-weight products (M 500,000) by initiators such as amines, phosphines, tetraalkyl titanates, or dimethyl formamide. The actual initiator in the DMF-initiated polymerization is probably the fluoride ion (from HF, present as impurity)  

PSUs are available in opaque colors and in mineral-filled and glass- and other reinforced compounds to provide higher strength, stiffness, and thermal stability. For example, reinforced carbon-fiber PSU is used in human hip joints. 

PSU s creep, compared with that of other TPs, is exceptionally low at elevated temperatures and under continuous loads. For example, its creep at 99°C (210 F) is less than that of acetal or heat-resistant ABS at room temperature. 

The hydrolytic stability of these materials makes them resistant to water absorption in aqueous acidic and alkaline environments. Their combination of hydrolytic stability and heat resistance results in their having exceptional resistance to boiling water and steam, even under autoclave pressures and cyclic exposure to hot-to-cold and wet-to-dry repetitions. The PSUs also share the conunon drawback of absorbing UV rays, which gives them poor weather resistance. Thus, they are not recommended for outdoor service unless they are protected with paint or are plated or UV stabilized. 

The polyurethanes (PURs) produced by the reaction of polyisocyantes with polyester- or polyether-based resins can be either TPs or TSs. Extremely wide variations in form and physical or mechanical properties are available in PUR, which exhibit an extraordinary range of toughness, flexibility, and abrasion resistance (see Fig. 6-20). Its grades can range in density from Ib./ft. in its cellular form to 70 Ib./ft. in a solid form. PUR s hardness runs from rigid, solid forms at 85 Shore D to soft elastomers. 

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The isopropylidene linkage imparts chemical resistance, the ether linkage imparts temperature resistance, and the sulfone linkage imparts impact strength. The brittleness temperature of polysulfones is — 100°C. Polysulfones are clear, strong, nontoxic, and virtually unbreakable. They do not hydrolyze during autoclaving and are resistant to acids, bases, aqueous solutions, aliphatic hydrocarbons, and alcohols. 

Styrene-acrylonitrile copolymer Styrene- butadiene copolymer, high-impact Polysulfone ... 

Polysulfide sealants Polysulfide units Polysulfonates Polysulfone... 

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