Polysulfones are a family of high performance

thermoplastic A thermoplastic, or thermosoftening plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling. Most thermoplastics have a high molecular weight. The polymer chains as ...

s. These

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

s are known for their toughness and stability at high temperatures. Technically used polysulfones contain an

aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used ...

- SO₂-aryl subunit. Due to the high cost of raw materials and processing, polysulfones are used in specialty applications and often are a superior replacement for

polycarbonate Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate ester, carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, toughness, tough materials, and some grades are optically transp ...

s. Three polysulfones are used industrially: polysulfone (PSU), polyethersulfone (PES/PESU) and polyphenylene sulfone (PPSU). They can be used in the temperature range from -100 to +200 °C and are used for electrical equipment, in vehicle construction and

medical technology Health technology is defined by the World Health Organization as the "application of organized knowledge and skills in the form of devices, medicines, vaccines, procedures, and systems developed to solve a health problem and improve quality of liv ...

. They are composed of para-linked aromatics,

sulfonyl group In organosulfur chemistry, a sulfonyl group is either a functional group found primarily in sulfones, or a substituent obtained from a sulfonic acid by the removal of the hydroxyl group, similarly to acyl groups. Group Sulfonyl groups can be wr ...

s and

ether group In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R′ re ...

s and partly also

alkyl groups In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...

. Polysulfones have outstanding resistance to heat and oxidation, hydrolysis resistance to aqueous and alkaline media and good electrical properties.

Nomenclature

The term "polysulfone" is normally used for polyarylethersulfones (PAES), since only aromatic polysulfones are used commercially. Furthermore, since ether groups are always present in these polysulfones, PAESs are also referred to as polyether sulfones (PES), poly(arylene sulfone)s or simply polysulfone (PSU).

Production

Historical

The simplest polysulfone poly(phenylene sulfone), known as early as 1960, is produced in a Friedel-Crafts reaction from

benzenesulfonyl chloride Benzenesulfonyl chloride is an organosulfur compound with the formula C6H5SO2Cl. It is a colourless viscous oil that dissolves in organic solvents, but reacts with compounds containing reactive N-H and O-H bonds. It is mainly used to prepare sulfo ...

: :n C₆H₅SO₂Cl → (C₆H₄SO₂)_n + n HCl With a melting point over 500 °C, the product is difficult to process. It exhibits attractive heat resistance, but its mechanical properties are rather poor. Polyarylether sulphones (PAES) represent a suitable alternative. Appropriate synthetic routes to PAES were developed almost simultaneously, and yet independently, from

3M Corporation 3M Company (originally the Minnesota Mining and Manufacturing Company) is an American multinational conglomerate operating in the fields of industry, worker safety, and consumer goods. Based in the Maplewood suburb of Saint Paul, Minnesota, ...

Union Carbide Corporation Union Carbide Corporation (UCC) is an American chemical company headquartered in Seadrift, Texas. It has been a wholly owned subsidiary of Dow Chemical Company since 2001. Union Carbide produces chemicals and polymers that undergo one or more f ...

in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

, and

ICI #REDIRECT ICI {{redirect category shell, {{R from other capitalisation{{R from ambiguous page ...

's Plastics Division in the United Kingdom. The polymers found at that time are still used today, but produced by a different synthesis process. The original synthesis of PAES involved

electrophilic aromatic substitution Electrophilic aromatic substitution (SEAr) is an organic reaction in which an atom that is attached to an aromatic ring, aromatic system (usually hydrogen) is replaced by an electrophile. Some of the most important electrophilic aromatic substitut ...

of an di

aryl ether In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R′ r ...

with the bis (sulfonyl chloride) of benzene. Reactions typically use a Friedel-Crafts catalyst, such as

ferric chloride Iron(III) chloride describes the inorganic compounds with the formula (H2O)x. Also called ferric chloride, these compounds are some of the most important and commonplace compounds of iron. They are available both in anhydrous and in hydrated f ...

antimony pentachloride Antimony pentachloride is a chemical compound with the formula SbCl5. It is a colourless oil, but typical samples are yellowish due to dissolved chlorine. Owing to its tendency to hydrolyse to hydrochloric acid, SbCl5 is a highly corrosive subs ...

: :n O(C₆H₅)₂ + n SO2Cl2 → _n + 2n HCl : This route is complicated by the formation of isomers arising from both para- and ortho- substitution. Furthermore, cross-linking was observed, which strongly affects the mechanical properties of the polymer. This method has been abandoned.

Contemporary production methods

PAES are currently prepared by a polycondensation reaction of di

phenoxide Phenolates (also called phenoxides) are anions, salts, and esters of phenols, containing the phenolate ion. They may be formed by reaction of phenols with strong base. Properties Alkali metal phenolates, such as sodium phenolate hydrolyze in aq ...

and bis(4-chlorophenyl)sulfone (DCDPS). The sulfone group activates the chloride groups toward substitution. The required diphenoxide is produced in situ from a diphenol and

sodium hydroxide Sodium hydroxide, also known as lye and caustic soda, is an inorganic compound with the formula . It is a white solid ionic compound consisting of sodium cations and hydroxide anions . Sodium hydroxide is a highly corrosive base (chemistry), ...

. The cogenerated water is removed by

azeotropic distillation In chemistry, azeotropic distillation is any of a range of techniques used to break an azeotrope in distillation. In chemical engineering, ''azeotropic distillation'' usually refers to the specific technique of adding another component to genera ...

using

toluene Toluene (), also known as toluol (), is a substituted aromatic hydrocarbon with the chemical formula , often abbreviated as , where Ph stands for the phenyl group. It is a colorless, water Water is an inorganic compound with the c ...

chlorobenzene Chlorobenzene (abbreviated PhCl) is an aryl chloride and the simplest of the chlorobenzenes, consisting of a benzene ring substituted with one chlorine atom. Its chemical formula is C6H5Cl. This colorless, flammable liquid is a common solvent a ...

). The polymerization is carried out at 130–160 °C under inert conditions in a polar, aprotic solvent, e.g.

dimethyl sulfoxide Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula . This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is ...

, forming a

polyether In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R� ...

concomitant with elimination of

sodium chloride Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...

: Bis(4-fluorophenyl)sulfone can be used in place of bis(4-chlorophenyl)sulfone. The difluoride is more reactive than the dichloride but more expensive. Through chain terminators (e.g.

methyl chloride Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula . One of the haloalkanes, it is a colorless, sweet-smelling, flammable gas. Methyl chloride is a crucial reagent in indus ...

), the chain length can be controlled for melt-processing. The diphenol is typically

bisphenol-A Bisphenol A (BPA) is a chemical compound primarily used in the manufacturing of various plastics. It is a colourless solid which is Solubility, soluble in most common organic solvents, but has very poor solubility in water. BPA is produced on a ...

or 1,4-dihydroxybenzene. Such step polymerizations require highly pure monomer and precise stoichiometry to ensure high molecular weight products. DCDPS is the precursor to polymers known as Udel (from bisphenol A), PES, and Radel R. Udel is a high-performance amorphous sulfone polymer that can molded into a variety of different shapes. It is both rigid and temperature-resistant, and has applications in everything from

plumbing Plumbing is any system that conveys fluids for a wide range of applications. Plumbing uses piping, pipes, valves, piping and plumbing fitting, plumbing fixtures, Storage tank, tanks, and other apparatuses to convey fluids. HVAC, Heating and co ...

pipes, to printer cartridges, to automobile

fuse Fuse or FUSE may refer to: Devices * Fuse (electrical), a device used in electrical systems to protect against excessive current ** Fuse (automotive), a class of fuses for vehicles * Fuse (hydraulic), a device used in hydraulic systems to protec ...

s. DCDPS also reacts with

bisphenol S Bisphenol S (BPS, dioxydiphenylsulfone) is an organic compound with the formula . It has two phenol functional groups on either side of a sulfonyl group. It is commonly used in curing fast-drying epoxy resin adhesives. It is classified as a bisp ...

to form PES. Like Udel, PES is a rigid and thermally-resistant material with numerous applications.

Properties

Polysulfones are rigid, high-strength and transparent. They are also characterized by high strength and stiffness, retaining these properties between −100 °C and 150 °C. The glass transition temperature of polysulfones is between 190 and 230 °C. They have a high dimensional stability, the size change when exposed to boiling water or 150 °C air or steam generally falls below 0.1%. Polysulfone is highly resistant to

mineral acid A mineral acid (or inorganic acid) is an acid derived from one or more inorganic compounds, as opposed to organic acids which are acidic, organic compounds. All mineral acids form hydrogen ions and the conjugate base when dissolved in water. Ch ...

alkali In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The a ...

, and

electrolyte An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble Salt (chemistry), salts, acids, and Base (chemistry), bases, dissolved in a polar solven ...

s, in pH ranging from 2 to 13. It is resistant to oxidizing agents (although PES will degrade over time), therefore it can be cleaned by

bleach Bleach is the generic name for any chemical product that is used industrially or domestically to remove color from (i.e. to whiten) fabric or fiber (in a process called bleaching) or to disinfect after cleaning. It often refers specifically t ...

es. It is also resistant to

surfactant Surfactants are chemical compounds that decrease the surface tension or interfacial tension between two liquids, a liquid and a gas, or a liquid and a solid. The word ''surfactant'' is a Blend word, blend of "surface-active agent", coined in ...

s and

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...

s. It is not resistant to low-polar

organic solvent A solvent (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for p ...

s (e.g.

ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...

s and

chlorinated hydrocarbon Organochlorine chemistry is concerned with the properties of organochlorine compounds, or organochlorides, organic compounds that contain one or more carbon–chlorine bonds. The chloroalkane class (alkanes with one or more hydrogens substituted ...

s) and

aromatic hydrocarbon Aromatic compounds or arenes are organic compounds "with a chemistry typified by benzene" and "cyclically conjugated." The word "aromatic" originates from the past grouping of molecules based on odor, before their general chemical properties were ...

s. Mechanically, polysulfone has high compaction resistance, recommending its use under high pressures. It is also stable in aqueous acids and bases and many non-polar solvents; however, it is soluble in

dichloromethane Dichloromethane (DCM, methylene chloride, or methylene bichloride) is an organochlorine compound with the formula . This colorless, volatile liquid with a chloroform-like, sweet odor is widely used as a solvent. Although it is not miscible with ...

and

methylpyrrolidone ''N''-Methyl-2-pyrrolidone (NMP) is an organic compound consisting of a 5-membered lactam. It is a colorless liquid, although impure samples can appear yellow. It is miscible with water and with most common organic solvents. It also belongs to t ...

.David Parker, Jan Bussink, Hendrik T. van de Grampel, Gary W. Wheatley, Ernst-Ulrich Dorf, Edgar Ostlinning, Klaus Reinking, "Polymers, High-Temperature" in ''Ullmann's Encyclopedia of Industrial Chemistry'' 2002, Wiley-VCH: Weinheim. Polysulfones are counted among the

high performance plastics High-performance plastics are plastics that meet higher requirements than ''standard'' (commodity) or ''engineering'' plastics. They are more expensive and used in smaller amounts. Definition High performance plastics differ from standard plas ...

. They can be processed by

injection molding Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...

extrusion Extrusion is a process used to create objects of a fixed cross section (geometry), cross-sectional profile by pushing material through a Die (manufacturing), die of the desired cross-section. Its two main advantages over other manufacturing pro ...

or hot forming.

Structure-property relationship

Poly(aryl ether sulfone)s are composed of aromatic groups,

s and

s. For a comparison of the properties of individual constituents poly(phenylene sulfone) can serve as an example, which consists of sulfonyl and phenyl groups only. Since both groups are thermally very stable, poly(phenylene sulfone) has an extremely high melting temperature (520 °C). However, the polymer chains are also so rigid that poly(phenylene sulfone) (PAS) decomposes before melting and can thus not be thermoplastically processed. Therefore, flexible elements must be incorporated into the chains, this is done in the form of ether groups. Ether groups allow a free rotation of the polymer chains. This leads to a significantly reduced melting point and also improves the mechanical properties by an increased

impact strength In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing. The

in bisphenol A act also as a flexible element. The stability of the polymer can also be attributed to individual structural elements: The

(in which

sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

is in the highest possible

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical Electrical charge, charge of an atom if all of its Chemical bond, bonds to other atoms are fully Ionic bond, ionic. It describes the degree of oxidation (loss of electrons ...

) attracts electrons from neighboring benzene rings, causing

electron deficiency In chemistry, electron deficiency (and electron-deficient) is jargon that is used in two contexts: chemical species that violate the octet rule because they have too few valence electrons and species that happen to follow the octet rule but have el ...

. The polymer therefore opposes further electron loss, thus substantiating the high oxidation resistance. The sulfonyl group is also linked to the aromatic system by mesomerism and the bond therefore strengthened by mesomeric energy. As a result, larger amounts of energy from heat or radiation can be absorbed by the molecular structure without causing any reactions (decomposition). The result of the mesomerism is that the configuration is particularly rigid. Based on the biphenylsulfonyl group, the polymer is thus durable heat resistant, oxidation resistant and still has a high stiffness even at elevated temperatures. The ether bond provides (as opposed to

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

s) hydrolysis resistance as well as some flexibility, which leads to impact strength. In addition, the ether bond leads to good heat resistance and better flow of the melt.

Applications

Polysulfone has one of the highest service temperatures among all melt-processable thermoplastics. Its resistance to high temperatures gives it a role of a

flame retardant Flame retardants are a diverse group of chemicals that are added to manufactured materials, such as plastics and textiles, and surface finishes and coatings. Flame retardants are activated by the presence of an combustion, ignition source and pr ...

, without compromising its strength that usually results from addition of flame retardants. Its high hydrolysis stability allows its use in medical applications requiring autoclave and steam sterilization. However, it has low resistance to some solvents and undergoes

weathering Weathering is the deterioration of rocks, soils and minerals (as well as wood and artificial materials) through contact with water, atmospheric gases, sunlight, and biological organisms. It occurs '' in situ'' (on-site, with little or no move ...

; this weathering instability can be offset by adding other materials into the polymer.

Membranes

Polysulfone allows easy manufacturing of

membranes A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Membranes can be generally classified into synthetic membranes and biological membranes. B ...

, with reproducible properties and controllable size of pores down to 40 nanometers. Such membranes can be used in applications like

hemodialysis Hemodialysis, American and British English spelling differences#ae and oe, also spelled haemodialysis, or simply ''"'dialysis'"'', is a process of filtering the blood of a person whose kidneys are not working normally. This type of Kidney dialys ...

waste water Wastewater (or waste water) is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of do ...

recovery, food and beverage processing, and gas separation. These polymers are also used in the automotive and electronic industries. Filter cartridges made from polysulfone membranes offer extremely high flow rates at very low differential pressures when compared with

nylon Nylon is a family of synthetic polymers characterised by amide linkages, typically connecting aliphatic or Polyamide#Classification, semi-aromatic groups. Nylons are generally brownish in color and can possess a soft texture, with some varieti ...

polypropylene Polypropylene (PP), also known as polypropene, is a thermoplastic polymer used in a wide variety of applications. It is produced via chain-growth polymerization from the monomer Propene, propylene. Polypropylene belongs to the group of polyolefin ...

media. Polysulfone can be used as filtration media in filter sterilization.

Materials

Polysulfone can be reinforced with

glass fiber Glass fiber ( or glass fibre) is a material consisting of numerous extremely fine fibers of glass. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the inventio ...

s. The resulting

composite material A composite or composite material (also composition material) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or physical properties and are merged to create a ...

has twice the tensile strength and three times increase of its

Young's modulus Young's modulus (or the Young modulus) is a mechanical property of solid materials that measures the tensile or compressive stiffness when the force is applied lengthwise. It is the modulus of elasticity for tension or axial compression. Youn ...

Fuel cells

Polysulfone is often used as a

copolymer In polymer chemistry, a copolymer is a polymer derived from more than one species of monomer. The polymerization of monomers into copolymers is called copolymerization. Copolymers obtained from the copolymerization of two monomer species are som ...

. Recently, sulfonated polyethersulfones (SPES) have been studied as a promising material candidate among many other aromatic hydrocarbon-based polymers for highly durable proton-exchange membranes in fuel cells. Several reviews have reported progress on durability from many reports on this work. The biggest challenge for SPES application in fuel cells is improving its chemical durability. Under oxidative environment, SPES can undergo sulfonic group detachment and main chain scission. However the latter is more dominant; midpoint scission and unzip mechanism have been proposed as the degradation mechanism depending on the strength of the polymer backbone.

Food service industry

Polysulfone food pans are used for the storage, heating, and serving of foods. The pans are made to

Gastronorm Gastronorm (GN), sometimes spelled Gastro-Norm, is a European standard for kitchenware tray and container sizes that is commonly seen worldwide in the catering and professional food industry, as well as in certain parts of the high-end consumer m ...

standards and are available in the natural transparent amber colour of polysulfone. The wide working temperature range of -40°C to 190°C allow these pans to go from a deep freezer directly to a steam table or microwave oven. Polysulfone provides a non-stick surface for minimal food wastage and easy cleaning.

Industrially relevant polysulfones

Some industrially relevant polysulfones are listed in the following table:

References

{{Plastics Polymers Plastics Thermoplastics Sulfones Engineering plastic