Polysulfone

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Polysulfone (PSU) repeating unit. Polysulfone.svg
Polysulfone (PSU) repeating unit.
Polyethersulfone (PES) repeating unit. Polyethersulfones V.1.svg
Polyethersulfone (PES) repeating unit.

Polysulfones are a family of high performance thermoplastics. These polymers are known for their toughness and stability at high temperatures. Technically used polysulfones contain an aryl-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 polycarbonates.

Contents

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. [1] They are composed of para-linked aromatics, sulfonyl groups and ether groups and partly also alkyl groups. Polysulfones have outstanding resistance to heat and oxidation, hydrolysis resistance to aqueous and alkaline media and good electrical properties. [2]

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: [3]

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, [4] Union Carbide Corporation in the United States, [5] and ICI's Plastics Division [6] 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 of an diaryl ether with the bis (sulfonyl chloride) of benzene. Reactions typically use a Friedel-Crafts catalyst, such as ferric chloride or antimony pentachloride:

n O(C6H5)2 + n SO2Cl2 → {[O(C6H4)2]SO2}n + 2n HCl
Synthesis Polysulfone possibility 2 part 1.svg Synthesis Polysulfone possibility 2 part 2.svg

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. [7] [4] This method has been abandoned.

Contemporary production methods

PAES are currently prepared by a polycondensation reaction of diphenoxide 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. The cogenerated water is removed by azeotropic distillation using toluene or chlorobenzene). The polymerization is carried out at 130–160 °C under inert conditions in a polar, aprotic solvent, e.g. dimethyl sulfoxide, forming a polyether concomitant with elimination of sodium chloride:

Synthesis Polysulfone possibility 1 part 1.svg Synthesis Polysulfone possibility 1 part 2.svg

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), the chain length can be controlled for melt-processing.

The diphenol is typically bisphenol-A or 1,4-dihydroxybenzene. Such step polymerizations require highly pure monomer and precise stoichiometry to ensure high molecular weight products. [8]

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 pipes, to printer cartridges, to automobile fuses. DCDPS also reacts with bisphenol S 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. [9] 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%. [10] Polysulfone is highly resistant to mineral acids, alkali, and electrolytes, in pH ranging from 2 to 13. It is resistant to oxidizing agents (although PES will degrade over time [11] ), therefore it can be cleaned by bleaches. It is also resistant to surfactants and hydrocarbon oils. It is not resistant to low-polar organic solvents (e.g. ketones and chlorinated hydrocarbons) and aromatic hydrocarbons. 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 and methylpyrrolidone. [8]

Polysulfones are counted among the high performance plastics. They can be processed by injection molding, extrusion or hot forming.

Structure-property relationship

Poly(aryl ether sulfone)s are composed of aromatic groups, ether groups and sulfonyl groups. 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. [7] The alkyl groups in bisphenol A act also as a flexible element.

The stability of the polymer can also be attributed to individual structural elements: The sulfonyl group (in which sulfur is in the highest possible oxidation state) attracts electrons from neighboring benzene rings, causing electron deficiency. 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 esters) 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. [12]

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

Membranes

Polysulfone allows easy manufacturing of membranes, with reproducible properties and controllable size of pores down to 40 nanometers. Such membranes can be used in applications like hemodialysis, waste water 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 or polypropylene media.

Polysulfone can be used as filtration media in filter sterilization.

Materials

Polysulfone can be reinforced with glass fibers. The resulting composite material has twice the tensile strength and three times increase of its Young's modulus.[ citation needed ]

Fuel cells

Polysulfone is often used as a copolymer. 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. [13] Several reviews have reported progress on durability from many reports on this work. [14] 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. [15]

Food service industry

Pair of high heat food pans made of polysulfone Polysulfone food pans.jpg
Pair of high heat food pans made of polysulfone

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

Structural formula trade nameSystematic NameCAS
Polyarylensulfone PAS.svg Poly(arylene sulfone) (PAS)
Polybisphenylsulfone PSF.svg poly(bisphenol-A sulfone) (PSF)Poly[oxy-1,4-phenylensulfonyl-1,4-phenylenoxy-1,4-phenylen(1-methylethyliden)-1,4-phenylen]25135-51-7
Polyethersulfone PES.svg Structure shown is incorrect (missing ether linkage)Polyether sulfone (PES)Poly(oxy-1,4-phenylsulfonyl-1,4-phenyl)25608-63-3
Polyphenylensulfone PPSU.svg Polyphenylenesulfone (PPSU)25608-64-4
Polysulfone PSU.svg Polysulfone (PSU)Poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene)25667-42-9
Victrex HTA.svg Victrex HTA121763-41-5

Related Research Articles

<span class="mw-page-title-main">Ether</span> Organic compounds made of alkyl/aryl groups bound to oxygen (R–O–R)

In organic chemistry, ethers are a class of compounds that contain an ether group—an oxygen atom connected to two alkyl or aryl groups. They have the general formula R−O−R′, where R and R′ represent the alkyl or aryl groups. Ethers can again be classified into two varieties: if the alkyl or aryl groups are the same on both sides of the oxygen atom, then it is a simple or symmetrical ether, whereas if they are different, the ethers are called mixed or unsymmetrical ethers. A typical example of the first group is the solvent and anaesthetic diethyl ether, commonly referred to simply as "ether". Ethers are common in organic chemistry and even more prevalent in biochemistry, as they are common linkages in carbohydrates and lignin.

<span class="mw-page-title-main">Thermoplastic</span> Plastic that softens with heat and hardens on cooling

A thermoplastic, or thermosoft plastic, is any plastic polymer material that becomes pliable or moldable at a certain elevated temperature and solidifies upon cooling.

<span class="mw-page-title-main">Epoxy</span> Type of material

Epoxy is the family of basic components or cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional group is also collectively called epoxy. The IUPAC name for an epoxide group is an oxirane.

<span class="mw-page-title-main">Polycarbonate</span> Family of polymers

Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily worked, molded, and thermoformed. Because of these properties, polycarbonates find many applications. Polycarbonates do not have a unique resin identification code (RIC) and are identified as "Other", 7 on the RIC list. Products made from polycarbonate can contain the precursor monomer bisphenol A (BPA).

<span class="mw-page-title-main">Nafion</span> Brand name for a chemical product

Nafion is a brand name for a sulfonated tetrafluoroethylene based fluoropolymer-copolymer discovered in the late 1960s by Dr. Walther Grot of DuPont. Nafion is a brand of the Chemours company. It is the first of a class of synthetic polymers with ionic properties that are called ionomers. Nafion's unique ionic properties are a result of incorporating perfluorovinyl ether groups terminated with sulfonate groups onto a tetrafluoroethylene (PTFE) backbone. Nafion has received a considerable amount of attention as a proton conductor for proton exchange membrane (PEM) fuel cells because of its excellent chemical and mechanical stability in the harsh conditions of this application.

An artificial membrane, or synthetic membrane, is a synthetically created membrane which is usually intended for separation purposes in laboratory or in industry. Synthetic membranes have been successfully used for small and large-scale industrial processes since the middle of twentieth century. A wide variety of synthetic membranes is known. They can be produced from organic materials such as polymers and liquids, as well as inorganic materials. The most of commercially utilized synthetic membranes in separation industry are made of polymeric structures. They can be classified based on their surface chemistry, bulk structure, morphology, and production method. The chemical and physical properties of synthetic membranes and separated particles as well as a choice of driving force define a particular membrane separation process. The most commonly used driving forces of a membrane process in industry are pressure and concentration gradients. The respective membrane process is therefore known as filtration. Synthetic membranes utilized in a separation process can be of different geometry and of respective flow configuration. They can also be categorized based on their application and separation regime. The best known synthetic membrane separation processes include water purification, reverse osmosis, dehydrogenation of natural gas, removal of cell particles by microfiltration and ultrafiltration, removal of microorganisms from dairy products, and Dialysis.

<span class="mw-page-title-main">Step-growth polymerization</span>

Step-growth polymerization refers to a type of polymerization mechanism in which bi-functional or multifunctional monomers react to form first dimers, then trimers, longer oligomers and eventually long chain polymers. Many naturally occurring and some synthetic polymers are produced by step-growth polymerization, e.g. polyesters, polyamides, polyurethanes, etc. Due to the nature of the polymerization mechanism, a high extent of reaction is required to achieve high molecular weight. The easiest way to visualize the mechanism of a step-growth polymerization is a group of people reaching out to hold their hands to form a human chain—each person has two hands. There also is the possibility to have more than two reactive sites on a monomer: In this case branched polymers production take place.

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<span class="mw-page-title-main">Sulfone</span> Organosulfur compound of the form >S(=O)2

In organic chemistry, a sulfone is a organosulfur compound containing a sulfonyl functional group attached to two carbon atoms. The central hexavalent sulfur atom is double-bonded to each of two oxygen atoms and has a single bond to each of two carbon atoms, usually in two separate hydrocarbon substituents.

<span class="mw-page-title-main">Hot-melt adhesive</span> Glue applied by heating

Hot-melt adhesive (HMA), also known as hot glue, is a form of thermoplastic adhesive that is commonly sold as solid cylindrical sticks of various diameters designed to be applied using a hot glue gun. The gun uses a continuous-duty heating element to melt the plastic glue, which the user pushes through the gun either with a mechanical trigger mechanism on the gun, or with direct finger pressure. The glue squeezed out of the heated nozzle is initially hot enough to burn and even blister skin. The glue is sticky when hot, and solidifies in a few seconds to one minute. Hot-melt adhesives can also be applied by dipping or spraying, and are popular with hobbyists and crafters both for affixing and as an inexpensive alternative to resin casting.

<span class="mw-page-title-main">Carbonate ester</span> Chemical group (R–O–C(=O)–O–R)

In organic chemistry, a carbonate ester is an ester of carbonic acid. This functional group consists of a carbonyl group flanked by two alkoxy groups. The general structure of these carbonates is R−O−C(=O)−O−R' and they are related to esters, ethers and also to the inorganic carbonates.

<span class="mw-page-title-main">Polyester</span> Category of polymers, in which the monomers are joined together by ester links

Polyester is a category of polymers that contain the ester functional group in every repeat unit of their main chain. As a specific material, it most commonly refers to a type called polyethylene terephthalate (PET). Polyesters include naturally occurring chemicals, such as in plants and insects, as well as synthetics such as polybutyrate. Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not. Synthetic polyesters are used extensively in clothing.

Polyphenylsulfone is a high performance polymer made of aromatic rings linked by sulfone (SO2) groups.

<span class="mw-page-title-main">Polyphenyl ether</span> Class of polymers

Phenyl ether polymers are a class of polymers that contain a phenoxy or a thiophenoxy group as the repeating group in ether linkages. Commercial phenyl ether polymers belong to two chemical classes: polyphenyl ethers (PPEs) and polyphenylene oxides (PPOs). The phenoxy groups in the former class of polymers do not contain any substituents whereas those in the latter class contain 2 to 4 alkyl groups on the phenyl ring. The structure of an oxygen-containing PPE is provided in Figure 1 and that of a 2, 6-xylenol derived PPO is shown in Figure 2. Either class can have the oxygen atoms attached at various positions around the rings.

<span class="mw-page-title-main">4,4'-Dichlorodiphenyl sulfone</span> Chemical compound

4,4′-Dichlorodiphenyl sulfone (DCDPS) is an organic compound with the formula (ClC6H4)2SO2. Classified as a sulfone, this white solid is most commonly used as a precursor to polymers that are rigid and temperature-resistant such as PES or Udel.

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A thermoset polymer matrix is a synthetic polymer reinforcement where polymers act as binder or matrix to secure in place incorporated particulates, fibres or other reinforcements. They were first developed for structural applications, such as glass-reinforced plastic radar domes on aircraft and graphite-epoxy payload bay doors on the Space Shuttle.

Polyaryletherketone (PAEK) is a family of semi-crystalline thermoplastics with high-temperature stability and high mechanical strength whose molecular backbone contains alternately ketone (R-CO-R) and ether groups (R-O-R). The linking group R between the functional groups consists of a 1,4-substituted aryl group.

Poly(<i>p</i>-phenylene oxide) Chemical compound

Poly(p-phenylene oxide) (PPO), poly(p-phenylene ether) (PPE), often referred to simply as polyphenylene oxide, is a high-temperature thermoplastic. It is rarely used in its pure form due to difficulties in processing. It is mainly used as blend with polystyrene, high impact styrene-butadiene copolymer or polyamide. PPO is a registered trademark of SABIC Innovative Plastics IP B.V. under which various polyphenylene ether resins are sold.

<span class="mw-page-title-main">High-performance plastics</span> Plastics that meet higher requirements than engineering plastics

High-performance plastics are plastics that meet higher requirements than standard or engineering plastics. They are more expensive and used in smaller amounts.

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