Polysulfone
Polysulfones are a family of thermoplastic polymers. These polymers are known for their toughness and stability at high temperatures. They contain the subunit aryl-SO2-aryl, the defining feature of which is the sulfone group. Polysulfones were introduced in 1965 by Union Carbide. Due to the high cost of raw materials and processing, polysulfones are used in specialty applications and often are a superior replacement for polycarbonates.
Production
A typical polysulfone is produced by the reaction of a diphenol and bis(4-chlorophenyl)sulfone, forming a polyether by elimination of sodium chloride:
- n HOC6H4OH + n (ClC6H4)2SO2 + n Na2CO3 → [OC6H4OC6H4SO2C6H4]n + 2n NaCl + n H2O + n CO2.
The diphenol is typically bisphenol-A or 1,4-dihydroxybenzene. Such step polymerizations require highly pure monomer to ensure high molecular weight products.[1]
Chemical and physical properties
These polymers are rigid, high-strength, and transparent, retaining these properties between −100 °C and 150 °C. It has very high dimensional stability; the size change when exposed to boiling water or 150 °C air or steam generally falls below 0.1%. Its glass transition temperature is 185 °C.
Polysulfone is highly resistant to mineral acids, alkali, and electrolytes, in pH ranging from 2 to 13. It is resistant to oxidizing agents, 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.[1]
Polyethersulfone (PES) is a similar polymer with low protein retention.
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.
Polysulfone allows easy manufacturing of membranes, with reproducible properties and controllable size of pores down to 40 nanometres. 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. Additionally, filter cartridges made from polysulfone can be sterilized with in-line steam or in the autoclave without loss of integrity up to 50 times.
Polysulfone can be reinforced with glass fibers. The resulting composite material has twice the tensile strength and three time increase of its Young's modulus.
Polysulfone is used as a dielectric in capacitors.
Polysulfone is commercially available from Solvay Specialty Polymers, BASF, and PolyOne Corporation.
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.[2] Several reviews have reported progress on durability from many reports on this work.[3] 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.[4]
Polysulfone is used as filtration media. The pore size can be very small, down to 0.2 µm or less for use in filter sterilization.
Polysulfone was the primary component of the gold-plated lunar extravehicular visor assembly, the iconic gold-film visor portion of the Apollo space-suits worn by Apollo astronauts during their lunar excursions.[5]
See also
- Polyetheretherketone (PEEK)
- Polyetherimide (PEI)
References
- ^ a b 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. doi:10.1002/14356007.a21_449
- ^ Hickner et al. Alternative polymer systems for proton exchange membranes (PEMs). Chemical Reviews (2004) vol. 104 (10) pp. 4587–4611.
- ^ Borup et al. Scientific aspects of polymer electrolyte fuel cell durability and degradation. Chemical Reviews (2007) vol. 107 (10) pp. 3904–3951.
- ^ Lawrence and Yamaguchi. The degradation mechanism of sulfonated poly(arylene ether sulfone)s in an oxidative environment. Journal of Membrane Science (2008) vol. 325 (2) pp. 633–640.
- ^ Lunar Extravehicular Visor Assembly (LEVA). NASA. Retrieved 21 July 2010.
