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 + n2SO2 + 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.
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 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.
Polyethersulfone 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 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.
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.
See also Polyetheretherketone
Polyetherimide References