(Polytetrafluoroethene)(Polytetrafluoroethene)PTFE is a polymer (from the greek word 'many parts') made from the monomer ('one part') tetrafluoroethene, which is an alkene fully saturated by fluorine molecules.
(Tetrefluoroethene) Tetrafluoroethene is formed from the partial fluorination of chloroform using HF in the presence of SbFCl4, which is the catalyst. The product then undergoes thermolysis to form C2F4:
Tetrafluorethene (TFE) is usually polymerized with free readical initiators at an elevated pressure in the presence of H2O. Redox initiation may be used, where persulfates and hydrogen peroxide are employed as the initiators. Redox initiation is the decomposition of peroxide-type initiators in aqueous systems, which is greatly accelerated by the presence of a reducing agent. This therefore allows high rates of radical formation to take place at low teperatures in an emulsion system.
Below is an example of a typical redox system with H2O as the initiator:
Another widely used initiator is the persulfate ion with a reducing agent (R):
The tetrafluoroethene monomers then undergo radical polymerisation under high pressure to form the polymer PTFE. Below shows the mechanism of the reaction using the free radical ·OH as the initiator:
The unique thing about this polymerisation is that it is performed in solution. Normally, no solvents are used as it is difficult to separate the polymer product from the solvent. But as PTFE interacts with no other molecules, it precipitates from all known solvents and can be isolated easily by filtration.
