Polytetrafluoroethylene polymerisation

Tetrafluoroethylene. Emulsion polymerisation of tetrafluoroethylene, catalysed by oxygen, yields polytetrafluoroethylene (Tejlon) as a very tough horn-hke material of high melting point. It possesses excellent electrical insulation properties and a remarkable inertness towards all chemical reagents, including aqua regia. 

There is much evidence that weak links are present in the chains of most polymer species. These weak points may be at a terminal position and arise from the specific mechanism of chain termination or may be non-terminal and arise from a momentary aberration in the modus operandi of the polymerisation reaction. Because of these weak points it is found that polyethylene, polytetrafluoroethylene and poly(vinyl chloride), to take just three well-known examples, have a much lower resistance to thermal degradation than low molecular weight analogues. For similar reasons polyacrylonitrile and natural rubber may degrade whilst being dissolved in suitable solvents. 

When Y is not H, X and Y may be the same type of atom or group, as with poly(vinylidene chloride) (X and Y are Cl), or they may differ, as in poly-(methyl methacrylate) (X is —CH3, Y is —COOCH3) and poly(a-methyl styrene) (X is —CH3, Y is — ). When the substituents are small, polymerisation of a tetra-substituted monomer is possible, to produce a polymer such as polytetrafluoroethylene (PTFE), with the repeat unit )CF2—CF2, but if large substituents are present on both carbon atoms of the double bond there is usually steric hindrance to polymerisation, i.e. the substituents would overlap each other if polymerisation took place. 

Polytetrafluoroethylene is the polymer resulting from the free radical polymerisation of tetrafluoroethylene CF2=CF2. The reaction is usually carried out in an aqueous emulsion which produces sub-micron particles of the polymer, or in a suspension which gives rise to particles of 100 xm or greater. The polymer is processed from various resin grades, which differ in fineness, by means of preforming followed by sintering as in powder metallurgy. 

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