Polychlorotrifluoroethylene (PCTFE) is more expensive than poly tetrafluoroethylene and its use is comparatively limited.
The preferred commercial method of preparation of polychlorotrifluoroethylene is by suspension polymerization using procedures similar to
those used for polytetrafluoroethylene. In order to obtain polymer of high
molecular weight, reaction temperatures are generally kept in the range
0-40°C. Initiation is commonly by means of a redox system activated by a
metal salt, e.g. persulphate - bisulphite with a ferrous salt. Average molecular
weights of commercial polymers are within the range 50000-500000.
Polychlorotrifluoroethylene is a white solid. Compared to poly tetrafluoroethylene, it has greater tensile strength, hardness and resistance to
creep. The presence of a chlorine atom, which is larger than a fluorine atom, in the polymer does
not permit such close chain packing as is possible with polytetrafluoroethylene. Thus polychlorotrifluoroethylene has a lower softening point and can be
processed in the melt. Because of the lower tendency to crystallize, it is
possible to produce thin transparent films by rapid quenching. The presence
of chlorine in the polymer results in greater interchain attraction and
accounts for the better mechanical strength of polychlorotrifluoroethylene.
On the other hand, the unsymmetrical structure leads to poorer electrical
insulation properties.
The chemical resistance of polychlorotrifluoroethylene is very good but
not as good as that of polytetrafluoroethylene. Molten alkali metals and
molten caustic alkalis attack the polymer and a few halogenated solvents
swell or dissolve the polymer at elevated temperatures.
Polychlorotrifluoroethylene may be melt processed. Standard techniques of extrusion and injection moulding may be used
but careful temperature control is required since degradation occurs at
processing temperatures, which are normally in the range 230-290°C.
Degradation is accompanied by development of unsaturation and may
involve the following chain splitting rearrangement:
The temperature range of useful performance is from about -loooe to
200°C.
Polychlorotrifluorethylene finds limited use for such items as
diaphragms, gaskets, electrical components and transparent windows for
chemical equipment. Dispersions are used for the preparation of films
and coatings.
