Chemistry Reference
In-Depth Information
6.17.2 Polychlorotrifluoroethylene
The monomer can be prepared by dechlorination of trichlorotrifluoroethane with zinc dust and
ethanol.
F
F
F
F
Zn
Cl
Cl
+
ZnCl
2
C
2
H
5
OH
Cl
F
Cl
F
It is a toxic gas that boils at
26.8
C. Polymerization of chlorotrifluoroethylene is usually carried
out commercially by free-radical suspension polymerization. Reaction temperatures are kept between
0 and 40
C to obtain a high molecular weight product. A redox initiation based on reactions of
persulfate, bisulfite, and ferrous ions is often used. Commercial polymers range in molecular weights
from 50,000 to 500,000.
Polychlorotrifluoroethylene exhibits greater strength, hardness, and creep resistance than does
polytetrafluoroethylene. Due to the presence of chlorine atoms in the chains, however, packing cannot
be as tight as in polytetrafluoroethylene, and it melts at a lower temperature. The melting point is 214
C.
The degree of crystallinity varies from 30 to 85%, depending upon the thermal history of the polymer.
Polytrifluorochloroethylene is soluble in certain chloro fluoro compounds above 100
C. It flows above
its melting point. The chemical resistance of this material is good, but inferior to polytetrafluoroethylene.
6.17.3 Poly(vinylidine fluoride)
The monomer can be prepared by dehydrochlorination of 1,1,1-chlorodifluoroethane:
Cl
F
+
HCl
F
F
H
or by dechlorination of 1,2-dichloro-1,1-difluoroethane [
280
]:
F
Cl
F
F
F
F
84
C. The monomer is polymerized in aqueous systems under
pressure. Details of the process, however, are kept as trade secrets. Two different molecular weight
materials are available commercially, 300,000 and 6,000,000. Poly(vinylidine fluoride) is crystalline
and melts at 171
C. The material exhibits fair resistance to solvents and chemicals, but is inferior to
polytetrafluoroethylene and to polytrifluorochloroethylene.
Vinylidine fluoride boils at
6.17.4 Poly(vinyl fluoride)
Vinyl fluoride monomer can be prepared by addition of HF to acetylene. The monomer is a gas at
room temperature and boils at
72.2
C. Commercially, vinyl fluoride is polymerized in aqueous
medium using either redox initiation or one from thermal decomposition of peroxides. Pressures of up
