Chemistry Reference
In-Depth Information
F
CF
3
F
F
2
+
H
2
N
NH
2
n
R
F
F
F
CF
3
F
F
n
F
F
HN
NH
R
F
F
n
CF
3
F
F
Free diamines, used for cross-linking, are too reactive and can cause premature gelation. It is
common practice, therefore, to add these diamine compounds in the form of carbamates, like
ethylenediamine carbamate or hexamethylene diamine carbamate. The above fluoro elastomers
exhibit good resistance to chemicals and maintain useful properties from
50 to +300
C.
Copolymers of tetrafluoroethylene with hexafluoropropylene are truly thermoplastic polyperfluor-
oolefins that can be fabricated by common techniques. Such copolymers soften at about 285
C and
have a continuous use temperature of
260 to +205
C. Their properties are similar to, though
somewhat inferior to, polytetrafluoroethylene.
6.17.6 Miscellaneous Fluorine Containing Chain-Growth Polymers
One of the miscellaneous fluoroolefin polymers is a copolymer of trifluoronitrosomethane and
tetrafluoroethylene [
287
], an elastomer:
F
F
O
N
n
F
CF
3
F
It can be formed by suspension polymerization. One procedure is to carry out the reaction in an
aqueous solution of lithium bromide at
25
C with magnesium carbonate as the suspending
agent. No initiator is added and the reaction takes about 20 h. Because the reaction in inhibited by
hydroquinone and accelerated by ultra-violet light, it is believed to take place by a free-radical
mechanism. Whether it is chain-growth polymerization, however, is not certain. A 1:1 copolymer is
always formed regardless of the composition of the monomer feed, and the copolymerization
takes place only at low temperatures. At elevated temperatures, however, cyclic oxazetidines form
instead:
CF
3
N
O
F
2
C
CF
2
