Miscellaneous Fluorine Containing Chain-Growth Polymers
One of the miscellaneous fluoroolefin polymers is a copolymer of tri fluoro nitro somethane and tetra fluoro ethylene [287], an elastomer:
It can be formed by suspension polymerization. One procedure is to carry out the reaction in an aqueous solution of lithium bromide at 25C 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:
Two polyfluoro acrylates are manufactured on a small commercial scale for some special uses in jet engines. These are poly (1,1-dihyroperfluorobutyl acrylate):
and poly (3-perfluoromethoxy-1,1-dihydroperfluoropropyl acrylate):
The polymers are prepared by emulsion polymerization with persulfate initiators. Although many other fluorine containing polymers were described in the literature, it is not possible to describe all of them here. They are not utilized commercially on a large scale. A few, however, will be mentioned as examples. One of them is polyfluoroprene [288]:
The polymer is formed by free-radical mechanism, in an emulsion polymerization using redox initiation. All three possible placements of the monomer occur [267]. Polyfluorostyrenes are described in many publications. A b-fluor styrene can be formed by cationic mechanism [289]. The material softens at 240–260C. An a,b,b-trifluorostyrene can be polymerized by free-radical mechanism to yield an amorphous polymer that softens at 240C[290]. Ring-substituted styrenes apparently polymerize similarly to styrene. Isotactic poly(o-fluorostyrene) melts at 265C. It forms by polymerization with Ziegler–Natta catalysts [291]. The meta-analog, however, polymerized under the same conditions yields an amorphous material [291].
