Perfluoroalkenes and fluorination products thereof

The present invention relates to the synthesis of new terminal olefins, perfluoro 2,4-dimethyl 3-ethylpentene and perfluoro 2-isopropyl 3,3-dimethylbutene, and to the subsequent fluorination thereof in order to obtain highly branched perfluoroalkanes, capable of providing perfluoroalkyl radicals, which are utilizable as initiators for the polymerization of ethylenically unsaturated monomers.

The present invention relates to the synthesis of new terminal olefins, 
perfluoro 2,4-dimethyl 3-ethylpentene and perfluoro 2-isopropyl 
3,3-dimethylbutene, and to the subsequent fluorination thereof in order to 
obtain highly branched perfluoroalkanes, capable of providing 
perfluoroalkyl radicals, which are utilizable as initiators for the 
polymerization of ethylenically unsaturated monomers. 
Object of the present invention are new initiators for the polymerization 
of ethylenically unsaturated products and in particular of fluorinated 
olefins. More in particular, the present invention relates to 
perfluorinated compounds capable of releasing radicals which are highly 
reactive under the polymerization conditions. Actually, the perfluoroalkyl 
radicals are very interesting as they do not exhibit the drawbacks caused 
by inorganic peroxides, such as for example the persulphates, which 
introduce reactive end groups into the polymer, what requires subsequent 
expensive treatments in order to convert again the polymer end groups to 
non-reactive groups (D.I. Mc Cane Encyclopedia of Polymer Science and 
Technology, vol. 12, pages 623-670). 
However, at present, the generators of perfluoroalkyl radicals are often 
too stable, such as e.g. CF.sub.3 I, which requires too high utilization 
temperatures and which could interfere with the polymerization process, 
thereby causing undesirable drawbacks, or they are too expensive, such as 
the perfluoroacyl peroxides. 
In EP 121,898, by partial fluorination of the C.sub.3 F.sub.6 trimers, 
stable perfluoroalkyl radicals are obtained. However, these products are 
obtained with not very high yields and in admixture with the reaction raw 
products. Therefore these radicals are little utilizable because the 
olefins can interfere with the monomers during the polymerization step. 
In Italian patent application 20061 A/87 in the name of the Applicant 
hereof, the hexafluoropropene trimer of formula (I): 
##STR1## 
prepared according to the process described in U.S. Pat. No. 3917724 was 
subjected to fluorination in the presence of U.V. radiation, so obtaining 
the compounds of formulae (II) and (III): 
##STR2## 
These perfluoroalkanes, when subjected to temperatures higher than 
100.degree. C., decompose, thereby generating perfluoroalkyl radicals, 
which are utilized in radical polymerization. 
Other perfluoroalkanes capable of providing perfluoroalkyl radicals to be 
utilized as initiators for radical polymerization have now surprisingly 
been found. 
In fact, when the olefin of formula (I) is subjected to U.V. radiation, it 
isomerizes and provides the terminal olefins of formulas (IV) and (V): 
##STR3## 
which, when subjected to fluorination, give rise to the perfluoroalkanes 
of formulas (VI) and (IX): 
##STR4## 
which, since they are highly ramified, are capable of generating 
perfluoroalkyl radicals at temperatures higher than 100.degree. C. 
The isomerization reaction is generally conducted at room temperature by 
irradiating with U.V. radiation (the source of which is a high pressure 
Hg-vapor lamp type Hanau TQ 150W) the perfluoroolefin of formula (I); the 
reaction raw product is then purified by rectification. 
The further fluorination reaction to obtain the compound of formula (VI) 
and of formula (IX) from perfluorooilefins (IV) and (V) is generally 
conducted at room temperature, by introducing, at the beginning, the 
fluorine diluted with an inert gas and by gradually raising the fluorine 
flow as the reaction proceeds. The products of formulas (VI) and (IX) are 
isolated by rectification. 
By the process according to the invention, besides the mentioned 
perfluoroalkanes, other perfluoroalkanes are obtained, in particular the 
product (VIII), which, however, is not utilizable as a generator of 
radicals 
Furthermore, the perfluorooolefins of formulas (IV) and (V) according to 
the present invention, besides being useful intermediates for the 
preparation of perfluoroalkanes utilizable as sources of perfluoroalkyl 
radicals, prove to be advantageous starting products for the preparation 
of fine chemicals. 
The following examples are given merely to illustrate the present invention 
and are not to be construed as a limitation of the scope thereof.

EXAMPLE 1 
Into a quartz photochemical immersion reactor, having an optical path of 1 
cm, there were introduced 350 g of the olefin of formula (I), containing, 
2% of its isomer of formula (VII): 
EQU [(CF.sub.3).sub.2 CF].sub.2 C.dbd.CFCF.sub.3 (VII) 
The starting compound was subjected to ultraviolet radiation by means of a 
high pressure Hg-vapor lamp (Hanau TQ 150W). 
In the course of the reaction it was possible to observe, by means of a 
gas-chromatographic analysis, a progressive decrease of the product of 
formula (I) and a simultaneous appearing of 2 new peaks in a ratio to each 
other of 3 to 2. After approximately a 200-hour irradiation, although the 
perfluorononene of formula (VII) initially contained in the starting 
product was still present, the conversion of the olefin of formula (I) 
resulted to be complete The final mixture was subjected to 
gas-chromatographic analysis and revealed the following composition : 
______________________________________ 
perfluoroolefin of formula (IV) 
56% 
perfluoroolefin of formula (V) 
38% 
perfluoroolefin of formula (VII) 
6% 
______________________________________ 
The reaction raw product was purified by rectification on a column equipped 
with 90 plates. Isolated were the products of formula (IV) and (V), which 
boiled at 116.degree. C. and 118.degree. C. respectively. 
The structure of the product was confirmed by NMR (.sup.19 F, 
.delta.CFCl.sub.3), the results being as follows: 
##STR5## 
EXAMPLE 2 
Into a tubular reactor having a diameter of 3.5 cm there were charged 370 g 
of a mixture consisting for 60% of the olefin of formula (IV) and for 40% 
of the olefin of formula (V) in order to have in the reactor a liquid 
height of about 20 cm. After having put the whole under a nitrogen 
atmosphere, a 1:1 mixture of N.sub.2 /F.sub.2 (total flow of 2 1/h), and 
then pure F.sub.2 (flow of 1 1/h) were bubbled thereinto, at an inner 
temperature of 30 C. Exothermicity of the reaction was observed and the 
trend thereof was followed by means of gas-chromatographic analysis; a 
progressive decrease of the peaks relating to the starting products was 
observed. 
After 20 hours, while maintaining constant the F.sub.2 flow equal to 1 1/h, 
the reaction was complete and the mixture resulted to be composed by the 
following three products: 
______________________________________ 
perfluoroalkane of formula (VIII) 
24% 
perfluoroalkane of formula (IX) 
26% 
perfluoroalkane of formula (VI) 
50%. 
______________________________________ 
Products (VIII), (IX) and (VI) were isolated by rectification on a 90 
plates column and were subjected to NMR analysis (.sup.19 
F,.delta.CFCl.sub.3), which enabled to determine the structure. The 
results were as follows: 
##STR6## 
EXAMPLE 3 
30 g of the product of formula (V) were subjected to an analogous 
fluorination: obtained were high yields of the perfluoroalkane of formula 
(VI) and little amounts of products having a lower number of carbon atoms 
deriving from the rupture of the carbon-carbon single bonds. 
EXAMPLE 4 
The perfluoroalkane having formula (VI) was heated in sealed glass phials 
at different temperatures and times. The decomposition was followed by 
gaschromatographic analysis and the results are showed hereinbelow: 
______________________________________ 
Time Temperatures 
(h) (.degree.C.) 
% of product decomposed 
______________________________________ 
11 200 52 
3,30 210 72 
5 210 85 
8 180 3 
______________________________________ 
EXAMPLE 5 
560 mg (1.2 m moles) of the perfluoroalkane of formula (VI) were loaded 
into a reactor having a volume of 30 ml and an inner diameter of 1 cm and 
after degasification 1,4 g of tetrafluoroethylene were charged and heated 
at 100.degree. C. for 1 hour and 20 minutes. Obtained are 19 g of 
polytetrafluoroethylene having a molecular weight of 145,000 . 370 mg of 
the polymeric initiator are recovered.