Polymerization process in aqueous emulsion of fuluorinated olefinic monomers

In a process of (co)polymerization in aqueous emulsion of fluorinated olefinic monomers it is added to the reaction medium a microemulsion of fluoropolyoxyalkylenes having hydrogenated end groups and/or hydrogenated repetitive units. A remarkable reduction in the reaction induction period is so obtained, with formation of a product with improved mechanical properties and higher thermal and chemical resistance.

The present invention relates to a (co)polymerization process in aqueous 
emulsion of fluorinated olefinic monomers. More particularly the present 
invention relates to a (co)polymerization process in aqueous emulsion of 
fluorinated olefinic monomers, in which microemulsions of 
fluoropolyoxyalkylenes having hydrogenated end groups and/or hydrogenated 
repetitive units are employed. 
It is known that in the (co)polymerization in aqueous emulsion of 
fluorinated olefinic monomers, the addition of chlorofluorocarbons (CFC) 
increases the reaction rate (see for instance the patent U.S. Pat. No. 
3,635,926). 
A remarkable improvement has been obtained by the process described in the 
patent U.S. Pat. No. 4,864,006, where the fluorinated monomers are 
(co)polymerized in the presence of perfluoropolyoxyalkylenes prepared in 
the form of aqueous microemulsion. Besides avoiding the use of CFC, which 
deplete the ozone layer of the atmosphere, such a process allows to obtain 
a further increase in the reaction rate, in particular for the least 
reactive monomers, and a reduction of the working pressure. 
The Applicant has now surprisingly found that, in (co)polymerization 
processes in aqueous emulsion of fluorinated olefinic monomers, by adding 
to the reaction medium an aqueous microemulsion of a fluoropolyoxyalkylene 
having hydrogenated end groups and/or hydrogenated repetitive units, it is 
possible to obtain a remarkable reduction in the induction period compared 
with the same process carried out in the presence of a microemulsion of 
perfluoropolyoxyalkylenes. By induction period it is meant the time 
running from the moment when the addition of the radical initiator begins 
to the moment when the actual starting of the (co)polymerization is 
observed, as pointed out by a monomer consumption. 
This fact constitutes a remarkable advantage both for the quality of the 
final product and for the industrial application of the process. In fact, 
a short induction period minimizes the formation of low molecular weights, 
which, as known, mainly occurs in the first phase of the reaction, and 
then leads to a narrower molecular weight distribution. As evidenced by 
the experiments carried out by the Applicant, the product obtained with 
the process object of the present invention is also characterized by a 
lower concentration of end groups deriving from the radical initiator and 
therefore by a higher thermal stability. Moreover, when operating with a 
discontinuous process, a lower induction period involves a reduction in 
the "cycle time", namely the time running from a productive cycle to the 
other, with evident advantages for a production on an industrial scale. 
It is therefore object of the present invention a process of radical 
(co)polymerization in aqueous emulsion of one or more fluorinated olefinic 
monomers, optionally in association with one or more non-fluorinated 
olefins, wherein it is operated in the presence of fluoropolyoxyalkylenes 
having hydrogenated end groups and/or hydrogenated repetitive units, added 
to the reaction medium in the form of an aqueous microemulsion. 
Such fluoropolyoxyalkylenes are constituted by repetitive units, randomly 
distributed along the chain, selected from: 
##STR1## 
and by hydrogenated end groups selected from --CF.sub.2 H, --CF.sub.2 
CF.sub.2 H, --CFH--CF.sub.3, and --CFH--OR.sub.f, where R.sub.f is defined 
as above, or perfluorinated end groups selected from --CF.sub.3, --C.sub.2 
F.sub.5 and --C.sub.3 F.sub.7, at least one of the end groups being 
hydrogenated. 
The average molecular weight is generally comprised between 300 and 4000, 
preferably between 400 and 1500. 
In particular, such fluoropolyoxyalkylenes can be selected from the 
following classes: 
##STR2## 
where: T.sub.1 and T.sub.2, equal or different from each other, are 
hydrogenated groups --CF.sub.2 H, --CFH--CF.sub.3, or perfluorinated 
groups --CF.sub.3, --C.sub.2 F.sub.5, --C.sub.3 F.sub.7, at least one of 
the end groups being hydrogenated; X is --F or --CF.sub.3 ; a, b are 
numbers such that the molecular weight is comprised in the range indicated 
above, a/b is comprised between 5 and 15; 
(b) T.sub.3 --O(CF.sub.2 CF.sub.2 O).sub.c (CF.sub.2 O).sub.d --T.sub.4 
where: 
T.sub.3 and T.sub.4, equal or different from each other, are hydrogenated 
groups --CF.sub.2 H or --CF.sub.2 --CF.sub.2 H, or perfluorinated groups 
--CF.sub.3, --C.sub.2 F.sub.5, at least one of the end groups being 
hydrogenated; c, d are numbers such that the molecular weight is comprised 
in the range indicated above, c/d is comprised between 0.3 and 5; 
##STR3## 
where: T.sub.5 and T.sub.6, equal or different from each other, are 
hydrogenated groups --CF.sub.2 H, --CF.sub.2 CF.sub.2 H, or 
--CFH--CF.sub.3, or perfluorinated groups --CF.sub.3, --C.sub.2 F.sub.5, 
--C.sub.3 F.sub.7, at least one of the end groups being hydrogenated; X is 
--F or --CF.sub.3 ; e, f, g are numbers such that the molecular weight is 
comprised in the range indicated above, e/(f+g) is comprised between 1 and 
10, f/g is comprised between 1 and 10; 
##STR4## 
where: T.sub.7 and T.sub.8 are hydrogenated groups --CFH--CF.sub.3, or 
perfluorinated groups --C.sub.2 F.sub.5, --C.sub.3 F.sub.7, at least one 
of the end groups being hydrogenated; h is a number such that the 
molecular weight is comprised in the range indicated above; 
(e) T.sub.9 --O(CZ.sub.2 CF.sub.2 CF.sub.2 O).sub.i --T.sub.10 
where: 
Z is F or H; T.sub.9 and T.sub.10, equal or different from each other, are 
hydrogenated groups --CF.sub.2 H or --CF.sub.2 CF.sub.2 H, or 
perfluorinated groups --CF.sub.3, --C.sub.2 F.sub.5, --C.sub.3 F.sub.7, at 
least one of the end groups being hydrogenated; i is a number such that 
the molecular weight is comprised in the range indicated above; 
##STR5## 
where: R.sub.f is --CF.sub.3, --C.sub.2 F.sub.5, or --C.sub.3 F.sub.7 ; 
T.sub.11 and T.sub.12, equal or different from each other, are 
hydrogenated groups --CF.sub.2 H, --CF.sub.2 CF.sub.2 H, --CFH--OR.sub.f, 
or perfluorinated groups --CF.sub.3, --C.sub.2 F.sub.5, --C.sub.3 F.sub.7, 
at least one of the end groups being hydrogenated; j, k, l are numbers 
such that the molecular weight is comprised in the range indicated above, 
k+l and j+k+l are at least equal to 2, k/(j+l) is comprised between 
10.sup.-2 and 10.sup.3, l/j is comprised between 10.sup.-2 and 10.sup.2 ; 
##STR6## 
where: T.sub.13 and T.sub.14, equal or different from each other, are 
hydrogenated groups --CF.sub.2 H, --CFH--CF.sub.3, or perfluorinated 
groups --CF.sub.3, --C.sub.2 F.sub.5, --C.sub.3 F.sub.7, at least one of 
the end groups being hydrogenated; X is --F or --CF.sub.3 ; m, n, o, p are 
numbers such that the molecular weight is comprised in the range indicated 
above, m/n is comprised between 5 and 40, m/(o+p) is comprised between 2 
and 50, o+p is at least 3, o is lower than p; 
(h) T.sub.15 --O(CF.sub.2 CF.sub.2 O).sub.q (CF.sub.2 O).sub.r (CFHO).sub.s 
(CF.sub.2 CFHO).sub.t --T.sub.16 
where: 
T.sub.15 and T.sub.16, equal or different from each other, are hydrogenated 
groups --CF.sub.2 H, --CF.sub.2 --CF.sub.2 H, or perfluorinated groups 
--CF.sub.3, --C.sub.2 F.sub.5, at least one of the end groups being 
hydrogenated; q, r, s, t are numbers such that the molecular weight is 
comprised in the range indicated above, q/r is comprised between 0.5 and 
2, (q+r)/(s+t) is comprised between 3 and 40, s+t is at least 3, s is 
lower than t; 
##STR7## 
where: T.sub.17 and T.sub.18, equal or different from each other, are 
hydrogenated groups --CF.sub.2 H, --CF.sub.2 CF.sub.2 H, --CFH--CF.sub.3, 
or perfluorinated groups --CF.sub.3, --C.sub.2 F.sub.5, --C.sub.3 F.sub.7, 
at least one of the end groups being hydrogenated: X is --F or --CF.sub.3 
; u, v, w, x, y are numbers such that the molecular weight is comprised in 
the range indicated above, (u+v)/w is comprised between 5 and 40, 
(u+v)/(x+y) is comprised between 2 and 50, x+y is at least 3, x is lower 
than y. 
They are products obtainable by hydrolysis and subsequent decarboxylation 
of the --COF groups present in the corresponding 
perfluoropolyoxyalkylenes, as described for instance in the patents 
EP-154,297, U.S. Pat. No. 4,451,646 and U.S. Pat. No. 5,091,589. 
The starting perfluoropolyethers containing the --COF groups as end groups 
and/or along the chain are described, for instance, in the patents 
GB-1,104,482 (class (a)), U.S. Pat. No. 3,715,378 (class (b)), U.S. Pat. 
No. 3,242,218 (class (c)), U.S. Pat. No. 3,242,218 (class (d)), EP-148,482 
(class (e)), EP-445,738 (class (f)), EP-244,839 and EP-337,346 (classes 
(g), (h), (i)). 
Analogously to the microemulsions of perfluoropolyoxyalkylenes described in 
the patent U.S. Pat. No. 4,990,283, which is herein incorporated by 
reference, by aqueous microemulsion of fluoropolyoxyalkylenes having 
hydrogenated end groups and/or hydrogenated repetitive units it is meant a 
microemulsion of the oil-in-water or water-in-oil type, macroscopically 
formed by a sole liquid phase having a limpid or opalescent appearance, 
stable in a certain temperature range, comprising: 
(a) an aqueous solution; 
(b) a fluoropolyoxyalkylene having hydrogenated end groups and/or 
hydrogenated repetitive units, as above defined; 
(c) a fluorinated surfactant. 
Said microemulsions can also contain co-surfactants, such as low chain 
(C.sub.1 -C.sub.6) hydrogenated or fluorinated alcohols. Salts soluble in 
water can also be added, in order to increase the ionic strength of the 
aqueous phase and to modify the interface tension between the immiscible 
liquids. 
The fluorinated surfactant can be either of the ionic or of the non-ionic 
type, and can be selected from the following classes: perfluorocarboxylic 
or perfluorosulphonic acids C.sub.5 -C.sub.11 and salts thereof; non-ionic 
surfactants disclosed in the patent application EP-51,526; mono- or 
bicarboxylic acids deriving from perfluoropolyoxyalkylenes and salts 
thereof; non-ionic surfactants formed by a perfluoropolyoxyalkylene chain 
bound to a polyoxyalkylene chain; cationic surfactants having one or more 
perfluoroalkyl and/or perfluoropolyoxyalkylene chains; etc. 
The preparation of the microemulsions is performed by simply mixing the 
components, without the need of supplying the system with a remarkable 
dispersion energy, as it occurs, on the contrary, in the case of 
conventional emulsions. 
According to the experiments carried out by the Applicant, the replacement 
of a perfluoropolyoxyalkylene with a fluoropolyoxyalkylene having 
hydrogenated end groups and/or hydrogenated repetitive units as oil phase 
does not involve substantial modifications of the criteria reported in the 
above patent U.S. Pat. No. 4,990,283 to lead the skilled person in the 
formulation of the microemulsions. Of course, under the same conditions, 
the presence of hydrogenated end groups and/or hydrogenated repetitive 
units involves a different affinity with respect to the other components, 
whereby it is often necessary to slightly modify the concentration of the 
components with respect to the corresponding perfluoropolyoxyalkylene 
microemulsions. However, for the skilled person it is sufficient to carry 
out some tests in order to find the proper combination of parameters which 
allow to obtain the desired microemulsion. 
As well known in the art, the (co)polymerization reaction occurs in the 
presence of suitable initiators, such as inorganic peroxides (for 
instance, ammonium or alkali metal persulphates) or organic peroxides (for 
instance, disuccinylperoxide, terbutyl-hydroperoxide, diterbutylperoxide), 
or also azocompounds (see U.S. Pat. No. 2,515,628 and U.S. Pat. No. 
2,520,338). It is also possible to employ organic or inorganic redox 
systems, such as ammonium persulphate/sodium sulphite, hydrogen 
peroxide/aminoimimomethansulphinic acid. 
The amount of radical initiator is that usually employed for the 
(co)polymerization of fluorinated olefinic monomers, and it is generally 
comprised between 0.003% and 5% by weight with respect to the total amount 
of (co)polymerized monomers. 
It is important to point out that the use of fluoropolyoxyalkylenes having 
hydrogenated end groups and/or hydrogenated repetitive units instead of 
the corresponding perfluoropolyoxyalkylenes allows a greater flexibility 
in the selection of the initiator, since the presence of hydrogenated end 
groups increases the affinity with nonfluorinated products. Particularly, 
in the process object of the present invention it is possible to employ 
hydrogenated organic peroxides insoluble in water and in 
perfluoropolyoxyalkylenes, such as for example bis-(4-t-butylcyclohexyl) 
peroxydicarbonate. 
As known, the emulsion technique requires also the presence of surfactants 
to stabilize the polymer particles in the latex. Since the surfactants 
used in the fluoropolyoxyalkylenes microemulsion are of the same kind of 
those commonly used in this kind of (co)polymerizations, generally it is 
not necessary to add other surfactants, the amount present in the 
microemulsion being per se sufficient to the purpose. If this situation 
does not occur, it is always possible to add other surfactants, which can 
be selected from the products having the formula: 
EQU R.sub.f --X.sup.- M.sup.+ 
where R.sub.f is a (per)fluoroalkyl chain C.sub.5 -C.sub.16 or a 
(per)fluoropolyoxyalkylene chain, X.sup.- is --COO.sup.- or 
--SO.sub.3.sup.-, M.sup.+ is selected from: H.sup.+, NH.sub.4.sup.+, 
alkali metal ion. Among those most commonly used we cite: ammonium 
perfluoro-octanoate, (per)fluoropolyoxyalkylenes terminated with one or 
more carboxylic groups, etc. 
The reaction temperature can vary within a wide range, generally comprised 
between 10.degree. and 150.degree. C., preferably between 50.degree. and 
80.degree. C., while the pressure is generally comprised between 1 and 10 
MPa, preferably between 1.5 and 4 MPa. 
The process object of the present invention can be employed with all kinds 
of fluorinated olefinic monomers, optionally containing hydrogen and/or 
chlorine and/or bromine and/or iodine and/or oxygen, provided that they 
are able to give (co)polymers by reaction with radical initiators in 
aqueous emulsion. Among them we can cite: perfluoroolefins C.sub.2 
-C.sub.8, such as tetrafluoroethylene (TFE), hexafluoropropene (HFP), 
hexafluoroisobutene; hydrogenated fluoroolefins C.sub.2 -C.sub.8, such as 
vinylfluoride (VF), vinylidene fluoride (VDF), trifluoroethylene, 
perfluoroalkylethylenes CH.sub.2 .dbd.CH--R.sub.f, where R.sub.f is a 
perfluoroalkyl C.sub.1 -C.sub.6 ; chloro- and/or bromo- and/or 
iodo-fluoroolefins C.sub.2 -C.sub.8, such as chlorotrifluoroethylene 
(CTFE) and bromotrifluoroethylene; (per)fluorovinylethers CF.sub.2 
.dbd.CFOX, where X is a (per)fluoroalkyl C.sub.1 -C.sub.6, for instance 
trifluoromethyl, pentafluoropropyl, bromodifluoromethyl, or a 
perfluorooxyalkyl C.sub.1 -C.sub.9 having one or more ether groups, for 
instance perfluoro-2-propoxypropyl; perfluorodioxols. 
The fluoroolefins can also be copolymerized with nonfluorinated olefins 
C.sub.2 -C.sub.8, such as ethylene, propylene, isobutylene. 
Among the polymers to which the process object of the present is 
applicable, there are particularly comprised: 
(a) "modified" polytetrafluoroethylene, containing small amounts, generally 
comprised between 0.1 and 3% by mols, preferably lower than 0.5% by mols, 
of one or more comonomers such as, for instance: perfluoropropene, 
perfluoroalkylvinylethers, vinylidene fluoride, hexafluoroisobutene, 
chlorotrifluoroethylene, perfluoroalkylethylenes; 
(b) TFE thermoplastic polymers containing from 0.5 to 8% by mols of at 
least a perfluoroalkylvinylether, where the alkyl has from 1 to 6 carbon 
atoms, such as, for instance, TFE/perfluoropropylvinylether, 
TFE/perfluoromethylvinylether, TFE/perfluoroalkylethylene copolymers; 
(c) TFE thermoplastic polymers containing from 2 to 20% by mols of a 
perfluoroolefin C.sub.3 -C.sub.8, such as, for instance, FEP (TFE/HFP 
copolymer), to which other comonomers having vinylether structure (see for 
instance the patent U.S. Pat. No. 4,675,380), can be added in small 
amounts (lower than 5% by mols); 
(d) TFE or CTFE copolymers with ethylene, propylene or isobutylene, 
optionally containing a third fluorinated comonomer in amounts comprised 
between 0.1 and 10% by mols (see for instance the patents U.S. Pat. No. 
3,624,250 and U.S. Pat. No. 4,513,129); 
(e) TFE elastomeric copolymers with a perfluoroalkylvinylether or a 
perfluorooxyalkylvinylether, optionally containing propylene or ethylene, 
besides lower amounts of a "cure-site" monomer (see for instance the 
patents U.S. Pat. No. 3,467,635 and U.S. Pat. No. 4,694,045); 
(f) polymers having dielectric characteristics, comprising 60-79% by mols 
of VDF, 18-22% by mols of trifluoroethylene and 3-22% by mols of CTFE (see 
the patent U.S. Pat. No. 5,087,679); 
(g) VDF elastomeric polymers, such as VDF/HFP copolymers and VDF/HFP/TFE 
terpolymers (see, for instance, the patent GB-888.765 and Kirk-Othmer, 
"Encyclopedia of Chemical Technology", Vol. 8, pag. 500-515--1979); such 
polymers can also contain: hydrogenated olefins, such as ethylene and 
propylene (as described for instance in EP-518,073); 
perfluoroalkylvinylethers; brominated "cure-site" comonomers and/or 
terminal iodine atoms, as described, for instance, in U.S. Pat. No. 
4,243,770, U.S. Pat. No. 4,973,633 and EP-407,937; 
(h) polyvinylidene fluoride or modified polyvinylidene fluoride containing 
little amounts, generally comprised between 0.1 and 10% by mols, of one or 
more fluorinated comonomers, such as hexafluoropropene, 
tetrafluoroethylene, trifluoroethylene. 
The polymers of the classes indicated above, and in particular the polymers 
based on TFE, can be modified with perfluorinated dioxols, as described 
for instance in the patents U.S. Pat. No. 3,865,845, U.S. Pat. No. 
3,978,030, EP-73,087, EP-76,581, EP-80,187. 
Some working examples are hereinunder reported, whose aim is merely 
illustrative but not limitative of the scope of the invention itself.

EXAMPLE 1 
Preparation of the Fluoropolyoxyalkylene Microemulsion Having Hydrogenated 
End Groups 
In a glass flask equipped with a stirrer, 26.1 g of demineralized H.sub.2 
O, 20.0 g of a surfactant of the formula: 
EQU CF.sub.3 O(CF.sub.2 CF(CF.sub.3)O).sub.m (CF.sub.2 O).sub.n CF.sub.2 
COO.sup.- K.sup.+ 
having a m/n ratio=26.2 and an average molecular weight of about 580, and 
14.5 g of a fluoropolyoxyalkylene having the formula: 
EQU CF.sub.2 H--O(CF.sub.2 CF.sub.2 O).sub.m (CF.sub.2 O).sub.n --CF.sub.2 H 
having a m/n ratio=0.95 and an average molecular weight of 365, were added. 
At a temperature comprised between 14.7 and 39.degree. C. the mixture is 
the form of microemulsion, and it appears as a limpid, thermodynamically 
stable solution. 
Copolymerization of Tetrafluoroethylene and Ethylene 
A 5 l AISI 316 steel chromium-plated autoclave, equipped with a stirrer 
working at 570 rpm, was evacuated and 3.5 l of demineralized H.sub.2 O; 
60.6 g of the fluoropolyoxyalkylene microemulsion having hydrogenated end 
groups previously prepared, corresponding to 20.0 g of surfactant, were 
added in sequence. 
The autoclave was then brought to the reaction temperature of 60.degree. C. 
and loaded with an ethylene/TFE gaseous mixture in such an amount to 
obtain, at the working pressure of 22 absolute bar, an ethylene/TFE ratio 
in the gas phase of about 20/80 by mols. The pressure was maintained 
constant during the reaction by feeding an ethylene/TFE mixture with a 
ratio 49/51 by mols. When the working pressure was reached, ammonium 
persulphate (APS), in the form of an aqueous solution, was fed 
continuously for 2 hours with a flow rate of 3.multidot.10.sup.-3 
g/l.multidot.min. 
Taking as reference the moment in which the introduction of the initiator 
began, the reaction started after 10 minutes; after 195 minutes the 
reaction was stopped by cooling the autoclave at room temperature. The so 
obtained latex was then discharged, coagulated by mechanical stirring, 
washed with H.sub.2 O and dried. 928 g of a copolymer ethylene/TFE were 
obtained. The values of productivity (R.sub.p) are reported in Table 1, 
expressed as grams of produced polymer per minute per H.sub.2 O liter. 
EXAMPLE 2 (comparative) 
Preparation of the Perfluoropolyoxyalkylene Microemulsion 
In a glass flask equipped with a stirrer, 20.0 g of the surfactant of the 
formula: 
EQU CF.sub.3 O--(CF.sub.2 --CF(CF.sub.3)O).sub.n (CF.sub.2 O).sub.m --CF.sub.2 
COO.sup.- K.sup.+ 
having n/m=10 and average molecular weight of 580, 18.0 g of demineralized 
water and 12.0 g of Galden.sup.(R) DO2, of the formula: 
EQU CF.sub.3 O--(CF.sub.2 --CF(CF.sub.3)O).sub.n (CF.sub.2 O).sub.m --CF.sub.3 
having n/m=20 and average molecular weight of 450, were mixed. At a 
temperature comprised between 0.degree. and 55.degree. C. the mixture is 
in the form of a microemulsion and appears as a limpid solution. 
Copolymerization of Tetrafluoroethylene and Ethylene 
Example 1 was repeated in the same conditions, using an amount of the 
perfluoropolyoxyalkylene microemulsion previously prepared such as to 
obtain 20.0 g of surfactant. By taking as zero time the time when the 
addition of the initiator began, the reaction started after 52 minutes; 
after 233 minutes the reaction was stopped and 934 g of a copolymer 
ethylene/TFE were obtained. The measured values of productivity (R.sub.p) 
are reported in Table 1. 
EXAMPLE 3 
A 5 l AISI 316 steel chromium-plated autoclave, equipped with a stirrer 
working at 570 rpm, was evacuated, and 3.4 l of demineralized H.sub.2 O; 
60.6 g of the fluoropolyoxyalkylene microemulsion having hydrogenated end 
groups of Example 1, corresponding to 20.0 g of surfactant; 64 g of 
terbutanol; 3 g of n-pentane as chain transfer agent, were introduced in 
sequence. 
The autoclave was then brought to the reaction temperature of 60.degree. C. 
and charged with an ethylene/TFE gaseous mixture in such an amount to 
obtain, at the working pressure of 22 absolute bar, an ethylene/TFE ratio 
in the gas phase of about 20/80 by mols. The pressure was kept constant 
during the raction by feeding an ethylene/TFE mixture in a molar ratio 
49/51. When the working pressure was reached, ammonium persulphate (APS), 
in the form of aqueous solution, was continuously fed for 2 hours with a 
flow rate of 3.multidot.10.sup.-3 g/l.multidot.min. Taking as zero time 
the time when the addition of the initiator began, the reaction started 
after 26 minutes; after 223 minutes the reaction was stopped by cooling 
the autoclave at room temperature. The so obtained latex was discharged, 
coagulated by mechanical stirring, washed with H.sub.2 O and dried. 310 g 
of an ethylene/TFE copolymer was obtained. The values of the Melt Flow 
Index (MFI) (according to ASTM Method D 3159-83) and of the radical 
concentration, expressed as grams of SO.sub.4.sup.- .multidot. radicals 
produced during the reaction per polymer gram, are reported in Table 2. 
From the so obtained copolymer a film having a thickness of 0.4 mm was 
molded, which was then submitted to aging in air at 235.degree. C. for 
144, 264 and 360 hours. The sample was analyzed at FT-IR in the absorption 
range corresponding to the double bonds (1800-1650 cm.sup.-1), which form 
as a consequence of the degradation of the product. The values of the area 
of the absorption band in said range (A.sub.t) are reported, measured at 
the different times of aging, to which the area of the band at zero time 
(A0) was subtracted. 
EXAMPLE 4 (comparative) 
Example 3 was repeated in the same conditions, using an amount of the 
perfluoropolyoxyalkylene microemulsion of Example 2 such as to obtain 20.0 
g of surfactant. By taking as zero time the moment when the addition of 
the initiator began, the reaction started after 42 minutes; after 266 
minutes the reaction was stopped and 310 g of an ethylene/TFE copolymer 
were obtained. The values of the MFI and of the radical concentration, 
measured as described in Example 3, are reported in Table 2. 
From the so obtained copolymer a film having a thickness of 0.4 mm was 
molded, whose thermal stability was tested according to the method 
described in Example 3. The so obtained data are reported in Table 2. 
TABLE 1 
__________________________________________________________________________ 
INDUCTION 
REACTION 
OBTAINED 
PERIOD TIME POLYMER 
R.sub.p 
RADICAL CONC. 
EX. 
(min) (min) (g) (g/l.sub.H2O /min) 
(rad.g./pol.g.) 
__________________________________________________________________________ 
1 10 195 928 1.36 4.81 .multidot. 10.sup.-5 
2.sup.( *.sup.) 
52 233 934 1.14 6.09 .multidot. 10.sup.-5 
__________________________________________________________________________ 
.sup.(*.sup.) comparative 
TABLE 2 
______________________________________ 
AGEING AT 
235.degree. C. (A.sub.t - A.sub.0) 
MFI RADICAL CONC. (optical density units .multidot. cm.sup.-1) 
EX. (g/10') (rad.g./pol.g.) 
144 h 264 h 360 h 
______________________________________ 
3 4.1 1.73 .multidot. 10.sup.-4 
2.6 4.3 5.7 
4.sup.( *.sup.) 
6.9 2.18 .multidot. 10.sup.-4 
3.0 5.4 6.4 
______________________________________ 
.sup.(*.sup.) comparative