CA1281489C - Process for the polymerization in aqueous dispersion of fluorinated monomers - Google Patents

Abstract

PROCESS FOR THE POLYMERIZATION IN AQUEOUS DISPERSION
OF FLUORINATED MONOMERS.

A B S T R A C T

A process for polymerizing or copolymerizing fluorin-ated monomers, in an aqueous dispersion, by using radicalic-type starters and fluorinated surfactants, characterized in that it is operated in the presence of a perifluoropolyether having neutral end groups and prepared in the form of an aqueous microemulsion, in order to increase the polymeriza-tion rate, to increase the process reproducibility and to mini mize the consumption of said perfluoropolyether.

Description

~L~81~89 The invention relates to a process for polymerizing and copolymerizing fluorinated monomers, in an aqueous dispersion, in the presence of radicalic starters, characterized in particular by a much higher polymerization rate than the one attainable in the known processes under analogous operative conditions.

As is well known, the fluoroolefins exhibit different reactivities in the polymerization process, some of them having very low or no reactivities in comparison with tetrafluoroethylene (TFE). In this connection, C3F6 may be cited as an example.

Also some perfluorinated vinylethers exhibit a very low reactivity in polymerization wi~h respect to the other fluoroolefins, in particular with respect to TFE (see US P 3,I32,123).

The consequence of this behaviour is that the preparation of copolymers from comonomers having very different reactivities from one another requires to operate with a high concentration of tne less reactive monomers and therefore to operate at a very high partial pressure of said comonomer.

For example, to prepare FEP (thermoplastic copolymer C2F4-C3F6) with a content of 5-25% by weight of C3F6, it is necessary to operate with a high concentration of C3F6 in the gas phase, corresponding to a total pressure of the monomers in the range of from 35 to 40 kg/cm2 abs.
(see US P 3,132,124).

., - 2 - ~
i2~

~Z~4~39 Thus, the necessity was felt to increase the polymerization rate for the low-reactive monomers in order to avoid operating at very high pressures, and at the same time to reduce -the polymerization times.

Objet of Canadian patent application no. 535,849 filed April 28, 1987 in the name of the same Applicant hereof is a process for polymerizing or copolymerizing fluorinated monomers in an aqueous dispersion, by using radicalic starters and fluorinated surfactants, in the presence of a perfluoropolyether having neutral end groups, being liquid under the polymerization conditions and in the form of an aqueous emulsion. This process exhibits a very great number of advantages in comparison with the usual polymerization in the absence of perfluoropolyether, while it rises some problems as regards the reproduceability of the emulsion when it is operated with autoclaves of great volume. Furthermore, the process requires the use of considerable amounts of perfluoropolyether in order to obtain remarkable effects on the polymerization rate, what leads, as is well known, to a considerable increase in costs. Moreover, the emulsion must be prepared at the moment, and it cannot be stored due to the limited shelf life of the perfluoropolyethereal emulsions.
It has now surprisingly been found that it is possible to overcome these problems by preparing the perfluoropolyether in the form of an aqueous microe~ulsion.

The term "microemulsion" is used to designate a system in which the perfluoropolyether having neutral end groups _ _ ~8~4~9 ~ olublli~ed by a Rur~a¢tant~ ~olut~on, to provido a monophase solution, which i8 ~tabl~ in the l~ng run~ without providlng dicper ~ion energy.
~ n ~act9 the ~icro~ul~ion ~z pr~pa~ed by ~imple mixing o~ tho oomponent~: water, perfluoropolyether ha~ing neutral end groups and a Plu~rinatad ~ur~acta~t, in particular of th~ typ~ o~
per~luoropol~thor ha~i~g carboxylie end group~ or c~tionic snd group~. Tho detailed de~crip~ion o~ tho ~icro~mul~ions utilized in the pro~nt ~n~ention i~ gi~n ~ Canadian patent application No. 535,845 filed April 28, 1987 of the same Applicant.
Tho ~icroe~uls~o~ prepara~ion i~ r~produceable i6 no~
~nfluenced by ~olume e~feet~ and pro~ide~ ~ ~yst~m~ in which ths int~rphaso area i~ ~er~ h: that por~t~ ~o tran~for polymer~-zat~on rocipe~ fro~ a laboratory ~c~le to a co~orcial scalo wlthout probl~s, and ~o ~en~ibly reduce -the polym~rlzati~n kine-tic6 b~ing the ~a~- tho p~r~luoropolyeth~r ~ount whioh i~ pr~cnt ~n th~ polymeri~ation ~odiu~
It is o~ ~port~nco that por~luoropolyoth~r ~hould b~
in th~ for~ o~ a ~iorvo~ul~ion~ at tho ~o~en~ o~ ~t~ additio~ to the poly~rization ~odiu~ whil~ it ~u~t not n~cos3arily b~ in this ~or~ oncc it ~ dilut~d in the ~olution ln tho autocla~o.

Any per~luoropolyether co~pos~d o~ 6equen~e~ o~ per-~luorooxralkylen~ units can be advantageously utili~ed.
The mean molecular weighto o~ thç per~luoropolyethor~
can Yary o~er a wide ran~e starting ~rom a ~aluo o~ about 500.
In the proco~ o~ the inYention, however, it i6 prefera blo to use p~rfluoropolyethers with a ~ol~cular wei~ht ranging ~ro~ 600 to 3000.
Suitable per~luoropolyothcr~ a~o, for oxample, the ones oP the followlng cla~sos:

1 ) R~?o(cF-cF2o)n(~ ~o)m(cF2o)pR~p ~F3 ~F3 with a random di~tribution o~ the perfluoro-oxyallcylene unit~, wh~r~ ~f and Rl~ llke or di~r~nt ~rom ~ach other, ar~

-C~3~ -C`2F5~ -C3F7~ 8nd m~ n, ha~e ~uch value~ as to meet the abov~said condition~ r~garding the ~ean molecular weight;
2) RpO(CF2cF20)ntcF2~)~R f with a random distributlon o~ tho p~rfluoro_oxyalkyl~n~ unitB~
wh~re R~ and Rl~ lik~ or di~er~nt ~rom ~ach oth~r, are -CF3 or _C2F5, and ~ and n ha~ ~ueh values aæ to meet the abo~aid conditionsl 3) Rfo(cF2cF29)ntcF2o)m ( IFO ) p (C~-CF ~ _R7~

with a random distribution of the p~rfluoro~oxyalk~lene unitB~ whçr~ Rf and Rt~, lik~ or dif~eront ~rom ~ach other, are _CF3~ C2F5 or -C3F~ and m 3 n~ have such valuos a3 to ~aot the abo~esaid conditions;

~.2~3~4~3~

4) RfO (IF-CF2 ~ n ~ R'f ~CF3 J

where Rf or R'f, like or different Erom each other, are -C2F5 or -C3F7, and n has such a value as to meet the above-said conditions:

5) RfOtCF2CF2O)nR f;
where Rf and R'~, like or different from each other, are -CF3, -C2F5, and n has such a value as to meet the above-said conditions;

6) RfO(CF2CF'2CF2O)nR'f, where Rf and R'f, like or different from each other, are -CF3 or -C2F5 or C3F7, n having such a value as to meet the abovesaid conditions, ~ ICF3 R"f Rl'f 7) RfO-~ C O Cl ~ C - O ~ R'f and ~ CF3 R f f ~ n ICF3 IR"f R"f IR"f ~
RfO ~ C - C - C C t R'f ~ CF3 R f R f R f ~ n wherein Rf and R'f are perfluoroalkyl, R"f are F or perfluoroalkyl, n having a such value as to fulfil the abovesaid conditions.
Perfluoropolyethers of class 1) are commercially known under the trademark Fombli ~ Y or Galden~; the ones of class 2), under the trademark Fombli ~ Z, all of them being manufactured by Montedison.

~L~8~4~9 Commercially known products of cla~ 4) are ~rytox (Du PQnt). The product~ o~ clas~ S) aro d~scribed in US patent 4~523~039 or in J. A~. Che~. Soc~ 1985~ 107~ 1197-1201. Tho product~ o~ clas~ 6) are described in European patent EP 148,482 in th~ name o~ Daikin, The product~ o~ clas~ 3) are prepared according to P 3~665~041.
The products o~ cla~ 7) are described in PCT patent application wo.87/00S38, Th~ amount o~ per~luoropolyether -ko be u~ed in the prooe~s o~ the in~ention i~ ~ery low. The amou~t iE of the order o~ 0.05_2 ml per liter of polym~rization aqu~ous solutlon. The preferred amountB are 0.4 - 1.5 ml per liter.
A~ a radicalic ~tarter it i8 possiblo to use any type which i~ well known for tho poly~orization in aqu~ouR dispersion o~ ~luorinat~d ~ono~er~.
Peroxidized compounds in ~enoral~ either inorganlc or or~a~ic~ are suitabl~: a~ong the former~ pota~sium or ammonium por~ulphatee are particularly ~ui~ableD A~ organic peroxides, there are ~u~ tabl~ both tho~e wh~ch aro watar-soluble, such as diRucci-nyl peroxid~ and tho~e wh~ch aro wat~r-in~olublo (~ee for exa~plo EP 75~ 312). It is po~ibl~ ~o us~ al~o the known radicalic ~tar-tors of the tgpe of the azo~oo~pound~ ~uch a~ ~.g. the onos describ ed in US P 2~515~628 and 2~520~338. Whon it i~ de~irablo to operate at low polymorization temperaturo~ t~or ~xampl~ from 10 to 50C)~
a Redox starter csn b~ used, . ~ ~

~8~L489 The rad~calic starter amount ~ the onc which i~ usually employed in th~ polymeri~ation of ~luoro-ole~inss it range~ from 0.003% to 2% by weight re~erred to th~ total amount oP polymeri~-od monomer~, The radicalic startar or -aocording to th~ ca~a- the R~dox system components, can be all lntroduced into the reactor at the beginning of polymerization7 or they can bo gradually ad-dad in the cour~e o~ polymerization.
Th~ ~urfactant requir~d to etabiliz~ th~ latex particle~
i8 contained ~n part or in whole in th~ neutral pcrfluoropolyether microemul~ion. G~nerally, the surfact~nt conta~ned in the microemul ~ion ~ B su~fici~nt for the polymorization proc~
Suitabl~ surfa¢tant~ ar~ the known one~, whiah con~i~t of p~rfluorinatod compounds, in particular those ha~ing 6 to 11 carbon atoms~ o~ tho class of oarboxylic and sulphonic acids.
Furth~r ~uitabl~ eur~actantB are tho~e of ~he clas~ of th~ p~r~luoropol~ether3 ha~in~ one or two acid ond groups.
Thc latter cla~ o~ ~ur~actants i~ the pre~errcd, a8 it o~or6 the ad~Antags o~ a bott~r solubllizing e~ct towards the per~luoropolyoth~r having n~utral ond ~roup~.
The per~luoropoly~thor microemulsion mu~t be introd-uced into tho aqueou~ phaAe a* the b~ginning o~ polymerization: r~o assumption ar~ made on the per~luoropolyeth0r dlsp~r~ion degree, a~tor th~ micro~mulsion ha~ b~on dilut~d in th~ pol~mori~ation medi~m: it could b~ ~till in tho ~orm o~ ~ mi~roemul~ion~ or in a lo~ ~inely particled state, Probably, howeYer, the per~luoro-polyether di~persion degree i~ roluarkably higher than the one at-~,a~4as tainable by th~ proces6 according to Canadian patent application No. 535,849 of the same Applicant hereof. Subsequently, the other ingrodients ~onom~r~ ~tartor~ mol~cular woight regula-tors~ i~ any) are introduced.
The proces~ ~or the polymerlzation in aqueou~ disper-~ion according to tho present inventlon can b~ advantageouely utilized also in the preparatlon o~ copolymer~ o~ C2F4 of the ~ollowing cla~se~:
polytetraPluoro~thylene of nmodified~ typ~ i.e. contain~ng little amounts~ lower than 0.5% by w~i~ht~ o~ ono or mor~ eo-mono~er~ such a~ ~Or example: per~luoropropene~ perfluoroalkyl--perfluoro~inylether~ Yinylid~n~ ~luorldo, hexw~luoroi~obu-t~n~ chlorotrifluoro~thyl~n~;
thermoplas*ic copolymers ~ C2F4 co~pri~in~ the copolymer~ con taining from 7 to 27% by wei~ht o~ C3F~ (t~p~ FEP produced by Du Pont~ th~ one~ contain~ng fro~ 0~5 to 10%~ in particular from 2 to 4~ b~ wei~ht o~ p~r~luorial~ylp~r~luoro~inylother~
~type PFA), the one~ contai~ing a high amount o~ C2H4 plu8 a littlo amount o a third como~omer of the ~luor~nat~d ty,oe (~uoh as Tofz~l ~ produc~d by Du Pont).
- sla~tomoric copol~ers containing Prom 20% to 50% by ~019 0 per~luoroalkylperfluoro~inylother (or o~ perPluoro-oxyalkyl--per~luorovinyl e~hor) and a cure sit~ monomer (for o~amplo Kalræz ~ produced by Du Pont);

-~Z8~ 39 - elastomeric terpolymers of classes CF2 = CH2/C2F4/C3F6 and As a further case in which -the polymerization process of the invention can be usefully employed we can cite the thermoplastic copolymer ClFC - CF2/ethylene (type Halar).
The process according to the invention offers, besides the advantages described hereinbefore, also the same advantages (possibility to operate at lower polymerization pressures than the one of the art) which are illustrated in Applicant's Canadian application No. 535,849 relating to the copolymerization of fluorinated monomers; a particular feature of the process forming the object of the present invention is the obtainment of fluoropolymer aqueous dispersions characterized by an extremely high number of particles per liter and by an extremely little diameter of the particles. Typical examples of values of number of polymer particles per litre are of the order of 0.5 - 5.1018.
A further characteristic of the process forming the object of the present invention is that -~ith equal polymerization kinetics- the utilized perfluoropolyether amount is lower by about an order of magnitude than the one indicated in the examples of Canadian patent application No.
505 849 filed by the Applicant, and this leads to the above mentioned advantages.
The examples given hereinafter are merely illustrative of a few practical embodiments of the process according to the invention.

~X~3~4~39 ThC ~ollowing methods o~ analy~i~ and characterization havo ~e~n utilizod to determin~ the propert~es of the polymeric ma~erial~ obtain~d in the oxampll~x.
a) The dstermination o~ the me~t~ng ~tart temperaturo~ of the melting peak temperature and of the m~lting ~nd temperature was carr~ed out by dif~rential calorim~try, u~ing a Perkin-El~er calorimetor~ t~pe DSC IV. About 10 mg o~ copolymer were heated from room temperature up to 350C at a heating rate of 10C/minute D
The polymer wa~ oooled to room temporatur~ at a rate of 10C/
minute and heatod again to 350C at the ~a~o heating rate. The tamp~rature corr~ponding to the ~axi~u~ o~ the m~lt endotherm i~ horeinafter indicated as s~cond melt peak.
b) Thc ~PF contont in tho C2F4~C3F6 copolymer ~a~ determined by FTIR fipoctroæcopy u~ing a ~icolot ~prectroscope mod. 20SXB on a thin ~ilm ~0.05 mm - 0.01 mm) ~orm2d by oxtru~ion at 340C.
The ratio b~tween the abo6rbanc~ of thc band characteri6tic6 of HFP at 983 c~ and the absorbanco of the re~r~nee band at 2353 cm i~ h~relnaftcr indi~at~3;i as ab~orbance 6pecific ratio.
Tho w~i~ht perc~nt conten~ o~ H~P 1~ calculated ~rou~h proper calibration ohtained from d~ferential mas~ balance, by multi-plying th~ ad orbance opeci~ic ra~io by 4.5.
c) For dotormining the Yi~Co~ity of the m~lt or th~ mel~ flow index (MFI) use was made o~ th~ apparatu~ d~cribed in stand-ard ASTM D-l 238-65T~ with the exception that the cylinder~ the ~ ~14~39 pi~ton and the outlet nozzle wero manufactured ~ro~ corrosion-proo~ material. Tho outlet nozzl~ had a length of 8 m~ and it~
insido diameter was o~ 2.0955 mm, The diamet~r oP the cylinder was 0.95 cm~ A certain amount o~ pol~mer was molten ln the cylin der and wa~ maintained at 372C ~or about ten minutes. The molten polymar wa~ than ~xtru~ed through a nozzlo, maintainin6 a constant ~xtruslon pr~s~ure o~ 5 kg on the pi~ton. The MFI
~alue wa~ calculated on the basis of the gram~ of polymer extrud ed throu~h *he noz~le in 10 ~inutes. To obtain the m~lt apparent v~eo~ity sxpre6sed in pois~ it i~ ~u~loi~nt to di~ide 53,500 by M~I value.
d3 The volatility ind~x (V.I.~ w~ doter~ined by w~i~hing 10 g o~
r~sin on an aluminium ~hc~t, which was placed into a gla66 ~ial connecte~ with a vacuum ~stem. Vacuwm (2 ~m Hg) wa~ generated in the vial and, once the equilibrium was attained, the vial was heated to 3800C. The pro~ur~ in th~ ~ial wa~ recorded with re~pcct to tho tim~. The volatility ind~x ~afi calculated by thc ~ollowing ~ormula:

(P40 _ P ) V
.I. ----------_ __ ____ ~0 where P and P40 aro thc pro~suro~ expres~ed ln ~m of Hg, in the ~ial at timo 0 a~d after 40 minutcs, r~pecti~ely~ and V i~ tho ~ial ~olume of 121 ~ O.2 cm3.

c) The moan diamater of the particlo~ was mea~ured by means o~ a Coulter nano sizer by la~er light dlf~u~ion. A lat~x sample was diluted from 1 to 100 and filt0red on a Millipor~ l.O-micron filtor. Six mea6ure~nts were th~n carri~d out, the ma~imum valuo and the minimum ~alu~ w~ro di~card~d and tho arithmetical m~an of the values ~o found was a~umed a~ m~an diameter Yalue of the particles. The data wore in good accordance with the ones ~ound by transmis~ion slectron microscopy~ w~ich i~ anoth~r method util i~able to determino th~ m~an diamotcr of the partlclc~.
f) The polym4r r~sin wa~ extrud~d in a Brab~nder extruder, type Plasticord PL 651, to cylindrlcal pellet~ ha~ing a diam~ter of about 3~5 mm and a thickne 8 from 1.5 to 3 ~m. The color of the granules wa~ detcrmined by projecting white light through tho ~ample, by causing the r~locted light to pa~ through a ~et o~ ~iltora and by m~a~ur~ng, at laæt, ~h~ int~n~ity of the light.
A high peroontago o~ re~lect~d grean li~ht indicates a high whit~nes6. U~ ed was a Gardner ~olor~meter, type XL lOA, Into a gla~s ~sel there w~ro introduced S parts of an acid having tho structure of a per~luoropolyether belonging to : cla~ 13 wher~in ~ ~ _CF2COOH or -COOH, havin~ a acidimetric mole culsr weight o~ 632, 3 part~ of a p~rfluoropoly~ther o~ clas6 1 with perfluoroalkyl and groups and PM 800, 5 parts of an aqu~ous ~olution o~ 10% N~40H and 10 part6 of water.

~2~3~489 The re~ulting dispersion wa6 heated to 75C under slight stirring. A per~ectly limpid ~olution wa~ obtained. By cool-ing to room temperature, the solution ~eparated into two phase~, but the system behaved reversely to heating. The sy6tem wa~ identified as a microemul~ion ~table in the range of 60 - 90C. 15.3 ml o~ the microcmulsion at 75C, which contained 2 ml of th~ ab~e-indicated neutral per~luoropolyether, w~re added to 2 1 o~ care~ully deaerat-~d wator in a 4.2 1 autoclave made of Bteel AISI 316, oquipp~d with a mechanical stirrer, in which vacuum had been previsouly generated.
The temporature in tho autoclave was brought to 95C undor mcchanical ~tirrlng (600 rpm). The pro~sure was brought to 20 kg/cm g. u~ing a gaseou~ mixture containing 63% by mole~ o~ C3F6 and 37%
o~ C2F4. 62 ml o~ an aqueouc ~olution propared by di~solqing 0.73 g of (NH4)2S208 and 0.73 ~ o~ K2S209 in 500 ml ~ ~2 wero then in-troduced into the autocla~e. AB Boon as the pr~ssure in the autocla ve bogan to decrease, it was re6tored by ~e~ding~ ~y meanfi of a compre~sor~ a C3F6/C2F4 mixturo containing 5.8% by mole~ of hexa-~luoropropene. APtor 15 minutes, the abo~esaid per6ulphate ~olution was fed at a flowrate of 88 ml/h. Stirring in the reactor wa~ con-tinusd for 60 minutes~ whereafter the roaction was stopped and the gas mixture was discharged. An aqu~ous dispersion containin~ 224 g/l o~ a polymeric rosin wafi obtainod.
The m~an diameter oP the di~per~lon particle~, determin ed through eloctron microscopy, was oqual to 0.041 ~ . The num-ber o~ particl~s per liter of watcr (N /1) wa~ equal to 2,9-~ol -~X~31489 The aqueous dispersion was coagulated by mechanical stirring, was filtered and the solid product was repeatedly washed with distilled water and dried in a fan cooled oven at 200C. The product had a M.F.I. (melt flow index) of 0.65 g/10 minutes and a second melt peak at 262.4C. The resulting powder was extruded in a Brebender single-screw extruder. Regular and perfectly white pellets were obtained. The product did not need any further stabilization and whitening treatment. The thermovolatility index was of 59 and the whiteness of 71.

It was operated as in example 1 using 11 ml of the microemulsion according to example 1, containing 1.43 ml of neutral perfluoropolyether.
The reaction was stopped after 65 minutes and the latex was discharged. An aqueous dispersion containing 225 g/l of a polymeric resin was obtained. The average diameter of the particles was determined by electron microscopy and resulted to be equal to 0.046 ~um, corresponding to a number of particles per litre of water of 2.2 . 1013.
The coagulated powder exhibited a melt flow index of 0.92 and an absorbance specific ratio of 3.5.

EXAMPLE 3 ( cosllparison test ~

8 ml of the perfluoropolyether of example l with perfluoroalkyl end groups were added to 250 ml of distilled water.

~ 15 -12~3~489 The suspension was stirred for 5 minutes by means of an Ultraturrax~ s~irrer modO T65 (10,000 rpm) manufactured by IKA Werke. There was added an aqueous solution containing 4 g of CF3~(fF~CF2~)n~CNH4 having an equivalent acidimetric molecular weight of 690.
The emulsion so obtained was homogenized for further 5 minutes. The dispersion was charged into a steel AISI 316 autoclave of 4.2 liter volume, wherein vacuum had been previously generated. Distilled water was added up to a totalvolume of 2,000 ml. The temperature in the autoclave was brought to 95C; the pressure was brought to 20 kg/cm gauge using a gaseous mixture containing 62% by moles of C3F6 and 38% by moles of C2F4. 62 ml of an aqueous solution obtained by dissolving 0.73 g oE (NH4)2S2O8 and 0.73 g of H2S2O8 in 500 ml of H2O were then introduced into the autoclave. As soon as the pressure in the autoclave began to decrease, it was brought to the initial value by feeding, through a compressor, a C3F6/C2F~ mixture containing 6.7% by moles of hexafluoropropene. After 15 minutes, the above-mentioned persulphate solution was fed at a rate of 88 ml/h.
Stirring in the reactor was conducted for 65 minutes, whereafter it was stopped and the reactor content was discharged.
An aqueous dispersion containing 230 g/l of the polymeric resin was obtained.

'iX~3~4~39 The aqueou~ dispcrsion was coagulated by mechanioal ~tirring and wa6 filtorcd; the ~olid product wa~ repeatedly wash od with di~tilled water and wa~ dricd in air circulating o~en at 200C. The product had a melt specific visco~ity o~ 1.063 x 10 poi~e and a melt flow index (M.F.I.) oP 0.5 g/10 minutes and exhi-biked a 6econd melting peak at 264.9C. Thc resulting powder wa8 extruded Ln a Brabender ~ingle-screw extrud~r: regular and per~ec-tly white pellete~ wer~ obtained. The product did not require any ~urther atabilizing and whitoning trcatment. The thcrmovolatility index was of 60 and the wh~teno~ o~ 71.

4.7 ml of a carboxylic acid haYing the structure o~ a p~r~luoropolyether belon~ing to cla~ 1) and having a mean molecu lar woight oP 632 were noutralized wLth S ml o~ 10% NH3. 10 ml o~ H20 and 3 ml o~ per~luoropolycthor oil o~ example 1 havin~ per ~luoro~l~yl end group~ were added.
By heatlng to a tempersturo o~ 70C, a limpid and ~table 8ingl~-phaBC 8y8tom w~s obtained, which re~ulted to be a mLcro-emul~Lon o~ the per~luoropolyoth~r.
The microemul~ion 80 prepared was added, at a temper~-ture o~ 75C, to 3 l o~ throroughly deaeratod water, contained in an ~ISI 316 ~teel autoclave of 4.2 1 volumo, equipped with a me-chanical stirror, in which ~acuum had beon pr~viou~ly gonerated.

The temperature ~n the autoclaYe wa8 brought to 95C
undor mechanical ~tirrlng (600 rpm). The autoclave was pre~uriz ed to 20 k~/cm gauge with a ga~ ml~turç containing 11.57% by moles of por~luoromethyl~lnylother C3F60 and 88.43% o~ C2~4.
124 ml of a solution containing 0.362 g/l o~ K2S208 ~d 0.362 ~/1 of (NH4)2S208 were th~n introduced into the auto cl~v~.
As soon a~ the prossuro in the autocla~e began to ~ink, it was re~torod by foeding, through a compre~or, a C3F60/C2F4 ~ixtur~ containing 2.71~ by molo~ o~ C3F60. After 15 minuteC~ the abo~e-speclfied per~ulphate solution was fed at a ratc of 88 ml/hour.
After stirrîng ~or 60 minutes, the reaction wa~ lnter--ruptod and the Ea~ mi~ture ~a~ di~charged.
An aqueou~ dlsper~ion containing 214 g/l o~ polymer wa~ obtained.
The average C3F60 content in the polymer, dotermined by mass balance~ waB of 3.1% by mole~.
EXAMPLE S
It wa~ oporated a~ i~ defioribod in example 1, using ~10 ml o~ tho microemul~ion described therein, containing 1.3 ml o~ neutral perfluoropolyethor.
The autoclave wau brought to 30C, wheroafter 100 mg of tNH4)2S20g wcre introduced and thc pres~ure W8~ brought to 20 atm. by mean~ o~ a mixture of TFE and perfluoromethyl~inyl-other (PFMVE) (1.6% by mole~ of PFMVE comonomer).

- 18 _ . . .

4~9 A~ aqueous ~olution containing 30 mg of Mohr salt was thon introducod into the autoclave. A~ ~oon a~ the pres~ure in the autocla~e began to decr~ase, it wa restored by mean~ o~
C2F4. The roaction temperature wa~ gradually raisod during the roaction up to 60C. A~tor 75 minutes, stirring wa~ ~topped and the ga~ mixture wa~ di~charged, thereby obtaining an aqeuous disporsion containing 200 g/l of polymer. Thc a~erage diamcter o~ tho disper~ion particle~, determined by electron micro~copy, re~ultcd to bo oP 0.070 micron~.
The number of particles por liter o~ water (N /1) was equal to 5.2 x 10. 7.
Tho comonomer content (PFMVE) o~ the coagulated poly-~or~ det~rmined by ~as6 balance and FTIR sprectroscop~, resulted to be of 0.62% by weight.

Claims (8)

1. A process for polymerizing and copolymerizing fluorinated monomers, in an aqueous dispersion, by using radicalic star ters and fluorinated surfactants, characterized in that it is operated in the presence of porfluoropolyethers having neutral end groups prepared in the form of an aqueous micro-emulsion, said perfluoropolyethers being liquid under the polymerization conditions.

2. The process for polymerizing and copolymorizing fluorinated monomers, in an aqueous dispersion, according to claim 1, wherein the perfluoropolyether has a mean molecular weight not lower than 500, the perifluoropolyether amount being not lower than 0.05 ml per liter of polymerization aqueous solu tion.

3. The process according to claim 2, wherein the perfluoropolyo ther is selected from the following classes:
1) with a random distribution of the porfluorooxyalkyl-eno units, where Rf and R'f, equal or different from each other, are -CF3, -C2F5, -C3F7, and m, n, p have such values as to fulfil the abovesaid mean molecular weight conditions;

2) Rf0(CF2CF20)n(CF20)mR'f with a random distribution of the perfluorooxyalkylene units, where Rf and R'f, equal or different from each other, are -CF3 or -C2F5, and m and n have such values as to fulfil the abovesaid conditions;
3) with a random distribution of perfluorooxyalkylene units, where Rf and R'f, equal or different from each other, are -CF3, -C2F5 or -C3F7, and m, n, p, q have such values as to fulfil the abovesaid conditions;

4) where Rf and R'f, equal or different from each other, are -C2F5 or -C3F7, and n has such a value as to fulfil the abovesaid conditions;

5) Rf0(CF2CF20)nR'f, where Rf and R'f, equal or different from each other are -CF3, -C2F5, and n has such a value as to fulfil the abovesaid conditions;

6) Rf0(CF2CF2CF20) R7, where Rf and R'f, equal or different from each other, are -CF3 or -C2F5 or -C3F7, n having such a value as to fulfil the abovesaid conditions.

7) and wherein Rf and R'f are perfluoroalkyl, R"f are F or perfluoroalkyl, n having a such a value as to fulfil the abovesaid conditions.

4. The process according to claim 1, wherein the surfactant belongs to the class of the perfluoropolyethers having an acid end group.

5. The process according to claim 1, wherein C2F4 is copolymerized with C3F6 in such a ratio as to obtain a copolymer containing from 7% to 27% by weight of C3F6.

6. The process according to claim 1, wherein C2F4 is copolymerized with a perfluoroalkylperfluorovinylether in such a ratio as to obtain a copolymer containing less than 0.5% by weight of perfluoroalkylperfluoro-vinylether.

7. The process according to claim 1, wherein C2F4 is copolymerized with a perfluoroalkylperfluorovinylether in such a ratio as to obtain a copolymer containing from 0.5 to 10% by weight of perfluoroalkylperfluoro-vinylether.

8. Polymers and copolymers prepared from fluorinated monomers according to the polymerization process claimed in claim 1.