U.S. patent application number 13/502478 was filed with the patent office on 2012-08-09 for process for the isolation of sulfonyl fluoride polymers and polymers obtained therefrom.
This patent application is currently assigned to Solvay Specialty Polymers Italy S.P.A.. Invention is credited to Martina Corasaniti, Alessandro Ghielmi, Claudio Oldani, Alessandro Veneroni.
Application Number | 20120202946 13/502478 |
Document ID | / |
Family ID | 42014806 |
Filed Date | 2012-08-09 |
United States Patent
Application |
20120202946 |
Kind Code |
A1 |
Veneroni; Alessandro ; et
al. |
August 9, 2012 |
Process for the isolation of sulfonyl fluoride polymers and
polymers obtained therefrom
Abstract
The invention relates to a process for the isolation of
(per)fluorinated polymers containing sulfonyl fluoride functional
groups from a polymerization latex. The process comprises adding
the polymerization latex to an aqueous electrolyte solution under
high shear stirring at a temperature equal to or lower than the
glass transition temperature of the polymer. The invention further
relates to the (per)fluorinated polymers containing sulfonyl
fluoride functional groups isolated by the process and
characterised by a loss of weight at 200.degree. C. lower than 1%
as determined by thermogravimetric analysis.
Inventors: |
Veneroni; Alessandro;
(Novate Milanese (MI), IT) ; Oldani; Claudio;
(Nerviano (MI), IT) ; Corasaniti; Martina;
(Caronno Pertusella (VA), IT) ; Ghielmi; Alessandro;
(Frankfurt am Main, DE) |
Assignee: |
Solvay Specialty Polymers Italy
S.P.A.
Bollate MI
IT
|
Family ID: |
42014806 |
Appl. No.: |
13/502478 |
Filed: |
October 22, 2010 |
PCT Filed: |
October 22, 2010 |
PCT NO: |
PCT/EP2010/065921 |
371 Date: |
April 17, 2012 |
Current U.S.
Class: |
524/805 ;
526/243 |
Current CPC
Class: |
C08F 14/18 20130101;
C08J 5/225 20130101; C08J 5/18 20130101; C08J 2327/18 20130101;
C08F 214/18 20130101; C08J 2327/12 20130101; C08F 6/22 20130101;
C08F 14/18 20130101; C08F 2/22 20130101; C08F 2/04 20130101; C08L
27/12 20130101; C08F 6/22 20130101; C08F 214/26 20130101 |
Class at
Publication: |
524/805 ;
526/243 |
International
Class: |
C08F 28/02 20060101
C08F028/02; C08F 2/16 20060101 C08F002/16 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 29, 2009 |
EP |
09174439.1 |
Claims
1. A polymer comprising recurring units derived from at least one
ethylenically unsaturated (per)fluorinated monomer (A) containing
at least one sulfonyl fluoride group said polymer having a loss of
weight at 200.degree. C. lower than 1% as measured by
thermogravimetric analysis according to ASTM E1131-86.
2. The polymer according to claim 1 further comprising recurring
units of at least one ethylenically unsaturated (per)fluorinated
monomer (B).
3. The polymer according to claim 1 wherein said monomer (A) is
present in an amount such that the equivalent weight of the polymer
when converted into its acid form is less than 750 g/eq.
4. The polymer according to claim 3 wherein the equivalent weight
is at least 400 g/eq.
5. The polymer according claim 1 having a melt flow rate measured
according to ASTM D1238-04 at 200.degree. C./5 kg of less than 50
g/10 min.
6. The polymer according to claim 1 wherein said monomer (A) is
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F and said monomer (B) is
tetrafluoroethylene.
7. Process for the isolation of a polymer of claim 1 from a
polymerization latex comprising adding said latex under high shear
stirring to an aqueous electrolyte solution held at a temperature
equal to or lower than the glass transition temperature of the
polymer.
8. The process of claim 7 wherein the rate of stirring is such that
the Reynolds number Re=.rho.Nd.sub.I.sup.2/.mu. wherein .rho. is
the density of water (kg/m.sup.3), N the number of revolutions per
second of the impeller (1/s), d.sub.I the diameter of the impeller
(m) and .mu. the dynamic viscosity of water (Pas) is greater than
10,000.
9. The process of claims 7 wherein the electrolyte is selected from
the group consisting of HNO.sub.3, Al(NO.sub.3).sub.3,
Al.sub.2(SO.sub.4).sub.3, Ca(NO.sub.3).sub.2, Zn(NO.sub.3).sub.2,
ZnSO.sub.4, CaCl.sub.2, MgSO.sub.4.
10. An extruded film comprising the polymer of claim 1.
11. A membrane comprising the film of claim 10 in hydrolysed
form.
12. A process for preparing a polymerization latex comprising the
polymerization of at least one ethylenically unsaturated
(per)fluorinated monomer (A) containing at least one sulfonyl
fluoride group in a liquid phase in the presence of a free radical
initiator, at least a portion of said free radical initiator being
added to the liquid phase held at a temperature T1, said process
characterised in that after an incubation time the temperature of
the liquid phase is brought to a temperature T2 lower than T1.
13. The process according to claim 12 wherein the incubation time
is at least 5 seconds.
14. The process according to claim 12 wherein T1 is at least
0.degree. C. and does not exceed 150.degree. C.
15. The process according to claim 12 wherein T2 is at least
5.degree. C. lower than T1.
Description
[0001] This application claims priority to European application No.
09174439.1 filed on Oct. 29, 2009, the whole content of which being
incorporated herein by reference for all purposes.
TECHNICAL FIELD
[0002] The invention relates to a process for the isolation of
(per)fluorinated polymers containing sulfonyl fluoride functional
groups from a polymerization latex and to the polymers obtained
therefrom.
[0003] The invention further relates to a process for the
preparation of a polymerization latex comprising (per)fluorinated
polymers containing sulfonyl fluoride functional groups
characterized by a high rate of incorporation of the functional
monomer into the polymer chain and by the high molecular weight of
the polymer.
BACKGROUND ART
[0004] (Per)fluorinated polymers containing sulfonyl fluoride
functional groups are known in the prior art as precursors for a
class of ion exchange (per)fluorinated polymers generally referred
to as "ionomers".
[0005] Due to their ionic properties, (per)fluorinated ionomers are
suitable in the manufacture of electrolyte membranes for
electrochemical devices such as fuel cells, electrolysis cells,
lithium batteries.
[0006] Fuel cells are electrochemical devices that produce
electricity by catalytically oxidizing a fuel, such as hydrogen or
methanol. Among known fuel cells of particular interest are proton
exchange membrane (PEM) fuel cells which employ hydrogen as the
fuel and oxygen or air as the oxidant. In a typical PEM fuel cell,
hydrogen is introduced into the anode portion, where hydrogen
reacts and separates into protons and electrons. The membrane
transports the protons to the cathode portion, while allowing a
current of electrons to flow through an external circuit to the
cathode portion to provide power. Oxygen is introduced into the
cathode portion and reacts with the protons and electrons to form
water and heat.
[0007] The membrane requires an excellent ion conductivity, gas
barrier properties (to avoid the direct mixing of hydrogen and
oxygen), mechanical strength and chemical, electrochemical and
thermal stability at the operating conditions of the cell.
[0008] One of the most important requirements for the long-term
functioning of a PEM fuel cell is the ability of the membrane to
maintain a suitable water content in the membrane itself to ensure
the required level of ion conductivity.
[0009] Fuel cell membranes, when operated using dry reactants and
high operating temperatures, have a tendency to dry out with a
negative impact on their proton transport capabilities, which in
turn causes a loss in cell efficiency. Moreover, if the water
transport through the membrane is not efficient, the water which is
produced at the cathode is not made available to the anode, which
consequently dries out, again with a loss in cell efficiency. It is
therefore important that, under dry operating conditions, the
membrane maintains a high proton transport capability and
efficiently transfers water generated during the cell operation
from one side of the membrane to the other.
[0010] A preferred way of obtaining a membrane with these
characteristics is to use an ionomer having a high number of ion
exchange groups and to reduce the thickness of the membrane.
[0011] The number of ion exchange groups in an ionomer is typically
indicated by the equivalent weight of the ionomer. The lower the
equivalent weight, the higher the percentage of sulfonic groups
present in the chain.
[0012] One problem encountered in the preparation of ionomers with
low equivalent weight, typically lower than 750 g/eq, is that, in
general, the molecular weight of the precursor sulfonyl fluoride
polymer, and consequently of the ionomer, is reduced.
[0013] Low molecular weight polymers result in scarce mechanical
properties, which in turn means inadequate properties of the final
proton exchange membrane. Moreover, a low molecular weight of the
polymer renders impractical to process the polymer by melt
extrusion.
[0014] On the other hand, melt extrusion would be an advantageous
process for the production of thin polymeric films. Melt extrusion
requires the starting polymer not only to be thermally stable at
the processing temperatures but also to possess an adequate melt
rehology, which is partly dependent on the molecular weight of the
polymer.
[0015] It would therefore be desirable that sulfonyl fluoride
polymers used for the production of films by melt extrusion
processes be provided with no or limited loss of volatile
substances at the melt processing temperatures.
[0016] Furthermore, it would be desirable to have available
sulfonyl fluoride polymers, precursors of low equivalent weight
ionomers, which are melt processable and have no or limited loss of
volatile substances at their melt processing temperatures.
SUMMARY OF THE INVENTION
[0017] An objective of the invention is to provide a process for
the isolation of sulfonyl fluoride polymers from a polymerization
latex which provides for a reduced content of volatile substances
in the sulfonyl fluoride polymer that can be volatilized at the
melt processing temperatures, as indicated by the reduced loss of
weight of the polymer at high temperatures, in particular at
200.degree. C. According to this process the sulfonyl fluoride
polymer is isolated from the polymerization latex by addition under
high shear stirring to an electrolyte solution held at a
temperature equal to or lower than the glass transition temperature
of the polymer.
[0018] Another objective of the invention is to provide a process
of preparing a polymerization latex comprising sulfonyl fluoride
polymers with sufficiently high molecular weight to be melt
processable and characterized by an equivalent weight lower than
700 g/eq when converted into acid form.
[0019] A further objective of the present invention is a polymer
comprising recurring units of at least one ethylenically
unsaturated (per)fluorinated monomer containing at least one
sulfonyl fluoride group characterized by a loss of weight at
200.degree. C. lower than 1%. Preferably the loss of weight is
lower than 0.8%, more preferably lower than 0.7%, even more
preferably lower than 0.5% by weight as measured by
thermogravimetric analysis (TGA) according to ASTM E 1131-86.
[0020] In an aspect of the invention the sulfonyl fluoride polymer
comprises recurring units of at least one ethylenically unsaturated
(per)fluorinated monomer containing at least one sulfonyl fluoride
group in an amount sufficient to provide a polymer having an
equivalent weight of less than 750 g/eq when converted into acid
form. Preferably the monomer containing at least one sulfonyl
fluoride group is present in an amount sufficient to provide a
polymer having an equivalent weight less than 700 g/eq when
converted into acid form. The monomer containing at least one
sulfonyl fluoride group is present in an amount sufficient to
provide a polymer having an equivalent weight of at least 400 g/eq
when converted into acid form.
[0021] In a further aspect of the invention the melt flow rate of
the sulfonyl fluoride polymer does not exceed 50, preferably it
does not exceed 45, more preferably it does not exceed 40 g/10 min
when measured according to ASTM D1238-04 at 200.degree. C./5 kg.
The melt flow rate of the sulfonyl fluoride polymer is at least
0.1, preferably at least 0.2, more preferably at least 0.5 g/10 min
when measured according to ASTM D1238-04 at 200.degree. C./5
kg.
[0022] Further objectives of the present invention are an extruded
film made of the sulfonyl fluoride polymer as well as a proton
exchange membrane comprising the extruded film in hydrolysed form,
i.e. wherein the sulfonyl fluoride polymer making the extruded film
has been converted into its acid form by hydrolysis.
Definitions
[0023] The term (per)fluorinated is used herein to refer to
compounds (e.g.
[0024] monomers, polymers etc.) that are either totally or
partially fluorinated, i.e wherein all or only a part of the
hydrogen atoms have been replaced by fluorine atoms.
[0025] The expression "sulfonyl fluoride polymer" is used herein to
refer to a (per)fluorinated polymer comprising recurring units of
at least one ethylenically unsaturated (per)fluorinated monomer
containing at least one sulfonyl fluoride group (--SO.sub.2F).
[0026] The term "ionomer" is used in the present application to
refer to a (per)fluorinated polymer comprising recurring units
derived from at least one ethylenically unsaturated
(per)fluorinated monomer comprising at least one ion exchange group
--SO.sub.3--.
[0027] The term "equivalent weight" is defined as the weight of the
polymer in acid form required to neutralize one equivalent of NaOH,
wherein the phrase "acid form of a polymer" means that
substantially all the ion exchange groups of the polymer are
protonated.
[0028] The phrase "melt processable" is used herein to refer to a
polymer that can be processed in the melt (i.e. fabricated into
shaped articles such as films, fibres, tubes, wire coatings and the
like) with conventional polymer processing equipment such as
extruders and injection molding machines. Typically melt
processable polymers have melt flow rates at the processing
temperatures of from 0.1 to 100 g/10 min.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The first object of the present invention is a process for
the isolation of a sulfonyl fluoride polymer from a polymerization
latex comprising adding under high shear stirring said latex to an
aqueous electrolyte solution held at a temperature below the glass
transition temperature of the polymer. The process allows to obtain
sulfonyl fluoride polymers with a reduced content of volatile
substances, in particular sulfonyl fluoride polymers having a loss
of weight at 200.degree. C. lower than 1% as measured by
thermogravimetric analysis.
[0030] The process has been found to be particularly advantageous
for the isolation of sulfonyl fluoride polymers containing a high
amount of ethylenically unsaturated (per)fluorinated monomer
containing at least one sulfonyl fluoride group, typically an
amount sufficient to provide a polymer having an equivalent weight
of less than 750 g/eq when converted into its acid form.
[0031] The expression "polymerization latex" is used herein to
refer to a latex (or dispersion of a sulfonyl fluoride polymer)
obtained directly by a dispersed phase polymerization process of at
least one ethylenically unsaturated (per)fluorinated monomer
containing at least one sulfonyl fluoride group. For the purpose of
the present invention a "dispersed phase polymerization process"
includes dispersion or emulsion, including microemulsion or
miniemulsion, polymerization processes. The polymerization latex is
advantageously obtained by any process comprising a dispersed phase
polymerization step.
[0032] The term "latex" is used to denote a colloid in which solid
polymer particles having a size of between 1 and 1000 nm are
dispersed in a suspending medium. Preferably the suspending medium
is water.
[0033] The sulfonyl fluoride polymer dispersed in the
polymerization latex comprises recurring units derived from at
least one ethylenically unsaturated (per)fluorinated monomer (A)
containing at least one sulfonyl fluoride group.
[0034] Preferably the sulfonyl fluoride polymer comprises recurring
units derived from at least one monomer (A) and at least one
ethylenically unsaturated (per)fluorinated monomer (B).
[0035] The phrase "at least one monomer" is used herein with
reference to monomers of both type (A) and (B) to indicate that one
or more than one monomer of each type can be present in the
polymer. Hereinafter the term monomer will be used to refer to both
one or more than one monomer of a given type.
[0036] Non limiting examples of suitable monomers (A) are: [0037]
sulfonyl fluoride (per)fluoroolefins of formula:
CF.sub.2.dbd.CF(CF.sub.2).sub.nSO.sub.2F wherein n is an integer
between 0 and 6, preferably n is equal to 2 or 3; [0038] sulfonyl
fluoride (per)fluorovinylethers of formula:
CF.sub.2.dbd.CF--O--(CF.sub.2).sub.mSO.sub.2F [0039] wherein m is
an integer between 1 and 10, preferably between 1 and 6, more
preferably between 2 and 4, even more preferably m equals 2; [0040]
sulfonyl fluoride (per)fluoroalkoxyvinylethers of formula:
[0040]
CF.sub.2.dbd.CF--(OCF.sub.2CF(RF.sub.1)).sub.w--O--CF.sub.2(CF(RF-
.sub.2)).sub.ySO.sub.2F
wherein w is an integer between 0 and 2, RF.sub.1 and RF.sub.2,
equal or different from each other, are independently --F, --Cl or
a C.sub.1-C.sub.10 perfluoroalkyl group, optionally substituted
with one or more ether oxygens, y is an integer between 0 and 6;
preferably w is 1, RF.sub.1 is --CF.sub.3, y is 1 and RF.sub.2 is
--F; [0041] sulfonyl fluoride aromatic (per)fluoroolefins of
formula CF.sub.2.dbd.CF--Ar--SO.sub.2F wherein Ar is a
C.sub.5-C.sub.15 aromatic or heteroaromatic substituent.
[0042] Preferably monomer (A) is selected from the group of the
sulfonyl fluoride perfluorovinylethers of formula
CF.sub.2.dbd.CF--O--(CF.sub.2).sub.m--SO.sub.2F, wherein m is an
integer between 1 and 6, preferably between 2 and 4.
[0043] More preferably monomer (A) is
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F
(perfluoro-5-sulfonylfluoride-3-oxa-1-pentene).
[0044] Preferably monomer (A) is present in an amount sufficient to
provide a polymer having an equivalent weight of less than 750 g/eq
when converted into its acid form.
[0045] Non limiting examples of suitable ethylenically unsaturated
(per)fluorinated monomers of type (B) are: [0046] C.sub.2-C.sub.8
(per)fluoroolefins, such as tetrafluoroethylene (TFE),
pentafluoropropylene, hexafluoropropylene (HFP), and
hexafluoroisobutylene; [0047] vinylidene fluoride (VDF); [0048]
C.sub.2-C.sub.8 chloro- and/or bromo- and/or
iodo-(per)fluoroolefins, such as chlorotrifluoroethylene (CTFE) and
bromotrifluoroethylene; [0049] (per)fluoroalkylvinylethers of
formula CF.sub.2.dbd.CFOR.sub.f1, wherein R.sub.f1 is a
C.sub.1-C.sub.6 (per)fluoroalkyl, e.g. --CF.sub.3,
--C.sub.2F.sub.5, --C.sub.3F.sub.7; [0050]
(per)fluoro-oxyalkylvinylethers of formula CF.sub.2.dbd.CFOX,
wherein X is a C.sub.1-C.sub.12 perfluoro-oxyalkyl having one or
more ether groups, for example perfluoro-2-propoxy-propyl; [0051]
fluoroalkyl-methoxy-vinylethers of formula
CF.sub.2.dbd.CFOCF.sub.2OR.sub.f2 in which R.sub.f2 is a
C.sub.1-C.sub.6 fluoro- or perfluoroalkyl, e.g. --CF.sub.3,
--C.sub.2F.sub.5, --C.sub.3F.sub.7 or a C.sub.1-C.sub.6
(per)fluorooxyalkyl having one or more ether groups, like
--C.sub.2F.sub.5 --O--CF.sub.3; [0052] fluorodioxoles, of
formula:
##STR00001##
[0052] wherein each of R.sub.f3, R.sub.f4, R.sub.f5, R.sub.f6,
equal or different each other, is independently a fluorine atom, a
C.sub.1-C.sub.6 fluoro- or per(halo)fluoroalkyl, optionally
comprising one or more oxygen atom, e.g. --CF.sub.3,
--C.sub.2F.sub.5, --C.sub.3F.sub.7, --OCF.sub.3,
--OCF.sub.2CF.sub.2OCF.sub.3.
[0053] Preferably monomer (B) is selected among: [0054]
C.sub.3-C.sub.8 perfluoroolefins, preferably tetrafluoroethylene
(TFE) and/or hexafluoropropylene (HFP); [0055] chloro- and/or
bromo- and/or iodo-C.sub.2-C.sub.6 (per)fluoroolefins, like
chlorotrifluoroethylene (CTFE) and/or bromotrifluoroethylene;
[0056] perfluoroalkylvinylethers of formula
CF.sub.2.dbd.CFOR.sub.f1 in which R.sub.f1 is a C.sub.1-C.sub.6
perfluoroalkyl, e.g. --CF.sub.3, --C.sub.3F.sub.7; [0057]
perfluoro-oxyalkylvinylethers of formula CF.sub.2.dbd.CFOX, in
which X is a C.sub.1-C.sub.12 perfluorooxyalkyl having one or more
ether groups, like perfluoro-2-propoxy-propyl.
[0058] More preferably monomer (B) is TFE.
[0059] Optionally, in addition to monomers (A) and (B) bis-olefins
can be used in the process of the present invention. Non limiting
examples of suitable bis-olefins are selected form those of
formulae below: [0060]
R.sub.1R.sub.2C.dbd.CH--(CF.sub.2).sub.j--CH.dbd.CR.sub.3R.sub.4
wherein j is an integer between 2 and 10, preferably between 4 and
8, and R.sub.1, R.sub.2, R.sub.3, R.sub.4, equal or different from
each other, are --H, --F or C.sub.1-C.sub.5 alkyl or
(per)fluoroalkyl group; [0061]
A.sub.2C.dbd.CB-O-E-O--CB.dbd.CA.sub.2, wherein each of A, equal or
different from each other, is independently selected from --F,
--Cl, and --H; each of B, equal or different from each other is
independently selected from --F, --Cl, --H and --OR.sub.B, wherein
R.sub.B is a branched or straight chain alkyl radical which can be
partially, substantially or completely fluorinated or chlorinated;
E is a divalent group having 2 to 10 carbon atoms, optionally
fluorinated, which may be inserted with ether linkages; preferably
E is a --(CF.sub.2).sub.z-- group, with z being an integer from 3
to 5; a preferred bis-olefin is
F.sub.2C.dbd.CF--O--(CF.sub.2).sub.5--O--CF.dbd.CF.sub.2; [0062]
R.sub.6R.sub.7C.dbd.CR.sub.5-E-O--CB.dbd.CA.sub.2, wherein E, A and
B have the same meaning as above defined; R.sub.5, R.sub.6,
R.sub.7, equal or different from each other, are --H, --F or
C.sub.1-C.sub.5 alkyl or (per)fluoroalkyl group.
[0063] When a bis-olefin is employed in the polymerization process
of the invention the resulting polymer typically comprises from
0.01% to 5% by moles of units deriving from the bis-olefin with
respect to the total amount of units in the polymer.
[0064] Optionally, in addition to monomers (A) and (B) brominated
and/or iodinated monomers may also be used in the process of the
present invention to provide iodine and/or bromine atoms in the
sulfonyl fluoride polymer chain as possible cure sites in
cross-linking reactions. Suitable monomers are for instance bromo-
and/or iodo-olefins having from 2 to 10 carbon atoms, or iodo-
and/or bromo-fluoroalkylvinylethers. Typically brominated and/or
iodinated monomers are added in amounts of from 0.05 to 2% by moles
with respect to the total amount of monomers in the polymer. The
introduction of iodine and/or bromine atoms in the sulfonyl
fluoride polymer chain can be carried out, alternatively or
additionally, by addition during the polymerization process of
chain transfer agents containing iodine or bromine atoms. Suitable
chain transfer agents are, for example, alkaline or alkaline-earth
metal iodides and/or bromides or compounds of formula
R.sub.g1(I).sub.d(Br).sub.e, wherein R.sub.g1 is a (per)fluoroalkyl
or a (per)fluorochloroalkyl chain having from 1 to 8 carbon atoms,
while d and e are integers between 0 and 2, with d+e comprised
between 1 and 2. Chain transfer agents containing iodine or bromine
atoms are preferably used in combination with monomer units derived
from bis-olefins.
[0065] The polymerization latex suitable for the isolation process
of the invention may be conveniently obtained by any dispersed
phase polymerization process. Suitable processes for the
preparation of polymerization latexes are instance those described
in U.S. Pat. No. 4,940,525, EP-A-1,167,400, EP-A-1,323,751,
EP-A-1,172,382.
[0066] In a typical dispersed phase polymerization process, such as
the process described in EP-A-1,323,751 the following general steps
can be identified: [0067] formation of an emulsion (or solution)
containing water, a surfactant and at least one ethylenically
unsaturated (per)fluorinated monomer comprising at least one
sulfonyl fluoride group at the polymerization temperature; [0068]
addition to said emulsion (or solution) of at least one
ethylenically unsaturated (per)fluorinated monomer when present;
[0069] addition of a free radical initiator at said polymerization
temperature to initiate the polymerization reaction; [0070]
optionally feeding of the ethylenically unsaturated
(per)fluorinated monomer(s) for a period of time; [0071] recovery
of the polymerization latex.
[0072] Dispersed phase polymerization processes are generally
carried out in a liquid medium comprising water.
[0073] The polymerization latex comprising the sulfonyl fluoride
polymer may conveniently be prepared according to an alternative
dispersed phase polymerization process.
[0074] Accordingly, a second object of the invention is a process
for the preparation of a polymerization latex, said process
comprising the polymerization of recurring units derived from:
[0075] at least one monomer (A); and [0076] optionally, at least
one monomer (B), [0077] in a liquid phase in the presence of a free
radical initiator, at least a portion of said free radical
initiator being added to the liquid phase held at a temperature T1,
said process characterised in that after an incubation time the
temperature of the liquid phase is brought to a temperature T2
lower than T1.
[0078] Monomers (A) and (B) are as above defined.
[0079] Preferably, monomer (A) is present in an amount such that
the equivalent weight of the polymer when converted into its acid
form is less than 750, preferably less than 700, more preferably
less than 690, even more preferably less than 680 g/eq. Monomer (A)
is present in an amount such that the equivalent weight of the
polymer when converted into its acid form is at least 400,
preferably at least 450, more preferably at least 500 g/eq.
[0080] The process of the invention is carried out in the presence
of water. Typically water is at least 30%, preferably at least 40%
by weight with respect of the total weight of the liquid phase. The
expression "liquid phase" is used herein to indicate the continuous
aqueous phase wherein the dispersed organic phase is suspended. The
organic phase may typically comprise, among the others, monomers,
surfactants, oligomers and polymer chains.
[0081] This process advantageously provides polymerization latexes
comprising sulfonyl fluoride polymers characterized by a melt flow
rate (measured according to ASTM D1238-04 at 200.degree. C./5 kg)
that does not exceed 50 g/10 min. The melt flow rate of the polymer
is at least 0.1 g/10 min (measured according to ASTM D1238-04 at
200.degree. C./5 kg).
[0082] In an embodiment of the invention the polymerization latex
is obtained by means of an emulsion, including miniemulsion or
microemulsion, polymerization process. Emulsion of the liquid
monomer, typically of the monomer containing the sulfonyl fluoride
group, in water can be prepared, for instance, by high speed
mechanical stirring of a mixture of the monomer and water in the
presence of a surfactant.
[0083] Suitable surfactants for the process of the present
invention are for instance anionic fluorinated surfactants, for
example salts of fluorinated carboxylic acids or of sulphonic
acids, having a perfluoro-polyether or perfluorocarbon structure or
partially fluorinated, cationic surfactant, for example quaternary
ammonium fluorinated salts, or even fluorinated non ionic
surfactants. The above surfactants can be also used in
mixtures.
[0084] Non limiting examples of surfactants having a
perfluorocarbon structure are for instance ammonium or alkaline
metal salts of C.sub.8-C.sub.10 perfluorcarboxylic acids or
perfluorooxycarboxylates of formula R.sub.sO--CF.sub.2
CF.sub.2--O--CF.sub.2--COOX.sub.a wherein R.sub.s is a
perfluoro(oxy)alkyl group, and X.sub.a is H, a monovalent metal or
an ammonium group of formula NR.sup.N.sub.4, with R.sup.N, equal or
different at each occurrence, being H or a C.sub.1-6 hydrocarbon
group.
[0085] Non limiting examples of surfactants having a
perfluoropolyether structure are for instance selected from those
with formula
F.sub.2ClO(CF.sub.2CF(CF.sub.3)O).sub.p(CF.sub.2O).sub.qCF.sub.2COOR'
wherein R'.dbd.H, Na, K, NH.sub.4, p/q=10. Generally these
fluorinated surfactant(s) have an average molecular weight in the
range 500-700.
[0086] Monomer (B), when present, is introduced into the reactor at
the same time, before or after the introduction of monomer (A).
[0087] The liquid phase is brought to a first temperature T1. As in
typical free radical polymerization reactions temperature T1 will
be chosen with regard to the decomposition temperature of the
initiator selected.
[0088] Any initiator or initiator system suitable for free radical
polymerization may be used in the process of the present invention.
Non limiting examples of suitable free radical initiators are for
instance organic initiators selected among
bis(fluoroacyl)peroxides, bis(chlorofluoroacyl)peroxides, dialkyl
peroxydicarbonates, diacyl peroxides, peroxyesters, azo compounds
or inorganic initiators such as ammonium and/or potassium and/or
sodium persulphate, optionally in combination with ferrous,
cupreous or silver salts or a redox system such as ammonium
persulphate/disulfite and potassium permanganate. Preferably the
free radical initiator used in the process of the present invention
is an inorganic initiator soluble in the aqueous phase, more
preferably ammonium and/or potassium and/or sodium persulphate.
[0089] Typically T1 will be at least 0.degree. C., preferably at
least 15.degree. C., more preferably at least 20.degree. C. and
even more preferably at least 30.degree. C. Temperature T1 will
generally not exceed 150.degree. C., preferably will not exceed
120.degree. C., more preferably will not exceed 100.degree. C.,
even more preferably will not exceed 80.degree. C.
[0090] The maximum and minimum values of T1 will depend on the free
radical initiator. When, in a preferred embodiment of the process,
the initiator is selected among ammonium, potassium and sodium
persulphate temperature T1 is at least 25.degree. C., preferably at
least 30.degree. C., more preferably at least 40.degree. C. and
even more preferably at least 55.degree. C. T1 does not exceed
150.degree. C., preferably does not exceed 100.degree. C., more
preferably does not exceed 80.degree., even more preferably does
not exceed 65.degree. C.
[0091] The appropriate range for temperature T1 for a given free
radical initiator can be identified by the person skilled in the
art by routine experiments.
[0092] When the liquid phase is at temperature T1 at least a
portion of the initiator is fed to the reactor. After a time
sufficient for the polymerization reaction to start, defined herein
as "incubation time", the temperature of the liquid phase is
brought to a temperature T2 lower than T1. The incubation time
corresponds to the time required for the initiator to decompose and
generate a sufficient amount of active polymer chain carriers to
start the polymerization reaction. Active polymer chain carriers
are the active radical centers from which polymer particles are
grown. In such a way it is possible to perform the initiation phase
of the polymerization reaction at a first condition, which favours
the formation of a high number of active polymer chain carriers
(e.g. at T1), and then performing the propagation phase of the
polymerization reaction at a second condition, which favours
monomer incorporation over the chain termination reactions (e.g. at
T2).
[0093] The incubation time is generally at least 5 seconds,
preferably at least 10 seconds, more preferably at least 30
seconds, even more preferably at least 1 minute. The incubation
time generally does not exceed 1 hour.
[0094] The incubation time can be defined for any given system of
monomers, initiator and temperature by routine experiments. For
instance, when at least one of the monomers is a gas, the
incubation time may be taken as the time required for the pressure
inside the reactor to reach a certain value with respect to its
value at the time the initiator was added.
[0095] As discussed above for T1, T2 will depend on the choice of
the free radical initiator. Typically T2 is at least 5.degree. C.
lower than T1, preferably between 5 and 15.degree. C. lower than
T1, more preferably between 5 and 10.degree. C. lower than T1.
[0096] For instance, when the initiator is selected among ammonium,
potassium and sodium persulphate T2 is at least 25.degree. C.,
preferably at least 30.degree. C., more preferably at least
40.degree. C. Temperature T2 does not exceed 55.degree. C.,
preferably it does not exceed 50.degree. C.
[0097] The polymerization system may optionally comprise small
amounts of auxiliaries such as buffers, complex-formers, chain
transfer agents or perfluorinated oils such as those used in
microemulsion processes, for instance those having formula
CF.sub.3O(CF.sub.2--CF(CF.sub.3)O).sub.l(CF.sub.2O).sub.kCF.sub.3
wherein l/k=20 (average molecular weight in the range 400-600)
which are commercially available from Solvay Solexis SpA (Bollate,
Italy) under the trade name Galden.RTM. D02.
[0098] The polymerization can be carried out at any suitable pH, pH
is typically not critical but depends on the initiator system used.
To avoid the conversion of the sulfonyl fluoride group into the
ionic form during polymerization, the pH is typically equal to or
lower than 7, more typically equal to or lower than 6.
[0099] In an embodiment of the polymerization process monomer (B)
is a gaseous monomer, preferably TFE. When gaseous monomers are
used the pressure inside the reactor is generally employed to
control the ratio of the gaseous monomer to the liquid monomer. The
polymerization reaction is typically carried out under a partial
pressure of the gaseous monomer of at least 0.1 MPa, preferably of
at least 0.2 MPa. The pressure does not exceed 1.5 MPa, preferably
1 MPa, even more preferably 0.8 MPa.
[0100] In the particular case where the initiator is added to the
reactor as an aqueous solution, which causes an increase in the
pressure within the reactor, the incubation time can conveniently
be taken to be the time required by the pressure inside the reactor
to resume the value prior to the addition of the initiator
solution.
[0101] When the pressure inside the reactor has returned to the
value before addition of the initiator solution, the temperature of
the liquid phase is brought to temperature T2 lower than T1.
[0102] At the end of the polymerization reaction the pressure
inside the reactor is lowered by venting any unreacted gaseous
monomer and the polymerization latex is discharged from the
reactor.
[0103] Alternatively, after venting of the reactor to remove the
unreacted gaseous monomer vacuum is created inside the reactor to
remove from the latex any additional volatile compound, such as any
residual unreacted liquid monomer. This operation is typically
carried out under stirring at a residual pressure inside the
reactor of from 0.01 to 0.05 MPa.
[0104] At the end of the polymerization reaction a polymerization
latex is obtained. Typically, the solid content of the latex is
between 10 and 50% by weight.
[0105] Traces of other polymerization additives and/or
polymerization residues may be emulsified and/or dissolved in the
latex. Examples of such other polymerization additives and residues
are for instance: chain transfer agents, initiators, unreacted
monomers, low molecular weight perfluorocarbons, soluble oligomers,
etc.
[0106] The addition of the polymerization latex to the aqueous
electrolyte solution is carried out under high shear stirring.
[0107] The phrase "high shear stirring" is used herein to refer to
a rate of stirring such that the Reynolds number is greater than
10,000. The Reynolds number (Re) is calculated from the following
formula:
Re=.rho.Nd.sub.l.sup.2/.mu. [0108] wherein .rho. is the density of
water (kg/m.sup.3), N the number of revolutions per second of the
impeller (1/s), d.sub.l the diameter of the impeller (m) and .mu.
the dynamic viscosity of water (Pas).
[0109] Typically, the diameter of the vessel is chosen such that is
does not exceed 2 to 4 times the diameter of the impeller.
[0110] Electrolytes suitable for the isolation process are salts
such as Al(NO.sub.3).sub.3, Al.sub.2(SO.sub.4).sub.3,
Ca(NO.sub.3).sub.2, Zn(NO.sub.3).sub.2, ZnSO.sub.4, CaCl.sub.2,
(NH.sub.4).sub.2SO.sub.4, NH.sub.4NO.sub.3, Na.sub.2SO.sub.4,
NaHSO.sub.4, MgSO.sub.4 as well as acids such as HNO.sub.3, HCl,
H.sub.2SO.sub.4, citric acid. Preferably the electrolyte is
selected from the group consisting of HNO.sub.3,
Al(NO.sub.3).sub.3, Al.sub.2(SO.sub.4).sub.3, Ca(NO.sub.3).sub.2,
Zn(NO.sub.3).sub.2, ZnSO.sub.4, CaCl.sub.2, MgSO.sub.4. Preferably
the electrolyte is selected from the group consisting of
Al(NO.sub.3).sub.3, Al.sub.2(SO.sub.4).sub.3, Ca(NO.sub.3).sub.2,
Zn(NO.sub.3).sub.2, ZnSO.sub.4, CaCl.sub.2, MgSO.sub.4. Even more
preferably the electrolyte is Al.sub.2(SO.sub.4).sub.3.
[0111] Typically the concentration of the electrolyte in the
aqueous solution is at least 3 g/l, preferably at least 4 g/l. The
concentration of the electrolyte can be up to 50 g/l, preferably up
to 40 g/l.
[0112] The volume of the electrolyte solution is generally adjusted
so that the ratio between the volume of the electrolyte solution
and the volume of the polymerization latex is at least 1:1,
preferably at least 1.5:1.
[0113] The electrolyte solution is held at a temperature equal to
or lower than the glass transition temperature of the polymer.
[0114] For instance, copolymers of TFE and
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F precursors to ionomers
with an equivalent weight in the range from 1180 to 650 g/eq have
glass transition temperatures in the range from 50 to 15.degree.
C., respectively.
[0115] Anti-freezing agents, such as alcohols, may be added to the
aqueous electrolyte solution to avoid freezing when temperatures
below 0.degree. C. are required for the isolation process.
[0116] After addition of the polymerization latex to the aqueous
electrolyte solution the coagulated polymer is separated from the
liquid phase and washed according to standard procedures.
[0117] Typically the coagulated polymer is treated with an aqueous
solution of a diluted acid followed by washing with deionized
water.
[0118] The dried polymer may then be subjected to conventional
post-treatment and pelletization procedures. For instance, the
polymer may be subjected to a fluorination treatment to remove
unstable chain-end groups as known in the art.
[0119] The sulfonyl fluoride polymers coagulated according to the
inventive process are characterized by a lower amount of volatile
low molecular weight components than polymers isolated by other
conventional methods, such as by freeze-thawing. The amount of low
molecular weight components is measured by the loss of weight of
the polymer at high temperature.
[0120] Accordingly the third object of the present invention is a
(per)fluorinated polymer comprising recurring units derived from:
[0121] at least one monomer (A); and [0122] optionally, at least
one monomer (B), [0123] said polymer having a loss of weight at
200.degree. C. lower than 1% as measured by TGA according to method
ASTM E 1131-86.
[0124] Monomers (A) and (B) are as defined above.
[0125] Preferably the polymer of the present invention is a
copolymer of TFE and CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F
and optionally a bis-olefin as above defined.
[0126] Preferably the loss of weight at 200.degree. C. is lower
than 0.8%, more preferably lower than 0.7%, even more preferably
lower than 0.5%.
[0127] A low weight loss of the polymer indicates a reduced content
of volatile components in the polymer itself. The absence of
volatile components, in particular those that can be volatilized
during the polymer extrusion process, is advantageous when
processing the polymer into a film by means of extrusion.
[0128] The equivalent weight of the sulfonyl fluoride polymer of
the invention when converted into its acid form may range from 380
to 1800 g/eq. Preferably the equivalent weight is less than 800,
preferably less than 750, more preferably less than 730, even more
preferably less than 700 g/eq. The equivalent weight is at least
400, preferably at least 450, more preferably at least 480, even
more preferably at least 500 g/eq.
[0129] The sulfonyl fluoride polymer has a melt flow rate measured
according to ASTM D1238-04 at 200.degree. C./5 kg of less than 50,
preferably of less than 45, more preferably of less than 40 g/10
min.
[0130] The sulfonyl fluoride polymer has a melt flow rate measured
according to
[0131] ASTM D1238-04 at 200.degree. C./5 kg of at least 0.1,
preferably of at least 0.2 more preferably of at least 0.5 g/10
min.
[0132] Advantageously the sulfonyl fluoride polymer of the
invention has a melt flow rate of less than 50, preferably of less
than 45, more preferably of less than 40 g/10 min (measured
according to ASTM D1238-04 at 200.degree. C./5 kg) and an
equivalent weight when converted into its acid form of less than
700 g/eq.
[0133] Typically the complex melt viscosity of the sulfonyl
fluoride polymer of the invention measured according to ASTM
D4440-01 at 160.degree. C. is greater than 800 Pas at 10 rad/s and
greater than 1100 Pas at 1 rad/s.
[0134] The polymers of the invention may be converted into films by
conventional film extrusion equipment. Typically the sulfonyl
fluoride polymers of the invention may be melt processed at
temperatures of from 120 to 250.degree. C., preferably of from 150
to 220.degree. C. Typically the films have a thickness of less than
250 .mu.m, preferably in the range from 1 to 150 .mu.m, preferably
from 3 to 100 .mu.m, more preferably from 5 to 60 .mu.m, even more
preferably from 5 to 30 .mu.m.
[0135] The extruded films can subsequently be converted into
electrolyte membranes by hydrolysis, i.e. conversion of the
sulfonyl fluoride polymer making the film into the corresponding
acid form, according to methods known in the art.
[0136] The membranes of the present invention may optionally be
reinforced, for instance by lamination of the extruded film to a
porous support. Lamination may be carried out by conventional
methods, such as hot lamination or glue lamination. Lamination is
typically carried out on the film before conversion of the sulfonyl
fluoride groups into their acid form.
[0137] Porous supports may be made from a wide variety of
components. The porous supports may be made from hydrocarbon
polymers such as polyolefins, e.g. polyethylene or polypropylene,
or polyesters, e.g. poly(ethylene terephthalate). (Per)halogenated
polymers, such as poly(chlorotrifluoroethylene) and copolymer of
chlorotrifluoroethylene and ethylene may also be used. Higher
temperature and chemical resistance may be obtained when the porous
support is made of perfluorinated polymers such as PTFE. Typical
perfluorinated porous supports are chosen from bistretched PTFE and
uniaxially stretched PTFE films.
[0138] Should the disclosure of any of the patents, patent
applications, and publications that are incorporated herein by
reference conflict with the present description to the extent that
it might render a term unclear, the present description shall take
precedence.
[0139] The invention will be illustrated by means of the following
non-limiting examples.
EXAMPLES
[0140] Characterization
[0141] Melt flow rate was measured following the procedure of ASTM
D1238-04 at a temperature of 200.degree. C. and under a weight of 5
kg.
[0142] Glass transition temperature was determined by DSC at a
heating rate of 20.degree. C./min following the procedure of ASTM
D3418-03. The indicated value corresponds to the midpoint
temperature.
[0143] Determination of the Equivalent Weight
[0144] The equivalent weight was determined according to the
following procedure. A film was prepared from a sample of dry
polymer by heating and pressing it at 200.degree. C. in a press. A
film sample (10 cm.times.10 cm) was cut and treated with a 10% by
weight (wt %) aqueous KOH solution at 80.degree. C. for 24 hours.
After washing with deionized water, the film was treated with a 20
wt % aqueous HNO.sub.3 solution (at room temperature for 1 hour)
and washed with deionized water. After drying in vacuum at
80.degree. C. for 16 hours, the film sample was weighed, dispersed
in a hydro-alcoholic solution and a measured excess of a 0.1N NaOH
solution was added. The alkaline excess was counter-titrated with a
0.1N HCl solution.
[0145] Complex Melt Viscosity Determination
[0146] The complex melt viscosity (.eta.*) was measured at
160.degree. C. using a rheogoniometer Rheometrics RMS 800 according
to ASTM D4440-01. The polymer sample was sheared in oscillatory
mode between two 25 mm parallel plates under a dry nitrogen
atmosphere. The range of frequency was between 0.05 and 100
rad/s.
[0147] Weight Loss Determination
[0148] The weight loss determination at 200.degree. C. was carried
out using a TGA PYRIS 1 equipment from Perkin-Elmer according to
method ASTM E 1131. A 10 mg sample of the polymer was subjected to
constant heating in air at a rate of 10.degree. C./min from
23.degree. C. up to 750.degree. C. The weight loss was determined
as the weight difference between 23.degree. C. and 200.degree.
C.
[0149] General Polymer Isolation Procedure
[0150] An aqueous solution of Al.sub.2(SO.sub.4).sub.3
(concentration of 12 g/l) was introduced in a closed glass vessel
and the temperature maintained at 10.+-.2.degree. C. under
stirring. Stirring rate (stirrer revolutions per minute) was
adjusted to obtain a Reynolds number greater than 10,000. The
polymerization latex was slowly added to the aqueous solution in
about 40 min in an amount of 1 kg per liter of
Al.sub.2(SO.sub.4).sub.3 solution. Polymer coagulation started
immediately. After addition of all the latex, the coagulated
mixture was stirred, at the same rate and temperature, for 15 min.
The stirring was stopped and the polymer allowed to settle. The
liquid phase above the coagulum was removed. The coagulum was
washed twice with an aqueous solution of HNO.sub.3 (3 wt % in an
amount of 1 l/l of initial Al.sub.2(SO.sub.4).sub.3 solution for
each washing step) at a temperature between 10 and 15.degree. C.
and then twice with deionized water (in an amount of 1 l/l of
initial Al.sub.2(SO.sub.4).sub.3 solution for each washing step) at
the same rate and temperature as above. The coagulated polymer was
then dried at 80.degree. C. for 20 hours in a ventilated oven.
[0151] General Fluorination Procedure
[0152] Polymer pellets obtained by extrusion of the sulfonyl
fluoride polymer were dried in a ventilated oven at 60.degree. C.
for 20 hours and treated with a gaseous F.sub.2 (2.5 Nl/h)/N.sub.2
(1 Nl/h) mixture at 40.degree. C. for 20 hours. After treatment
with the F.sub.2/N.sub.2 mixture, the material was further treated
first with N.sub.2 (5Nl/h) for 4 hours at 40.degree. C., and then
at 60.degree. C. for 20 hours in a ventilated oven.
Example 1
[0153] (1) Polymer Synthesis
[0154] In a 22 liter reactor, were introduced the following
reactants: 3100 g of an aqueous solution containing 5 wt % of a
surfactant of formula CF.sub.2ClO(CF.sub.2
CF(CF.sub.3)O).sub.p(CF.sub.2O).sub.qCF.sub.2COOK (p/q=10, average
molecular weight 527 g/mol) and 95 wt % of water; 9 l of deionized
water; 756 ml of the monomer of formula
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F.
[0155] The reactor, stirred at 540 rpm, was heated up to 60.degree.
C. The pressure inside the reactor was brought to 1.5 absolute MPa
with a mixture of with carbon dioxide and TFE. The partial pressure
of TFE inside the reactor was 0.41 MPa. 300 ml of an aqueous
solution having a concentration of 35 g/l of potassium persulphate
were fed into the reactor causing an increase in the pressure. The
reaction started after 6 min as indicated by the lowering of the
pressure within the reactor to its initial value. The reactor
temperature was lowered to 50.degree. C. The pressure was
maintained constant by introducing TFE. During the polymerization,
160 ml of CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F were added
every 160 g of TFE. The total mass of TFE fed into the reactor was
3200 g. The reaction was stopped after 447 min by venting TFE and
successively lowering the reactor pressure until reaching 0.03
absolute MPa. At the end of this operation, stirring was slowed
down and the reactor brought to ambient pressure and temperature
recovering a polymerization latex with a solid content of 31.6 wt
%.
[0156] The equivalent weight of the corresponding acid form of the
polymer was determined to be 606 g/eq corresponding to 23.5% moles
of CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F.
[0157] (2) Polymer Isolation
[0158] 250 g of the polymerization latex were coagulated according
to the general polymer isolation procedure. The impeller (diameter
d.sub.l=5 cm) was set at a speed of 800 rpm corresponding to
Re=24,690.
[0159] The polymer had the following properties: weight loss at
200.degree. C.: 0.3%; glass transition temperature: 13.degree. C.;
melt flow rate (200.degree. C./5kg): 49.5 g/10 min; complex
viscosity (at 160.degree. C.): .eta.*=1210 Pas at 1 rad/s and
n*=910 Pas at 10 rad/s.
Comparative Example 1
[0160] 250 g of the polymerization latex obtained in Example 1 were
coagulated following the general polymer isolation procedure but
maintaining the aqueous Al.sub.2(SO.sub.4).sub.3 solution at
60.degree. C. Rinsing with HNO.sub.3 and deionized water were
carried out at room temperature. Weight loss of the polymer at
200.degree. C. was 2.6%.
Comparative Example 2
[0161] 250 g of the polymerization latex obtained in Example 1 were
coagulated by freezing (20 h at -20.degree. C.) and thawing (6 h at
23.degree. C.). The coagulated polymer was separated from the
liquid phase, washed at room temperature with water (4.times.1.5
liters) under high shear stirring (Re=20,830) and dried for 20
hours at 80.degree. C.
[0162] The polymer had the following properties: weight loss at
200.degree. C.: 4.4%; melt flow rate (200.degree. C./5kg): 50 g/10
min.
[0163] The polymer was milled into granules after cooling with
liquid nitrogen. The granules were dried in a ventilated oven at
60.degree. C. for 20 hours. The granular material was extruded into
pellets using a twin screw extruder at a temperature of
125-135.degree. C.
[0164] The polymer pellets had a light blue color, which was
attributed to metals extracted during the pelletization phase.
Signs of chemical degradation were detected in the extruder
screw.
[0165] The melt flow rate measured on the pellets was 79 g/10 min
(200.degree. C./5 kg). Weight loss of the polymer pellets at
200.degree. C. was 1.2%.
[0166] After the fluorination treatment the polymer pellets had a
dark brown color indicating that material degradation and/or
contamination had taken place.
[0167] The loss of weight of the polymer of Example 1 isolated
according to the inventive polymer isolation process is almost 9
times lower than that of a polymer isolated from the same polymer
latex but using an electrolyte solution held at a temperature
(60.degree. C.) higher than the glass transition temperature of the
polymer (13.degree. C.) (Comp. Example 1) and about 14 times lower
than that of the polymer isolated from the same polymer latex using
a conventional freeze-thawing method (Comp. Example 2).
Example 2
[0168] (1) Polymer Synthesis
[0169] Following the procedure of Example 1 a polymerization latex
comprising a copolymer of TFE and
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F was prepared by setting
the partial pressure of TFE at 0.46 absolute MPa and T1=60.degree.
C. After 6 minutes from the addition of the potassium persulphate
initiator the temperature within the reactor was lowered to
T2=50.degree. C.
[0170] The polymerization latex had a solid content of 30.6 wt
%.
[0171] The equivalent weight of the corresponding acid form of the
polymer was determined to be 649 g/eq corresponding to 21.3% moles
of CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F.
[0172] (2) Polymer Isolation
[0173] 7 kg of the polymerization latex were coagulated according
to the general polymer isolation procedure. The impeller, with a
diameter d.sub.l=10 cm, was set at a speed of 650 rpm corresponding
to Re=180,560.
[0174] The polymer had the following properties: weight loss at
200.degree. C.: 0.05%; glass transition temperature: 14.degree. C.;
complex viscosity (at 160.degree. C.): .eta.*=14,490 Pas at 1 rad/s
and .eta.*=8150 Pas at 10 rad/s.
[0175] (3) Processing
[0176] The polymer was extruded into pellets with a twin screw
extruder at a temperature of 125-135.degree. C. The pellets were
subjected to a fluorination treatment according to the general
procedure described above.
[0177] The polymer pellets appeared translucent and colorless. The
pellets had a melt flow rate (200.degree. C./5 kg) of 19 g/10 min
and a weight loss at 200.degree. C. of 0.03%.
Example 3
[0178] (1) Polymer Synthesis
[0179] The procedure of Example 2 was repeated terminating the
reaction after 404 minutes obtaining a polymerization latex with a
solid content of 31% by weight.
[0180] The equivalent weight of the corresponding acid form of the
polymer was determined to be 630 g/eq corresponding to 22.2% moles
of CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F.
[0181] (2) Polymer Isolation
[0182] 250 g of the polymerization latex were coagulated according
to the general polymer isolation procedure. The impeller, with a
diameter d.sub.l=5 cm, was set at a speed of 800 rpm corresponding
to Re=24,690.
[0183] The polymer had the following properties: weight loss at
200.degree. C.: 0.09%; glass transition temperature: 13.degree. C.;
melt flow rate (200.degree. C./5 kg): 18 g/10 min.
Comparative Example 3
[0184] 250 g of the polymerization latex obtained in Example 3 were
coagulated by addition to a 0.5M aqueous HNO.sub.3 solution at
23.degree. C. under low shear stirring (Re=2130). The coagulated
polymer was washed with deionized water and dried in a ventilated
oven. Weight loss of the polymer at 200.degree. C. was 2.6%.
[0185] The loss of weight of the polymer of Example 3 isolated
according to the inventive polymer isolation process is almost 30
times lower than that of a polymer isolated from the same polymer
latex under low shear stirring and using an electrolyte solution
held at a temperature (23.degree. C.) higher than the glass
transition temperature of the polymer and (13.degree. C.) (Comp.
Example 3).
Example 4
[0186] (1) Polymer Synthesis
[0187] In a 22 liter reactor, were introduced the following
reactants: 1350 g of a microemulsion previously obtained by mixing
473 g of a surfactant of formula
CF.sub.2ClO(CF.sub.2CF(CF.sub.3)O).sub.p(CF.sub.2O).sub.qCF.sub.2COOK
(p/q=10; average molecular weight 527 g/mol), 338 g of a
perfluoropolyether oil of formula
CF.sub.3O(CF.sub.2--CF(CF.sub.3)O).sub.l(CF.sub.2O).sub.kCF.sub.3
(l/k=20;average molecular weight 400-600; Galden.RTM. D02 Solvay
Solexis SpA, Bollate, Italy) and 540 g of water; 10 l of deionized
water; 756 ml of the monomer of formula
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F.
[0188] The procedure of Example 1 was then followed by setting the
partial pressure of TFE at 0.36 absolute MPa and T1=60.degree. C.
The reaction started after 5 seconds from the addition of 300 ml of
an aqueous solution having a concentration of 30 g/l of potassium
persulphate and the reactor temperature was lowered to 50.degree.
C. The pressure was maintained constant by introducing TFE. During
the polymerization, 160 ml of
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F were added every 140 g
of TFE. The total mass of TFE fed into the reactor was 2800 g. The
reaction was stopped after 174 min recovering a polymerization
latex with a solid content of 32 wt %.
[0189] The equivalent weight of the corresponding acid form of the
polymer was determined to be 646 g/eq corresponding to 21.5% moles
of CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F.
[0190] (2) Polymer Isolation
[0191] 250 g of the polymerization latex were coagulated according
to the general polymer isolation procedure. Drying of the polymer
was carried out in a ventilated oven at 180.degree. C. for 20
hours. The impeller, with a diameter d.sub.l=5 cm, was set at a
speed of 800 rpm corresponding to Re=24,690.
[0192] The polymer had the following properties: weight loss at
200.degree. C.: 0.6%; glass transition temperature: 14.degree. C.;
melt flow rate (200.degree. C./5 kg): 8.5 g/10 min.
Comparative Example 4
[0193] 250 g of the polymerization latex obtained in Example 3 were
coagulated by freezing (20 h at -20.degree. C.) and thawing (6 h at
23.degree. C.). The coagulated polymer was separated from the
liquid phase, washed at room temperature with water (4.times.1.5 l)
under high shear stirring (Re=20,830) and dried for 20 hours at
80.degree. C. Weight loss of the polymer at 200.degree. C. was
3.3%.
Example 5
[0194] (1) Polymer Synthesis
[0195] In a 5 liter reactor, were introduced the following
reactants: 720 g of an aqueous solution containing 5 wt % of a
surfactant of formula
CF.sub.2ClO(CF.sub.2CF(CF.sub.3)O).sub.p(CF.sub.2O).sub.qCF.sub.2COOK
(p/q=10, average molecular weight 527 g/mol) and 95 wt % of water;
2.6 l of deionized water; 134 ml of the monomer of formula
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F.
[0196] The reactor, stirred at 650 rpm, was heated up to 60.degree.
C. The pressure inside the reactor was brought to 0.9 absolute MPa
with TFE. 66 ml of an aqueous solution having a concentration of 18
g/l of potassium persulphate were fed into the reactor causing an
increase in the pressure. The reaction started after 5 min as
indicated by the lowering of the pressure within the reactor to its
initial value. The temperature was maintained at 60.degree. C.
throughout the polymerization reaction. The pressure was maintained
constant by introducing TFE. During the polymerization, 36.6 ml of
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F were added every 45 g
of TFE. The total mass of TFE fed into the reactor was 900 g. The
reaction was stopped after 426 min by venting TFE, stirring was
slowed down and the reactor brought to room temperature recovering
a polymerization latex with a solid content of 26 wt %.
[0197] The equivalent weight of the corresponding acid form of the
polymer was determined to be 596 g/eq corresponding to 24% moles of
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2--SO.sub.2F.
[0198] (2) Polymer Isolation
[0199] 250 g of the polymerization latex were coagulated according
to the general polymer isolation procedure. The impeller, with a
diameter d.sub.l=5 cm, was set at a speed of 800 rpm corresponding
to Re=24,690.
[0200] The polymer had the following properties: weight loss at
200.degree. C.: 0.2%; glass transition temperature: 12.degree. C.;
melt flow rate (200.degree. C./5 kg): 186.7 g/10 min.
Comparative Example 5
[0201] 250 g of the polymerization latex obtained in Example 5 were
coagulated by freezing (20 h at -20.degree. C.) and thawing (6 h at
23.degree. C.). The coagulated polymer was separated from the
liquid phase, washed at room temperature with water (4.times.1.5 l)
under high shear stirring (Re=20,830) and dried for 20 hours at
80.degree. C. Weight loss of the polymer at 200.degree. C. was
1.4%.
[0202] The loss of weight of the polymer of Example 5 isolated
according to the inventive polymer isolation process is almost 7
times lower than that of a polymer isolated from the same polymer
latex using a conventional freeze-thawing method (Comp. Example
5).
* * * * *