U.S. patent application number 09/729427 was filed with the patent office on 2001-08-30 for preparation of hexafluoropropene oxide polymers.
Invention is credited to Koike, Noriyuki, Sakano, Yasunori.
Application Number | 20010018506 09/729427 |
Document ID | / |
Family ID | 18385179 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010018506 |
Kind Code |
A1 |
Sakano, Yasunori ; et
al. |
August 30, 2001 |
Preparation of hexafluoropropene oxide polymers
Abstract
A perfluorodicarboxylic fluoride of the formula:
F--CO--CF.sub.2--O--Rf--O- --CF.sub.2--CO--F or perfluorodiketone
of the formula: R.sup.1--CO--Rf--CO--R.sup.1 wherein Rf is a
perfluoroalkylene group and R.sup.1 is a C.sub.1-8 perfluoroalkyl
group is mixed with an alkali metal fluoride in an aprotic polar
solvent to form an initiator solution. Hexafluoropropene oxide is
fed to the initiator solution for polymerization, obtaining
difunctional hexafluoropropene oxide polymers of high purity.
Inventors: |
Sakano, Yasunori; (Usui-gun,
JP) ; Koike, Noriyuki; (Usui-gun, JP) |
Correspondence
Address: |
MILLEN, WHITE, ZELANO & BRANIGAN, P.C.
Arlington Courthouse Plaza I, Suite 1400
2200 Clarendon Boulevard
Arlington
VA
22201
US
|
Family ID: |
18385179 |
Appl. No.: |
09/729427 |
Filed: |
December 5, 2000 |
Current U.S.
Class: |
528/220 ;
528/365; 528/402 |
Current CPC
Class: |
C08G 65/226
20130101 |
Class at
Publication: |
528/220 ;
528/365; 528/402 |
International
Class: |
C08G 002/22; C08G
004/00; C08G 065/26 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 1999 |
JP |
11-346692 |
Claims
1. A method for preparing a hexafluoropropene oxide polymer
comprising the steps of: mixing a perfluorodicarboxylic fluoride or
perfluorodiketone of the following general formula (1) or (2):
15wherein Rf is a perfluoroalkylene group which may be separated by
an oxygen atom, and R.sup.1, which may be the same or different, is
a perfluoroalkyl group of 1 to 8 carbon atoms, with a metal
fluoride in an aprotic polar solvent to form a solution, and
feeding hexafluoropropene oxide to the solution.
2. The method of claim 1 further comprising the step of adding a
perfluoroolefin to the solution before the feeding step.
3. The method of claim 1 further comprising the step of adding a
perfluoroolefin to the solution simultaneously with the feeding
step.
Description
[0001] This invention relates to a method for preparing
hexafluoropropene oxide (referred to as HFPO, hereinafter)
polymers, and more particularly to a method for preparing
essentially difunctional HFPO polymers having a minimized content
of monofunctional HFPO polymer.
BACKGROUND OF THE INVENTION
[0002] One prior art method for preparing difunctional HFPO
polymers is described in U.S. Pat. No. 3,250,807. This method is to
react FOC--(CF.sub.2).sub.n--COF wherein n is from 0 to 6 with HFPO
in an aprotic polar solvent in the presence of a catalyst such as
an alkali metal fluoride or activated carbon, thereby forming
difunctional HFPO polymers, as shown by the following reaction
scheme. 1
[0003] An attempt to add HFPO to previously furnished --COF groups
as above, however, often gives rise to the problem that chain
transfer side reaction occurs to form a HFPO polymer having a
hexafluoropropyl group at one end (monofunctional HFPO polymer) as
shown by the following scheme. 2
[0004] An improved method for preparing essentially difunctional
HFPO polymers while preventing such chain transfer is disclosed in
U.S. Pat. No. 3,660,315 or JP-B 53-5360. This method involves
mixing the compound of the formula:
FOCCF(CF.sub.3 )OCF.sub.2CF.sub.2OCF(CF.sub.3)COF (3)
[0005] with cesium fluoride in tetraethylene glycol dimethyl ether
to form the compound of the formula:
CsOCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2OCF(CF.sub.3)CF.sub.2OCs
(4),
[0006] and removing the excess of cesium fluoride from the
solution, thereby forming a uniform solution, which is used as an
initiator for the polymerization of HFPO. Specifically, after the
excess of cesium fluoride is separated off, polymerization is
effected at a low temperature of -60.degree. C. to -30.degree. C.,
thereby forming pure difunctional HFPO polymers having a number
average molecular weight of about 50.
[0007] However, it is described in J. Macromol. Sci. Chem., A8(3),
499 (1974) that if the molar ratio of HFPO to the initiator is
increased in order to produce difunctional HFPO polymers having a
higher degree of polymerization, the side reaction to produce a
monofunctional HFPO polymer increases and the purity of
difunctional HFPO polymers lowers.
[0008] U.S. Pat. No. 4,356,291 or JP-A 57-175185 describes that a
HFPO polymer having a number average molecular weight of 445 is
obtained using highly purified HFPO in addition to the above
initiator. It is pointed out that HFPO generally contains
impurities such as hydrogen fluoride, acid fluorides and water,
which limit the maximum degree of polymerization of polymers
resulting from polymerization of HFPO. Then by subjecting highly
purified HFPO to polymerization, a HFPO polymer having a high
molecular weight is produced. However, no reference is made therein
to the by-produced monofunctional HFPO polymer and the purity of
the desired difunctional HFPO polymer.
[0009] Understandably, the prior studies on difunctional HFPO
polymers placed a main focus on the reduction of undesired
monofunctional HFPO polymers resulting from chain transfer and the
formation of HFPO polymers having a high degree of
polymerization.
[0010] All these methods, however, have the drawback that the
compound of formula (3) itself contains monofunctional impurities.
More particularly, the compound of formula (3) is generally
prepared by the following method. 3
[0011] Upon reaction of oxalic fluoride with HFPO, there are
produced not only the end compound of formula (3), but also HFPO
oligomers as shown by formulas (3') and (3"). A precise
distillation operation is necessary to separate these oligomers
from the end compound. Still worse, the end compound purified by
such a precise distillation operation yet contains about 4 to 6% by
weight of the monofunctional component having a cyclic structure
shown by the above formula (5). Undesirably, since this by-product
of formula (5) has the same molecular weight as the end compound of
formula (3), it is almost impossible in practice to separate the
by-product by further distillation. Use of the fraction resulting
from distillation as the initiator means that the monofunctional
component already exists prior to the polymerization of HFPO.
[0012] On the other hand, known perfluorodicarboxylic fluorides
include perfluoroadipic fluoride, perfluoroglutaric fluoride and
perfluorosuccinic fluoride. If a polymerization initiator is
prepared from these compounds in the same manner as the compound of
the above formula (3), side reaction such as esterification can
take place, failing to obtain an alcoholate equivalent to the
perfluorodicarboxylic fluoride added. If polymerization of HFPO is
carried out using this polymerization initiator, there are produced
polymers having a wide molecular weight distribution because of the
increased content of low molecular weight components. This
polymerization initiator is inadequate.
[0013] Under the circumstances, it is desired in the polymerization
of HFPO to prepare a polymerization initiator using a starting
reactant which is available at a relatively low cost, which
quantitatively forms an alcoholate with an alkali metal fluoride in
an aprotic polar solvent and which is free of monofunctional
impurities.
SUMMARY OF THE INVENTION
[0014] An object of the invention is to provide a method for
preparing difunctional HFPO polymers having a minimized content of
monofunctional HFPO polymer, using a polymerization initiator
prepared from a starting reactant which is available at a
relatively low cost.
[0015] We have found that when a perfluorodicarboxylic fluoride or
perfluorodiketone of the general formula (1) or (2) shown below is
mixed with an alkali metal fluoride in an aprotic polar solvent,
there is obtained a uniform solution in which a quantitative amount
of an alcoholate is formed. Subsequent polymerization of HFPO using
this solution as a polymerization initiator results in a
difunctional HFPO polymer which is substantially free from the
terminal ether structure based on the compound of the above formula
(5), has a narrow molecular weight distribution, and has a
minimized content of monofunctional HFPO polymer.
[0016] Accordingly, the invention provides a method for preparing a
hexafluoropropene oxide polymer comprising the steps of mixing a
perfluorodicarboxylic fluoride or perfluorodiketone of the
following general formula (1) or (2) with a metal fluoride in an
aprotic polar solvent, and feeding hexafluoropropene oxide to the
resulting solution. 4
[0017] Herein Rf is a perfluoroalkylene group which may be
separated by an oxygen atom, and R.sup.1, which may be the same or
different, is a perfluoroalkyl group of 1 to 8 carbon atoms.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] The method for preparation of HFPO polymers according to the
invention uses as the polymerization initiator a solution which is
prepared by mixing a perfluorodicarboxylic fluoride or
perfluorodiketone of the general formula (1) or (2) with an alkali
metal fluoride in an aprotic polar solvent. More particularly, the
polymerization initiator is prepared by suspending an alkali metal
fluoride in an aprotic polar solvent, adding a
perfluorodicarboxylic fluoride or perfluorodiketone to the
suspension, and agitating the mixture.
[0019] The alkali metal fluoride used herein is preferably cesium
fluoride. Examples of the aprotic polar solvent include glymes such
as monoglyme, diglyme, triglyme and tetraglyme, tetrahydrofuran and
1,4-dioxane, with the glymes being especially preferred.
[0020] With respect to the perfluorodicarboxylic fluoride or
perfluorodiketone used herein, an inexpensive hydrocarbon
dicarboxylic acid or hydrocarbon diester of the following general
formula (6) or (7) is fluorinated by well-known fluorinating
methods (including direct fluorination and electrolytic
fluorination) to form a corresponding perfluoro compound of the
general formula (1) or (2). 5
[0021] In the formulas, R.sup.2 is an alkylene group which may be
separated by an oxygen atom, Rf is a perfluoroalkylene group
obtained by substituting fluorine atoms for all the hydrogen atoms
in R.sup.2. R.sup.3 is an alkyl group of 1 to 8 carbon atoms, the
R.sup.3 groups may be the same or different, and R.sup.1 is a
perfluoroalkyl group of 1 to 8 carbon atoms obtained by
substituting fluorine atoms for all the hydrogen atoms in R.sup.3.
R.sup.4 is a substituted or unsubstituted monovalent hydrocarbon
group, and the R.sup.4 groups may be the same or different.
[0022] In formula (1) or (2), Rf is a perfluoroalkylene group which
may be separated by an oxygen atom, as exemplified by the
following. 6
[0023] In formula (2), R.sup.1 is a perfluoroalkyl group of 1 to 8
carbon atoms, as exemplified by the following:
C.sub.cF.sub.2c+1--
[0024] wherein c is an integer of 1 to 8. These alkyl groups may be
straight or branched.
[0025] In the practice of the invention, a polymerization initiator
solution is prepared by adding the compound of formula (1) or (2)
to a mixture of an aprotic polar solvent and an alkali metal
fluoride. In the solution, the carbonyl group-bearing compound
reacts with the alkali metal fluoride to form a corresponding
alcoholate as shown below. The conversion to an alcoholate can be
confirmed by infrared absorption analysis of the mixture solution.
Depending on the type of the compounds of formulae (1) and (2), the
alcoholate may be deposited as solid in the solution at room
temperature (for example, 15 to 25.degree. C.). In this case, by
maintaining the temperature of the solution to 5.degree. C. or
less, unexpectedly or contrary to the ordinary compounds, the
alcoholate may not be deposited in the solution and may be
dissolved therein. So, it is preferred to maintain the temperature
of the solution to 5.degree. C. or less. 7
[0026] Rf and R.sup.1 are as defined above.
[0027] The polymerization initiator represented by the above
formula is present in the polymerization initiator solution
desirably in a concentration of 10 to 60% by weight, especially 25
to 45% by weight.
[0028] To the polymerization initiator solution, a second solvent
different from the solvent used upon preparation may be added for
improving the flow at low temperatures. The second solvent may be
one which is uniformly miscible with the initiator solution even at
a low temperature below -30.degree. C. and has a freezing point of
lower than -50.degree. C. Desirable are hydrocarbon compounds
having one to three ether bonds in the molecule, for example,
dimethyl ether, diethyl ether, ethyl methyl ether, methyl propyl
ether, ethylene glycol dimethyl ether and tetrahydrofuran. The
second solvent is added to reduce the viscosity of the initiator
solution at a polymerization temperature in the range of
-40.degree. C. to -30.degree. C. for thereby helping achieve
efficient agitation. An appropriate amount of the second solvent
added is about 20 to 60 parts by weight per 100 parts by weight of
the initiator solution. Preferably the second solvent is previously
dried to a water content of 50 ppm or lower.
[0029] Next, a perfluoroolefin such as hexafluoropropene (HFP) is
reacted with the polymerization initiator solution in optional
admixture with the second solvent for forming oligomers. This
operation is necessary to remove any chain transfer-inducing
substance in the polymerization initiator solution and second
solvent, for helping initiate polymerization upon subsequent supply
of HFPO.
[0030] The perfluoroolefins used herein include those of 2 to 9
carbon atoms, especially 3 to 6 carbon atoms. Examples are given
below. 8
[0031] Of these, the following are especially preferred. 9
[0032] The amount of the perfluoroolefin used is not critical
although it is usually used in an amount of about 0.5 to 100 parts,
especially about 3 to 30 parts by weight per 100 parts by weight of
the polymerization initiator solution.
[0033] Reaction with the perfluoroolefin is usually effected at a
temperature of -30.degree. C. to 50.degree. C., preferably
-25.degree. C. to 30.degree. C. Outside the range, too low a
reaction temperature will require a longer time for reaction
whereas too high a reaction temperature may cause decomposition of
the initiator. The reaction time is not critical although the
reaction time at a temperature of -25.degree. C. to 30.degree. C.
is typically about 10 minutes to 2 hours, especially about 20
minutes to 1 hour including the time required for the
perfluoroolefin addition.
[0034] While the initiator solution, preferably in admixture with
the second solvent, is being agitated and cooled in a reactor, HFPO
is fed to the reactor, thereby obtaining difunctional HFPO
polymers. It is possible to add hexafluoropropene (HFP) at the same
time as the HFPO feed. The addition of HFP is effective for
increasing flow because it dilutes the reaction solution which
gradually thickens with the progress of polymerization. During the
polymerization, the reaction solution is preferably kept at a
temperature of -45.degree. C. to -30.degree. C. Below -45.degree.
C., the reaction solution may increase its viscosity and
thixotropy, interfering with efficient agitation. Under such
situation, part of the non-flowing reaction product will stick to
the reactor inner wall or agitator blade to further interfere with
uniform agitation, resulting in polymers having a wider molecular
weight distribution. Temperatures above -30.degree. C. tend to
induce chain transfer reaction to form monofunctional HFPO
polymers.
[0035] Agitation is important for the reaction solution as a whole
to maintain uniform fluidity. A choice is generally made of anchor,
paddle, helical ribbon and impeller agitators, depending on the
shape and size of the reactor. The number of revolutions is not
critical and may be adjusted in accordance with the shape of
agitator blade so as to achieve an optimum agitation
efficiency.
[0036] Preferably the HFPO is continuously fed using a flow meter
such as a mass flow controller. A constant rate of HFPO feed is
necessary in order to maintain the temperature of the reaction
solution in an appropriate range. An appropriate hourly feed rate
is about 3 to 15 mol, especially about 5 to 10 mol of HFPO per mol
of the initiator. The feed amount is determined as appropriate in
accordance with the desired molecular weight and may range from
about 30 to 400 mol per mol of the initiator. Since increasing the
relative amount of HFPO to a higher level will result in HFPO
polymers having a non-negligible amount of monofunctional polymer
mixed therein, the feed amount is usually about 30 to 200 mol per
mol of the initiator.
[0037] The HFP may be fed at the same time as the HFPO and in an
amount equal to 1/4 to 3/4 of the weight of HFPO. After the
completion of HFPO feed, agitation is continued for a further 1 to
2 hours. Thereafter, the reaction solution is heated and the end
product is separated out. In this way, difunctional HFPO polymers
of the following formula (8) or (9) are obtained. 10
[0038] Rf and R.sup.1 are as defined above, x and y are positive
integers.
[0039] The difunctional HFPO polymers of the formula (8) or (9)
will contain a minor amount of monofunctional HFPO polymers formed
during the reaction process. Since the starting reactant,
perfluorodicarboxylic fluoride or perfluorodiketone does contain
little of monofunctional impurities, the final content of
monofunctional impurities in the difunctional HFPO polymers of the
formula (8) or (9) is suppressed dramatically low.
[0040] The thus obtained difunctional HFPO polymers are terminated
with --COF groups. Then a variety of useful derivatives can be
synthesized therefrom by converting the terminal groups into other
functional groups. These derivatives will find use in liquid
rubber, coating material and sealing material.
[0041] Since a perfluorodicarboxylic fluoride or perfluorodiketone
which is available at a relatively low cost, which quantitatively
forms an alcoholate with an alkali metal fluoride in an aprotic
polar solvent and which is free of monofunctional impurities is
used as the starting reactant, the invention is successful in
producing difunctional HFPO polymers of high purity having a
minimized content of monofunctional HFPO polymer and low molecular
weight components.
EXAMPLE
[0042] Examples of the invention are give below by way of
illustration and not by way of limitation.
Example 1
[0043] Preparation of Initiator
[0044] A 2-liter glass flask was thoroughly purged with dry
nitrogen and charged with 31.0 g of cesium fluoride and 115.3 g of
tetraglyme. With stirring at 0.degree. C. in a dry nitrogen
atmosphere, 33.3 g of perfluorodicarboxylic fluoride of 99.0%
purity represented by the formula (10) below was added to the flask
using a syringe. 11
[0045] Immediately after addition, heat generation was observed.
The alcoholate obtained would be deposited as solid in the solution
at room temperature. So, the temperature of the solution was kept
at 5.degree. C. or less. After about 5 hours of agitation, the
reaction solution was allowed to stand. The reaction solution was a
uniform, pale yellow, clear liquid except for some precipitates of
excessive cesium fluoride at 0.degree. C.
[0046] A sample taken from the solution was analyzed by infrared
absorption spectroscopy, in which the absorption peak in proximity
to 1880 cm.sup.-1 attributable to --COF group was not observed.
Another sample of the solution was dissolved in water. The amount
of carboxylic acid and hydrofluoric acid resulting from hydrolysis
was determined by alkali titration, and the amount of alcoholate in
the original solution was computed as the --CF.sub.2OCs
concentration (mmol/g), which was 1.09 mmol/g. These measurement
results are shown in Table 1 together with the theoretical
--CF.sub.2OCs concentration (the amount of alcoholate equivalent to
the amount of perfluorodicarboxylic fluoride (assumed to be 100%
pure) added).
[0047] Polymerization of HFPO
[0048] A 0.5-liter reactor equipped with an anchor agitator was
charged with 12.9 g of the above-prepared initiator solution and
3.7 g of ethylene glycol dimethyl ether. While agitating at 180
rpm, the reactor was cooled in a coolant bath adjusted at
-10.degree. C.
[0049] Step 1
[0050] When the internal temperature of the reactor reached
-7.degree. C., 2.1 g of HFP was fed at a rate of 4.2 g/hr.
[0051] Step 2
[0052] The coolant bath was reset at -40.degree. C. When the
internal temperature of the reactor reached -38.degree. C., 2.1 g
of HFP was further fed at a rate of 4.2 g/hr.
[0053] Step 3
[0054] Next, 114 g of HFPO and 57 g of HFP were fed over about 15
hours at a rate of 7.6 g/hr and 3.8 g/hr, respectively.
[0055] Mass flow controllers were used for adjusting the flow rate.
The liquid within the reactor was kept between -38.degree. C. and
-35.degree. C. during the HFPO feed.
[0056] After the completion of HFPO feed, agitation was continued
for a further 1 hour, and the coolant bath was allowed to warm up
to room temperature. During the process, some heat generation was
ascertained and evaporation of HFP observed.
[0057] The reactor contents were poured into 100 g of ethanol,
which was thoroughly agitated. The lower layer was washed with 100
g of ethanol. By holding for phase separation, taking out the lower
layer, filtering off the solids, and distilling off the volatiles
at 120.degree. C./10 mmHg, 118 g of a terminally ethyl esterified
HFPO polymer was collected as a colorless clear oil.
[0058] The oily HFPO polymer was measured for viscosity at
25.degree. C. and analyzed by .sup.19F-NMR, by which a number
average molecular weight and the content of monofunctional
heptafluoropropyl (--C.sub.3F.sub.7) group were determined. The
results are shown in Table 2.
[0059] .sup.19F-NMR
[0060] The number average molecular weight and the content of
terminal heptafluoropropyl group formed during polymerization were
determined as follows. 12
[0061] Number average molecular weight=2r/(s+t/2) --C.sub.3F.sub.7
content=t/(s+t/2).times.100 mol %
1 Chemical shift (ppm) Integration ratio (1) -145.4 r (2) -132.3 s
(3) -130.7 t
Example 2
[0062] Preparation of Initiator
[0063] A 2-liter glass flask was thoroughly purged with dry
nitrogen and charged with 31.0 g of cesium fluoride and 115.3 g of
tetraglyme. With stirring in a dry nitrogen atmosphere, 40.2 g of
perfluorodiketone of 98.7% purity represented by the formula (11)
below was added to the flask using a syringe. 13
[0064] Immediately after addition, heat generation was observed.
After about 5 hours of agitation, the reaction solution was allowed
to stand. The reaction solution was a uniform, pale yellow, clear
liquid except for some precipitates of excessive cesium
fluoride.
[0065] A sample taken from the solution was analyzed by infrared
absorption spectroscopy, in which the absorption peak in proximity
to 1880 cm.sup.-1 attributable to --COF group was not observed.
Another sample of the solution was dissolved in water. The amount
of carboxylic acid and hydrofluoric acid resulting from hydrolysis
was determined by alkali titration, and the amount of alcoholate in
the original solution was computed as the --CF.sub.2OCs
concentration (mmol/g), which was 1.06 mmol/g. These measurement
results are shown in Table 1 together with the theoretical
--CF.sub.2OCs concentration (the amount of alcoholate equivalent to
the amount of perfluorodiketone (assumed to be 100% pure)
added).
[0066] Polymerization of HFPO
[0067] A 0.5-liter reactor equipped with an anchor agitator was
charged with 13.2 g of the above-prepared initiator solution and
3.7 g of ethylene glycol dimethyl ether. While agitating at 180
rpm, the reactor was cooled in a coolant bath adjusted at
-10.degree. C.
[0068] Step 1
[0069] When the internal temperature of the reactor reached
-7.degree. C., 2.1 g of HFP was fed at a rate of 4.2 g/hr.
[0070] Step 2
[0071] The coolant bath was reset at -40.degree. C. When the
internal temperature of the reactor reached -38.degree. C., 2.1 g
of HFP was further fed at a rate of 4.2 g/hr.
[0072] Step 3
[0073] Next, 114 g of HFPO and 57 g of HFP were fed over about 15
hours at a rate of 7.6 g/hr and 3.8 g/hr, respectively.
[0074] Mass flow controllers were used for adjusting the flow rate.
The liquid within the reactor was kept between -38.degree. C. and
-35.degree. C. during the HFPO feed.
[0075] After the completion of HFPO feed, agitation was continued
for a further 1 hour, and the coolant bath was allowed to warm up
to room temperature. During the process, some heat generation was
ascertained and evaporation of HFP observed.
[0076] The reactor contents were poured into 100 g of ethanol,
which was thoroughly agitated. The lower layer was washed with 100
g of ethanol. By holding for phase separation, taking out the lower
layer, filtering off the solids, and distilling off the volatiles
at 120.degree. C./10 mmHg, 120 g of a terminally ethyl esterified
HFPO polymer was collected as a colorless clear oil.
[0077] The oily HFPO polymer was measured for viscosity at
25.degree. C. and analyzed by .sup.19F-NMR, by which a number
average molecular weight and the content of monofunctional
heptafluoropropyl (--C.sub.3F.sub.7) group were determined. The
results are shown in Table 2.
[0078] .sup.19F-NMR
[0079] The number average molecular weight and the content of
terminal heptafluoropropyl group formed during polymerization were
determined by the same procedure as in Example 1.
Comparative Example 1
[0080] Preparation of Initiator
[0081] A polymerization initiator was prepared by the same
procedure as in Example 1, using 52.8 g of perfluorodicarboxylic
fluoride of the formula (3) shown below containing 5.3 mol % of
cyclic monofunctional component of formula (5) as an impurity, 37.7
g of cesium fluoride and 140.1 g of tetraglyme. The resulting
reaction solution was a uniform, pale yellow, clear liquid except
for some precipitates of excessive cesium fluoride. 14
[0082] A sample taken from the solution was analyzed by infrared
absorption spectroscopy, in which the absorption peak in proximity
to 1880 cm.sup.-1 attributable to --COF group was not observed. The
amount of alcoholate in the original solution was similarly
computed as the --CF.sub.2OCs concentration, which was 1.02 mmol/g.
These measurement results are shown in Table 1 together with the
theoretical --CF.sub.2OCs concentration.
[0083] Polymerization of HFPO
[0084] A reactor as used in Example 1 was charged with 14.5 g of
the above-prepared initiator solution and 4.3 g of ethylene glycol
dimethyl ether. While agitating at 180 rpm, the reactor was cooled
in a coolant bath adjusted at -10.degree. C.
[0085] Step 1
[0086] When the internal temperature of the reactor reached
-7.degree. C., 2.1 g of HFP was fed at a rate of 4.3 g/hr.
[0087] Step 2
[0088] The coolant bath was reset at -40.degree. C. When the
internal temperature of the reactor reached -38.degree. C., 2.1 g
of HFP was further fed at a rate of 4.3 g/hr.
[0089] Step 3
[0090] Next, 125 g of HFPO and 63 g of HFP were fed over about 15
hours at a rate of 8.3 g/hr and 4.2 g/hr, respectively.
[0091] The liquid within the reactor was kept between -38.degree.
C. and -35.degree. C. during the HFPO feed.
[0092] After the completion of HFPO feed, the same process as in
Example 1 was followed, collecting 125 g of a terminally ethyl
esterified HFPO polymer. The HFPO polymer was similarly analyzed,
with the results shown in Table 2.
Comparative Example 2
[0093] Preparation of Initiator
[0094] A polymerization initiator was prepared by the same
procedure as in Example 1, using 30.0 g of perfluoroadipic
fluoride, 36.5 g of cesium fluoride and 135.7 g of tetraglyme. Even
after about 5 hours of agitation of the resulting solution, the
liquid phase remained separate, indicating that cesium fluoride was
not fully dissolved. In infrared absorption spectroscopy of the
upper liquid phase, a sharp peak attributable to the carbonyl group
was observed in proximity to 1820 cm.sup.-1. The amount of
alcoholate was similarly computed as the --CF.sub.2OCs
concentration by alkali titration as in Example 1. The
concentration was 0.74 mmol/g which is only 64% of the theoretical
value.
2TABLE 1 Polymerization initiator E1 E2 CE1 CE2 --CF.sub.2OCs
concentration, found (mmol/g) 1.09 1.06 1.02 0.74 --CF.sub.2OCs
concentration, calc., (mmol/g) 1.12 1.08 1.07 1.03 IR absorption of
carbonyl not not not found
[0095]
3TABLE 2 Polymerization of HFPO E1 E2 CE1 Number average molecular
weight 97 105 101 --C.sub.3F.sub.7 content (mol %) 4.8 6.1 5.7
Monofunctional component content in <1.5 <1.5 5.3 initiator
(mol %) Viscosity (25.degree. C., cs) 3160 3200 3280
[0096] Although the content of monofunctional HFPO polymer
(represented by the --C.sub.3F.sub.7 content in Table 2) formed
during the polymerization process to difunctional HFPO polymers
does not substantially differ between Examples 1, 2 and Comparative
Example 1, the content of monofunctional impurity in the final
product is extremely low in Examples 1, 2 because the content of
monofunctional impurities in the polymerization initiator is
extremely lower in Examples 1, 2 than in Comparative Example 1. In
the preparation of the polymerization initiator, the alcoholate was
formed in an amount approximately equivalent to the starting
perfluorodicarboxylic fluoride or perfluorodiketone, and
consequently, the difunctional HFPO polymers in Examples 1 and 2
have a sharp degree-of-polymerization distribution.
[0097] Japanese Patent Application No. 11-346692 is incorporated
herein by reference.
[0098] Although some preferred embodiments have been described,
many modifications and variations may be made thereto in light of
the above teachings. It is therefore to be understood that the
invention may be practiced otherwise than as specifically described
without departing from the scope of the appended claims.
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