Note: Descriptions are shown in the official language in which they were submitted.
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W098/38242 PCT~S98/04072
COPOLYMERS OF VINYLIDENE FLUORIDE AND
~EXAFLUOROPROPYLENE HAVING REDUCED
~ EXTRACTABLE CONTENT AND IMPROVED SOLUTION CLARITY
This application claims the benefit of
provisional application serial number 60/038,346 filed
Feb. 28, 1997.
BACKGROUND OF THE INVENTION
This invention relates to compositions of matter
classified in the art of chemistry as fluoropolymers,
more specifically as copolymers of vinylidene fluoride
~VDF), more specifically as copolymers of vinylidene
fluoride and hexafluoropropylene (HFP), still more
specifically as copolymers of VDF and HFP having
reduced extractable content, longer gel times and
improved solution clarity, to novel compositions of
matter and articles of manufacture containing such
copolymers, as well as to processes for the
preparation and use of the copolymers, of compositions
of matter containing such copolymers and of the
articles of manufacture containing such copolymers.
.. . .
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W098/38242 PCT~S~8JC1~72
.
VDF/HFP copolymers are well known and are used
for their thermoplastic engineering properties,
chemical resistance and inertness toward degradation.
They may be found in applications such as chemically
resistant piping, gasketing, plenum cable jacketing,
filtration and extraction membranes and in the
construction of lithium batteries.
The present invention provides VDF/HFP copolymers
containing up to about 24 weight % ~12 mole%) HFP
having among other improved properties, substantially
improved solution clarity, longer gel times and
reduced extractables as these terms are defined
hereinafter.
The process used to make the instant copolymers
re~uires one ratio of VDF and HFP for the initial fill
of the reactor, and a different ratio of VDF and HFP
during a subsequent continuous feed of the monomers.
Any particular desired average HFP content in the
copolymer product has corresponding particular initial
fill and subsequent feed ratios. The uniformity of
compositions prepared this way provide uni~ue and
useful properties in comparison to VDF/HFP copolymers
described in the prior art.
DISCLOSURE OF PRIOR ART
Rexford in U.S. Pat. No. 3,051,677 described
VDF/HFP copolymers of HFP content 30 to 70 wt% (15 to
50 mol~) which showed utility as elastomers. To make
the copolymers, a batch process with certain initial
ratios of VDF and HFP, and a continuous process with
fixed ratios of VDF and HFP throughout the process
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W098/38242 PCT~S98/04072
were described. The processes described were such
that polymers lacking the improved solution clarity,
longer gel times and low extractables of the present
invention were made.
Lo in U.S. Pat. No. 3,178,399 described VDF/HFP
copolymers of HFP content of 2 to 26 wt~ (1 to 13
mol~) which showed a numerical value for the product
of the tensile strength (psig) and percent reversible
elongation of at least 1,000,000. A batch process
with certain initial ratios of VDF and HFP, or,
alternately, a semicontinuous process with fixed
ratios of VDF and HFP throughout the process were used
to make the copolymers. The processes discussed were
such that copolymers lacking the improved solution
clarity, longer gel times and low extractables of the
present invention copolymers were made.
Moggi, et al. in Polymer Bulletin 7, 115-122
(1982) analyzed the microstructure and crystal
structure of VDF/HFP copolymers by nuclear magnetic
resonance and x-ray diffraction experiments. The
copolymers of up to 31 wt% (up to 16 mol%) HFP were
made in a batch emulsion process which was carried
only to low conversion. While the low conversion
batch process is capable of producing copolymers
having solution clarity and low extractables, no such
properties are described. It is not a practical
process for industrial use because of the low
conversions required to make the materials. In
addition, no detailed polymerization examples were
offered.
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W098/38242 PCT~S98/04072
Bonardelli et al.- in Polymer, vol. 27, 905-909
(June 1986) studied the glass transition temperatures
of VDF/HFP copolymers having HFP content up to 62 wt.
(up to 41 mol%). The glass transition temperatures
were correlated to the overall HFP content in the
copolymers. In making the copolymers for analysis, a
semioontinuous emulsion process was used which
employed different VDF/HFP ratios for the initial fill
of the reactor and for the subsequent continuous feed
of monomers. Although reference was made to the use
of reactivity ratios to set the VDF/HFP ratio for the
initial fill, no detailed polymerization examples were
offered, and no mention of copolymers having solution
clarity, gel times and low extractables comparable to
that of the copolymers of the present invention was
made.
Pianca et al. in Polymer, vol. 28, 224-230 (Feb.
1987) examined the microstructure of VDF/HFP
copolymers by nuclear magnetic resonance, and the
microstructure determinations were used to explain the
trend in glass transition temperatures of the
copolymers. The synthesis of the copolymers involved
a semicontinuous emulsion process which used different
VDF/HFP ratios for the initial fill of the reactor and
for the subsequent continuous feed of monomers. No
detailed synthesis examples were provided, and there
was no discussion of copolymers having improved
solution clarity, longer gel times and low
extractables as provided by the copolymers of the
present invention.
.
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Abusleme et al. in Eur. Pat. Appl. No. 650,982 Al
showed an emulsion process to make polymers and
copolymers of fluorinated olefins optionally with one
or more non-fluorinated olefins. The process relied
on photochemical initiation of polymerization so that
lower temperatures and pressures could be used than
those used for thermally initiated processes. While
there was general mention of the structural regularity
of the resulting polymers, the only evidence of
regularity concerned poly(vinylidene fluoride)
homopolymer, and no claims were made as to regularity
of composition. Examples of VDF/HFP copolymerization
were given, but no discussion of the solution
extraction properties of the copolymers was given, and
there was no relation made between physical properties
and the structure of the VDF/HFP copolymers.
Morgan in U.S. Pat. No. 5,543,217 disclosed
uniform tetrafluoroethylene/hexafluoropropylene
copolymers (TFE/HFP copolymers) made by a
semicontinuous emulsion process. Uniformity was
simply defined as there being a low proportion of
adjacent HFP units in the polymer chains; there was no
disclosure of the disposition of TFE and HFP units
otherwise, and there was no discussion of VDF/HFP
copolymers or the properties to be expected therefrom.
U.S. Patent 2,752,331 describes the synthesis of
VDF/chlorotrifluoroethylene (CTFE) copolymers having a
high uniformity of comonomer distribution in its
molecular chains.
Baggett and Smith in High Polymers , Vol . XVIII,
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Ham, John Wiley (1964)-, Chapter X, Copolymerization,
pp. 587 et seq., particularly at pp. 593 and 610
describe the synthesis of uniform composition
distribution copolymers of vinylidene chloride and
vinyl chloride and of vinyl chloride and vinyl
acetate.
None of these references teaches or suggests a
way to obtain VDF/HFP copolymers having solvent
solution clarity and fluidity, longer gel times and
low extractables comparable to the VDF/HFP copolymers
of the instant invention or that such properties are
attainable from VDF/HFP copolymers.
SI~ARY OF THE INVENTION
The invention provides in a first composition
aspect a copolymer of vinylidene fluoride and
hexafluoropropylene containing a maximum of about 24
weight percent hexafluoropropylene, having solutions
of improved clarity and fluidity; for the copolymers
having up to about 8 weight percent nominal HFP
content, having weight percent extractables within
plus or minus 1.5% of the percent by weight
extractables calculated by an equation selected from
the group consisting of:
a) Wt.% Extractables = 1.7(HFP mole%) - 3.2, and
b) Wt.% Extractables = -1.2 + 1.5(HFP mole~ x 10~6(Mn),
and for the copolymers having greater than about
8 weight percent nominal HFP content, having a DSC
(differential scanning calorimetry) melting point at
least 2.5~C lower than the DSC melting point of
copolymers having the same nominal weight percent HFP
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W098/38242 PCT~S98/04072
prepared by methods for which the prior art provides
detail.
The tangible embodiments of this first
compositlon aspect of the invention are straw colored
to colorless semi crystalline solids having melting
points, as determined by differential scanning
calorimetry (DSC), lower than VDF/HFP copolymers
having the same nominal HFP percentage content
prepared by processes reported in detail in the prior
art.
The tangible embodiments of this first
composition aspect of the invention also possess
longer gelation times from solution than VDF/HFP
copolymers having the same nominal HFP content
prepared by processes reported in detail in the prior
art.
The aforementioned physical characteristics taken
together with the method of synthesis positively tend
to confirm the structure and the novelty of the
compositions sought to be patented.
The tangible embodiments of the first composition
aspect of the invention have the inherent applied use
characteristics of being suitable for paint and powder
coating vehicles and as chemically resistant shaped
objects and films both supported and unsupported.
Particular mention is made of copolymers of the first
composition aspect of the present invention having
from about 2 weight~ HFP content to about 8 weight~
HFP, still more particularly copolymers having about 3
to 6 weight~ HFP which possess the inherent applied
use characteristics of being particularly suitable as
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PCT~S98/04072
polymeric separators and polymeric electrode matrices
for batteries, particularly lithium batteries. The
prior art, see for example U.S. 5,296-,318 has reported
lithium batteries made from PVDF/HFP copolymers having
from 8~ to 25~ by weight HFP. It is understood that
the copolymers of the present invention having HFP
content in that range are suitable for use in such
batteries and would represent an improvement therein.
Such improved batteries are also contemplated by the
invention as equivalents.
Particular mention is also made of copolymers of
the first composition aspect of the invention having
from about 7 weight percent HFP content to about 15
weight percent HFP content, more particularly
copolymers having about 10 weight percent HFP content
which possess the inherent applied use characteristic
of being suitable as flame resistant insulation for
wire and cable.
Still further mention is made of copolymers of
the first composition aspect of the invention having
greater than about 15 weight percent HFP content,
still more particularly of copolymers having about 16
by weight or greater HFP content which have the
inherent applied use characteristic as clear,
flexible, chemically resistant films.
The invention provides in a second composition of
matter aspect, an improved article of manufacture
comprising an electrochemical cell having a positive
electrode, an absorber separator and a negative
electrode wherein at least either one of the
electrodes comprises a vinylidene fluoride polymer
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W098/38242 PCT~S98/04072
.
having an electrolyte material combined therewith or
said absorber separator comprises a vinylidene
fluoride polymer having an electrolyte material
combined therewith wherein the improvement comprises
the polyvinylidene fluoride polymer consisting
essentially of a vinylidene
fluoride/hexafluoropropylene copolymer as defined in
the first composition aspect of the invention.
Special mention is made of embodiments of the
second composition of the invention wherein the
VDF/HFP copolymer has a hexafluoropropylene content of
from about 2 weight ~ hexafluoropropylene to about 8
weight ~ particularly those having from about 3 weight
~ to about 6 weight ~ hexofluoropropylene, still more
particularly, those having about 3 weight
hexafluoropropylene.
The electrochemical cells of which the second
composition of matter aspect of this invention is an
improvement are described in PCT Application WO
95/06332, European Patent Application 95 120 660.6-
1215, published as number 73(),316 A1 on September 4,
1996 and U.S. Patent 5,296,318. The disclosures of
the PCT application, the European application and the
U.S. Patent are hereby incorporated by reference. In
addition to use of solution casting techniques for
preparation of films for use in battery constructions
as described in the aforementioned references, use of
extrusion techniques to prepare such films and the
g
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PCT~S98/04072
,
batteries fabricated therefrom are also contemplated
It has also been noted that batteries fabricated
from the PVDF-HFP copolymers of the present invention
have better adhesion of the polymers to metallic
portions of electrodes and higher use temperatures
than batteries fabricated from PVDF-HFP copolymers
having similar percentage HFP content synthesized by
prior art processes described in sufficient detail for
reproduction. It has also been observed that PVDF-HFP
copolymers of the present invention provide batteries
having improved electrical properties including the
capability of higher discharge rates than batteries
fabricated from PVDF-HFP copolymers of having similar
percentage HFP content synthesized by processes
described in the prior art in sufficient detail for
reproduction.
The invention provides in a third composition
aspect, a solution of a composition of the first
composition aspect of the invention having improved
solution clarity and fluidi~y.
Copolymers of vinylidene fluoride and
hexafluoropropylene of up to about 24 wt%
hexafluoropropylene are useful semicrystalline
thermoplastics. As the HFP content increases in the
materials, the crystallinity decreases, and,
correspondingly, the flexibility and solvent
sensitivity increase. Other properties change as
well, such as the final melting point, which decreases
with increasing HFP content. In high-purity
applications such as membrane filtration or
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W098/38242 PCT~S98/04072
extraction, lithium battery construction, high-
transparency film from solution casting, and fluid
storage and transport requiring low contaminant
levels, it -is desirable to have materials with low
levels of extractables, little gel formation in the
presence of solvent, and good clarity. The VDF/HFP
copolymers provided here show lower extractables,
improved solution properties, improved clarity and
fluidity, and lower melting points in comparison to
the nonuniform VDF/HFP copolymers of otherwise similar
HFP content and manufacture known in the prior art.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a comparison of the final
differential scanning colorimeter/(DSC) melting point
of copolymers of the invention with DSC melting points
of prior art compounds whose synthesis is described in
detail.
Figure 2 shows the effect on HFP level on polymer
extractibles in dimethyl carbonate (DMC) at 40~C for
copolymers of the invention and copolymers of the
prior art whose synthesis is described in detail.
Figure 3 shows the relationship between HFP
content and log of gelation time from solution (20 wt~
in propylene carbonate) of copolymers of the present
invention and of copolymers of the prior art having
sufficient synthesis detail for reproduction.
~ DETATLED DESCRIPTION
The invention provides copolymers of vinylidene
fluoride and hexafluoropropylene having
hexafluoropropylene content of up to about 24 wt~ and
CA 022~1~35 1998-10-14
W098/38242 PCT~S98/04072
having improved soluti-on clarity and fluidity and
reduced extractables. The copolymers are conveniently
made by an emulsion polymerization process, but
suspension and solution processes may also be used.
In an emulsion polymerization process a reactor is
charged with deionized water, water-soluble surfactant
capable of emulsifying the reaction mass during
polymerization, paraffin antifoulant, vinylidene
fluoride, hexafluoropropylene, chain-transfer agent to
control copolymer molecular weight, and initiator to
start and maintain the polymerization. To obtain the
VDF/HFP copolymers of the present invention, the
initial charge of VDF and HFP monomers is such that
the amount of HFP is up to 48~ of the combined weight
of the monomers initially charged, and then VDF and
HFP are fed continuously throughout the reaction such
that the amount of the HFP is up to 24~ of the
combined weight of the monomers fed continuously. The
VDF/HFP ratios are different in the initial charge and
during the continuous feed, and each final polymer
composition has definite and related ratios for the
initial charge and continuous feed. The process uses
total amounts of VDF and HFP monomers such that the
amount of HFP used is up to about 24~ of the combined
total weight of the monomers.
The reactor is a pressurized polymerization
reactor equipped with a stirrer and heat control
means. The temperature of the polymerization can vary
depending on the characteristics of the initiator
used, but it is typically between 65~ and 105~C, and
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most conveniently it is between 75~ and 95~C. The
temperature is not limited to this range, however, and
might be hi~her or lower if a high-temperature or low-
temperature initiator is used. The VDF/HFP ratios
used in the polymerization will be dependent on the
temperature chosen for reaction. The pressure of the
polymerization is typically between 2750 and 6900 kPa,
but it can be higher if the equipment permits
operation at higher pressure. The pressure is most
conveniently between 3790 and 5860 kPa.
Surfactants used in the polymerization are water-
soluble, halogenated surfactants, especially
fluorinated surfactants such as the ammonium,
substituted ammonium, quaternary ammonium, or alkali
metal salts of perfluorinated or partially fluorinated
alkyl carboxylates, the perfluorinated or partially
fluorinated monoalkyl phosphate esters, the
perfluorinated or partially fluorinated alkyl ether or
polyether carboxylates, the perfluorinated or
partially fluorinated alkyl sulfonates, and the
perfluorinated or partially fluorinated alkyl
sulfates. Some specific, but not limiting examples
are the salts of the acids described in U.S. Pat. No.
2,559,752 of the formula X(CF2)nCOOM, wherein X is
hydrogen or fluorine, M is an alkali metal, ammonium,
substituted ammonium (e.g., alkylamine of 1 to 4
carbon atoms), or quaternary ammonium ior., and n is an
integer from 6 to 20; sulfuric acid esters of
polyfluoroalkanols of the formula X(CF2)nCH2OSO3M,
where X and M are as above; and salts of the acids of
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the formula CF3(CF2)n(CX2)mS03M, where X and M are as
above, n is an integer from 3 ~o 7, and m is an
integer from 0 to 2, such as in potassium
perfluorooctyl sulfonate. The surfactant charge is
from 0.05% to 2~ by weight on the total monomer weight
used, and most preferably the surfactant charge is
from 0.1~ to 0.2~ by weight.
The paraffin antifoulant is conventional, and any
long-chain, saturated, hydrocarbon wax or oil may be
used. Reactor loadings of the paraffin are from 0.01
to 0.3% by weight on the total monomer weight used.
After the reactor has been charged with deionized
water, surfactant, and paraffin antifoulant, the
reactor is either purged with nitrogen or evacuated to
remove oxygen. The reactor is brought to temperature,
and chain-transfer agent may optionally be added. The
reactor is then pressurized with a mixture of
vinylidene fluoride and hexafluoropropylene.
Chain-transfer agents which may be used are well-
known in the polymerization of fluorinated monomers.
Alcohols, carbonates, ketones, esters, and ethers are
oxygenated compounds which serve as chain-transfer
agents. Specific, but not limiting examples, are
isopropyl alcohol, such as described in U.S. Pat. No.
4,360,652, acetone, such as described in U.S. Pat. No.
3,857,827, and ethyl acetate, as described in the
Published Unexamined Application (Kokai) JP 58065711.
other classes of compounds which serve as chain-
transfer agents in the polymerization of fluorinated
monomers are halocarbons and hydrohalocarbons such as
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; W098/38242 PCT~S98/04072
chlorocarbons, hydrochlorocarbons,
chlorofluorocarbons, and hydrochlorofluorocarbons;
specific, but not limiting examples are
trichloro~luoromethane, such as described in U.S. Pat.
No. 4,569,978, and 1,1-dichloro-2,2,2-trifluoroethane.
Chain-transfer agents may be added all at once at the
beginning of the reaction, in portions throughout the
reaction, or continuously as the reaction progresses.
The amount of chain-transfer agent and mode of
addition which is used depends on the activity of the
agent and the desired molecular weight characteristics
of the product. The amount of chain-transfer agent
used is from 0.05% to 5~ by weight on the total
monomer weight used, and preferably it is from 0.1 to
2% by weight.
The reactor is pressurized by adding vinylidene
fluoride and hexafluoropropylene monomers in a
definite ratio (first effective ratio) such that the
hexafluoropropylene ranges up to 48% of the combined
weight of the monomers initially charged. The first
effective ratio used will depend on the relative
reactivity of the two monomers at the polymerization
temperature chosen. The reactivity of vinylidene
fluoride and hexafluoropropylene has been reported in
Bonardelli et al., Polymer, vol. 27, 905-909 (June
1986). The relative reactivity is such that to obtain
~ a particular uniform copolymer composition, more
hexafluoropropylene has to be charged to the reactor
in the initial fill than will be incorporated into the
copolymer. At the convenient polymerization
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W098/38242 PCT~S98/04072
temperature range of this invention, about twice as
much hexafluoropropylene has to be charged to the
reactor in the initial fill as will appear in the
polymer.
The reaction can be started and maintained by the
addition of any suitable initiator known for the
polymerization of fluorinated monomers including
inorganic peroxides, "redox" combinations of oxidizing
and reducing agents, and organic peroxides. Examples
of typical inorganic peroxides are the ammonium or
alkali metal salts of persulfates, which have useful
activity in the 65~C to 105~C temperature range.
"Redox" systems can operate at even lower temperatures
and examples include combinations of oxidants such as
hydrogen peroxide, t-butyl hydroperoxide, cumene
hydroperoxide, or persulfate, and reductants such as
reduced metal salts, iron (II) salts being a
particular example, optionally combined with
activators such as sodium formaldehyde sulfoxylate or
ascorbic acid. Among the organic peroxides which can
be used for the polymerization are the classes of
dialkyl peroxides, peroxyesters, and
peroxydicarbonates. Exemplary of dialkyl peroxides is
di-t-butyl peroxide, of peroxyesters are t-butyl
peroxypivalate and t-amyl peroxypivalate, and of
peroxydicarbonates are di(n-propyl) peroxydicarbonate,
diisopropyl peroxydicarbonate, di(sec-butyl)
peroxydicarbonate, and di(2-ethylhexyl)
peroxydicarbonate. The use of diisopropyl
peroxydicarbonate for vinylidene fluoride
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polymerization and copolymerization with other
fluorinated monomers is taught in U.S. Pat. No.
3,475,396, and its use in making vinylidene
fluoride/hexafluoropropylene copolymers is further
illustrated in U.S. Pat. No. 4,360,652. The use of
di(n-propyl) peroxydicarbonate in vinylidene fluoride
polymerizations is described in the Published
unexamined Application (Kokai) JP 58065711. The
quantity of an initiator required for a polymerization
is related to its activity and the temperature used
for the polymerization. The total amount of initiator
used is generally between 0.05~ to 2.5~ by weight on
the total monomer weight used. Typically, sufficient
initiator is added at the beginning to start the
reaction and then additional initiator may be
optionally added to maintain the polymerization at a
convenient rate. The initiator may be added in pure
form, in solution, in suspension, or in emulsion,
depending upon the initiator chosen. As a particular
example, peroxydicarbonates are conveniently added in
the form of an aqueous emulsion.
As the reaction progresses, a mixture of
vinylidene fluoride and hexafluoropropylene monomers
is fed in a definite ratio ( second effective ratio)
so as to maintain reaction pressure. The second
effective ratio used corresponds to the monomer unit
ratio desired in the final composition of the
copolymer, and it can range up to 24~ of the combined
weight of the monomers being fed continuously
throughout the reaction. The feed of vinylidene
,
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W098/38242 PCT~S98/04072
fluoride, hexafluroropropylene, and optionally
initiator and chain-transfer agent is continued until
the desired reactor fill is obtained.
Upon reaching the desired reactor fill, the
monomer feeds are terminated. To achieve the
copolymer having optimum solution clarity and minimal
extractables, all other feeds are stopped at the same
time as the monomer feeds, and the reactor is vented
as soon as is practicable. Alternatively, to achieve
highest yield at the expense of solution clarity and
extractables, a react-out period to consume residual
monomer is used with optional continuation of
initiator feed. For react-out, the reaction
temperature and agitation are maintained for a period
of 20 to 30 minutes, but a longer period can be used
if required in order to consume monomer to the point
where the reactor pressure is no longer falling to any
significant degree. A settling period of typically 10
to 40 minutes may be used following the react-out
period. During the settling period, temperature is
maintained but no initiator feed is used. The reactor
is then cooled and vented.
The product is recovered as a latex. To obtain
dry resin, the latex is coagulated, the coagulum is
separated and the separated coagulum may be washed.
To provide powder, the coagulum is dried.
For the coagulation step, several well-known
methods can be used including freezing, the addition
of acids or salts, or mechanical shear with optional
heating. The powder, if desired, can be further
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processed into pellets or other convenient resin
forms.
The following Examples further illustrate the
best mode contemplated by the inventors for carrying
out their invention and are to be construed as
illustratlve and not as in limitation thereof.
Melt viscosity measurements are by ASTM D3835 at
232~C and lO0 s-1.
Thermal properties are measured with a
Differentlal Scanning Calorimeter (DSC) according to
ASTM D3418.
HFP content was determined by 19F NMR according
to the slgnal assignments and method described in
Pianca et al., Polymer, vol. 28, 224-230 (Feb. 1987) .
A Unity 400 spectrometer at 376.3 MHz was used.
Spectra were obtained either in deuterated dimethyl
formamide at 50~ C with an excitation pulse width of
8.0 microseconds and a recycle delay of 10 seconds, in
deuterated dimethyl sulfoxide at 80~ C with an
excitation pulse width of 6.0 microseconds and recycle
delay of 5 seconds, or in deuterated acetone at 50~ C
with an excitation pulse width of 8.0 microseconds and
a recycle delay of 20 seconds.
Molecular weights were measured by size exclusion
chromatography (SEC). A Waters 150 C chromatographic
device with a set of PL gel 2 mixed B columns with
bead size of 10 microns was used at an operating
temperature of 105 degrees C. HPLC grade dimethyl
sulfoxide (DMSO) was used as the eluant at flow rate
of ~.0 mL/min. The samples were prepared by
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W O 98/38242 PCT/US98/04072
dissolution in DMSO for 5 hours at 100 degrees C,
followed by filtration.
EXAMPLE 1
Into a 7.5 liter, stainless steel reactor were
charged 4.799 kg of deionized water, 0.230 kg of a l
wt~ solution of a mixture of perfluoroalkanoate salts,
and 0.004 kg of paraffin wax. The mixture was purged
with nitrogen and agitated for 30 minutes. The
reactor was sealed and heated to 80 degrees Celsius.
The reactor was charged with 0.355 kg of vinylidene
fluoride, 0.049 kg of hexafluoropropylene (a ratio of
88 vinylidene fluoride/12 hexafluoropropylene), and
0.120 kg of a 5 wt~ solution of ethyl acetate in
deionized water. The reaction conditions were
stabilized at 80 degrees Celsius and 4480 kPa, and
then the polymerization was begun by introducing 0.026
kg of an initiator emulsion consisting of 2 wt~ di-n-
propyl peroxydicarbonate and 0.15 wt~ mixed
perfluoroalkanoate salts dispersed in deionized water.
The pressure rose to 4550 kPa with the addition of the
initiator emulsion. The polymerization was maintained
by the addition of the initiator emulsion at the rate
of 0.112 kg per hour, and by the addition of a mixture
of vinylidene fluoride/hexafluoropropylene in the
ratio 95 vinylidene fluoride/5 hexafluoropropylene so
as to maintain pressure. After 4.2 hours, totals of
1.890 kg of vinylidene fluoride and 0.140 kg of
hexafluoropropylene had been charged to the reactor.
All feeds were stopped, and the reactor was cooled.
After 5 minutes of cooling, agitation speed was
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W098/38242 PCT~S98/04072
.
reduced by 78~ and surplus gases were vented.
Agitation was stopped, the reactor was further cooled,
and then it was emptied of latex. Polymer resin was
isolated by-coagulating the latex, washing the
resulting solids with boiling water, and drying the
solids at 110 degrees Celsius to yield fine powder.
The resin so made had a melt viscosity of 2770 Pa.s,
had a DSC melting point of 152 degrees Celsius, and
had a hexafluoropropylene content as measured by NMR
of 5.4 wt~.
~22~PLE 2
Into a 7.5 liter, stainless steel reactor were
charged 4.913 kg of deionized water, 0.230 kg of a 1
wt~ solution of a mixture of perfluoroalkanoate salts,
and 0.004 kg of paraffin wax. The mixture was purged
with nitrogen and agitated for 30 minutes. The
reactor was sealed and heated to 80 degrees Celsius.
The reactor was charged with 0.415 kg of vinylidene
fluoride, 0.215 kg of hexafluoropropylene (a ratio of
66 vinylidene fluoride/34 hexafluoropropylene), and
0.010 kg of ethyl acetate. The pressure was at 4895
kPa. The reaction conditions were stabilized at 80
degrees Celsius, and then the polymerization was begun
by introducing 0.040 kg of an initiator emulsion
consisting of 2 wt~ di-n-propyl peroxydicarbonate and
0.15 wt~ mixed perfluoroalkanoate salts dispersed in
deionized water. The pressure dropped upon initiation
and it was then maintained at 4825 kPa. The
polymerization was maintained by the addition of the
initiator emulsion at the rate of 0.176 kg per hour,
CA 022~l~3~ l998-l0-l4
W098/38242 PCT~S98/04072
and by the addition of a mixture of vinylidene
fluoride/hexafluoropropylene in the ratio 84
vinylidene fluoride/16 hexafluoropropylene so as to
maintain pressure. After 2.2 hours, totals of 1. 585
kg of vinylidene fluoride and 0. 445 kg of
hexafluoropropylene had ~een charged to the reactor.
Monomer feeds were stopped, and residual monomer was
consumed by maintaining the initiator emulsion feed
and 80 degrees Celsius for 20 minutes. The initiator
feed and agitation were stopped and the reactor was
allowed to settle 10 minutes. The reactor was cooled
to 45 degrees Celsius, vented, and then it was emptied
of latex. Polymer resin was isolated by coagulating
the latex, washing the resulting solids with boiling
water, and drying the solids at 80 degrees Celsius to
yield fine powder. The resin so made had a melt
viscosity of 1220 Pa.s, had a DSC melting point of 114
degrees Celsius, and had a hexafluoropropylene content
as measured by NMR of 17. 2 wt.~.
EXAMPLE 3 (Comparative Example to Example 1)
Into a 7.5 liter, stainless steel reactor were
charged 4.799 kg of deionized water, 0.230 kg of a 1
wt~ solution of a mixture of perfluoroalkanoate salts,
and 0. 004 kg of paraffin wax. The mixture was purged
with nitrogen and agitated for 30 minutes. The
reactor was sealed and heated to 80 degrees Celsius.
The reactor was charged with 0.400 kg of vinylidene
fluoride, 0.030 kg of hexafluoropropylene (a ratio of
93 vinylidene fluoride/7 hexafluoropropylene), and
0.120 kg of a 5 wt.~ solution of ethyl acetate in
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CA 022~l~3~ l998-l0-l4
W098/38242 PCT~S98/04072
deionized water. The reaction conditions were
stabilized at 80 degrees Celsius and 4480 kPa, and
then the polymerization was begun by introducing 0.026
kg of an i-nitiator emulsion consisting of 2 wt% di-n-
propyl peroxydicarbonate-and 0.15 wt% mixed
perfluoroalkanoate salts dispersed in deionized water.
The polymerization was maintained by the addition of
the initiator emulsion at the rate of 0.112 kg per
hour, and by the addition of a mixture of vinylidene
fluoride/hexafluoropropylene in the ratio 93
vinylidene fluoride/7 hexafluoropropylene so as to
maintain pressure. After 3.1 hours, totals of 1.890
kg of vinylidene fluoride and 0.140 kg of
hexafluoropropylene had been charged to the reactor.
~onomer feeds were stopped, and residual monomer was
consumed by maintaining the initiator emulsion feed
and 80 degrees Celsius for 20 minutes. The initiator
feed and agitation were stopped, and the reactor was
allowed to settle for 10 minutes. The reactor was
cooled to 45 degrees Celsius, vented, and then it was
emptied of latex. Polymer resin was isolated by
coagulating the latex, washing the resulting solids
with boiling water, and drying the solids at 110
degrees Celsius to yield fine powder. The resin so
made had a melt viscosity of 2550 Pa.s, had a DSC
melting point of 154 degrees Celsius, and had a
hexafluoropropylene content as measured by NMR of 6.0
wt.%.
EXAMpr-F 4
Into a 293 liter stainless steel reactor were
- 23 -
CA 022~1~3~ 1998-10-14
; W098/38242 PCT~S98/04072
charged 200.0 kg of deionized water, 1.00 kg of a 10
wt% solution of a mixture of perfluoroalkanoate salts,
and 0.015 kg of paraffin oil. The reactor was
evacuated and heated to a temperature of 91 degrees
Celsius during the charging, and agitation was used.
To the reactor were added 12.6 kg of vinylidene
fluoride, 0.8 kg of hexafluoropropylene (a ratio of 94
vinylidene fluoride/6 hexafluoropropylene), and 0.5 kg
of ethyl acetate, which brought the reactor pressure
to 4480 kPa. During the pressurization, when the
pressure reached 3445 kPa, a feed of initiator
emulsion consisting of 2 wt% di-n-propyl
peroxydicarbonate and 0.15 wt~ mixed
perfluoroalkanoate salts dispersed in deionized water
was begun and was maintained at 9.0 kg/h until 4.6 kg
of initiator emulsion had been added. The rate of
further initiator emulsion addition was adjusted so as
to maintain a total monomer feed rate of 27.0 kg/h. A
monomer mixture in the ratio 94 vinylidene fluoride/6
hexafluoropropylene was fed to the reactor so as to
maintain pressure at 4480 kPa until the totals of 85.3
kg of vinylidene fluoride and 5.4 kg of
hexafluoropropylene had been charged to the reactor.
All feeds were stopped, and residual monomer was
consumed by maintaining 91~ Celsius and agitation for
20 minutes and then by maintaining 91~ Celsius for 35
minutes. The reactor was cooled, vented, and emptied
of latex. Polymer resin was isolated by coagulating
the latex, washing the resulting solids with water,
and drying the solids to yield fine powder. The resin
so made had a melt viscosity of 1740 Pa.s, had a DSC
- 24 -
CA 0225153j 1998-10-14
WO 98/38242 PCT/US98/01~7
melt1ng polnt of 155 dègrees Celslus, and had a
hexafluoropropylene content as measured by NMR of 4.7
wt.~.
EXAMPLES 5 to 12
Copolymers of examples 5 to 8 are made slmllarly to
copolymers of Examples 1 or 2, and copolymers of
examples 9 to 12 are made slmilarly to copolymers of
Examples 3 or 4 and are shown ln Table I.
CA 02251535 1998-10-14
W O 98/38242 PCT~US98/04072
.
~ ,,~ Cl~ o oUl Ul ~
a~r ~ ,~ ~~~ ~ b ~ ~ ~D O ~O ~ 3
~ ~~ b b b b ~ o b
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ob ~ '' ' ~ ~ r r~ ~ o
N ~D ~I r-1
CO U- O O f" Ul Ul ~
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r o r o ~ o
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ct) .r ~r b b b b ~ o o N ~1 ~r ~
o ~ o I o .r
O~ O O O ~D O O u~ C
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r ~r o ,. I o ~D .. ~ru~ ~r a
000 0 ~00
r~ O r o o o ,1 ~
r ~ N ('~1 I OU~ ~ ~r O
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O t~ ~o ~ r~r~ t~O ~1 N
~ ~ r ~ o m r .r ~ _l I o r ~ ro r N ~r Ul
X rD ~ o o o o,~ o o
i_ il r~
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rD ~r d' O O O O~ O O r1 ~ ~--1
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Vl tD r~l O O I OU\ O ~r N W -r _
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rD ~rd' O O O O .-1 O O ~1 ~1 ~-
tr~ Ul tn O ~D O O ~D ~
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o o ~ . .~ - 3 - C
L ~ V.r1 l~ to
tv ~ , ~ . n- u u c o t-.
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r-~U U -r tV ~ I >t_ tV 1 r~
3 rl ~ i O O ~ O g ~ z L ~V r~ r~
i,n o in o
-26-
CA 022~l~3~ l998-l0-l4
W098/38242 PCT~S98/04072
The term "solut'ion(s) having improved clarity
and fluidity" as used in the specification and
claims of this application means that the
solution-(~) of any particular copolymer of this
- invention having a particular nominal HFP content
will provide solution(s) having descriptive
properties analogous to those shown by Example 2 in
Table II when dissolved in any of the solvents
listed at the same concentration levels at which a
copolymer having about the same particular nominal
HFP content made by a typical process described in
detail in the prior art provides solution
descriptive properties analogous to those shown in
Table II for Example 12.
EVALUATION OF THE SOLUTION PROPERTIES OF THE
EXAMPLES
The solution properties of examples 2 and 12
are shown in Table II. Mixtures of the indicated
weight percent were prepared, using heat when
necessary to dissolve the polymer completely and
form a clear solution. Solutions were then allowed
to cool and observed daily over a period of two
weeks. The copolymer 2 showed a reduced tendency to
gel and to be clearer than the copolymer 12. The
retention of fluidity and clarity by the copolymer 2
is advantageous in applications which rely on
polymer solutions, such as in the production of cast
films and membranes.
The reduction in tendency toward gelation by
the copolymers of the present invention is further
- 27 -
CA 022~l~3~ 1998-l0-l4
W098/38242 PCT~S98/04072
shown in Table II A. The gelation times of
propylene carbonate solutions of some of the
examples are shown in the table. A Rheometrics
dynamic stress rheometer DSR-200 was used to measure
the gelation times of 20 wt~ solutions of the
polymers in propylene carbonate (the propylene
carbonate was of nominal 99.7~ purity). The
rheometer was fitted with a Peltier fixture and
solvent trap. A 40 mm parallel plate geometry was
used with a gap of 1 mm. Solid copolymer was mixed
with propylene carbonate at room temperature on the
day of measurement, the container was sealed, and
the solution was formed by heating and stirring the
mixture in the sealed container for 1.0 hour in a
Pierce Reacti-Therm Heating/Stirring Module set at
120~C. The solutions were quickly loaded at the end
of the dissolution period into the test fixture,
which was preset at 100~C. A temperature cooling
ramp in dynamic oscillatory mode at 1 Hz was begun
as soon as the fixture temperature re-equilibrated
at 100~Ci re-equilibration typically required a
minute or less. The cooling ramp was from 100~C to
15~C at a rate of 30~C/m. When 15~C was reached, a 1
minute equilibration time was used, and then a time
sweep measurement was begun. The sample was held at
15~C during the time sweep measurement performed at
1 radian/s. The time sweep was continued until the
gel point was reached. The gel point was taken as
the point at which the solution storage modulus, G',
and the loss modulus, G", became equal. The gel
time was taken as the time duration in the time
CA 02251535 1998-10-14
- W098/38242
PCT~S98/04072
sweep to reach the gel point.
The relation between HFP content and the
logarithm of the gelation time of the 20 wt%
propylene~carbonate solutions is shown in Figure 3.
It can be seen that the copolymers of the present
invention have longer gelation times than the
copolymers prepared according to the prior art over
the whole range of HFP content. The reduced
tendency toward gelation by the copolymers of the
present invention is advantageous in processing such
solutions for film casting and other solution
applications.
CA 022~1~3~ 1998-10-14
WO 98/38242 PCT/US98/04072
TABLE II
SOLUTION PROPERTIES
Polymer Appearance
concentration and
solvent
Example 2 ~xample 12
10% in MEK fluid, clear fluid clear
0 20~ in MEK fluid, clear by day 2~ loose gel,
clear
30'O in MEK by day 14,some gel,clear by day 1, loose gel,
cloudy; by day 4, gel,
cloudy
10~ in MPK fluid, clear fluid, clear
20~ in MPK fluid, clear by hour 2, some gel,
clear; by day 1, gel,
slightly cloudy
10% in MiBK fluid, clear by day 4, gel, clear
10% in CPO fluid, clear fluid, clear
10% in CHO fluid, clear fluid, clear
20~o in CHO by day 2~ some gel,clear by day 1, some gel,
clear;
by day 2, some gel,
cloudy
10% in EtoAC fluid, clear by day 7, some gel,
clear
20% in EtoAC fluid, clear by day 1, fluid,
cloudy; ~y day 3, some
gel, cloudy
10% in n-PrOAc fluid, clear fluld, clear
10% in i-PrOAc fluid, clear by day 6, some gel,
clear
10% in EGMEA fluid, clear by day 6, gel, clear
10% in DMC fluid, clear by day 7, some gel,
clear
20% in DMC fluid, clear by day 1, some gel,
cloudy; by day 2,
mostly
gel, cloudy
20% in Blend 2 fluid, clear by day 14, fluid,
cloudy
- 30 -
CA 022~1~3~ 1998-10-14
W098/38242 PCT~S98/04072
Notes for Tab]e II
[a] Polymer concentrations are Wt~ unless stated
otherwise. MEK iS methyl ethyl ketone, MPK is
methyl pr~pyl ketone, MiBK is methyl isobutyl
ketone, CPO is cyclopentanone, CHO is cyclohexanone,
EtOAc is ethyl acetate, N-PrOAc is n-propyl acetate,
i-PrOAc is isopropyl acetate, EGMEA is ethylene
glycol monomethyl ether acetate, DMC is dimethyl
carbonate, Blend 2 is composed of 35.4 parts MiBK,
29.8 parts CHO, and 30 parts DMC by weight.
CA 02251535 1998-10-14
wog8a8242 PCT~S98/04072
TABLE II A
- SOLUTION GELATION TIME [a]
~xample Num~er Gelation Time
1 425
1 512
3 342
3 394
6 4,913
6 8,322
6 ~2,92
1010 934
1,553
3,191
2 77,000
2 62,400
1512 14,100
12 47~500
[a~ 20 wt~ solutions at 15~C in propylene
carbonate. Gelation time is in seconds.
EVALUATION OF FTT~ GLOSS AND CLA~TTY
Some of the non-gelled solutions from the
solution property tests were used to make films
- 32 -
CA 022~l~3~ l998-l0-l4
W098/38242 PCT~S98~ 72
which were tested for gloss and clarity. The films
were cast on a Leneta Form 2A opacity chart using a
0.127 meter draw down applicator having a 250
micrometer gap. The cast films were dried for three
days at room temperature. Film gloss was determined
using a HunterLab Progloss PG-2 gloss meter, and the
results are shown in Table III. Film haze was
measured by determining the whiteness index (CIELAB
L* value) of the film on the black portion of the
opacity chart using a HunterLab Labscan 2
colorimeter, and the results are shown in Table IV.
Films from copolymer 2 showed higher gloss from a
wider range of solvents than films from copolymer
12. The haze in films from 2 and 12 was generally
similar, but noticeably less haze was observed in
films from 2 in several instances. The results,
taken together, show that VDF/HFP copolymer of the
present invention demonstrates an increased utility
for high-gloss, high-transparency film applications.
- 33 -
CA 022~1~3~ 1998-10-14
W0 98/38242 PCT/US98/04072
TABLE III
GLOSS OF CAST FILMS
Polymer Gloss, 20 degree / 60 degree
concentration
and solvent [a] Example 2 Example 12
20~ in MEK 33.6 / 69.0 31.3 / 68.7
10g in MPR 31.4 / 68.9 1.3 / 18.7
10% in CPO 0.7 / 16.92.0 / 27.7
10% in EtOAc 29.4 / 66.6 29.4 / 68.0
10% in n-PrOAc 31.9 / 70.1 16.0 / 57.0
10% in l-PrOAc 31.6 / 69.4 15.4 / 56.2
10% in DMC 35.4 / 70.6 30.1 / 68.6
20% in Blend 234.6 / 71.2 0.1 / 2.4
[a] Polymer concentration and solvent lndicates the wt~ and
solvent the films were cast from. MEK is methyl ethyl ketone,
MPK is methyl propyl ketone, CPO is cyclopentanone, EtOAc is
ethyl acetate, n-PrOAc is n-propyl acetate, i-PrOAc is
isopropyl acetate, DMC is dimethyl carbonate, Blend 2 is
composed of 35.4 parts methyl iso~utyl ketone, 29.8 parts
cyclohexanone, and 30 parts DMC by weight.
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WO 98/38242 PCTAJ~3~ 1'72
TABLE IV
CLARITY OF CAST FILMS
Polymer Clarity, CIELAB L* [b]
concentration
and solvent [a] Example 2 Example 12
20~ in MEK 6.59 6.22
10~ in MPK 6.19 14.48
10~ in CPO 15.18 15.56
10~ in EtOAc 7.38 5.84
1010~ in n-PrOAc 5.64 7.34
10~ in i-PrOAc 5.61 7.79
10~ in DMC 6.21 5.73
20~ in Blend 2 5.36 17.85
[a] Polymer concentration and solvent indicates the wt~ and
solvent the films were cast from. MEK is methyl ethyl ketone,
MPK is methyl propyl ketone, CPO is cyclopentanone, EtOAc is
ethyl acetate, n-PrOAc lS n-propyl acetate, i-PrOAc is
isopropyl acetate, DMC is dimethyl carbonate, 81end 2 is
composed of 35.4 parts methyl isobutyl ketone, 29.8 parts
cyclohexanone, and 30 parts DMC by welght.
[b] Guide to haze:
L* < 7 no haze
257 ~ L* < 9 very slight haze
9 c L* < 11 slight haze
ll ~ L* < 15 moderate haze
15 ~ L* severe haze
.
CA 022~l~3~ l998-l0-l4
W098/38242 PCT~S98/04072
EVALUATION OF THE T~F~M~T- PROPERTIES OF THE EXAMPLES
The final melting point is an important
parameter in the use and processing of
semicrystalline polymers. It is known that the
final melting point of VDF/HFP copolymers is related
to the HFP content in the copolymers. The relation
between HFP content and final melting point of the
VDF/HFP copolymer examples is shown in Figure 1.
The copolymers of the present invention and the
copolymers prepared according to the prior art
synthesis which details are available can be seen to
fall on different melting point curves, indicating
that they are different materials, with the prior
art copolymers having a higher melting point at a
given H~P content. The lower melting point property
of the copolymers of the present invention can allow
lower processing temperatures than for the prior art
synthesis copolymers.
EVALUATION OF EXTRACTABT.~S IN DIMETHYL CARBONATE
General Procedure
lg of polymer and 9g of dimethyl carbonate were
placed in a closed 25 ml container. The contents of
the container were continually agitated by
appropriate means while maintaining the desired
temperature by appropriate means for 24 hours. The
entire contents of the container were then
transferred to a centrifuge tube and centrifuged to
separate undissolved polymer. The liquid phase was
transferred to a suitable tared container and the
solvent evaporated. The residue in the container
- 36 -
CA 022~1~3~ 1998-10-14
W098/38242 PCT~S98104072
,
was weighed and reported as percent by weight
extractables.
The amount of polymer extracted into dimethyl
carbonate at 40~C was measured. The data is shown
in Table V. Copolymers prepared according to
synthetic methods in the prior art for which details
are available are labeled "N". Copolymers prepared
according to the methods described for the present
invention are labeled "U".
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WO 98/38242 PCT/US98/04072
- TABLE V
Effect of HFP Content, Molecular Number and
Uniformity of Compositional Distribution on Polymer
Dissolution in DMC
Sample HFP Mw Mn Extractable Compo~ition
Lot # (mole%) (40~C) DMC
K2801 4.5 460000 145000 12.0% N
K2801 4.5 495000 157000 10.5% N
9521 2.1 427000 167000 3.11~ N
9527 3.6 473000 150000 14.30% N
9529 2.8 417000 148000 9.29% N
88 3.6 375000 138000 4.04% U
go 2.3 483000 188000 0.23% U
94 2.4 676000 240000 0.41% U
96(Exl) 2.4 409000 159000 0.28% U
98 2.4 351000 144000 1.11~ U
lOO(Ex5) 1.5 523000 194000 0.41~ U
104 3.1 433000 157000 1.61% U
A cursory examination shows that all N samples
have higher levels of polymer extracted into
dimethyl carbonate. Figure 2 shows a plot of the
extractables as a function of HFP content (mole%).
Two distinct curves are outlined for the two classes
of materials. The upper curve (N samples) shows
significantly higher levels of extractables for a
given level of HFP compared to the U curve.
Measured slopes for these curves are 3%
extractables/mole % HFP for the N polymers and 1.7%
extractables/mole % HFP for the U polymers.
- 38 -
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W098/38242 PCT~S98/04072
The observed and calculated ~ extractables
under both the single and dual functional model-are
shown for the N polymers in Table VI and for the U
polymers in Table VII.
Table VI
Comparison of Wt. ~~ Extractables of N polymer as a
function of HFP content or HFP content and Mn
% Extractable % Extractable% Extractable
(meas) (calc model 1)(calc model 2)
12.0% 12.6~ 13.4
10.5~~ 12.6~~ 10.1~~
3.11~ 5.7~ 3.2
14.30~ 10.0~~ 10.5~~
9.29~ 7.7~~ 9.7~~
(Model l)Wt ~ Extractable = 2.9 (HFP mole~) - 0.4
(Model 2)Wt 96 Extractable = 46.4 + 1.7(HFP mole g6) -
0.00028(Mn).
- 39 -
CA 022~l~3~ l998-l0-l4
. W098/38242 PCT~S~8/01~72
Table VII
Comparison of Wt.~ Extractables of U polymer as a
function of HFP content of HFP content of Mn
% Extractable % Extractable% Extractable
(meas) (calc model 1)(calc model 2)
4.04~ 2.9~ 3.1
0.23~ 0.71~ 0.75
0.41~ 0.88~ 0.48
0.28~ 0.88
1.11~ 0.88~ 1.2
0.41% -0.65~ -0.50
1.61~ 2.1~ 2.2
(Model 1) ~ Extractable = 1.7(HFP mole~) - 3.2
(Model 2) % Extractable = -1.2 + 1.5(HFP mole~) - 8 x 10~6(Mn).
In the specification and the attached claims,
the expression "having weight percent extractables
within 1.5% of the percent by weight extractables
calculated by an equation selected from the group
consisting of:
a) Wt~ Extractable = 1.7(~FP mole~) - 3.2, and
b) Wt96 Extractable = -1.2 + 1.5(~FP mole96) - 8 x 10~6(Mn)
means that the measured value of weight percent
extractables in dimethylcarbonate at 40~C must be
within 1.5 absolute percentage points from the
extractable value calculated for the particular
polymer by either equation.
That is, if the calculated value of ~
extractables by either equation 1 or 2 is 3.0 and
the observed value is between 1.5 and 4.5~ it falls
- 40 -
CA 022~1~3~ 1998-10-14
W O 98/38242 PCTAJS98/04072
within the intended coverage value. Similarly if
the observed value is 8.0~ it will be within the
intended coverage if the calculated value from
either equa~tion ranges from 6.5~ to 9.5~.
In the above described proceedure for
determining extractables in dimethyl carbonate,
centrifugation for thirty minutes at 1500 rpm at
ambient temperature was employed to separate the
solution from the insoluble matter and drying at
50 deg. C for 70 hours under mechanical pump vacuum
was used to determine the weight of solids in the
separated solution.
- 41 -
,
