Note: Descriptions are shown in the official language in which they were submitted.
S~
TITLE
COPOLYMER OF TETRAFLUOROETHYLENE ~ND
FLUORINATED ALKYL SUBSTITUTED ETHYLENE
FIELD OF THE INVENTION
This invention relates to polymers of
tetrafluoroethylene, and more specifically to
copolymers of tetrafluoroethylene and fluorinated
alkyl ethylenes.
BACKGROUND OF THE INVENTION
A number of copolymers of tetrafluoroethylene
are known, but new copolymers of tetrafluoroethylene
are always of interes-t due to a desire to obtain
polymers having improved properties over polymers
known heretofore.
U.S. 4,123,602 to H. Ukihashi, et al.,
describes tetrafluoroethylene/ethylene copolymers
modified with 0.1 to 10 mol % RfCH=CH2 where Rf
is CnF2n+l in which n is an integer between 2 and
10. These polymers contain between ~0 and 60 mol %
ethylene. The thermal instability against oxidation
limits their use above 150C for extended periods of
time.
U.S. 3,804,817 to L. ~. Wall and ~. W. Brown
describes copolymers of (perfluoropropyl)ethylene
(PFPE) and tetraEluoroethylene (TFE), and copolymers
oE (perfluoroe~hyl)ethylene and tetrafluoroethylene.
These copolymers are elastomeric, soluble in
fluorinated solvents, and possess only modest thermal
stability as evidenced by the thermal ~ravimetric
analysis (TGA) data shown in the patent. In J. Poly.
Sci. 8, 2441(1970) the patentees reproduce Table I of
the U.S. 3,804,817 and in the article describe that
~ .
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the copolymers of TFE and PFPE containing up to 89
mol ~ TF~ are amorphous by X-ray diffraction
measurement. The polymers appear amorphous on
testing by differential scanning calorimetry (D5C)
S techniques.
Also disclosed in U.S. Patent 3,804,817 is a
TFE copolymer containing about 6 mol % PFPE, in
Example 4~ This copolymer has the following
properties:
l. The mel~ing behavior by DSC is
essentially identical to PTFE. It is well known
(Polymer Handbook, Vol. 2I pV-32~ ~1975)) that
polytetrafluoroethylene (PTF~) has a reproducible
mel~ing point at 327C and occasionally contains
phases which exhibit higher melting points on the
initial heating cycle. The higher melting point can
be as high as 342C. The 94/6 copolymer of U.S.
Patent 3,804,817 Example 4 exhibits both of these
melting points and no lower melting points which
would correspond to crystalline copolymer phases.
2. Thermal stability of the melt at 350C,
i.e., approximately 20C above the melting point, as
measured by isothermal TGA in air, is low. A weight
loss of 8.7~ was seen at 140 minutes.
3. A small-angle x-ray scattering scan does
not show the broad diffraction peak at low angles (2
below 1) normally seen for crystalline TFE
copolymers. The 94/6 copolymer of U.S. Patent
3,804,817 Example 4 instead shows the steady increase
in intensity with decreasing angle that is shown by
homopolymer PTFE.
Based on these results, the copolymer of
U.S. Patent 3,804,817 Example 4 is believed to be
composed mostly of a fraction of crystalline TFE
homopolymer with a minor fraction of amorphous
ZV~97~
....
TFE/PFPE copolymer with high PFPE content. It is
well known that crystalline TFE homopolymer cannot be
processed by melt techniques, and that mixtures of
PTFE with melt pro~essible copolymers lead to the
formation of high local concentrations of PTFE, or
l'fisheyes", in finished parts which are undesirable.
In extreme cases, the presence of PTFE in a melt
processible copolymer can greatly lower the strength
of a finished article. ~he objective of
copolymerizing small amounts, e.g. 1-10 mol % of
comonomer, with TFE is to produce copolymers with
homogeneous, readily processible melts in which the
melting point has been lowered from that of PTFE.
U.S. Patent 3,804,817 does not teach how to achieve
this objective.
SUMMARY OF THE INVENTION
Copolymers of tetrafluoroethylene and
fluorinated alkyl ethylenes are obtained by this
inven~ion in which units of the copolymer derived
from the ethylene comonomer are substantially
uniformly positioned along the copolymer chain. This
positioning results in insoluble copolymers which
when molded are nonelastomeric and exhibit good
thermal stability.
In contrast to the copolymers of U.S~ Patent
3,804,817, especially the "94/6 copo~ymer" of Example
4, ~he copolymers o~ this invention exhibit the
following properties:
1. DSC melting poin~s are substantially
below that of PTFE and are in the range expected for
true random copolymers. The melting points are
usually between 260 and 318C.
2. Thermal stability by isothermal TGA in
air is good. These measurements were made at 350C,
i.e. between 30 and 90C above the melting poin~s o~
s~
these polymers. The weight loss is less than 5% at
140 minutes and is freguently 1~ or less.
3. Small angle X-ray scattering (SAXS)
scans show a diffraction peak at very low angles
S (less ~han 1 2~), normally seen for semicrystalline
copolymers of TFE.
Thus the term "substantially uniformly
positioned" means that the copolymers meet the
following conditions: D5C melting point is below
about 318C, the thermal stability is such that the
weight loss after 140 minutes at 350C in air is less
than 5%, and the small anyle X-ray scattering scan
shows a diffraction peak at angle~ below 1 23~
By "insoluble" is meant that the copolymer
does not dissolve in organic solvents maintained at
25C.
By "nonelastomeric" is meant tha~ the molded
copolymer is not a material which at room temperature
can be stretched repeatedly to at least twice its
original length and, upon immediate release o~ the
stress, will return with force to its approximate
original length.
The copolymers of this invention can more
specifically be described as copolymers o~ 93-99 mol
% tetrafluoroethylene, and complementally 7-1 mol ~
fluorlnated alkyl ethylene comonomers of the formula
R~CH=CH2 wherein R~ is perfluorinated alkyl of
2-10 carbon atoms or substituted perfluoroalkyl of
2-10 carbon atoms in which the perfluoroalkyl group
can be substituted with up to 3 substituents selected
from hydrogen, bromine,.chlorine or iodine, said
copolymer characteri2ed by having the units of the
comonomer substantially uniformly positionedr i.e.,
evenly distributed, throughout the copolymer chain.
. 35
The process aspect of the invention can be
described as a process for preparing the copolymer
described above which comprises
(a) combining and agitating
tetrafluoroe~hylene and the fluorinated alkyl
ethylene in the presence of a nonaqueous solvent or
in aqueous media in a reaction vessel at a
temperature of between 30C and 110C and a pres~ure
of between 1 kg/cm and 70 kg/cm and preferably
between 3 kg/cm2 and 35 kg/cm2, in the presence
of a free-radical polymerization initiator, said
combining of the tetrafluoroethylene and fluorinated
alkyl ethylene being carried out by continuously and
uniformly adding fluorinated alkyl ethylene to the
reaction vessel in a manner which maintains a
concentra~ion of fluorinated alkyl ethylene in the
vessel during agitation below 2.5 mol %, and
preferabty below 1 mol %, relative to
tetrafluoroethylene, said agitation being continued
until copolymer formatior, has occurred, and
(b) separating the copolymer from the other
ingredients present in step (a).
DBSCRIPTION OF THE INVENTION
The copolymer of this invention is obtained
by copolymerlzing tetrafluoroethylene and ~luorinated
alkyl ethylene in either a nonaqueous solvent or in
an aqueous medium in a manner which maintains the
concentration of the 1uorinated alkyl ethylene in
the reaction mixture at a relatively constant and low
concentration compared to the concentration of
tetrafluoroethylene. I~ a large concentration, i.e.,
over 2.5 mol ~, of perfluoroalkyl ethylene is
employed, the polymerization reaction is inhibited,
and uniform copolymer is not obtained.
.. 35
As nonaqueous solvents in the polymerization,
fluoro- or chlorofluoro-h~drocarbon, (preferably 1 to
4, and especially 1 to 2, carbon atoms) known as a
Freon* solvent or solvents similar thereto ~re
useful. Suitable ~Freon" solvents or solvents
similar thereto include: dichlorodifluoromethane,
trichloromonofluoromethane, dichloromonofluoro-
methane, monochlorodifl~oromethane,
chlorotrifluorsmethane, tetrafluoroethane,
trichlorotrifluoroethane, dichlorotetrafluoroethane,
fluorochloropropane, perfluoropropane,
fluorocyclobutaneD perfluorocyclobutane, etc. or
mixtures thereof. It is bes~ to use a saturated
fluoro- or chlorofluoro-hydrocarbon which does not
have a hydrogen atom in the molecule, such as
dichlorodifluoromethane, trichloromonofluoromethane,
trichlorotrifluoroethane, dichlorote~rafluoroeth~ne,
perfluorocyclobutane, etc., since such solvents have
a tendency of increasing the molecular weight of the
resulting copolymer. When a ~Freon" solvent or a
like solvent is used, good results are attainable
when used in amounts of 0.5-20 mol and especially
abou~ 1-10 mol of the solvent per mol of monomer
mixture of tetrafluoroethylene and
per~luoroalkylethylene monomer.
The copolymerization reaction can be carried
out by using less than 0~5 mol of the solvent per mol
of monomer mixture. However, it is advantageous to
use more than 1 mol of solvent in order to enhance
3~ the rate of the copolymerization. It i~ possible to
use more than 20 mols of solvent, but i~ is
advantageous to usP less than 10 mols per mol of
monomer mixture for economic reasons, such as solvent
recovery.
. 35
* Denotes trade mark
9~
A mixture of a "Freon" solvent or like
solvent and other organic solvents or aqueous medium
may be used. For example, it is possible to use a
mixed reaction medium of "Freon" solvent or like
solvent and water.
The advanta~e of using such a mixed solvent
consists in easy stirring of the reaction system and
easy removal of the heat of reaction. In accordance
with the process of the invention, the conditions of
the copolymerization can be varied depending upon the
type of polymerization initiator or the reaction
medium.
A wide variety of polymerization initiators
can be used depending upon the polymerization
system. However, when a "Freon" solvent or solvent
similar thereto is used, i~ is pre~erable to use a
soluble free-radical polymerization initiator, such
as an organic peroxy compound. It is possible to use
high energy ionizing radiation of 10-105 rad/hour
dose rate. Suitable peroxy compounds may be the
organic peroxides, e.g~, benzoylperoxide or
lauroylperoxide; peresterst e.g., t-butyl
peroxyisobutyrate; or peroxy dicarbonates~ e.g~,
diisopropylperoxy dicarbonate, etc. ~t is especially
pre~ered to use as the initiator in non-aqueous
systems, a peroxide having the formula
O O
RfC-O-O-C-Rf
wherein Rf each represent perfluoro~lkyl groups
containing from 3-13 carbon atoms, in a "Freon"
solvent or like solvent. Suitable such peroxides
include bis(perfluoropropionyl) peroxide,
bis(perfluorohexanoyl) peroxide, etc.
When the solvent system is an aqueous
system, initiators such as peroxides or persulfates
s~y
which are compatible with water should be used, such
as disuccinoyl peroxide or ammonium persulfate. Xn
an aqueous system, a non-telogenic dispersing agent
is commonly employed.
The polymerization can be carried out at a
temperature of between 30 and 110C, and preferably
at a temperature of between 40 and 80C. Pressures
employed in the polymerization are ordinarily those
pressures between 1 and 70 kg/cm2 and preferably
lQ are those between 3 and 35 kg/cm2.
~ t is often preferable to include a small
amoun~ of a telogenic material in the reaction medium
in order to control the molecular weight of the
resulting copolymer. Alcohols such as methanol or
ethanol, and alkanes such as ethane, butane,
cyclohexane, etc., are suitable telogens.
The mixture of comonomers is agitated during
polymerization.
The reaction may be carried out until solids
content o~ the reaction mixture reaches abou~ 20~ by
weight for aqueous reactions, and about 12% for
nonaqueous solvent based reac~ions.
It i5 important to control the concentration
of the fluorinated alkyl ethylene in the reaction mix
as heretofore described, and to maintain the
concentration at a relatively constant level. Both
these features result in copolymers in which the
units of fluorinated alkyl ethylene present are
substantially evenly dis~ributed along the copolymer
chain.
Representative comonomers include
perfluoroethyl ethylene, perfluorodecyl ethylener
~-chloroperfluoroethyl ethylene, ~-hydroperfluoro
ethyl ethylene,~-bromoperfiuorodecyl ethylene,
35 ~-iodoperfluoroethylethylene (ICF2CF2CH-C~2),
1,1,2,8,8,8-hexahydrodecafluoro octene-l
(CH3(CF2)5CH~CH~), or 1,1,2,4-tetrahydrohexa-
fluoropentene-l (CF3C~CF~C~=CH2). Preferably
the comonomer will be a perfluoroalkyl ethylene, and
5 most preferably perfl~orobu~yl ethylene.
The copolymers are useful as insulation
coating for electrical wires and as linings for
equipment exposed to harsh chemical environments.
EXAMPLES
In the following examples, apparent melt
vi~cosity was determined by calculations based on the
melt flow rate. The melt flow ra~e was determined
according to ASTM procedure D2116 at a load of 5000g
except that the melt flow rate was determined in
grams/minutes rather than grams/10 minutes. The
equation used to calculate the apparent melt
viscosity was:
MV = 10. 63_x lTotal mass Piston ~ weigh~ ~q)] .
melt flow rate
Melting point was determined by differential
s~anning calorimetry at a rate of 15C per minute.
Ultimate elongation, yield strength and
ultimate tensile strength were determined by ASTM
procedure D1708.
Thermal stability was determined by
isothermal thermo~ravimetric analysis (TGA) at 350C
in air using a Du Pont 90~ instrument.
Solubility of the polymers prepared in the
Examples was determined at 25C in a number of common
org~nic solvents including hexafluorobenzene,
acetone, and 1,1,2-~richloro-1,2,2-tri~luoroethane.
The polymers were insoluble~
X-ray scattering da~a was obtained wi ~h a
Rratky*diffractometer ~Anton Kaar, K.G., Graz,
Austria) operating digitally in an off-line mode~
*Denotes trade mark
The X-ray intensities were detected with a
scintillation counter followed by a single-channel
pulse~height analyzer set to pass 90~ of CuK
radiation symmetrically. The x-ray beam was filtered
with 0.02 mm Ni foil and the sample thickness was in
the range 0.3 to 0.4 mm. The raw data (x-ray counts,
time, position) were recorded on 8-channel punched
paper tape and read into an IBM 1130 computer. X-ray
intensities were calculated as the ra~io of counts to
time, and these results were smoothed and corrected
for sample thickness and instrumental background.
The resultant corrected intensities were plotted as
log-intensity vs. diffraction angle (2-~). The
results were not corrected for slit-smearing since
such a correction would not aid significantly in
distinguishing among samples containing a discrete
small angle peak and those not containing it.
The comonomer content of the
tetrafluoroethylene perfluorobutyl ethylene
copolymers was determined either by an infrared
method or by a melting point method.
The infrared method involves measuring the
intensity o~ absorption bands at 2360 cm 1 and 1355
cm in compresslon molded film. The band at
2360 cm 1 is used to determine the thickness of the
film using the equation
1 mil
Thickness (mils) = ~bs 2360 cm
The comonomer concentration can then be
calculated using the following eguation:
Concentra~ion (g/cm3~ = (340 Sgs cm2)(Thickn ( ))
This equation provides the comonomer concentration in
g/cm3. Rnowing the density of the polymer allows
Z059 7
11
conversion to weight percent by the following
equation:
Concentration (q/ccl X 100 = weight ~ comonomer
2.15(Density, g/cc)
5 The absorbance factor used in this calculation
(340 ~bs cm2) was determined by s~andard methods
using a homopolymer of perfluorobutyl ethylene in
nFreon" F-113 solvent.
The results obtained by the infrared method
agreed well with those obtained through the use of
melting point data and the ~ollowing equation-
1.98 (ln NTFE)
TM T~FE 685whexe
TM ~ melting point of the copolymer in K
TTFE = melting point of homopolymer PTFE (60~K)
NTFE = mole raction TFE in the copolymer
This equation was found to agree well with the
results obtained from the infrared method for
polymers containins up to 5 mol ~ perfluorobutyl
ethylene.
EYAMPLE 1
Into an evacuated~ agitated 1 liter
stainless s~eel autoclave were placed 800 ml o~
1,1,2-trichloro-1,2,~-trifluoroethane solvent and 2
ml of perfluorobutyl ethylene. The temperature of
the mixture was raised to 60C and the agi~ator speed
was set at about 1000 rpm. To this mixture was
charged tetrafluoroethylene to a total pressure of
9.1 kg/cm . To the autoclave was then charged 15
ml of a solution of 0.0~2 g/ml bisperfluoropropionyl
peroxide in the aforementioned solvent. The pressure
was kept constant by the continuous addition of
tetrafluoroethylene. Af ter 10 minutes, the above
mentioned peroxide solution was fed into the reactor
~Z2~?SS~
at a rate of 1 ml/min as was a solution of 0.04 g/ml
of perfluorobutylethylene in 1,1,2-trichloro-1,2,2-
trifluoroethane also at 1 ml/min. This rate
maintained a concentration of perfluorobutyl ethylene
of less than about 1.1 mol ~ based on total monomers.
The polymerization was continued ~or a total of 70
minutes at which time the contents of the autoclave
were discharged into a large stainless steel beaker.
The polymer was recovered by drying in an air oven at
150C for several hours. The dry polymer weighed 74
9. The polymer exhibited a sharp melting point at
315C with a small shoulder at 287C. The apparent
melt viscosity was too high to measure. The polymer
couid be compression molded into tvugh films.
Comonomer content was 1.1 mol %. Isothermal TGA in
air at 350~C showed a 4.8% weight loss at 140
rninutes. X-ray scattering data showed a diffraction
peak at
angles below 1 2~.
EXAMPLE 2
Into ~n evacuated, agitated 1 liter stalnless
steel autoclave were placed 800 ml 1,1~2-trichloro-
1,2,2-tri~luoroethane solvent, 2 ml o~ per1uorobutyl-
ethylene, and 0.25 ml of methanol. The temperature
25 of the mixture was raised to 60C and the agitator
speed was set at about 1000 rpm. ~o this mixture was
charged tetrafluoroethylene to raise the total
pressure to 9.L kg/cm2. To the autoclave was then
charged 15 ml of a solution of 0.002 g/ml
bis-perfluoropropionyl peroxide in the above
mentioned solvent. Af ter 4 minutes, the peroxide
solution was added continuously to the autoclave at a
rate of 1 ml/min. After an additional 4 minutesr the
addition of a solution of 0. 04 gjml perfluorobutyl-
S913
ethylene in the same solvent was begun, al50 at a
rate of 1 ml/min. This rate maintained perfluorobutyl
ethylene at a concentration of less than about 1.1
mol ~. ~he polymerization was allowed to continue
for an additional 60 minutes at which time the
contents of the autoclave were discharged into a
large stainless steel beaker. The polymer was
recovered by drying in an air oven at 150~C for
several hours. The dry polymer weighed 55.5 g and
had an apparent melt viscosity at 372C of 27 x 104
poise. The polymer was compression molded into tough
films. Comonomer content was 2~3 mol ~O Melting
point was 303C, Isothermal TGA in air at 350C
showed a weight loss of 1% at 140 minutes. X-ray
data indi~ated a diffraction peak at angles less than
1 2~.
Compression molded films prepared from the
polymer described above were placed in a forced air
oven ~nd heat aged at 250C for 200 hours. The
physical properties of the treated films were
measured ~nd are reported in Table 1.
TABLE 1
PHYSICAL PROPERTIES OF FILMS
Example 2 Example 2
Test (As made~ (Heat aged)
__
25 Ultimate Tensile
Strength
25C 4200 psi 3240 psi
250C 1480 137
Yield Strength
25C ~090 psi 2190 psi
Ultimate Elongation
25C 290~ 250%
250C. 610 6q~
MIT folding endurance, No failure No failure
cycles, 7-8 mil film after after
ASTM D2176 1.3MM cycles 1.7MM cycles
13
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EXAMPLE 3
Into all evacuated, agitated 1 liter
stainless steel autoclave were placed 800 ml
1,1,2-trichloro-1,2,2-trifluoroethane solvent and 1.6
S ml of perfluoropropyl ethylene. The temperature of
the mixture was raised to 6QC and the agitator speed
was set at about 1000 rpm. To this mixture was
charged tetrafluoroethylene to raise the total
pressure to 9.1 kg/cm2. To the autoclave was then
charged 15 ml of 0.023 g/ml bis-perfluoropropionyl
peroxide in the above-mentioned solvent. The
peroxide delivery pump was then set to add the
peroxide solution continuously to the autoclave at
the rate of 1 ml/min. After 7 min, the addition of a
solution of 0.04 g/ml of perfluoropropyl ethylene in
the same solvent was begun, also at a rate of 1
ml/min. This rate maintained the perfluoropropyl
ethylene at a concentration of less than about 1.1
mol %. Tetrafluoroethylene was added at such a rate
20 as to kee2 the pressure in the autoclave constant.
The polymerization was allowed to continue for an
additional 60 minutes at which time the contents of
the autoclave were discharged into a large stainless
steel beaker. The polymer was recovered by drying in
25 an air oven at 150C for several hours. The dry
polyme~ weighed 48.4 9 and exhibited sharp melting
points by differential scanning calorimetry at 284
and 310C. The apparent melt viscosity at 372C was
too high to measure. ~he polymer could be
30 compression molded into tough films. Comonomer
content wasl4.3 mol %. Isothermal TGA in air at
350C showed a weight loss of 0.9% at 140 minutes.
X-ray scattering data showed a diffraction peak at
angles less than 1 2~.
14
~ZZOS~7
EXAMPLE 4
Into an evacuated, agitated 1 liter
stainless steel autoclave were placed 800 ml
1,1,2-trichloro-1,2,2-trifl~oroethane solvent, 1.0 ml
3,3,4,4-tetrafluorobutene-1, and 0.25 ml methanol~
The temperature of the mixture was raised to 60C and
the agitator speed was set at about 1000 rpm. To
this mixture was charged tetrafluoroethylene to raise
the total pressure to ~.1 kg/cm2. To the autoclave
was then charged 15 ml of 0.0023 g/ml
bis-perfluoropropionyl peroxide in the
above-mentioned solvent. The peroxide delivery pump
was then se~ to add the peroxide solution
continuously to the autoclave at a rate of 1 ml/min.
After 15 minutes, the addition of a solution of 0.021
g/ml of 3,3,4,4-tetrafluorobutene-1 in the same
solvent was begun, also at a rate of 1 ml/min. This
rate maintained the tetrafluorobutene at a
concentration of less than about 1.1 mol %.
Tetrafluoroethylene was added at such a rate as to
keep the pressure in the autoclave constant. The
polymerization was allowed to proceed for an
additional 60 minutes at which time the contents of
the autoclave were discharged into a large stainle~s
steel beaker. The polymer was recovered by drying in
an air oven at 150C ~or several hours. The dry
polymer weighed 32.1 9 and exhibited a sharp melting
point by differential scanning calorimetry at 291C
with a small shoulder at 312C. The melt viscosity
at 372C was 0.62 x 103 Pa.s ~0.62 x 104 poise).
Comonomer content was 3.6 mol ~. Isothermal TGA in
air at 350C showed a weight loss of 1.1% at 140
minutes. X-ray scattering data showed a difraction
peak at angles less than 1 2~.
lZZ~59t~
16
COMPARISON
To show the effect of adding perfluorobutyl
ethylene in one initial charge prior to initiating
polymerization, the following experiment was carried
out.
A 110 ml stainless steel shaker tube was
charged with 50 ml 1,1,2-trichloro-1,2,2-trifluoro-
ethane solvent, 0.74 g perfluorobutylethylene and
0.02 g of bis-perfluoropropionyl peroxide. The tube
was cooled and evacuated and 10 9 of tetrafluoro-
ethylene was added. The tube was heated to 60C and
shaken for 4 hrs. The product was isolated by drying
in an air oven at 150C for several hours. The dry
polymer obtained wei~hed 0.25 9 ~2.3%) and was highly
swollen by 1,1,2-trich:Loro-1,2,~-trifluoroethane.
The polymer could not be compression molded into
films. The polymer showed no sharp crystalline
melting peaks by differential scanning calorimetry
between 220 and 350~C.
~0
2S
16
