Expandable TFE copolymers, method of making, porous, expanded article thereof

Abstract

A true tetrafluoroethylene (TFE) copolymer of the fine powder type is provided, wherein the copolymer contains polymerized comonomer units of at least one comonomer other than TFE in concentrations of at least or exceeding 1.0 weight percent, and which can exceed 5.0 weight percent, wherein the copolymer is expandable, that is, the copolymer may be expanded to produce strong, useful, expanded TFE copolymeric articles having a microstructure of nodes interconnected by fibrils. Articles made from the expandable copolymer may include tapes, membranes, films, fibers, and are suitable in a variety of end applications, including medical devices.

Claims

1. A medical device comprising: an expanded core-shell tetrafluoroethylene (TFE) copolymer comprising: (a) a first, core portion comprising a polymer chain of TFE monomers and at least one other comonomer comprising a perfluoroalkyl vinyl ether monomer; and (b) a second, shell portion consisting of a polymer chain consisting of TFE monomers, wherein said expanded core-shell tetrafluoroethylene copolymer comprises at least 3.0% by weight polymerized units of said at least one other comonomer based on total weight of said copolymer, wherein said copolymer exhibits adhesion after subjecting the copolymer to its first melt temperature or above.

2. The medical device of claim 1 in the form of an implantable medical device.

3. The medical device of claim 1 in the form of a vascular graft.

4. The medical device of claim 1 in the form of an endoluminal prosthesis.

5. The medical device of claim 1, having a matrix tensile strength in at least one direction exceeding 13,000 psi.

6. The medical device of claim 5 having a matrix tensile strength in at least one direction exceeding 15,000 psi.

7. The medical device of claim 5 having a matrix tensile strength in at least one direction exceeding 25,000 psi.

8. The medical device of claim 5 having a matrix tensile strength in at least one direction exceeding 30,000 psi.

9. The medical device of claim 1, wherein said perfluoroalkyl vinyl ether is selected from the group consisting of PMVE, PEVE and PPVE.

10. The medical device of claim 1, including more than one other comonomer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the accompanying drawings,

(2) FIG. 1, is a SEM photomicrograph of an expanded sheet of a copolymeric resin produced according the invention herein, taken at 200 magnification, showing the node 1 and fibril 2 microstructure of this material, the respective nodal intersections being interconnected by the multiplicity of fibrils 2;

(3) FIG. 2 is a SEM photomicrograph of the expanded beading specimen of the copolymeric resin produced in Example 6, taken at 200 magnification, showing the node 1 and fibril 2 microstructure of this material, the respective nodal intersections being interconnected by the multiplicity of fibrils 2;

(4) FIG. 3 is another SEM photomicrograph of the expanded sheet specimen of the copolymeric resin produced in Example 6, taken at 20,000 magnification, showing a node 1 and fibril 2 microstructure; and

(5) FIG. 4 includes differential scanning calorimetry (DSC) scans showing the melt transition temperature peaks of hie materials of Examples 10, 12 and 13, as well as that of a comparative PTFE homopolymer.

DESCRIPTION OF THE INVENTION

(6) A process for the polymerization of a true tetrafluoroethylene (TFE) copolymer of the fine powder type is provided, wherein the copolymer contains polymerized comonomer units of at least one comonomer other than TFE in concentrations of at least or exceeding 1.0 weight percent, and which can exceed 5.0 weight percent, wherein the copolymer is expandable, that is, the copolymer may be expanded to produce strong, useful, expanded TFE copolymeric articles having a microstructure of nodes interconnected by fibrils.

(7) The copolymer of this invention is produced by a polymerization process wherein the copolymerization reaction is started by a suitable initiator, after which initiator addition is stopped, allowing the reaction to slow down and proceed to completion, at a point between 15% and 90% of the progression of the reaction toward completion. Preferably the initiator addition is stopped at about the mid-point of the reaction, i.e., at 20-60% to completion.

(8) Substantially non-telogenic dispersing agents are used. Ammonium perfluoro octanoic acid (APFO or C-8) is one acceptable dispersing agent. Programmed addition (precharge and pumping) is known and is preferred. Attention must be paid to ingredient purity to achieve the desired properties in polymerizations as described herein. Ionic impurities, which can increase ionic strength, in addition to soluble organic impurities, which can cause chain transfer or termination, must be minimized. It is clearly important to employ ultra pure water in all such polymerization reactions.

(9) The break strength associated with an extruded and expanded (stretched) TFE polymeric beading produced from a particular resin s directly related to that resin's general suitability for expansion, and various methods have been employed to measure break strength. The following procedure was used to produce and test expanded beading specimens made from the copolymers of this invention, the data for which are reported hereinbelow.

(10) For a given resin, 113.4 g of fine powder resin is blended together with 130 cc/lb (24.5 g) of Isopar K. The blend is aged for about 2 hours at 22 C. in a constant temperature water bath. A 1-in. diameter cylindrical preform is made by applying about 270 psig of preforming pressure for about 20 seconds. The preform is inspected to ensure it is crack free. An extruded beading is produced by extruding the preformed, lubricated resin through a 0.100 in. diameter die having a 30 degree included inlet angle. The extruder barrel is 1-in. in diameter and the ram rate of movement is 20 in./min. The extruder barrel and die are at room temperature, maintained at 23 C., plus or minus 1.5 C. The Isopar K is removed from the beading by drying it for about 25 minutes at 225-230 C. Approximately the first and last 8 ft. of the extruded beading are discarded to eliminate end effects. A 2.0 in. section of the extruded beading is expanded by stretching at 290 C. to a final length of 50 in. (expansion ratio of 25:1) and at an initial rate of stretch of 100% per second, which is a constant rate of 2 in. per second. Approximately a 1 ft. length from near the center of the expanded beading is removed, and the maximum break load of the removed sample held at room temperature (23 C. plus or minus 1.5 C.) is measured using an Instron tensile tester using an initial sample length of 2 in and a crosshead speed of 12 in/min. Measurements in duplicate are obtained and reported as the average value for the two samples. This procedure is similar to that described in U.S. Pat. No. 6,177,533B1. The expansion here is carried out at 290 C. instead of 300 C.

(11) Core-shell resin structures containing polymerized monomers additional to TFE, structurally similar to those produced by the techniques described herein, and as described earlier herein, have been known for some time. See, e.g., U.S. Pat. No. 4,576,869 (Malhotra), U.S. Pat. No. 6,541,589B1 (Baillie) and U.S. Pat. No. 6,841,594B2 (Jones). In the examples which follow, and for the claimed compositions, the resins produced according to the present invention are all true copolymers, i.e., comonomer content exceeding 1.0 weight percent, verified using solid state NMR spectroscopy, as well as mass balance and detection of residual monomer in the gas phase of the polymerization batch, through gas chromatography. The compositions are all expandable to a stretch ratio of at least 25:1, to form expanded copolymeric articles having their unique node, 1, and fibril, 2, microstructure as shown in FIG. 1, verifiable through SEM examination, as demonstrated below. Further views of alternative unique node, 1, and fibril, 2, microstructures are shown in FIGS. 2 and 3.

(12) Characterization of copolymer materials can be performed via standard analytical techniques available in the art including, but not limited to, DCS, NMR (including fluorine, proton, carbon and other known NMR techniques), TGA, IR, FTIR, Raman spectroscopy, and other suitable techniques.

Tests

(13) Differential Scanning Calorimetry (DSC)

(14) This test was performed using a TA Instruments Q2000 DSC and TA Instruments standard aluminum pans and ids for Differential Scanning Calorimetry (DSC). Weight measurements were performed on a Sartorius MC 210P microbalance.

(15) Calibration of the Q2000 was performed by utilizing the Calibration Wizard available through the Thermal Advantage software supplied with the device. All calibration and resulting scans were performed under a constant nitrogen flow of 50 ml/min.

(16) The sample was loaded into the pan and the weight was recorded to 0.01 mg precision, with samples ranging from 5.00 mg to 10.00 mg. These values were entered into the Thermal Advantage control software for the Q2000. The lid was placed on the pan and crimped using a standard press. A similar pan for reference was prepared, with the exception of the sample article, and its weight was also entered into the software. The pan containing the sample article was loaded onto the sample sensor in the Q2000 and the empty pan was loaded onto the reference sensor. The samples were then equilibrated at 50 C. and ramped at 20 C./min to 400 C. Data were analyzed using Universal Analysis 2000 v.3.9A from TA Instruments.

(17) Adhesion Testing

(18) Extruded PTFE tapes were cut into rectangles with dimensions of 20 mm width width75 mm length and were thermally bonded in a Carver press model #3895, from Fred S. Carver Inc, Wabash, Ind. to aluminum foil substrates to create 90 degree peel samples. The tapes were bonded to 23 micron thick Heavy Strength aluminum foil from Reynolds Consumer Products Co, Richmond, Va. 23230. Polyimide release film, Upilex grade 25SDADB, 25 microns thick, available from UBE Industries, LTD., Tokyo, Japan was used to prevent adhesion to the press plates and provide a pre-crack to initiate peel during 90 degree peel testing. Melt press time, and normal force were 30 minutes and 450 Kg. Samples were prepared at melt press temperatures of 195 C., 290 C., and 350 C. Once bonded the samples were cooled while still under pressure to approximately 21 C. for approximately 20 minutes. Foil-PTFE tape peel samples at each bonding temperature were prepared simultaneously to maintain a common thermal history. A 90 degree peel test is conducted at a test speed of 1 mm/sec using an Imass SP-2000 Slip-Peel Tester, available from Instrumentors Inc., Strongsville, Ohio. Results were reported in J/m.sup.2, and any measurable value defined that the material exhibits adhesion. For samples where the sample fell apart prior to testing, a no adhesion value was reported.

(19) NMR Analysis

(20) A sample of 10 to 25 mg was packed into a 2.5 mm ZrO spinner using standard Bruker 2.5 mm packing accessories (Bruker BioSpin Inc., Boston, Mass.). .sup.19F spectra were collected at about 296 Kelvin on a Bruker-BioSpin 2.5 mm cross polarization magic angle spinning (CPMAS) probe positioned in a standard bore 7.05 T Bruker ultra shielded superconducting magnet. The samples were positioned at the magic angle and spun at 32.5 kHz. A Bruker BioSpin Avance II 300 MHz system was used to collect .sup.19F NMR data at 282.4 MHz. Software used for data acquisition and data processing was Topspin 1.3. The data was collected using the conditions specified in Table B. The spectra were externally referenced to PTFE at 123 ppm.

(21) TABLE-US-00001 TABLE A NMR Instrument Used Manufacturer Bruker BioSpin Model Avance II 300 MHz Magnet 7.05 T Ultrashielded Probe Bruker 2.5 mm CPMAS Multinuclear Rotor Standard Bruker 2.5 mm .sup.19F Frequency 282.4 MHz Software Topspin 1.3

(22) TABLE-US-00002 TABLE B NMP Acquisition Parameters Parameter Value MAS Spinning speed 32.5 kHz Pulse length (11) 0.4 s Spectral Window 113636 Hz (402 PPM) Transmitter offset 100 PPM Number of scans 2000 Recycle delay 3 s Acquisition Time 150 ms Acquired Data Points used in Fourier 8000 Transform Zero Fill before Fourier Transform 32k Line broadening 15 Hz
The following examples are intended to be illustrative of the invention, but are not to be construed as limiting the scope of the invention in any way.

Example 1

(23) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(24) The reactor was heated to 83 C and agitated at 60 rpm. Subsequently, 0.8 MPa of VDF was added followed by addition of TFE until the pressure reached 2.8 MPa. At this time, KMNO4 in a DI water solution (0.063 g/L) was injected at 80 mL/min until approximately 2 kg of TFE was added. After addition of the 2nd Kg of TFE, the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. The KMnO4 was added at 20 mL/min for the 3rd Kg of TFE and further reduced to 10 mL/min for the 4th Kg of TFE. After the 4th Kg of TFE was added, KMnO4 was no longer added.

(25) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(26) The polymerization reaction was then allowed to continue and the reaction stopped after 14.3 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 44.73 Kg containing 32.6% solids. The dispersion was coagulated with Nitric acid and dried at 170 C. The raw dispersion particle size (RDPS) of the polymer particle was 0.296 microns and the standard specific gravity was 2.156. The VDF concentration in the copolymer was measured to be 3.48 mol % (2.26 wt %). The break strength of the beading was 6.6 lbs.

(27) The matrix tensile strength of the specimen was measured to be 37,299 psi.

Example 2

(28) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluoro-octanoic acid (APFO) and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(29) The reactor was heated to 83 C. and agitated at 60 rpm. Subsequently, 0.8 MPa of trifluoroethylene (herein designated TrFE) was added followed by addition of TFE until the pressure reached 2.8 MPa. At this time, KMNO4 in a DI water solution (0.1 g/L) was injected at 80 mL/min until approximately 0.5 kg of TFE was consumed. At this time, the rate was reduced to 40 mL/min until a second Kg of TFE was consumed. The pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. The KMnO4 was again added at 40 mL/min for the next 0.5 Kg of TFE and continued until 4 Kg of TFE was consumed. After 4 Kg of TFE was consumed, KMnO4 was no longer added.

(30) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(31) The polymerization reaction was then allowed to continue and the reaction stopped after 16 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 45.74 Kg containing 35.8% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(32) The raw dispersion particle size (RDPS) of the polymer particle was 0.283 microns and the standard specific gravity was 2.213. The trifluoroethylene concentration in the copolymer was measured to be 32 mol % (2.6 wt %). The break strength of the beading specimen was 7.24 lbs.

(33) The matrix tensile strength of the specimen was measured to be 28,602 psi.

Example 3

(34) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(35) To the evacuated reactor, 8 mL of PFBE was charged, and the reactor was heated to 83 C. and agitated at 60 rpm. Subsequently, 0.8 MPa of VDF was added followed by addition of TFE until the pressure reached 2.8 MPa. At this time, KMNO4 in a DI water solution (0.1 g/L) was injected at 80 mL/min until approximately 2 kg of TFE was added. After addition of the second Kg of TFE, the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. The KMnO4 was added at 40 mL/min until the 4th Kg of TFE was consumed. After the 4th Kg of TFE was added, KMnO4 was no longer added.

(36) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(37) The polymerization reaction was then allowed to continue and the reaction stopped after 16 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 42.76 Kg containing 29.0% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(38) The raw dispersion particle size (RDPS) of the polymer particle was 0.263 microns and the standard specific gravity was 2.157. The VDF concentration in the copolymer was measured to be 4.30 mol % (2.80 wt %). The PFBE concentration in the copolymer was measured to be 0.03 mol % (0.07 wt %), yielding a total copolymer concentration in the composition of 2.87 wt %. The break strength of the beading specimen was 13.6 lbs.

(39) The matrix tensile strength of the specimen was measured to be 44,878 psi.

Example 4

(40) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(41) To the evacuated reactor, 19.94 g of PFOE was charged, and the reactor was heated to 83 C and agitated at 60 rpm. Subsequently, 0.8 MPa of VDF was added followed by addition of TFE until the pressure reached 2.8 MPa. At this time, KMNO4 In a DI water solution (0.1 g/L) was injected at 80 mL/min until approximately 2 kg of TFE was added. After addition of the second Kg of TFE, the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. The KMnO4 was again added at 40 mL/min until an additional 0.5 Kg of TFE was consumed and reduced to 20 mL/min until 4 Kg of TFE was consumed. After the 4th Kg of TFE was added, KMnO4 was no longer added.

(42) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(43) The polymerization reaction was then allowed to continue and the reaction stopped after 16 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 42.82 Kg containing 28.4% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(44) The raw dispersion particle size (RDPS) of the polymer particle was 0.240 microns and the standard specific gravity was 2.159. The VDF concentration in the copolymer was measured to be 3.50 mol % (2.20 wt %). The PFOE concentration in the copolymer was measured to be 0.03 mol % (0.16 wt %), yielding a total copolymer concentration in the composition of 2.36 wt %. The break strength of the beading specimen was 14.1 lbs.

(45) The matrix tensile strength of the specimen was measured to be 48,236 psi.

Example 5

(46) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(47) To the evacuated reactor, 8 mL of PFBE were charged, and the reactor was heated to 83 C. and agitated at 60 rpm. Subsequently, TFE was added until the pressure reached 2.8 MPa. At this time, KMnO4 in a DI water solution (0.063 g/L) was injected at 80 mL/min until approximately 1 kg of TFE was added. At this time the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with 0.8 MPa of VDF followed by addition of TFE until the pressure reached 2.8 MPa. The KMnO4 was again added at 80 mL/min until an additional 1 Kg of TFE was consumed at which time it was reduced to 40 mL/min until 4 Kg of TFE was consumed. After the fourth Kg of TFE was consumed the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. An additional amount of KMnO4 was added at 10 mL/min until the fifth Kg of TFE was consumed. After the consumption of the fifth Kg of TFE, no more KMnO4 was added.

(48) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(49) The polymerization reaction was then allowed to continue and the reaction stopped after 16 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 48.8 Kg containing 34.5% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(50) The raw dispersion particle size (RDPS) of the polymer particle was 0.234 microns and the standard specific gravity was 2.151. The VDF concentration in the copolymer was measured to be 3.15 mol % (2.04 wt %), and the PFBE concentration in the copolymer was measured to be 0.03 mol % (0.07 wt %), yielding a total copolymer concentration in the composition of 2.11 wt %. The break strength of the beading supermen was 8.6 lbs.

(51) The matrix tensile strength of the specimen was 10 measured to be 31,342 psi.

Example 6

(52) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(53) The reactor was heated to 83 C. and agitated at 60 rpm. Subsequently, TFE was added until the pressure reached 2.8 MPa. At this time, KMnO4 in a DI water solution (0.063 g/L) was injected at 80 mL/min until approximately 1 kg of TFE was added. At this time the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with 0.8 MPa of VDF followed by addition of TFE until the pressure reached 2.8 MPa. The KMnO4 was again added at 80 mL/min until an additional 2 Kg of TFE was consumed at which time it was reduced to 40 mL/min until 4 Kg of TFE was consumed. After the fourth Kg of TFE was consumed the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. An additional amount of KMnO4 was added at 40 mL/min until the fifth Kg of TFE was consumed. After the consumption of the fifth Kg of TFE, no more KMnO4 was added.

(54) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(55) The polymerization reaction was then allowed to continue and the reaction stopped after 16 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 46.86 Kg containing 35.0% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(56) The raw dispersion particle size (RDPS) of the polymer particle was 0.265 microns and the standard specific gravity was 2.158. The VDF concentration in the copolymer was measured to be 3.35 mol % (2.17 wt %). The break strength of the beading specimen was 6.6 lbs. An SEM of the microstructure of the beading specimen is shown in FIG. 2.

(57) The matrix tensile strength of the specimen was measured to be 26,053 psi.

(58) The copolymer material formed in this example was then blended with Isopar K (Exxon Mobil Corp., Fairfax, Va.) in the proportion of 0.196 g/g of fine powder. The lubricated powder was compressed into a cylinder to form a pellet and placed into an oven set at 49 C. for approximately 12 hours. The compressed and heated pellet was ram extruded to produce a tape approximately 16.0 cm wide by 0.73 mm thick. The extruded tape was then rolled down between compression rolls to a thickness of 0.256 mm. The tape was then transversely stretched to approximately 56 cm wide (i.e., at a ratio of 3.5:1) and dried at a temperature of 250 C. The dry tape was longitudinally expanded between banks of rolls over a heated plate set to a temperature of 345 C. The speed ratio between the second bank of rolls and the first bank of rolls was 10:1. The width of the expanded tape was 12.1 cm. The longitudinally expanded tape was then expanded transversely at a temperature of approximately 360 C. to a ratio of approximately 25:1 and then constrained from shrinkage and heated in an oven set at 380 C. for approximately 24 seconds. An SEM SEM of the resulting sheet is shown in FIG. 3, taken at 20,000 magnification, showing a node 1 and fibril 2 microstructure.

Example 7

(59) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(60) To the evacuated reactor, 8 mL of PFBE was charged, and the reactor was heated to 83 C. and agitated at 60 rpm. Subsequently, TFE was added until the pressure reached 2.8 MPa. At this time, KMnO4 in a DI water solution (0.063 g/L) was injected at 80 mL/min until approximately 1 kg of TFE was added. At this time the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with 0.8 MPa of TrFE followed by addition of TFE until the pressure reached 2.8 MPa. The KMnO4 was again added at 80 mL/min until an additional 3 Kg of TFE was consumed. After the fourth Kg of TFE was consumed the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. An additional amount of KMnO4 was added at 40 mL/min until the fifth Kg of TFE was consumed. After the consumption of the fifth Kg of TFE, no more KMnO4 was added.

(61) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(62) The polymerization reaction was then allowed to continue and the reaction stopped after 16 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 46.9 Kg containing 33.1% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(63) The raw dispersion particle size (RDPS) of the polymer particle was 0.227 microns and the standard specific gravity was 2.217. The TrFE concentration in the copolymer was measured to be 4.2 mol % (3.5 wt %), and the PFBE concentration in the copolymer was measured to be 0.03 mol % (0.07 wt %), yielding a total copolymer concentration in the composition of 3.57 wt %. The break strength of the beading specimen was 3.48 lbs.

(64) The matrix tensile strength of the specimen was measured to be 13,382 psi.

Example 8

(65) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(66) The reactor was heated to 83 C. and agitated at 60 rpm. Subsequently, TFE was added until the pressure reached 2.8 MPa. At this time, KMnO4 in a DI water solution (0.063 g/L) was injected at 80 mL/min until approximately 1 kg of TFE was added. At this time the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with 0.8 MPa of TrFE followed by addition of TFE until the pressure reached 2.8 MPa. The KMnO4 was again added at 80 mL/min until an additional 3 Kg of TFE was consumed. After the fourth Kg of TFE was consumed the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. An additional amount of KMnO4 was added at 40 mL/min until the fifth Kg of TFE was consumed. After the consumption of the fifth Kg of TFE, no more KMnO4 was added.

(67) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(68) The polymerization reaction was then allowed to continue and the reaction stopped after 16 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 47.22 Kg containing 34.8% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(69) The raw dispersion particle size (RDPS) of the polymer particle was 0.276 microns and the standard specific gravity was 2.219. The TrFE concentration in the copolymer was measured to be 4.17 mol % (3.5 wt %). The break strength of the beading specimen was 3.95 lbs.

(70) The matrix tensile strength of the specimen was measured to be 15,329 psi.

Example 9

(71) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(72) The reactor was heated to 83 C. and agitated at 6 0 rpm. Subsequently, TFE was added until the pressure reached 2.8 MPa. At this time, KMnO4 in a DI water solution (0.063 g/L) was injected at 80 mL/min until approximately 1 kg of TFE was added. At this time the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with 1.2 Kg of HFP followed by addition of TFE until the pressure reached 1.9 MPa. The KMnO4 was again added at 80 mL/min until an additional three Kg of TFE was consumed. After the 4.sup.th Kg of TFE was consumed the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. An additional amount of KMnO4 was added at 80 mL/min until the fifth Kg of TFE was consumed. After the consumption of the fifth Kg of TFE, no more KMnO4 was added.

(73) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(74) The polymerization reaction was then allowed to continue and the reaction stopped after 18 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 48.54 Kg containing 30.4% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(75) The raw dispersion particle size (RDPS) of the polymer particle was 0.302 microns and the standard specific gravity was 2.157. The HFP concentration in the copolymer was measured to be 0.77 mol % (1.25 wt %). The break strength of the beading specimen was 7.60 lbs.

(76) The matrix tensile strength of the specimen was measured to be 34,178 psi.

Example 10

(77) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO), 0.2 g FeSO4 and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(78) The reactor was heated to 83 C. and agitated at 60 rpm. Subsequently, 0.81 MPa of CTFE was added followed by addition of TFE until the pressure reached 2.8 MPa. At this time, a solution containing 3 g ammonium persulfate and 3 g sodium hydrosulfite in 2000 mL of DI water was injected at 40 mL/min until 2 Kg of TFE was consumed. After addition of the second Kg of TFE, the pressure in the reactor was reduced to 50 Kpa using vacuum and pressurized with fresh TFE to 2.8 MPa. Additional initiator solution was again added at 20 mL/Min until a total of 2.5 Kg of TFE was consumed. At this time the rate was reduced to 10 mL/min. After 3 Kg of total TFE was consumed no more initiator was added.

(79) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(80) The polymerization reaction was then allowed to continue and the reaction stopped after 16 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 48.07 Kg containing 35.0% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(81) The raw dispersion particle size (RDPS) of the polymer particle was 0.245 microns and the standard specific gravity was 2.228. The CTFE concentration in the copolymer was measured to be 3.9 mol % (4.5 wt %). The break strength of the beading specimen was 7.6 lbs.

(82) The matrix tensile strength of the specimen was measured to be 23,991 psi.

(83) Adhesion tasting was performed, and the results are reported in Table 2. A DSC scan for this material is included in FIG. 4, which shows a first melt transition for the material at about 247 C.

Example 11

(84) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO), 0.2 g FeSO4 and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(85) To the evacuated reactor, 8 mL of PFBE was charged, and the reactor was heated to 83N C. and agitated at 60 rpm. Subsequently, 0.81 MPa of CTFE was added followed by addition of TFE until the pressure reached 2.8 MPa. A solution containing 3 g ammonium persulfate and 3 g sodium hydrosulfite in 2000 mL of DI water was injected at 40 mL/min until 2 Kg of TFE were consumed. After addition of the second Kg of TFE, the pressure in the reactor was reduced to 50 KPa using vacuum and pressurized with fresh TFE to 2.8 MPa. Additional initiator solution was again added at 20 mL/Min until a total of 3.0 Kg of TFE was consumed. After the third Kg of TFE was consumed, no more initiator was added.

(86) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 kg of TFE had been reacted.

(87) The polymerization reaction was then allowed to continue and the reaction stopped after 16 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 47.19 Kg containing 36.6% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(88) The raw dispersion particle size (RDPS) of the polymer particle was 0.178 microns and the standard specific gravity was 2.247. The CTFE concentration in the copolymer was measured to be 3.1 mol % (3.70 wt %) and the PFBE concentration in the polymer was measured to be 0.03 mol % (0.07 wt %), yielding a total copolymer concentration in the composition of 3.77 wt %.

(89) The break strength of the beading specimen was 3.48 lbs.

Example 12

(90) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO) and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax.

(91) The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(92) The reactor was heated to 83 C., and agitated at 60 rpm. Subsequently, 2.0 MPa of VDF was added followed by addition of TFE until the pressure reached 2.8 MPa. At this time, KMnO4 in a DI water solution (0.063 g/L) was injected at 80 mL/min until approximately 4 kg of TFE were added. The KMnO4 was added at 40 mL/min during addition of the next 2 kg of TFE. After 6 Kg of TFE was consumed, no more KMnO4 was added.

(93) Approximately 320 g of 20% APFO solution were added in 40 mL increments, the first increment being added after about 1 kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 kg of TFE had been reacted.

(94) The polymerization reaction was then allowed to continue and the reaction stopped after 16 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 48.64 Kg containing 31.2% solids. The dispersion was coagulated with Nitric acid and dried at 170 C.

(95) The raw dispersion particle size (RDPS) of the polymer particle was 0.321 microns and the standard specific gravity was 2.137. The VDF concentration in the copolymer was measured to be 11.8 mol % (7.90 wt %).

(96) The break strength of the beading specimen was 10.53 lbs. The matrix tensile strength of the specimen was measured to be 37,000 psi.

(97) Adhesion testing was performed, and the results are reported in Table 2. A DSC scan for this material is included in FIG. 4, which shows a first melt transition for the material at about 185 C.

Example 13

(98) To a 50-liter, horizontal polymerization reactor equipped with a 3-bladed agitator was added 1.5 Kg wax, 28 Kg of deionized (DI) water, 18 g of ammonium perfluorooctanoic acid (APFO), 1.5 g of ZnCl.sub.2, and 5 g of succinic acid dissolved in about 50 g of DI water. The reactor and contents were heated above the melting point of the wax. The reactor was repeatedly evacuated and pressurized (to about 1 Atm or less) with TFE until the oxygen level was reduced to 20 ppm or less. The contents were briefly agitated at about 60 rpm between evacuation and purge cycles to ensure that the water was deoxygenated.

(99) The reactor was heated to 83 C. and agitated at 60 rpm. Subsequently, 2.0 MPa of VDF was added followed by addition of TFE until the pressure reached 2.8 MPa. At this time, KMnO.sub.4 in a DI water solution (0.1 g/L) was injected at 80 mL/min until was approximately 4 kg of TFE were added. The KMnO.sub.4 was added at 40 mL/min during the next 2 Kg TFE addition. After 5 Kg of TFE was consumed an additional 200 g of initiator solution was added. The total amount of KMnO.sub.4 solution added was 3.375 Kg.

(100) Approximately 320 g of 20% APFO solution was added in 40 mL increments, the first increment being added after about 1 Kg of TFE had been added, followed by increments after each additional Kg of TFE, so that the final increment was added after 8 Kg of TFE had been reacted.

(101) The polymerization reaction was then allowed to continue and the reaction stopped after 9 Kg of TFE had been added to the reactor. The weight of the dispersion produced was 40.18 Kg containing 19.6% solids. The dispersion was coagulated with Nitric acid and dried at 170 C. The raw dispersion particle size (RDPS) of the polymer particle was 0.339 microns. The VDF concentration in the copolymer was measured to be 23.8 mol % (16.7 wt %). The Break strength of the beading specimen was 8.62 lbs. The matrix tensile strength of the specimen was measured to be 23,511 psi.

(102) Adhesion testing was performed, and the results are reported in Table 2. A DSC scan for this material is included in FIG. 4, which shows a first melt transition for the material at about 193 C.

(103) A summary of the results given in the above Examples is provided in Table 1. Adhesion results are reported in Table 2. The foregoing examples are provided to illustrate, without limitation, certain preferred embodiments of copolymers produced according to the principles described herein. Additional copolymers, terpolymers, etc., etc., incorporating comonomers that are known to be reactive with TFE, can also be used. These additional comonomers can be added in a predetermined concentration and allowed to react, with or without evacuation, based on the monomers' reactivity ratio to TFE, all of which is known to one skilled in the art, as illustrated in the published literature (see, e.g., Well-Architectured Fluoropolymers: Synthesis, Properties, and Applications; Elsevier; Amsterdam 2004, pp. 209).

(104) While the invention has been disclosed herein in connection with certain embodiments and detailed descriptions, it will be clear to one skilled in the art that modifications or variations of such details can be made without deviating from the gist of this invention, and such modifications or variations are considered to be within the to scope of the claims hereinbelow.

(105) TABLE-US-00003 TABLE 1 Particle Extrusion Extrudate Break Added size, pressure, strength, strength, MTS, Example comonomer(s) microns SSG psig psi lbs psi 1 VDF 0.296 2.156 3500 1046 10.40 37,299 2 TrFE 0.283 2.213 3501 926 7.24 28,602 3 VDF/PFBE 0.263 2.157 3956 1139 13.60 44,878 4 VDF/PFOE 0.240 2.159 4294 1257 14.10 48,236 5 VDF/PFBE 0.234 2.151 3434 944 8.60 31,342 6 VDF 0.265 2.158 3123 862 6.60 26,053 7 TrFE/PFBE 0.227 2.217 3522 963 3.48 13,382 8 TrFE 0.276 2.219 3085 847 3.95 15,329 9 HFP 0.300 2.157 3350 988 7.60 34,178 10 CTFE 0.245 2.228 3640 953 7.60 23,991 11 CTFE/PFBE 0.177 2.247 3817 1071 5.50 15,722 12 VDF 0.321 2.137 4110 1044 10.53 37,000 13 VDF 0.339 n/a 5680 1061 8.62 23,511

(106) TABLE-US-00004 TABLE 2 Adhesion Adhesion Adhesion measure at measure at measure at Materials 195 C. (J/m.sup.2) 290 C. (J/m.sup.2) 350 C. (J/m.sup.2) PTFE Homopolymer No Adhesion No Adhesion 69.2 Example 10 No Adhesion 88.5 89.2 Example 12 87.2 221 521 Example 13 15.3 105.3 383.5