Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-08-14
2004-06-01
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S250000, C526S253000, C429S249000, C429S252000
Reexamination Certificate
active
06743876
ABSTRACT:
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 relative to VDF, HFP copolymers known previously which otherwise have similar proportions of HFP in the bulk polymer, 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 manufacture containing such copolymers and of the articles of manufacture containing such copolymers.
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, reduced melting point (at HFP weight percent content of 8% or greater) when determined by differential scanning calorimetry, substantially improved solution clarity, longer gel times and reduced extractables as these terms are defined hereinafter.
The process used to make the instant copolymers requires 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 unique and useful properties in comparison to all VDF/HFP copolymers previously known. These differences are not due to the presence or absence of foreign material impurities.
The present invention also provides lithium batteries fabricated from the VDF/HFP copolymers of the present invention which are uniquely suitable for lithium battery construction.
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 also a continuous process with fixed ratios of VDF and HFP throughout the process were described. The polymers produced had HFP ratios higher than those contemplated by the present invention and they were made differently.
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 made according to these processes have higher melting points and lack the improved solution clarity, longer gel times and low extractables of the present invention copolymers.
Barber in U.S. Pat. No. 5,093,427 describes a synthetic method and copolymer produced thereby which are the exact antithesis of the synthetic method and copolymers of the present invention. The synthesis in Barber is intended to and has been demonstrated to produce copolymers having significantly higher melting points as well as other polymer properties such as solution clarity, solution stability and extractable content markedly different from the polymers of this invention.
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 a low conversion batch process is theoretically capable of producing copolymers having lower melting points, 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, since no detailed polymerization examples were offered, it is not possible to reproduce the polymers tested with any degree of certainty.
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 semicontinuous 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 (solution stability) and low extractables comparable to that of the copolymers of the present invention was made.
Pianca et al. in Polymer, vol. 28, 224-230 (February 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 lowered melting points, improved solution clarity, longer gel times and low extractables as provided by the copolymers of the present invention.
Abusleme et al. in Eur. Pat. Appl. No. 650,982 A1 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 melting points and/or 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. Pat. No. 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, Ham, John Wiley (1964), Chapter X, Copolymerization, pp. 587 et seq., particularly at pp. 593 and 610 describe the sythesis 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 lower melting temperatures (when the copolymer has greater than 8 w
Burchill Michael T.
Wille Roice Andrus
Atofina Chemicals, Inc.
Hu Henry S
Mitchell William D.
Wu David W.
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