Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-01-02
2003-11-18
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...
C526S247000, C526S250000
Reexamination Certificate
active
06649720
ABSTRACT:
BACKGROUND OF THE INVENTION
The emulsion polymerization at moderate pressure of vinylidene fluoride using fluorinated surfactant and, as a free-radical initiator, diisopropyl peroxydicarbonate (hereinafter referred to as IPP) is taught in U.S. Pat. No. 3,475,396 dated Oct. 28, 1969. The same patent teaches that the amount of fluorinated surfactant necessary in the system can be reduced if a chain transfer agent is present in the reaction system. The process was refined in U.S. Pat. No. 3,857,827 dated Dec. 31, 1974 wherein a particularly high molecular weight product was produced in a relatively fast reaction by the use of IPP initiator dissolved in a solution of acetone (the acetone acting as a chain transfer agent).
The process was further refined in U.S. Pat. No. 4,360,652 dated Nov. 23, 1982, which taught that high quality polymers were achieved when IPP (as an aqueous emulsion using a fluoroalkyl surfactant), isopropyl alcohol (hereinafter, IPA; used as the chain transfer agent) and monomer are added separately but simultaneously to an aqueous solution of the surfactant, either incrementally or continuously over the polymerization cycle.
In EP-387,938 vinylidene fluoride polymerization using peroxy disulfate as initiator and an alkyl acetate as a chain transfer agent (molecular weight regulator) is shown. Use of polar compounds as chain transfer agents introduces polar end-groups onto the molecular chains which causes the phenomenon of product discoloration and possibly cavities at the high temperatures encountered during the melt processing stage where the temperature can be in the vicinity of 550° F. (about 288° C.).
U.S. Pat. No. 4,569,978 disclosed the use of trichlorofluoromethane as a chain transfer agent to reduce or eliminate the discoloration and cavity formation phenomenon but this is an ozone depleting material and its use is being banned worldwide.
U.S. Pat. No. 5,473,030 proposes the substitution of 1,1,1-trifluoro 2,2-dichloroethane (HCFC-123) as a chain transfer agent to replace trichlorofluoromethane (CFC-11), but in practice this has not proven to be the answer, particularly to the discoloration problem.
U.S. Pat. No. 3,635,926 dated Jan. 18, 1972 discloses an aqueous process for making TFE/PVE copolymers in presence of chain transfer agents such as hydrogen and methane in combination with CFCs and HCFCs. In this patent only perfluoro-monomers (mainly TFE) were considered and methane was the most preferred chain transfer agent since it exhibited a reasonable chain transfer activity in the polymerization of perfluoro-monomers; however, high alkanes, including ethane were reported to be too active to be used in polymerization due to undesired (slowing) effect on polymerization rate.
EP 617058 demonstrates that combinations of branched aliphatic alcohols with lower alkanes in the polymerization of perfluoro-monomers (mainly TFE) were an effective chain regulator and improved melt flow index of perfluoro-polymers.
In contrast to above disclosures regarding perfluorinated monomers, surprisingly, it has been found that the use of the hydrocarbon ethane as a chain transfer agent in the vinylidene fluoride polymerization process results, particularly in the case of vinylidene fluoride homopolymers, in a product which has a reduced tendency to generate cavities at the high temperatures encountered in typical forming processes and which has a greater tendency to resist discoloration at those same temperatures.
Addition of ethane to the polymerization of VF2 introduces a number of ethyl group chain terminations. The ethyl group is non-polar, inert, and not heat degradable and as a result the vinylidene fluoride polymers with such ethyl chain ends exhibit greater tendency to resist discoloration at the normal processing temperature of PVDF.
The introduction of hydrocarbons in general into any polymerization reaction is known to have an unpredictable effect. For any given reaction, any particular hydrocarbon may have no effect. In fluorocarbon polymer synthetic reactions it has always been thought that hydrocarbons would simply slow down the reaction rate to unacceptable levels even though the effect of hydrocarbons on vinylidene fluoride polymerizations has not been previously reported to applicants' knowledge. Neither has the fact that ethane is unique in being an efficient chain transfer agent been previously suggested. Still more surprisingly, in the present work, ethane has been shown to be about four times as efficient as trichlorofluoromethane. The initiator consumption is also independent of ethane concentration in the process and the need for any other chain transfer agent is eliminated. In the previously disclosed polymerization of perfluoromonomers where hydrocarbons were employed, more active chain transfer agents such as branched alcohol, chlorocarbons, etc., were present.
SUMMARY OF THE INVENTION
The invention provides in a first composition aspect, a vinylidene fluoride polymer containing at least some molecular chains having ethyl groups on at least one chain end.
The products of the first composition aspect of the invention, particularly vinylidene fluoride homopolymers, are light colored polymers which resist discoloration and cavitation at normal temperatures for extrusion or other fabrication techniques. Such products have the inherent applied use characteristics known for vinylidene fluoride polymers.
The invention provides in a first process aspect, a process for the preparation of vinylidene fluoride polymers, optionally in the presence of other fluorinated olefins, in an aqueous medium in the presence of a radical initiator and of ethane as a chain transfer agent.
Special mention is made of processes of the first process aspect of the invention wherein vinylidene fluoride homopolymer is produced. Special mention is also made of processes of the first process aspect of the invention wherein free radical initiators such as di(n-propyl) peroxydicarbonate or diisopropyl peroxydicarbonate are used.
DETAILED DESCRIPTION
The manner of practicing the invention will now be generally described with respect to a specific embodiment thereof, namely polyvinylidene fluoride based polymer prepared in aqueous emulsion polymerization.
The polymers 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 reactant mass during polymerization and paraffin antifoulant.
The mixture is stirred and deoxygenated. A predetermined amount of ethane is then introduced into the reactor, the reactor temperature raised to the desired level and vinylidene fluoride fed into the reactor. Once the initial charge of vinylidene fluoride is introduced and the pressure in the reactor has reached the desired level, an initiator emulsion is introduced to start the polymerization reaction. The temperature of the reaction can vary depending on the characteristics of the initiator used and one of skill in the art will know how to do so. Typically the temperature will be from about 60° to 120° C., preferably from about 70° to 110° C.
Similarly, the polymerization pressure may vary, but, typically it will be within the range 40 to 50 atmospheres. Following the initiation of the reaction, the vinylidene fluoride is continuously fed along with additional initiator to maintain the desired pressure. Once the desired amount of polymer has been reached in the reactor, the monomer feed will be stopped, but initiator feed is continued to consume residual monomer. Residual gases (containing unreacted monomer and ethane) are vented and the latex recovered from the reactor. The polymer may then be isolated from the latex by standard methods, such as, acid coagulation, freeze thaw or high shear.
Although the process of the invention has been generally illustrated with respect to the polymerization of vinylidene fluoride homopolymer, one of skill in the art will recognize that analogous polymerization techni
Amin-Sanayei Ramin
Durali Mehdi
Toulin Valerie
Wempe Lawrence Kyran
Atofina Chemicals, Inc.
Hu Henry S.
Mitchell William D.
Wu David W.
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