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Nonaqueous polymerization of fluoromonomers
| Details |
Inventors: DeSimone, Joseph M.; Romack, Timothy;
Assignee: The University of North Carolina at Chapel Hill (Chapel Hill, NC)
Primary Examiner: Lipman; Bernard
Assistant Examiner: Sarofim; N.
Attorney, Agent or Firm: Myers Bigel Sibley & Sajovec
The present invention provides a process for making fluorinated polymers and copolymers having stable end groups. The process includes (1) contacting a fluoromonomer, an initiator capable of producing stable end groups on the polymer chain, and a polymerization medium comprising carbon dioxide, and (2) polymerizing the fluoromonomer. The polymerization medium preferably comprises liquid or supercritical carbon dioxide. Advantageously, the process may also include the step of separating the fluoropolymer from the polymerization medium. The present invention also provides polymerization reaction mixtures useful in the processes of the present invention. |
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DETAILED DESCRIPTION OF THE INVENTION As used herein, the tern "supercritical" has its conventional meaning in the art.
A supercritical fluid (SCF) is a substance above its critical temperature and critical pressure (or "critical point").
Compressing a gas normally causes a phase separation and the appearance of a separate liquid phase.
However, if the fluid is in a supercritical state, compression will only result in density increases; no liquid phase will be formed.
The use of supercritical fluids for carrying out polymerization processes has received relatively little attention.
The term "fluoropolymer," as used herein, has its conventional meaning in the art.
See generally Fluoropolymers (L.
Wall, Ed.
1972) (Wiley-Interscience Division of John Wiley & Sons); See also Fluorine-Containing Polymers, 7 Encyclopedia of Polymer Science and Engineering 256 (H.
Mark et al.
Eds.
, 2d Ed.
1985).
Likewise, the term "fluoromonomer" refers to fluorinated precursor monomers employed in the synthesis of fluoropolymers.
The phrase "stable end group(s)" as used herein refers to polymer chain end groups which essentially do not decompose when the polymer is heated to its melt processing temperature.
Such processing temperatures are generally known in the art, such as those described in Banks et al.
Organofluorine Chemistry: Principles and Commercial Applications (1994).
Specific examples of stable end groups include but are not limited to perfluoroalkyl end groups, perfluoroalkoxy end groups, perchloroalkyl end groups, and the like.
Typically, a polymer having stable end groups is a polymer which has fewer unstable end groups than would be observed in the same polymer, having substantially the same molecular weight, prepared according to aqueous polymerization techniques.
More specifically, a polymer having stable end groups is typically a polymer which has less than 400 unstable end groups which can be acid fluoride or carboxylic acid end groups, per million carbon atoms.
In particular embodiments, a polymer having stable end groups is a polymer which has 300 or less, 200 or less, or 100 or less, unstable end groups as defined above per million carbon atoms
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MEMS 
