Copolymers of tetrafluoroethylene
View Patent ↗A polymerization process for producing a tetrafluoroethylene copolymer, and the copolymer produced thereby, are provided. The copolymer is of the dispersion/fine powder type and contains polymerized tetrafluoroethylene monomer units and co-polymerized higher homologous comonomer units having the formula (C n F (2n+1) )CH═CH 2 , wherein 6≦n<10, in which the primary particles are believed to have a core and shell structure and the polymerized comonomer units are present in an amount from 0.01 mol % to 0.3 mol %, based upon total copolymer composition. The copolymer has a raw dispersion primary particle size (RDPS) of less than 0.210 microns coupled with a standard specific gravity (SSG) of less than 2.143. Preferably the copolymer has comonomer units present in an amount from 0.05 mol % and 0.25 mol % and the RDPS is within the range between 0.178 microns and 0.200 microns, coupled with a SSG of less than 2.140. Copolymers produced according to the invention, (perfluorohexyl)ethylene (PFHE) and (perfluorooctyl)ethylene (PFOE), may be shaped into the form of 0.1 inch diameter expanded beading, which expanded beading can have a break strength of at least 10.0 lbs, and which may exceed 13.0 lbs.
1. A process for the copolymerization of a fine powder tetrafluoroethylene copolymer, said copolymer containing essentially from 99.70 mol % to 99.99 mol % tetrafluoroethylene monomer units and from 0.01 mol % to 0.30 mol % copolymerized comonomer units having the formula
(C n F (2n+1) )CH═CH 2 ,
wherein 6≦n<10,
said process comprising:
(a) copolymerizing said monomer and comonomer in a pressurized reactor,
(b) initiating said copolymerization by adding potassium permanganate (KMnO 4 ),
(c) carrying out the entire reaction in the absence of any ionic strength enhancer, and
(d) stopping the addition of (KMnO 4 ) initiator at a point in the reaction no further than 80% of the reaction completion wherein
said polymerized comonomer units are present in an amount from 0.01 mol % to 0.30 mol % based upon total copolymer composition, and
said copolymer has a raw dispersion primary particle size (RDPS) less than 0.210 microns and has a standard specific gravity (SSG) of less than 2.143.
2. The process of claim 1 wherein said comonomer is (perfluorohexyl)ethylene (PFHE).
3. The process of claim 1 wherein said comonomer is (perfluorooctyl)ethylene (PFOE).
4. The process of claim 1 including adding said comonomer as a precharge in the copolymerization reaction.
5. The process of claim 1 including adding the comonomer incrementally and intermittently, from the beginning of the reaction through only a portion of the complete reaction.
6. The process of claim 1 including stopping the addition of KMnO 4 initiator at a point in the reaction no further than 60% of the reaction completion.
7. The process of claim 1 including stopping the addition of KMnO 4 initiator at a point in the reaction no further than 50% of the reaction completion.
8. The process of claim 1 for the copolymerization of a tetrafluoroethylene copolymer of the dispersion/fine powder type, wherein:
said polymerized comonomer units are present in an amount from 0.01 mol% to 0.30 mol% based upon total copolymer composition, and
said copolymer has a raw dispersion primary particle size (RDPS) less than 0.210 microns and has a standard specific gravity (SSG) of less than 2.143.
9. The process of claim 1 wherein said copolymer has a RDPS less than 0.200 microns and has a SSG of less than 2.140.
10. The process of claim 1 including adding the comonomer as a precharge in the copolymerization reaction.
11. The process of claim 1 including adding the comonomer incrementally and intermittently, from the beginning of the reaction through only a portion of the complete reaction.
12. The process of claim 1 including stopping the addition of KMnO 4 initiator at a point in the reaction no further than 60% of the reaction completion.
13. The process of claim 1 including stopping the addition of KMnO 4 initiator at a point in the reaction no further than 50% of the reaction completion.