Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1998-04-13
2002-06-11
Wilson, D. R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C250S253000, C250S254000, C250S265000, C250S909000
Reexamination Certificate
active
06403740
ABSTRACT:
FIELD OF THE INVENTION
The invention is in the field of polymers containing vinyl fluoride units, their preparation and use in making protective coatings and films.
BACKGROUND OF THE INVENTION
Polyvinyl fluoride (PVF) has been manufactured for many years and has found many uses as a protective film or coating over a variety of substrates because of its excellent weatherability, chemical resistance and mechanical properties. The fluorine atoms in PVF are largely responsible for these properties and, if polymers of higher fluorine content could be made, enhancement of these properties would be achieved. One way to increase polymer fluorine content is to prepare dipolymers in which tetrafluoroethylene (TFE) replaces some of the vinyl fluoride (VF). Such dipolymers were first described by Coffman and Ford, U.S. Pat. No. 2,419,009 (1947) and were produced with a benzoyl peroxide initiator in the presence of vinyl fluoride (VF) monomer and water in a high pressure bomb operated at 122-143 atmospheres pressure. This process produces polymer with nonionic phenyl end groups.
Sianesi and Caporiccio, J. Polymer Sci., Part A-1, 6, (1968) 335, and U.S. Pat. No. 3,513,116 (1970) studied the VF/TFE polymerization process in some detail. In all their examples the initiators used by Sianesi and Caporiccio were organometallic compounds whose decomposition was catalyzed by an oxidizing agent to yield alkyl radicals which initiated polymerization. Alcohols or alcohol/water mixtures were commonly used as the polymerization medium in these processes which afforded copolymers at pressures as low as 1 atmosphere. The initiating alkyl radicals of this process result in nonionic end groups on the polymers.
Stilmar, U.S. Pat. No. 3,531,441 (1970), reported preparation of tri- and tetra-polymers composed of VF, TFE and a wide variety of other vinyl monomers by using organic peroxide initiators in different organic solvents as polymerization media. The initiating radicals from the peroxide initiators formed nonionic end groups on the copolymers. Thus, all known previous work has reported the preparation of VF/TFE copolymers, by using radical generating species that place nonionic end groups on the polymer chains formed. These nonionic end groups are typically alkyl or aryl and, therefore, hydrophobic in nature.
The polymerization processes and attendant copolymers produced by the above prior art methods all have some important disadvantages. The process of Coffman and Ford requires high pressures. This demands expensive, robust high-pressure equipment for manufacture of the copolymer. Additionally, since the initiator is nonionic, the copolymer produced is not wetted by water and forms a lumpy heterogeneous mixture in the reactor. Complete removal of the polymer from the reactor is difficult and can only be accomplished by opening the vessel and manually removing it. This is a slow process with some associated danger and is impractical on all but small scale laboratory equipment.
The processes of Sianesi and Caporiccio require the use of flammable alcohol solvents and toxic organometallics such as tetraethyllead which pose some severe health and environmental risks. The polymerization rates reported for these processes are also low and would force the use of very large scale equipment. These requirements demand appropriate plant design for flammable and toxic materials as well as solvent recovery and refining equipment which serve to drive up equipment and operating costs and complicate the overall process.
Cook, et al. U.S. Pat. No. 3,428,618 (1969) teach the use of cyclic azoamidine free radical initiators in a process for polymerizing fluoroolefins. Although they allude to the preparation of dipolymers and terpolymers of fluoroolefins, examples in the patent are directed to the polymerization of VF homopolymer with cyclic 2,2′-azobis(N,N′-dimethylene-isobutyroamidine) dihydrochloride in preference to acyclic 2,2′-azobis(isobutyroamidine)dihydrochloride. Reference to or examples of other homopolymers or interpolymers, specifically VF/TFE interpolymers, is lacking. There is no recognition of producing a superior interpolymer product containing ionic end groups which product has a small uniform particle size and improved weather resistance, chemical resistance, and stain resistance coupled with improved release properties.
SUMMARY OF THE INVENTION
The present invention provides interpolymers containing polymer units derived from 1-99 mol % vinyl fluoride and 99-1 mol % of at least one highly fluorinated monomer, which interpolymers are characterized by the presence of ionic end groups. Further, the invention provides aqueous dispersions of the interpolymers comprising 5 to 30% by weight interpolymer and 95 to 70% by weight water. Further provided are processes for preparing the interpolymers by polymerizing VF and fluorinated monomer in water with water-soluble free-radical initiators, preferably azoamidine initiators or persulfate initiators, at temperatures within the range of 60 to 100° C. and reactor pressures within the range of 1 to 12 MPa (145 to 1760 psi). Nonaqueous dispersions of the interpolymer in polar organic solvents are also provided in accordance with the invention. The invention further provides protective self-supporting films and coatings formed from nonaqueous dispersions of the interpolymers, both for use on the surfaces of metal, plastic, ceramic, glass, concrete, fabric and wood substrates.
DETAILED DESCRIPTION
The compositions of this invention comprise an interpolymer of vinyl fluoride and at least one highly fluorinated monomer, which interpolymer is characterized by ionic end groups. The interpolymer has from 1-99 mol % vinyl fluoride and 99-1 mol % of at least one highly fluorinated monomer.
For the purposes of the present invention, “highly fluorinated” means that 50% or greater of the atoms bonded to carbon are fluorine excluding linking atoms such as O or S. Preferred highly fluorinated monomers useful for this invention include fluoroolefins such as those having 2-10 carbon atoms. Preferred monomers also include fluorinated dioxoles, and fluorinated vinyl ethers such as those having the formula CY
2
═CYOR or CY
2
═CYOR′OR wherein Y is H or F, and —R and —R′ are independently completely-fluorinated or partially-fluorinated alkyl or alkylene groups containing 1-8 carbon atoms and are preferably perfluorinated. Preferred —R groups contain 1-4 carbon atoms and are preferably perfluorinated. Preferred —R′— groups contain 2-4 carbon atoms and are preferably perfluorinated. The most preferred fluoroolefins for use in the present invention have 2-6 carbon atoms and include tetrafluoroethylene (TFE), hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), vinylidene fluoride, trifluoroethylene, hexafluoroisobutylene, and perfluorobutyl ethylene. The most preferred dioxoles include perfluoro-2,2-dimethyl-1,3-dioxole (PDD) and perfluoro-2-methylene-4-methyl-1,3-dioxolane (PMD).
A preferred composition is an interpolymer which consists essentially of 10-90 mol % vinyl fluoride units and 90-10% tetrafluoroethylene units, preferably 70-10 mol % tetrafluoroethylene units, most preferably 40-20 mol % tetrafluoroethylene units, also characterized by the presence of ionic end groups. For the purposes of the present invention, “Consists essentially of” means that, while the interpolymer may contain other polymer units, the significant properties of the interpolymer are determined by the named monomer units.
Preferred interpolymers in accordance with the invention have a melt viscosity in the range of 100-1000 Pa·s as determined by the method described herein below. Preferred interpolymers are substantially random interpolymers. The substantially random character of the polymer is indicated by nuclear magnetic resonance spectroscopy.
The process of the present invention is directed to the preparation of interpolymers, including dipolymers, terpolymers and higher interpolymers, of vinyl fluoride and other highly fluorinated monomers by emulsion
E. I. du Pont de Nemours and Company
Wilson D. R.
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