Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From fluorine-containing reactant
Reexamination Certificate
2000-03-08
2002-04-30
Wilson, Donald R. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From fluorine-containing reactant
C549S511000, C568S615000, C568S617000
Reexamination Certificate
active
06380351
ABSTRACT:
FIELD
This invention relates to prepolymer compositions and the polymers derived therefrom, oxetane monomers having asymmetric mono-substituted pendant fluorinated alkoxymethylene groups as the prepolymer precursors, methods of preparing the precursor monomers and methods of polymerization of the prepolymers to form fluorinated elastomers. The hydroxy-terminated prepolymers have a polyether backbone and are useful, inter alia, for the preparation of polyurethane elastomers, thermoset plastics and coatings. These compositions exhibit hydrophobic properties, very low surface energies, low glass transition temperatures, low di-electric constants, high abrasion resistance and tear strength, low coefficient of friction, high adhesion and low refractive indices.
BACKGROUND
Fluorinated Elastomers
Fluorinated polymers enjoy widespread use as hydrophobic, oleophobic coatings. These materials exhibit excellent environmental stability, high hydrophobicity, low surface energy and a low coefficient of friction, and are used in a number of applications ranging from non-stick frying pans to optical fiber cladding.
Most fluoropolymers, however, are plastics that are difficult to process, difficult to apply and are unsuitable as coatings for flexible substrates due to their high rigidity. One example of a widely used fluorinated material is Teflon, a polytetrafluoroethylene. Teflon is difficult to process in that it is a rigid solid which must be sintered and machined into its final configuration. Commercial application of Teflon as a coating is complicated by its poor adhesion to a substrate and its inability to form a continuous film. As Teflon is insoluble, application of a Teflon film involves spreading a thin film of powdered Teflon onto the surface to be coated, and thereafter the powdered Teflon is sintered in place resulting in either an incomplete film or having many voids. As Teflon is a hard inflexible plastic, a further limitation is that the substrate surface must be rigid otherwise the Teflon will either crack or peel off.
A limited number of commercial fluoropolymers, such as Viton, possess elastomeric properties. However, these materials have relatively high surface energies (as compared to Teflon), poor abrasion resistance and tear strength, and their glass transition temperatures are still high enough (>0° C. for Viton) to significantly limit their use in low temperature environments.
Accordingly there is a need for fluoroelastomers having hydrophobic properties, a surface energies and coefficients of friction at least equivalent to the fluorinated plastics (such as Teflon). Further, such fluoroelastomers must have high adhesion, high abrasion resistance and tear strength, low index of refraction and a low glass transition temperature so that it is suitable for any foreseeably low temperature environment use. Additionally, there is a need for fluoroelastomers that are easily produced in high yields and easy to use. Currently, there are no fluoroelastomers that satisfy all of these needs.
Premonomers
We have discovered and recognized that the conspicuous absence of fluorelastomers in the art exhibiting all of the above enumerated properties can be understood upon analysis of the upstream end of the current processes for synthesis of fluoropolymers and plastics. The kinds and properties of the premonomers currently used in turn result in the limitations in the properties of the monomers, which further limit the diversity and properties of currently known fluoropolymers and fluoroelastomers.
It is known that a haloalkyl oxetane can be substituted in the 3-position with methyl groups containing energetic functional groups such as nitrato, azide, nitro and difluoroamino. The polymerization of these substituted oxetanes in the presence of polyhydroxy aliphatic compounds produces hydroxy-terminated prepolymers having a polyether backbone with pendant energetic groups.
The use of substituted oxetanes as a starting material for the production of polyethers is not new. However, the theme running through the art is that bis-substituted oxetanes are of primary interest and commercial importance. This is understandable in that the bis-haloalkyl oxetane starting material or premonomer is easily produced, whereas the mono-substituted 3-haloalkyl methyl oxetane premonomer is difficult and expensive to produce. There is little teaching in the art for guidance on easy, inexpensive methods of preparation of 3-haloalkyl-3-methyl (mono-substituted) oxetane premonomers or their use in synthesizing mono-substituted fluorinated oxetane monomers.
Bis-haloalkyl oxetane premonomers as a starting material are described in Falk et al. (U.S. Pat. No. 5,097,048). Falk disclose 3,3′-bis perfluoroalkyl oxetane monomers derived from bis-haloalkyl oxetane as a starting material. Reaction of the bis-haloalkyl oxetane with a perfluoroalkyl thiol, a perfluoroalkyl amine, a perfluoroalkanol, or a perfluoroalkyl sulfonamide will produce the 3,3′-bis perfluoroalkyl oxetane monomer described in this reference.
Bis-haloalkyl oxetane premonomers are readily commercially available and their derivatives are fairly well covered in the art. Mono-haloalkyl oxetanes, however, are rarely mentioned in the art, appearing only as an incidental comparison in a more complete investigation of the bis-haloalkyl oxetanes. The lack of teaching regarding the mono-substituted fluorinated alkoxymethylene oxetanes (herein “FOX” compounds for
F
luorinated
OX
etane), and their relative commercial unavailability, is undoubtedly due to the fact that mono-substituted haloalkyl oxetanes are very difficult and expensive to make. Current processes for the production of mono-substituted haloalkyl oxetane premonomers, such as 3-bromomethyl-3-methyloxetane (“BrMMO”), are typified by low yields, long, complicated synthetic schemes and the use of toxic, expensive chemicals to convert 1,1,1-tris(hydroxymethyl)ethane (“TME”) into BrMMO.
In these processes, TME is reacted with diethyl carbonate to produce the corresponding cyclic carbonate. This in turn undergoes decarboxylation upon thermal decomposition at 160° C. to provide 3-hydroxymethyl-3-methyloxetane (“HMMO”). The HMMO is converted to the primary chloro compound with carbon tetrachloride and triphenyl phosphine. Reaction of the chloro compound with sodium bromide in methyl ethyl ketone results in S
N
2 displacement of the chlorine to produce BrMMO. This scheme is commercially impractical in that it is both labor intensive and requires expensive, toxic chemicals. Consequently, these disadvantages have precluded the use of mono-substituted fluorinated oxetane (FOX) monomers that may be derived from mono-substituted haloalkyl oxetanes, such as BrMMO, and production of polymer products thereof.
Accordingly, there is a need for a mono-substituted fluorinated alkoxymethylene oxetane monomer with a fluorinated side-chain capable of producing prepolymers and polymers having desirable properties, such as oil and water repellency, at least comparable to the bis-substituted perfluoroalkyl oxetanes known in the literature. Further, there is also a need for a high yielding reaction pathway for production of the mono-substituted haloalkyl premonomer, characterized by a minimum production of by-products, and a commercial feasibility for high volume, high yield production without the excessive labor and materials costs associated with the currently known processes.
Monomers and Prepolymers
The most important criteria in the development of release (i.e., non-stick), high lubricity coatings is the minimization of the free surface energy of the coating. Free surface energy is a measure of the wettability of the coating and defines certain critical properties, such as hydrophobicity and adhesive characteristics of the material. For most polymeric surfaces the surface energy (dispersion component) can be expressed in terms of the critical surface tension of wetting &ggr;
c
. For example, the surface energy of Teflon (represented by &ggr;
c
) is 18.5 ergs/cm
2
, whereas that of polyethylene is 31 erg
Archibald Thomas G.
Malik Aslam A.
Aerojet-General Corporation
Townsend & Townsend & Crew LLP
Wilson Donald R.
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