Amorphous polyether glycols based on bis-substituted oxetane...

Details Amorphous polyether glycols based on bis-substituted oxetane... Amorphous polyether glycols based on bis-substituted oxetane...

2002-11-08

2004-11-30

Sellers, Robert (Department: 1712)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From fluorine-containing reactant

C525S410000

Reexamination Certificate

active

06825316

ABSTRACT:

FIELD OF INVENTION
The present invention relates generally to amorphous polyether glycols based on bis-substituted oxetane monomers. More particularly, the present invention relates to hydroxy-terminated prepolymer compositions and to the polymers derived therefrom, oxetane monomers having bis-substituted pendant fluorinated alkoxymethylene groups as the prepolymer precursors, methods for preparing the precursor monomers and methods for polymerizing the prepolymers to form fluorinated elastomers. The hydroxyterminated prepolymers have a polyether backbone and are useful, inter alia, for the preparation of elastomers, thermoset plastics and coatings. These compositions exhibit hydrophobic properties, very low surface energies, low glass transition temperatures, low dielectric constants, high abrasion resistance and tear strength, low coefficient of friction, high adhesion and low refractive indices.
BACKGROUND OF THE INVENTION
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 nonstick 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 that must be sintered and machined into its final configuration. Commercial application of TEFLON™ as a coating is complicated by its poor adhesion to substrates 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 a film 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 (greater than 0° C. for Viton) to significantly limit their use in low-temperature environments.
Accordingly, there is a need for fluoroelastomers having hydrophobic properties, 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 low glass transition temperatures so that they are suitable for any foreseeably low temperature environmental use. In addition, there is a need for fluoroelastomers that are easily produced in high yields and easy to use.
The most important criteria in the development of release (i.e., nonstick), 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 can be expressed in terms of the critical surface tension of wetting ã
c
. For example, the surface energy of TEFLON™ (represented by ã
C
) is 18.5 ergs/cm
2
, whereas that of polyethylene is 31 ergs/cm
2
. Consequently, coatings derived from TEFLON™ are more hydrophobic and nonstick than those derived from polyethylene. A substantial amount of work has been done by the coating industry to develop coatings having surface energies lower than or comparable to TEFLON™, while at the same time exhibiting superior adhesion characteristics.
The literature teaches that in order to prepare coatings having the desirable low surface energy, the surface of the coating must be dominated by —CF
3
groups. Groups such as —CF
2
—H and —CFH
2
increase the surface energy of the material. The importance of the number of fluorine atoms in the terminal group (i.e., the group present on the surface) was demonstrated by Zisman, et al.,
J Phys. Chem.,
57:622 (1953), Zisman, et al.,
J. Colloid Sci.,
58:236 (1954); and Pittman, et al.,
J. Polymer Sci.,
6:1729 (1968). It was found that materials with terminal —CF
3
groups exhibited surface energies in the neighborhood of 6 ergs/cm
2
, whereas similar materials with terminal —CF
2
H groups exhibited values in the neighborhood of 15 ergs/cm
2
, i.e., more than twice the value for the material with terminal —CF
3
groups. TEFLON— incorporates the fluorine moieties on the polymer backbone and does not contain pendant —CF
3
groups. Consequently, TEFLON™ does not exhibit surface energies as low as polymers having terminal perfluorinated alkyl side chains.
A critical requirement in the production of an elastomer is that the elastomer have large zones, or “soft segments,” where little or no crosslinking occurs and where the polymer conformation is such that there is little or no compaction of the polymer as a result of crystallization. Intermediate of these soft zones are “hard blocks,” where there may be significant hydrogen bonding, crosslinking and compaction of the polymer. It is this alternating soft block and hard block that give the polymer its elastomeric properties. The longer the soft segment, the more elastic the elastomer.
Falk, et al. U.S. Pat. No. 5,097,048) disclose the synthesis of bis-substituted oxetane monomers having perfluoro-terminated alkyl group side chains from bis-haloalkyl oxetanes, the glycols having perfluoro-terminated alkyl group side chains derived therefrom, including related thiol and amine linked glycols and dimer diols. Most of the fluorinated side chains are attached to the glycol unit by a thio, an amine or a sulfonamide linkage. Only a few examples describe glycols having perfluoro-terminated alkoxymethylene side chains; however, such glycols are crystalline materials.
Falk, et al. (EP 03 48 350) report that their process yields perfluoro-terminated alkoxymethylene neopentyl glycols composed of a mixture of (1) approximately 64% of a bis-substituted perfluoro-terminated alkyl neopentyl glycol, and (2) approximately 36% of a mono-substituted perfluoro-terminated alkyl neopentyl glycol product with a pendant chloromethyl group. Evidently, the mono-substituted product results from incomplete substitution of the second chloride on the bis-chloroalkyl oxetane starting material. Consequently, as noted from the Zisman and Pittman work described above, the presence of the —CH
2
Cl as a side chain significantly increases the surface energy of the coatings made from these polymers, thereby reducing the hydrophobicity and oleophobicity of the coatings.
Falk, et al. U.S. Pat. No. 5,045,624) teaches preparation of dimers with fluorinated side chains having thio linkages, but not of dimers with fluorinated ether side chains. This is because the synthesis route used by Falk, et al. for preparing dimers with thio linkages cannot be used for the synthesis of dimers with ether linkages. In other words, Falk, et al. do not teach preparation of long chain polyethers with fluorinated ether side chains.
Falk, et al. (U.S. Pat. No. 4,898,981) teaches incorporation of their bis-substituted glycols into various foams and coatings to impart the desired hydrophobicity and oleophobicity. Classic polyurethane chemistry shows that while a plastic may form by reaction of Falk's glycols with diisocyantes, elastomers cannot form since there is no long chain soft segment. Such a soft segment is needed for the formation of an elastomer. Since the compounds of Falk, et al. are only one or two monomer units long, they are clearly too short to function as a soft segment for the formatio

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