Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1997-10-08
2003-07-22
Sergent, Rabon (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C002S159000, C002S161700, C036S02500A, C036S03200A, C128S844000, C399S350000, C522S134000, C522S135000, C522S136000, C522S137000, C522S138000, C522S141000, C522S142000, C522S143000, C522S144000, C522S162000, C522S164000, C522S165000, C522S166000, C525S445000, C525S529000, C525S530000, C604S096010, C604S103110, C604S264000, C604S349000, C604S523000, C604S532000, C604S915000, C606S007000, C606S228000, C606S231000
Reexamination Certificate
active
06596818
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the conversion of thermoplastic polymers into thermoset polymers and more specifically to such thermoset polymers exhibiting improved physical and chemical properties, relative to the corresponding thermoplastic polymers. Illustrative of such polymers are thermoset polyurethanes which are advantageously prepared using aliphatic diisocyanates and a reactive monomer crosslinker.
BACKGROUND OF THE INVENTION
Thermoplastic polymers, such as thermoplastic polyurethanes, are relatively easy to process into a wide variety of fabricated products. Unfortunately, however, the high temperature stability of these polymers and their physical properties such as mechanical strength at elevated temperatures, as well as their stability in some commonly-used organic solvents, are less than might be desired. Accordingly, methodology has been developed to provide heat-induced crosslinking to convert thermoplastic polymers, such as thermoplastic polyurethanes, into thermoset polyurethanes having the desired stability at high temperatures and in the presence of solvents. By way of illustration, U.S. Pat. No. 4,255,552 discloses thermoset polyurethane elastomers obtained by adding organic peroxides to a liquid polyurethane-forming composition prior to reacting the composition to form the polyurethane. The '552 patent teaches that the liquid polyurethane-forming composition containing “unactivated hydrogen peroxide” may be formed into a desired article and then heated to thermoset the article, or provided in solid form such as sheet, crumbs, or granules which are then formed into a desired article that is then thermoset by heating the article. The organic peroxides disclosed in the '552 patent are said to have a half-life of greater than one hour at 100° C. Unfortunately, these peroxide-containing compositions are less stable than might be desired during melt processing or thermoforming of the polyurethane composition into the desired finished article, thus providing technology that is not commercially practical.
As an alternative to heat induced crosslinking of thermoplastic polyurethanes, their conversion into thermoset polyurethanes by irradiation is known in the art. A technical journal article entitled “Radiation Crosslinked Thermoplastic Polyurethane”, published in the journal
International Polymer Science and Technology
, Vol. 19, No. 1, pp. T/6-T/9 (1992), discloses the production of such thermoset polyurethanes using a polyisocyanate and methacrylate monomer as a radiation-cross-linkable monomer. This technical journal article does not disclose the particular polyisocyanate used in making polyurethanes disclosed therein. Unfortunately, methacrylate is more heat sensitive than otherwise might be desired, causing a risk of premature cross-linking during storage, shipping, or processing, and prior to the desired conversion of the thermoplastic polyurethane into a thermoset polyurethane. Further, not all polyisocyanates perform alike in irradiation-crosslinking of TPUs. Indeed, the present inventor has been unsuccessful in attempts to cross-link TPU formulations based upon aromatic polyisocyanates to provide a desirable article.
Instead of cross-linking, the resulting article exhibits an undesirable discoloration.
U.S. Pat. No. 4,762,884 issued Aug. 9, 1988 for “Process for the Production of Radiation-Crosslinked Thermoplastic Polyurethanes”. This patent discloses the use of a cross-linking agent being a monomeric acrylate or methacrylates. These acrylates and methacrylates are more heat sensitive than might otherwise be desired. Further, although this patent discloses polyisocyanates generally, with a preference for aromatics, the present inventor (as pointed out hereinabove) has been unsuccessful in attempts to cross-link TPU formulations based upon aromatic polyisocyanates to provide a desirable article. As stated above, instead of cross-linking, the resulting article exhibits an undesirable discoloration.
Irradiation-induced cross-linking of other polymers, such as nylon, is known in the prior art, the use of these other polymers for property enhancement, such as the conversion of the nylon from a thermoplastic to a thermoset polymer in the form of an angioplasty balloon within the blood vessels of a human or other mammal, has not been disclosed heretofore to the knowledge of the present inventor.
In view of the above, there is a continuing need in the polymers manufacturing community for new polymer compositions that are readily thermoset by cross-linking when desired, but also less sensitive to unwanted heat-induced cross-linking during storage and prior to use than prior art compositions, such as the above-discussed prior art polyurethane-forming compositions, most notably prior art peroxide, acrylate, and methacrylate-containing compositions. Such compositions desirably would provide advantageous processing capability, such as by extrusion, when the composition is in the thermoplastic state, and advantageous elevated temperature stability and solvent resistance when the composition is thermoset after formation into the desired product. Moreover, new uses for compositions known to be cross-linkable in the presence of irradiation, such as nylon, would also be desirable. The present invention provides such desirable polymer compositions, together with processes for the production of the composition, as well as new uses for compositions known to be irradiation cross-linkable, such as nylon.
SUMMARY OF THE INVENTION
In one aspect, the present invention relates to a radiation-crosslinkable polymer composition comprising:
(a) a polymer selected from the group consisting of polyurethanes, styrene-based polymers, polyester-based polymers, polyether-based polymers, polyamide-based polymers, polylaurinlactam-based polymers, polytetrahydrofuran-based polymers, and combinations thereof, and
(b) a reactive monomer for cross-linking at least a portion of said polymer upon contacting said reactive monomer energy, such as ionizing radiation particles, from a radiation source. The “polymer” referred to in component (a) is intended to encompass polymers comprising the recited base component, as well as co-polymers containing the recited base component polymerized with a separate monomeric component. Preferably, the polymer of component (a) comprises a block co-polymer containing hard and soft segments. The “ionizing radiation particles” referred to in component (b) is intended to encompass any such particles, including photons, beta-particles and gamma-particles, or a combination thereof, emitted from a radiation source. Illustrative sources for such “ionizing radiation particles” include electron-beam radiation, ultraviolet radiation, and combinations thereof.
In another aspect, the present invention relates to a radiation-crosslinkable thermoplastic polyurethane composition comprising:
(a) a polyurethane produced by reacting:
(i) an aliphatic polyisocyanate, and
(ii) a polyahl, and
(b) a reactive monomer for cross-linking at least a portion of said polyurethane upon contacting said reactive monomer with ionizing radiation particles from a radiation source.
In still another aspect, the present invention relates to a process for preparing a thermoplastic article and for converting the thermoplastic article to a thermoset article, said process comprising the steps of:
(a) preparing a thermoplastic polymer product by mixing a solid, extrudable thermoplastic polymer product with a solid or liquid reactive monomer cross-linker and a polymer selected from the group consisting of nylon, polyurethanes, styrene-based polymers, polyester-based polymers, polyether-based polymers, polyamide-based polymers, polyaurinlactam-based polymers, polytetrahydrofuran-based polymers, and combinations thereof, (advantageously, in one embodiment causing said solid thermoplastic polymer product to adsorb or absorb liquid reactive monomer, thus providing a solid thermoplastic admixture),
(b) forming said thermoplastic mixture into a desired thermoplastic article,
Carlson Dale L.
Sergent Rabon
Wiggin & Dana LLP
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