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
1998-08-05
2001-04-03
Lipman, Bernard (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S351000
Reexamination Certificate
active
06211302
ABSTRACT:
This invention relates to coupling of polyolefins, more specifically coupling of polyolefins using insertion into carbon hydrogen (C—H) bonds.
As used herein, the term “rheology modification” means change in melt viscosity of a polymer as determined by dynamic mechanical spectroscopy. Preferably the melt strength increases while maintaining the high shear viscosity (that is viscosity measured at a shear of 100 rad/sec by DMS) so that a polymer exhibits more resistance to stretching during elongation of molten polymer at low shear conditions (that is viscosity measured at a shear of 0.1 rad/sec by DMS) and does not sacrifice the output at high shear conditions.
Polyolefins are frequently rheology modified using nonselective chemistries involving free radicals generated for instance using peroxides or high energy radiation. However, chemistries involving free radical generation at elevated temperatures also degrade the molecular weight, especially in polymers containing tertiary hydrogen such as polystyrene, polypropylene, polyethylene copolymers etc. The reaction of polypropylene with peroxides and pentaerythritol triacrylate is reported by Wang et al., in Journal of Applied Polymer Science, Vol. 61, 1395-1404 (1996). They teach that branching of isotactic polypropylene can be realized by free radical grafting of di- and tri-vinyl compounds onto polypropylene. However, this approach does not work well in actual practice as the higher rate of chain scission tends to dominate the limited amount of chain coupling that takes place. This occurs because chain scission is an intra-molecular process following first order kinetics, while coupling chains is an inter-molecular process with kinetics that are minimally second order. Chain scission results in lower molecular weight and higher melt flow rate than would be observed were the branching not accompanied by scission. Because scission is not uniform, molecular weight distribution increases as lower molecular weight polymer chains referred to in the art as “tails” are formed.
The teachings of U.S. Pat. Nos. 3,058,944; 3,336,268; and 3,530,108 include the reaction of certain poly(sulfonyl azide) compounds with isotactic polypropylene or other polyolefins by nitrene insertion into C—H bonds. The product reported in U.S. Pat. No. 3,058,944 is crosslinked. The product reported in U.S. Pat. No. 3,530,108 is foamed and cured with cycloalkane- di(sulfonyl azide) of a given formula. In U.S. Pat. No. 3,336,268 the resulting reaction products are referred to as “bridged polymers” because polymer chains are “bridged” with sulfonamide bridges. The disclosed process includes a mixing step such as milling or mixing of the sulfonylazide and polymer in solution or dispersion then a heating step where the temperature is sufficient to decompose the sulfonylazide (100° C. to 225° depending on the azide decomposition temperature). The starting polypropylene polymer for the claimed process has a molecular weight of at least about 275,000. Blends taught in U.S. Pat. No. 3,336,268 have up to about 25 percent ethylene propylene elastomer.
U.S. Pat. No. 3,631,182 taught the use of azido formate for crosslinking polyolefins. U.S. Pat. No. 3,341,418 taught the use of sulfonyl azide and azidoformate compounds to crosslink of thermoplastics material(PP (polypropylene), PS (polystyrene),PVC (poly(vinyl chloride)) and their blends with rubbers(polyisobutene, EPM, etc.).
Similarly, the teachings of Canadian patent 797,917 (family member of NL 6,503,188) include rheology modification using from about 0.001 to 0.075 weight percent poly(sulfonyl azide) to modify homopolymer polyethylene and its blend with polyisobutylene.
Copending U.S. patent applications Ser. No. 08/921641 U.S. Pat. No. 5,869,591 and Ser. No. 08/921642 U.S. Pat. No. 5,977,271 both filed Aug. 27, 1997 disclose the use of peroxides, poly(sulfonyl azides) and other reactive materials to crosslink polymers including interpolymers of vinyl aromatic monomers and alpha-olefins.
It would be desirable to have polymers rheology modified rather than crosslinked (that is having less than about 2 percent gel as determined by xylene extraction specifically by ASTM 2765). Advantageously, interpolymers of alpha-olefins and vinyl aromatic monomers would exhibit higher shear thinning compared with the same polymers not coupled by the practice of the invention. Preferably, a process of the invention would result in more consistent coupling than methods of coupling involving free radicals, that is use of the same reactants, amounts and conditions would result in consistent amounts of coupling or consistent (reproducible) property changes, especially consistent amounts of gel formation. Preferably, a process would be less subject to effects from the presence of oxygen than would a coupling or rheology modification involving agents which generate free radicals.
SUMMARY OF THE INVENTION
Polymers coupled by reaction with coupling agents according to the practice of the invention advantageously have at least one of these desirable properties and preferably have desirable combinations of these properties.
The invention includes a process of preparing a coupled polymer comprising heating an admixture containing (1) at least one interpolymer of an alpha olefin and vinyl aromatic monomer and (2) a coupling amount of at least one poly(sulfonyl azide) to at least the decomposition temperature of the poly(sulfonyl azide) for a period sufficient for decomposition of at least about 80 weight percent of the poly(sulfonyl azide) and sufficient to result in a coupled polymer. The polymer preferably. comprises ethylene, and a vinyl aromatic monomer, preferably styrene. The amount of poly(sulfonyl azide) is preferably from about 0.01 to about 1 weight percent of the interpolymer and the reaction preferably takes place at a temperature greater than about 150° C., more preferably 185° C. The process optionally and in one preferred embodiment additionally comprises steps (b) fabricating an article from the coupled polymer and (c) crosslinking the fabricated coupled polymer. The invention additionally includes any composition obtainable by a process of the invention and any article made from the composition, preferably articles formed from a melt of the composition, more preferably by blow molding, blowing a film, foaming, or profile extruding, most preferably to form a coating for wire or cable, a tube, a gasket, a seal, roofing, or fiber. The article is optionally calendared. Additionally, the invention includes the use of compositions of the invention as starting materials for forming processes in which the composition is melted and especially in blow molding, blowing a film, foaming, or profile extruding, most preferably to form a coating for wire or cable, a tube, a gasket, a seal, roofing, or fiber.
DETAILED DESCRIPTION OF THE INVENTION
Practice of the invention is applicable to any thermoplastic polymer which has at least one C—H bond that can react with azide particularly interpolymers of vinyl aromatic monomers and alpha-olefins. The interpolymers employed in the present invention include substantially random interpolymers prepared by polymerizing one or more a-olefin monomers with one or more vinyl aromatic monomers and/or one or more hindered aliphatic or cycloaliphatic vinylidene monomers, and optionally with other polymerizable ethylenically unsaturated monomer(s).
Suitable (&agr;-olefin monomers include for example, &agr;-olefin monomers containing from 2 to about 20, preferably from 2 to about 12, more preferably from 2 to about 8 carbon atoms. Preferred such monomers include ethylene, propylene, butene-1, 4-methyl-1-pentene, hexene-1 and octene-1. Most preferred are ethylene or a combination of ethylene with C2-8 &agr;-olefins. These &agr;-olefins do not contain an aromatic moiety.
Suitable vinyl aromatic monomers which can be employed to prepare the interpolymers employed in the blends include, for example, those represented by the following formula:
wherein R1 is selected from the group of radicals consisting of hydrogen
Cummins Clark H.
Drumright Ray E.
Ho Thoi H.
Mullins Michael J.
Silvis H. Craig
Lipman Bernard
The Dow Chemical Company
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