Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
2000-12-01
2002-05-28
Foelak, Morton (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
C521S079000, C521S081000, C521S134000, C525S071000
Reexamination Certificate
active
06395791
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
FIELD OF THE INVENTION
The present invention relates to grafted thermoplastic blend compositions and articles fabricated therefrom. The grafting of the polymers generally results in improvements in one or more of melt strength, hardness, modulus, upper service temperature in the resulting blends, over and above what is observed for the corresponding non-grafted blends. Furthermore the grafted blends may in turn be blended with additional thermoplastic polymers to further enhance one or more other properties. The various grafted blend compositions are useful in the preparation of a variety of fabricated articles including, but not limited to, foams, films, fibers, extrusion coatings, calandered and molded articles.
BACKGROUND OF THE INVENTION
Cross-linking or coupling of polymers has been used as a method of rheology modification of the polymer. As used herein, the term “rheology modification” means change in melt viscosity of a polymer as determined by dynamic mechanical spectroscopy (DMS). Cross-linking is typically employed to increase the melt strength of the polymer while maintaining the high shear viscosity (that is viscosity measured at a shear rate of 100 rad/sec by DMS). Thus a molten cross-linked polymer exhibits more resistance to stretching during elongation 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.
Various coupling agents may be employed to rheology modify and graft polymers. Such coupling agents include peroxides, silanes, and azides. Use of poly(sulfonyl azide) to react with polymers is known, for instance 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° C. depending on the azide decomposition temperature). The starting polypropylene polymer for the claimed process has a molecular weight of at least 275,000. Blends taught in U.S. Pat. No. 3,336,268 have up to about 25 percent ethylene propylene elastomer. Similarly, the teachings of Canadian patent 797,917 include rheology modification using from about 0.001 to 0.075 weight percent polysulfonyl azide to modify homopolymer polyethylene and its blend with polyisobutylene.
It would be highly desirable to have a polymer composition of enhanced melt strength, melt elongation greater than or equal to about 20 mm/s, increased upper service temperature, increased modulus, and increased hardness. Preferably, the polymer compositions would have little or no high shear viscosity increase over a corresponding polymer of the same chemical composition absent coupling agent.
In particular, it would be highly desirable to have a polymer composition of enhanced melt strength, and melt elongation greater than or equal to about 20 mm/s, that can be used to fabricate various articles including foams. Such foams should exhibit at least one of, (1) increased upper service temperature, (2) increased compressive strength at a specific foam density, or (3) increased hardness.
BRIEF SUMMARY OF THE INVENTION
This invention describes grafted blend compositions, processes for their preparation and fabricated articles, especially foams therefrom. The blends exhibit enhanced melt strength, melt elongation greater than or equal to about 20 mm/s, increased upper service temperature, increased modulus, and increased hardness. The grafted blend compositions have little or no high shear viscosity increase over a corresponding polymer of the same chemical composition absent the coupling agent.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
All references herein to elements or metals belonging to a certain Group refer to the Periodic Table of the Elements published and copyrighted by CRC Press, Inc., 1989. Also any reference to the Group or Groups shall be to the Group or Groups as reflected in this Periodic Table of the Elements using the IUPAC system for numbering groups.
Any numerical values recited herein include all values from the lower value to the upper value in increments of one unit provided that there is a separation of at least 2 units between any lower value and any higher value. As an example, if it is stated that the amount of a component or a value of a process variable such as, for example, temperature, pressure, time and the like is, for example, from 1 to 90, preferably from 20 to 80, more preferably from 30 to 70, it is intended that values such as 15 to 85, 22 to 68, 43 to 51, 30 to 32 etc. are expressly enumerated in this specification. For values which are less than one, one unit is considered to be 0.0001, 0.001, 0.01 or 0.1 as appropriate. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be considered to be expressly stated in this application in a similar manner.
The term “interpolymer” is used herein to indicate a polymer wherein at least two different monomers are polymerized to make the interpolymer. This includes copolymers, terpolymers, etc.
The term “melt processing” is used to mean any process in which the polymer is softened or melted, such as extrusion, pelletizing, molding, thermoforming, film blowing, compounding in polymer melt form, fiber spinning, and the like.
The term “melt strength” refers to the maximum force attained before significant draw resonance or breakage occurs when pulling strands of molten polymers at constant acceleration until draw resonance or breakage occurred. The velocity at which draw resonance or breakage occurred is defined as the “melt elongation” (the test method is described herein). Unless otherwise specified, both melt strength and melt elongation are measured at 190° C.
As used herein the term “grafted blend composition” means a polymer blend composition further comprising a coupling agent, with the proviso that the resulting grafted blend has a gel content (as determined in accordance with ASTM D-2765-84) which is 50 percent or less, preferably 40 percent or less, more preferably 30 percent or less, even more preferably 20 percent or less, most preferably 10 percent or less.
As used herein the term “alkenyl aromatic homopolymers, or copolymers” include homopolymers and copolymers derived from alkenyl aromatic compounds such as styrene, alphamethylstyrene, ethylstyrene, vinyl benzene, vinyl toluene, chlorostyrene, and bromostyrene. A preferred alkenyl aromatic polymer is polystyrene. Minor amounts of monoethylenically unsaturated compounds such as C
2-6
alkyl acids and esters, ionomeric derivatives, and C
4-6
dienes may be copolymerized with alkenyl aromatic compounds. Examples of copolymerizable compounds include acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, itaconic acid, acrylonitrile, maleic anhydride, methyl acrylate, ethyl acrylate, isobutyl acrylate, n-butyl acrylate, methyl methacrylate, vinyl acetate and butadiene.
For purposes of this invention, an alkenyl aromatic polymer is a melt-processable polymer or melt processable impact-modified polymer having at least 50%, preferably at least about 70% and most preferably at least 90% of its weight in the form of polymerized vinyl aromatic monomers as represented by the structure:
H
2
C═CRAr
wherein R is hydrogen or an alkyl radical that preferably has no more than
Chaudhary Bharat I.
DellaMea Jennifer
Ho Thoi H.
Oswald Thomas
Foelak Morton
The Dow Chemical Company
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