| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | March 26, 2002 |
| PATENT TITLE |
Thermoplastic compositions for durable goods applications |
| PATENT ABSTRACT |
Thermoplastic compositions have been discovered which are suitable for rotational molding. The compositions have improved processability and/or improved physical and mechanical properties. The compositions advantageously often exhibit one or more of the following: reduced low shear viscosity, reduced melt elasticity at low shear rate, reduced cycle times, improved sintering and a wide range of processing temperatures, improved low temperature and/or room temperature impact, good environmental stress crack resistance, acceptable heat distortion temperature, and acceptable flexural and secant modulus. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | August 12, 1999 |
| PATENT REFERENCES CITED |
James C. Randall, Polymer Sequence Determination Carbon-13 NMR Method, pp. 71-78, (1977). International Search Report dated Nov. 15, 2000 issued by the EPO acting as the International Searching Authority in PCT/US00/22231. |
| PATENT CLAIMS |
What is claimed is: 1. A rotational molding composition comprising; A) a majority component of one or more homopolymers or interpolymers; B) one or more impact additives selected from the group consisting of heterogeneous or homogeneous interpolymers with polymer units derived from ethylene and/or one or more C.sub.3 -C.sub.20 .alpha.-olefins having a density of 0.915 g/cm.sup.3 or less; and one or more substantially random interpolymers comprising; (1) polymer units derived from (i) at least one vinyl or vinylidene aromatic monomer, or (ii) at least one hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer; or (iii) a combination of at least one vinyl or vinylidene aromatic monomer and at least one hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer; and (2) polymer units derived from (i) ethylene, or (ii) C.sub.3-20 .alpha.-olefin; and mixtures thereof; wherein the impact strength of the composition at a fixed temperature is increased by at least 0.1 ft-lb/in from that of the majority component in the absence of the impact additive. 2. The composition of claim 1 wherein the majority component, Component A, comprises 70 percent or greater by weight of the composition. 3. The composition of claim 1 wherein the majority component, Component A, is selected from polyethylene, propylene homopolymers and copolymers, styrene homopolymers and copolymers, polycarbonates, nylon, polyesters, polybutylene, polyethylene terephthalate, and acrylic polymers; and mixtures thereof. 4. The composition of claim 1 wherein the majority component, Component A, is selected from ethylene and/or alpha olefin homopolymers or interpolymers, with the density of the ethylene homopolymers or copolymers being greater than 0.915 g/cm.sup.3. 5. The composition of claim 1 wherein the majority component, Component A, is linear low density polyethylene. 6. The composition of claim 1 wherein the majority component, Component A, is polypropylene. 7. The composition of claim 1 wherein the impact additive, Component B, comprises from about 2 to about 50 percent by weight of the composition. 8. The composition of claim 1 wherein the impact additive, comprises heterogeneous or homogeneous copolymers of ethylene and 1-propene, ethylene and 1-butene, ethylene and 1-pentene, ethylene and 1-hexene and ethylene and 1-octene of 0.850-0.915 g/cm.sup.3 density. 9. The composition of claim 1 wherein the vinyl aromatic monomer is styrene. 10. The composition of claim 1 which comprises from about 85 to about 95 percent by weight of linear low density polyethylene as Component A, and from about 5 to about 15 percent by weight of ethylene-styrene interpolymer having from about 5 to about 20 mole percent styrene as Component B; wherein the composition is in the form of a powder which is smaller than or equal to 35 mesh. 11. The composition of claim 1 which comprises from about 85 to about 95 percent by weight of linear low density polyethylene as Component A, and from about 5 to about 15 percent by weight of heterogeneous or homogeneous copolymers of ethylene and 1-propene, ethylene and 1-butene, ethylene and 1-pentene, ethylene and 1-hexene and ethylene and 1-octene of 0.850-0.915 g/cm.sup.3 density as Component B, wherein the composition is in the form of a powder which has a particle size smaller than or equal to 35 mesh. 12. A rotational molding composition comprising; A) 94 percent by weight or more of one or more thermoplastic polymers; and B) 6 percent by weight or less of one or more processing additives; wherein the sintering time of said composition will be decreased by at least 5 percent relative to the sintering time of Component A in the absence of Component B. 13. The composition of claim 12 wherein the one or more thermoplastic polymers are selected from the group consisting of substantially random ethylene-styrene interpolymers, ethylene and/or C.sub.3 -C.sub.20 .alpha.-olefin homopolymers or interpolymers, nylon, polyethylene terephthalate, polycarbonate, acrylic polymer, polystyrene, and mixtures thereof. 14. The composition of claim 12 wherein the amount of processing additive, Component B, is from about 0.01 to about 6 weight percent of the composition. 15. The composition of claim 12 wherein the processing additive, Component B, is a solid or liquid at from about 20 to about 300.degree. C. 16. The composition of claim 12 wherein the processing additive, Component B, has a molecular weight below about 10,000. 17. The composition of claim 12 wherein the processing additive, Component B, is selected from the group consisting of mineral oil, naphthenic oil, paraffinic oil, glycerol monostearate, pentaerythritol monooleate, adipic acid, sabacic acid, styrene-alpha-methyl-styrene, calcium stearate and mixtures thereof. 18. The composition of claim 12 wherein the processing additive, Component B, is mineral oil. 19. The composition of claim 17 which comprises from about 94 to about 99.9 weight percent of linear low density polyethylene as Component A, and from about 0.1 to about 6 weight percent of mineral oil as Component B; wherein said mineral oil is dispersed within the polyethylene and the composition is in the form of a powder which has a particle size smaller than or equal to 35 mesh. 20. The composition of claim 17 which comprises from about 99 to about 99.99 weight percent of linear low density polyethylene as Component A, and from about 0.01 to about 1 weight percent of calcium stearate as Component B, wherein said calcium stearate is dispersed substantially homogeneously within the polyethylene and the composition is in the form of a powder which has a particle size smaller than or equal to 35 mesh. 21. An injection molding composition; comprising A) a majority component of one or more homopolymers or interpolymers; and B) one or more impact additives selected from the group consisting of heterogeneous or homogeneous interpolymers with polymer units derived from ethylene and/or one or more C.sub.3 -C.sub.20 .alpha.-olefins having a density of 0.915 g/cm.sup.3 or less; and mixtures thereof; wherein the impact strength of the composition at a fixed temperature is increased by at least 0.1 ft-lb/in from that of the majority component in the absence of the impact additive. 22. The composition of claim 21 wherein the majority component, Component A, comprises 70 percent or greater by weight of the composition. 23. The composition of claim 21 wherein the majority component, Component A, is selected from polyethylene, propylene homopolymers and copolymers, styrene homopolymers and copolymers, polycarbonates, nylon, polyesters, polybutylene, polyethylene terephthalate, and acrylic polymers; and mixtures thereof. 24. The composition of claim 21 wherein the majority component, Component A, is selected from ethylene and/or alpha olefin homopolymers or interpolymers, with the density of the ethylene homopolymers or copolymers being greater than 0.915 g/cm.sup.3. 25. The composition of claim 21 wherein the majority component, Component A, is linear low density polyethylene. 26. The composition of claim 21 wherein the majority component, Component A, is polypropylene. 27. The composition of claim 21 wherein the impact additive, Component B, comprises from about 2 to about 50 percent by weight of the composition. 28. The composition of claim 21 wherein the impact additive, comprises heterogeneous or homogeneous copolymers of ethylene and 1-propene, ethylene and 1-butene, ethylene and 1-pentene, ethylene and 1-hexene and ethylene and 1-octene of 0.850-0.915 g/cm.sup.3 density. 29. The composition of claim 21 which comprises from about 85 to about 95 percent by weight of linear low density polyethylene as Component A, and from about 5 to about 15 percent by weight of heterogeneous or homogeneous copolymers of ethylene and 1-propene, ethylene and 1-butene, ethylene and 1-pentene, ethylene and 1-hexene and ethylene and 1-octene of 0.850-0.915 g/cm.sup.3 density as Component B, wherein the composition is in the form of a powder which has a particle size smaller than or equal to 35 mesh. 30. A rotationally molded or injection molded article prepared using the composition of any one of the preceding claims. 31. A cast film or blown film prepared using the composition of any one of the preceding claims. 32. An article prepared by blow molding, calendaring, or pulltrusion, and prepared from the composition of any one of the preceding claims. -------------------------------------------------------------------------------- |
| PATENT DESCRIPTION |
FIELD OF THE INVENTION This invention relates to compositions comprising thermoplastic polymers which are suitable for fabrication into products useful for durable goods applications by processes such as rotational molding, injection molding, blow molding, calendaring, pulltrusion, cast film, and blown film. The products made according to this invention are either flexible or rigid and are suitable for applications such as: lawn & garden equipment, building & construction materials, furniture, medical goods, sporting good, toys, storage tanks, boats, kayaks, canoes, sailboats, crash barriers and the like. BACKGROUND AND SUMMARY OF THE INVENTION One of the key fabrication methods covered herein is rotational molding (also known as rotomolding), which is used to manufacture hollow objects from thermoplastics. In the basic process of rotational molding, pulverized polymer is placed in a mold. While the mold is being rotated, the mold is heated and then cooled. The mold can be rotated uniaxially or biaxially and is usually rotated biaxially, i.e., rotated about two perpendicular axes simultaneously. The mold is typically heated externally and then cooled while being rotated. As such, rotomolding is a zero shear process and involves the tumbling, heating and melting of thermoplastic powder, followed by coalescence, fusion or sintering and cooling. In this manner, articles may be obtained which are complicated, large in size, and uniform in wall thickness. Many compositions have been employed in rotational molding. For example, U.S. Pat. No. 4,857,257 teaches rotational molding compositions comprising polyethylene, peroxide cross-linker, and a metal cationic compound while U.S. Pat. No. 4,587,318 teaches crosslinked compositions comprising ethylene terpolymer and organic peroxide. It would be desirable to discover new rotational molding compositions, which exhibit improved processability and/or improved properties achievable without necessarily having to crosslink the composition. Improved processability refers to reduced viscosity or melt elasticity at zero or low shear rates, which in turn results in shorter cycle times, faster sintering, and/or the ability to fabricate articles over wide ranges of processing temperatures. Some of the key properties of rotational molding compositions include impact strength at low or room temperature, and environmental stress crack resistance (ESCR). Another key process for fabricating durable goods is injection molding. The processability of an injection molding resin is related to its capability to fill the mold easily and without large pressure increase. Processability can be determined by measuring the viscosity/shear rate curve, using a rheometer. The slope of the viscosity curve provides information about the mechanical/rheological property balance. A polymer having a broad molecular weight distribution exhibits more shear thinning and therefore a relatively low viscosity (good processability) at the high shear rates (100-1000 s.sup.-1), which are typical of injection molding. In one aspect of the invention, thermoplastic compositions have been discovered which are especially suitable for rotational and injection molding and have improved physical and/or mechanical properties. The compositions comprise one or more polymers and an impact additive. In many cases, processability is also improved during rotational molding, as reflected in, for example, shorter cycle times, faster sintering, and/or the ability to fabricate articles over wide ranges of processing temperatures. Advantageously, the compositions often exhibit one or more of the following: improved low temperature and/or room temperature impact, improved environmental stress crack resistance, and acceptable flexural and secant modulus. In the case of rotational molding, the final density and melt index of the compositions is typically a compromise between processability and end-product properties. Conventional knowledge teaches that increasing polymer density (or modulus) results in decreasing impact, and increasing melt index (or decreasing molecular weight) results in increased processability and corresponding decreases in ESCR and impact. Furthermore, increased branching has been known to result in inferior processability. As a result, one typically must choose which property to increase with the expectation that the other property must be decreased. In contrast, the compositions of the present invention unexpectedly show that processability in rotational molding is improved even when the zero or low shear viscosity or branching is increased, and impact strength is improved without necessarily decreasing the polymer density. The compositions of the present invention with improved impact properties can also be utilized in other fabrication processes including, but not limited to blow molding, calendaring, pulltrusion, cast film, and blown film. In another aspect of the present invention, thermoplastic compositions have been discovered which are specifically suitable for rotational molding and have acceptable physical and mechanical properties, but exhibit improved processability. The compositions comprise one or more thermoplastic polymers and a small amount of a low molecular weight processing additive that is preferably not volatile at the processing conditions. These compositions advantageously exhibit reduced melt viscosity or elasticity at zero or low shear rates. This results in shorter cycle times, faster sintering, and/or the ability to fabricate articles over wide ranges of processing temperatures. DETAILED DESCRIPTION OF THE INVENTION As used herein, "Izod impact strength" was measured according to ASTM test D-256 conducted at a particular temperature, "2% secant modulus" was measured according to ASTM test D-790, "flexural modulus" was measured according to ASTM test D-790, "heat distortion temperature" was measured according to ASTM test D-648 (at 66 psi), "low shear viscosity" was measured at 0.1 s.sup.-1 shear rate using a dynamic mechanical spectrometer, "melt index" was measured according to ASTM test D-1238 (190.degree. C., 2.16 kg load), "density" was measured according to ASTM D-792, and "Environmental Stress Crack Resistance" (ESCR-F50) was measured according to ASTM D-1524 using 10% Igepal solution. The test methods used for measuring sintering times, conducting uniaxial or rotational molding experiments and measuring low temperature dart impact strength are described in the examples ahead. 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 "hydrocarbyl" as employed herein means any aliphatic, cycloaliphatic, aromatic, aryl substituted aliphatic, aryl substituted cycloaliphatic, aliphatic substituted aromatic, or aliphatic substituted cycloaliphatic groups. The term "hydrocarbyloxy" means a hydrocarbyl group having an oxygen linkage between it and the carbon atom to which it is attached. 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. A. Thermoplastic Compositions with Improved Impact Properties One aspect of the invention involves thermoplastic compositions having improved properties, for example, improved low temperature and/or room temperature impact, improved environmental stress crack resistance, etc. The compositions typically comprise one or more polymers as the majority component of the composition and one or more impact-improving additives, i.e., impact additives. 1. Majority Component The composition having improved impact properties typically comprises one or more polymers as the "majority component." As used herein the term, "majority component or majority", means a single polymer or mixture of polymers which comprises 50 percent or greater, preferably 60 percent or greater, most preferably 70 percent or greater by weight of the composition having improved impact properties. The polymers that are suitable include those polymers or mixtures of polymers that are thermoplastic when employed with the impact additives described herein. By "thermoplastic" is meant those substances that soften when heated to temperatures employed in rotational and injection molding and which return to their original condition upon cooling to about room temperature. Such polymers include those often employed in rotational molding and injection molding such as ethylene and/or alpha olefin homopolymers or interpolymers, for example, LLDPE, HDPE, LDPE, VLDPE, and mixtures thereof. Because of the presence of the impact additives employed in the composition of the invention, other polymers that have not been used extensively in rotational molding and injection molding, may also comprise the majority of the thermoplastic composition. For example, polymers such as propylene homopolymers and copolymers, styrene homopolymers and copolymers, polycarbonates, nylon, polyesters, polybutylene, polyethylene terephthalate, and acrylic polymers may also be employed as the one or more polymers that comprise the majority of the composition. The ethylene and/or .alpha.-olefin homopolymers or interpolymers employed as the majority component in the blends of the present invention are derived from ethylene and/or C.sub.3 -C.sub.20 .alpha.-olefins, and include, but are not limited to, polypropylene, propylene/C.sub.4 -C.sub.20 .alpha.-olefin copolymers, polyethylene, and ethylene/C.sub.3 -C.sub.20 .alpha.-olefin copolymers. In the case of all such homopolymers and interpolymers, with the exception of propylene homopolymers and interpolymers, their densities should be greater than 0.915 g/cm.sup.3. The interpolymers can be either heterogeneous ethylene/.alpha.-olefin interpolymers or homogeneous ethylene/.alpha.-olefin interpolymers, including the substantially linear ethylene/.alpha.-olefin interpolymers. Heterogeneous interpolymers are differentiated from the homogeneous interpolymers in that in the latter, substantially all of the interpolymer molecules have the same ethylene/comonomer ratio within that interpolymer, whereas heterogeneous interpolymers are those in which the interpolymer molecules do not have the same ethylene/comonomer ratio. The term "broad composition distribution" used herein describes the comonomer distribution for heterogeneous interpolymers and means that the heterogeneous interpolymers have a "linear" fraction, multiple melting peaks (i.e., exhibit at least two distinct melting peaks) by DSC and have a degree of branching less than or equal to 2 methyls/1000 carbons in about 10 percent (by weight) or more, preferably more than about 15 percent (by weight), and especially more than about 20 percent (by weight of the polymer). The heterogeneous interpolymers also have a degree of branching equal to or greater than 25 methyls/1000 carbons in about 25 percent or less (by weight of the polymer), preferably less than about 15 percent (by weight), and especially less than about 10 percent (by weight of the polymer). The Ziegler catalysts suitable for the preparation of the heterogeneous component of the current invention are typical supported, Ziegler-type catalysts, which are particularly useful at the high polymerization temperatures of the solution process. Examples of such compositions are those derived from organomagnesium compounds, alkyl halides or aluminum halides or hydrogen chloride, and a transition metal compound. Examples of such catalysts are described in U.S. Pat No. 4,314,912 (Lowery, Jr. et al.), U.S. Pat No. 4,547,475 (Glass et al.), and U.S. Pat No. 4,612,300 (Coleman, III), the teachings of which are incorporated herein by reference. Suitable catalyst materials may also be derived from an inert oxide supports and transition metal compounds. Examples of such compositions suitable for use in the solution polymerization process are described in U.S. Pat No. 5,420,090 (Spencer. et al.), the teachings of which are incorporated herein by reference. The heterogeneous polymer component can be an ethylene and/or .alpha.-olefin homopolymer preferably polyethylene or polypropylene, or, preferably, an interpolymer of ethylene with at least one C.sub.3 -C.sub.20 .alpha.-olefin and/or C.sub.4 C.sub.18 diolefins. Heterogeneous copolymers of ethylene and 1-butene, ethylene and 1-pentene, ethylene and 1-hexene and ethylene and 1-octene are especially preferred (with density greater than 0.915 g/cm.sup.3). The relatively recent introduction of metallocene-based catalysts for ethylene/.alpha.-olefin polymerization has resulted in the production of new ethylene interpolymers. Such polymers are known as homogeneous interpolymers and are characterized by their narrower molecular weight and composition distributions relative to, for example, traditional Ziegler catalyzed heterogeneous polyolefin polymers. The homogeneous polymer component can be an ethylene and/or .alpha.-olefin homopolymer preferably polyethylene or polypropylene, or, preferably, an interpolymer of ethylene with at least one C.sub.3 -C.sub.20 .alpha.-olefin and/or C.sub.4 -C.sub.18 diolefins. Homogeneous copolymers of ethylene and one or more C.sub.3 -C.sub.8 .alpha.-olefins are especially preferred. The substantially linear homogeneous ethylene/.alpha.-olefin polymers and interpolymers which can be employed as the majority component of the present invention (subject to the limitation of density greater than 0.915 g/cm.sup.3) are herein defined as in U.S. Pat. No. 5,272,236 (Lai et al.), and in U.S. Pat. No. 5,278,272, the entire contents of which are incorporated by reference. Commercially available products to be employed as the majority component include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), polyolefin plastomers, such as those marketed by The Dow Chemical Company under the AFFINITY.TM. tradename and by Exxon Chemical under the EXACT.TM. tradename. The C.sub.3 .alpha.-olefin homopolymers or copolymers employed as the majority component in the blends of the present invention are polypropylenes. The polypropylene is generally in the isotactic form of homopolymer polypropylene, although other forms of polypropylene can also be used (e.g., syndiotactic or atactic). Polypropylene impact copolymers (e.g., those wherein a secondary in-reactor copolymerization step reacting ethylene with the propylene is employed) and random copolymers (also reactor modified and usually containing 1.5-20% of ethylene or C.sub.4 -C.sub.8 .alpha.-olefin copolymerized ith the propylene), however, can also be used. A complete discussion of various polypropylene polymers is contained in Modern Plastics Encyclopedia/89, mid October 1988 Issue, Volume 65, Number 11, pp. 86-92, the entire disclosure of which is incorporated herein by reference. The molecular weight of the majority component for use in the present invention is conveniently indicated using a melt index or melt flow measurement such as ASTM D-1238, Condition 190.degree. C./2.16 kg (formerly known as "Condition (E)" and also known as I.sub.2) for ethylenic polymers. As one skilled in the art will appreciate, the melt index or melt flow rate is measured at different temperatures and loads for different polymers. For instance, the temperatures used are 190.degree. C. for ethylenic polymers, 200.degree. C. for polystyrene, 230.degree. C. for polypropylene, and 300.degree. C. for polycarbonate. Melt flow rate is inversely proportional to the molecular weight of the polymer. Thus, the higher the molecular weight, the lower the melt flow rate, although the relationship is not linear. Generally, the polymers which comprise the majority component of the thermoplastic composition will have a melt index or melt flow rate of from about 0.5 to about 5000, preferably from about 1 to about 2000, more preferably from about 2 to about 500 g/10 min. 2. Impact Additive The type of impact additive may vary depending upon the type and amount of polymer(s) employed as the majority of the rotational molding or injection molding composition, as well as, the desired properties of the articles to be made via rotational molding or injection molding. Generally, for rotational molding, the impact additive is selected from the group consisting of ethylene-vinyl acetate copolymer (EVA); heterogeneous or homogeneous interpolymers of polymer units derived from ethylene and/or one or more C.sub.3 -C.sub.20 .alpha.-olefins (with density of 0.915 g/cm.sup.3 or less); or one or more substantially random interpolymers comprising; (1) polymer units derived from (i) at least one vinyl or vinylidene aromatic monomer, or (ii) at least one hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer; or (iii) a combination of at least one vinyl or vinylidene aromatic monomer and at least one sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomer; and (2) polymer units derived from (i) ethylene, or (ii) C.sub.3-20 .alpha.-olefin; and mixtures thereof. Generally, for injection molding, the impact additive is selected from the group consisting of ethylene-vinyl acetate copolymer (EVA); heterogeneous or homogeneous interpolymers of polymer units derived from ethylene and/or one or more C.sub.3 -C.sub.20 .alpha.-olefins (with density of 0.915 g/cm.sup.3 or less); and mixtures thereof. The term "substantially random" (in the substantially random interpolymer comprising polymer units derived from ethylene and/or one or more .alpha.-olefin monomers with one or more vinyl or vinylidene aromatic monomers and/or sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers) as used herein means that the distribution of the monomers of said interpolymer can be described by the Bernoulli statistical model or by a first or second order Markovian statistical model, as described by J. C. Randall in polymer sequence determination, carbon-13 NMR method, Academic Press New York, 1977, pp. 71-78. Preferably, substantially random interpolymers do not contain more than 15 percent of the total amount of vinyl or vinylidene monomer in blocks of vinyl or vinylidene monomer of more than 3 units. More preferably, the interpolymer is not characterized by a high degree of either isotacticity or syndiotacticity. This means that in the carbon.sup.-13 NMR spectrum of the substantially random interpolymer the peak areas corresponding to the main chain methylene and methine carbons representing either meso diad sequences or racemic diad sequences should not exceed 75 percent of the total peak area of the main chain methylene and methine carbons. The substantially random interpolymers interpolymers used as the impact additive in the present invention can be prepared by polymerizing i) ethylene and/or one or more .alpha.-olefin monomers and ii) one or more vinyl or vinylidene aromatic monomers and/or one or more hindered aliphatic or cycloaliphatic vinyl or vinylidene monomers, and optionally iii) other polymerizable ethylenically unsaturated monomer(s). Suitable .alpha.-olefins include for example, .alpha.-olefins containing from 3 to about 20, preferably from 3 to about 12, more preferably from 3 to about 8 carbon atoms. Particularly suitable are ethylene, propylene, butene-1,4-methyl-1-pentene, hexene-1 or octene-1 or ethylene in combination with one or more of propylene, butene-1,4-methyl-1-pentene, hexene-1 or octene-1. These .alpha.-olefins do not contain an aromatic moiety. Other optional polymerizable ethylenically unsaturated monomer(s) include norbornene and C.sub.1-10 alkyl or C.sub.6-10 aryl substituted norbornene, with an exemplary interpolymer being ethylene/styrene/norbornene. Suitable vinyl or vinylidene aromatic monomers include, for example, those represented by the following formula: ##STR1## wherein R.sup.1 is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R.sup.2 is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; Ar is a phenyl group or a phenyl group substituted with from 1 to 5 substituents selected from the group consisting of halo, C.sub.1-4 -alkyl, and C.sub.1-4 -haloalkyl; and n has a value from zero to about 4, preferably from zero to 2, most preferably zero. Exemplary vinyl or vinylidene aromatic monomers include styrene, vinyl toluene, .alpha.-methylstyrene, t-butyl styrene, chlorostyrene, including all isomers of these compounds, and the like. Particularly suitable such monomers include styrene and lower alkyl- or halogen-substituted derivatives thereof. Preferred monomers include styrene, .alpha.-methyl styrene, the lower alkyl-(C.sub.1 --C.sub.4) or phenyl-ring substituted derivatives of styrene, such as for example, ortho-, meta-, and para-methylstyrene, the ring halogenated styrenes, para-vinyl toluene or mixtures thereof, and the like. A more preferred aromatic vinyl monomer is styrene. By the term "hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds", it is meant addition polymerizable vinyl or vinylidene monomers corresponding to the formula: ##STR2## wherein A.sup.1 is a sterically bulky, aliphatic or cycloaliphatic substituent of up to 20 carbons, R.sup.1 is selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; each R.sup.2 is independently selected from the group of radicals consisting of hydrogen and alkyl radicals containing from 1 to about 4 carbon atoms, preferably hydrogen or methyl; or alternatively R.sup.1 and A.sup.1 together form a ring system. The aliphatic or cycloaliphatic vinyl or vinylidene compounds are monomers in which one of the carbon atoms bearing ethylenic unsaturation is tertiary or quaternary substituted. Examples of such substituents include cyclic aliphatic groups such as cyclohexyl, cyclohexenyl, cyclooctenyl, or ring alkyl or aryl substituted derivatives thereof, tert-butyl, norbornyl, and the like. Most preferred aliphatic or cycloaliphatic vinyl or vinylidene compounds are the various isomeric vinyl-ring substituted derivatives of cyclohexene and substituted cyclohexenes, and 5-ethylidene-2-norbornene. Especially suitable are 1-, 3-, and 4-vinylcyclohexene. Simple linear non-branched .alpha.-olefins including for example, .alpha.-olefins containing from 3 to about 20 carbon atoms such as propylene, butene-1,4-methyl-1-pentene, hexene-1 or octene-1 are not examples of sterically hindered aliphatic or cycloaliphatic vinyl or vinylidene compounds. One method of preparation of the substantially random interpolymers includes polymerizing a mixture of polymerizable monomers in the presence of one or more metallocene or constrained geometry catalysts in combination with various cocatalysts, as described in EP-A-0,416,815 by James C. Stevens et al. and U.S. Pat. No. 5,703,187 by Francis J. Timmers and U.S. Pat. No. 5,872201 by Yunwa Cheung et al, all of which are incorporated herein by reference in their entirety. Preferred operating conditions for such polymerization reactions are pressures from atmospheric up to 3000 atmospheres and temperatures from -30.degree. c. to 200.degree. C. Polymerizations and unreacted monomer removal at temperatures above the autopolymerization temperature of the respective monomers may result in formation of some amounts of homopolymer polymerization products resulting from free radical polymerization. Examples of suitable catalysts and methods for preparing the substantially random interpolymers are disclosed in U.S. application Ser. No. 702,475, filed May 20, 1991 (EP-A-514,828); as well as U.S. Patents: U.S. Pat. Nos. 5,055,438; 5,057,475; 5,096,867; 5,064,802; 5,132,380; 5,189,192; 5,321,106; 5,347,024; 5,350,723; 5,374,696; 5,399,635; 5,470,993; 5,703,187; and 5,721,185 all of which patents and applications are incorporated herein by reference. The substantially random .alpha.-olefin/vinyl aromatic interpolymers can also be prepared by the methods described in JP 07/278230 employing compounds shown by the general formula ##STR3## where Cp.sup.1 and Cp.sup.2 are cyclopentadienyl groups, indenyl groups, fluorenyl groups, or substituents of these, independently of each other; R.sup.1 and R.sup.2 are hydrogen atoms, halogen atoms, hydrocarbon groups with carbon numbers of 1-12, alkoxyl groups, or aryloxyl groups, independently of each other; M is a group IV metal, preferably Zr or Hf, most preferably Zr; and R.sup.3 is an alkylene group or silanediyl group used to cross-link Cp.sup.1 and Cp.sup.2). The substantially random .alpha.-olefin/vinyl aromatic interpolymers can also be prepared by the methods described by John G. Bradfute et al. (W.R. Grace & Co.) in WO 95/32095; by R. B. Pannell (Exxon Chemical Patents, Inc.) in WO 94/00500; and in Plastics Technology, p. 25 (September 1992), all of which are incorporated herein by reference in their entirety. Also suitable are the substantially random interpolymers which comprise at least one .alpha.-olefin/vinyl aromatic/vinyl aromatic/.alpha.-olefin tetrad disclosed in U.S. application Ser. No. 08/708,869 filed Sep. 4, 1996 and WO 98/09999 both by Francis J. Timmers et al. These interpolymers contain additional signals in their carbon-13 NMR spectra with intensities greater than three times the peak to peak noise. These signals appear in the chemical shift range 43.70-44.25 ppm and 38.0-38.5 ppm. Specifically, major peaks are observed at 44.1, 43.9, and 38.2 ppm. A proton test NMR experiment indicates that the signals in the chemical shift region 43.70-44.25 ppm are methine carbons and the signals in the region 38.0-38.5 ppm are methylene carbons. It is believed that these new signals are due to sequences involving two head-to-tail vinyl aromatic monomer insertions preceded and followed by at least one .alpha.-olefin insertion, e.g. an ethylene/styrene/styrene/ethylene tetrad wherein the styrene monomer insertions of said tetrads occur exclusively in a 1,2 (head to tail) manner. It is understood by one skilled in the art that for such tetrads involving a vinyl aromatic monomer other than styrene and an .alpha.-olefin other than ethylene that the ethylene/vinyl aromatic monomer/vinyl aromatic monomer/ethylene tetrad will give rise to similar carbon-13 mnr peaks but with slightly different chemical shifts. These interpolymers can be prepared by conducting the polymerization at temperatures of from about -30.degree. C. to about 250.degree. C. in the presence of such catalysts as those represented by the formula ##STR4## wherein: each Cp is independently, each occurrence, a substituted cyclopentadienyl group .pi.-bound to M; E is C or Si; M is a group IV metal, preferably Zr or Hf, most preferably Zr; each R is independently, each occurrence, H, hydrocarbyl, silahydrocarbyl, or hydrocarbylsilyl, containing up to about 30 preferably from 1 to about 20 more preferably from 1 to about 10 carbon or silicon atoms; each R' is independently, each occurrence, H, halo, hydrocarbyl, hyrocarbyloxy, silahydrocarbyl, hydrocarbylsilyl containing up to about 30 preferably from 1 to about 20 more preferably from 1 to about 10 carbon or silicon atoms or two R' groups together can be a C.sub.1-10 hydrocarbyl substituted 1,3-butadiene; m is 1 or 2; and optionally, but preferably in the presence of an activating cocatalyst. Particularly, suitable substituted cyclopentadienyl groups include those illustrated by the formula: ##STR5## Wherein each R is independently, each occurrence, H, hydrocarbyl, silahydrocarbyl, or hydrocarbylsilyl, containing up to about 30 preferably from 1 to about 20 more preferably from 1 to about 10 carbon or silicon atoms or two R groups together form a divalent derivative of such group. Preferably, R independently each occurrence is (including where appropriate all isomers) hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl, benzyl, phenyl or silyl or (where appropriate) two such R groups are linked together forming a fused ring system such as indenyl, fluorenyl, tetrahydroindenyl, tetrahydrofluorenyl, or octahydrofluorenyl. Particularly preferred catalysts include, for example, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium dichloride, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium 1,4-diphenyl-1,3-butadiene, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium di-C1-4 alkyl, racemic-(dimethylsilanediyl)-bis-(2-methyl-4-phenylindenyl) zirconium di-C1-4 alkoxide, or any combination thereof and the like. It is also possible to use the following titanium-based constrained geometry catalysts, [N-(1,1-dimethylethyl)-1,1-dimethyl-1-[(1,2,3,4,5-.eta.)-1,5,6,7-tetrahydr o-s-indacen-1-yl]silanaminato(2-)-N]titanium dimethyl; (1-indenyl)(tert-butylamido)dimethyl-silane titanium dimethyl; ((3-tert-butyl)(1,2,3,4,5-.eta.)-1-indenyl)(tert-butylamido) dimethylsilane titanium dimethyl; and ((3-iso-propyl)(1,2,3,4,5-.eta.)-1-indenyl)(tert-butyl amido)dimethylsilane titanium dimethyl, or any combination thereof and the like. Further preparative methods for the interpolymers used in the present invention have been described in the literature. Longo and Grassi (Makromol. Chem., Volume 191, pages 2387 to 2396 [1990]) and D'Anniello et al. (Journal of Applied Polymer Science, volume 58, pages 1701-1706 [1995]) reported the use of a catalytic system based on methylalumoxane (mao) and cyclopentadienyltitanium trichloride (CpTiCl.sub.3) to prepare an ethylene-styrene copolymer. Xu and Lin (Polymer Preprints, Am. Chem. Soc., Div. Polym. Chem.) Volume 35, pages 686,687 [1994]) have reported copolymerization using a MgCl.sub.2 /TiCl.sub.4 /NdCl.sub.3 /Al(iBu).sub.3 catalyst to give random copolymers of styrene and propylene. Lu et al. (Journal of Applied Polymer Ccience, volume 53, pages 1453 to 1460 [1994]) have described the copolymerization of ethylene and styrene using a TiCl.sub.4 /NdCl.sub.3 /MgCl.sub.2 /Al(Et).sub.3 catalyst. Semetz and Mulhaupt, (Macromol. Chem. Phys., V. 197, pp. 1071-1083, 1997) have described the influence of polymerization conditions on the copolymerization of styrene with ethylene using Me.sub.2 Si(Me.sub.4 Cp)(n-tert-butyl)TiCl.sub.2 /methylaluminoxane Ziegler-Natta catalysts. Copolymers of ethylene and styrene produced by bridged metallocene catalysts have been described by Arai, Toshiaki and Suzuki (Polymer Preprints, Am. Chem. Soc., Div. Polym. Chem.) Volume 38, pages 349, 350 [1997]) and in U.S. Pat. No. 5,652,315, issued to Mitsui Toatsu Chemicals, Inc. The manufacture of .alpha.-olefin/vinyl aromatic monomer interpolymers such as propylene/styrene and butene/styrene are described in U.S. Pat. No. 5,244,996, issued to Mitsui Petrochemical Industries Ltd. or U.S. Pat. No. 5,652,315 also issued to Mitsui Petrochemical Industries Ltd. or as disclosed in DE 197 11 339 A1 and U.S. Pat. No. 5,883,213 both to Denki Kagaku Kogyo KK. All the above methods disclosed for preparing the interpolymer component are incorporated herein by reference. Also the random copolymers of ethylene and styrene as disclosed in Polymer Preprints Vol. 39, No. 1, March 1998 by Toru Aria et al. can also be employed as blend components for the present invention. While preparing the substantially random interpolymer, an amount of atactic vinyl aromatic homopolymer may be formed due to homopolymerization of the vinyl aromatic monomer at elevated temperatures. The presence of vinyl aromatic homopolymer is in general not detrimental for the purposes of the present invention and can be tolerated. The vinyl aromatic homopolymer may be separated from the interpolymer, if desired, by extraction techniques such as selective precipitation from solution with a non solvent for either the interpolymer or the vinyl aromatic homopolymer. For the purpose of the present invention it is preferred that no more than 30 weight percent, preferably less than 20 weight percent based on the total weight of the impact additive of atactic vinyl aromatic homopolymer is present. While the improvement in impact properties of the rotational molding and injection molding compositions will vary depending on the types, molecular weights and amounts of polymer(s) present as the majority of the composition, the improvement also varies according to the monomer content and molecular weights of the polymeric impact additives. For example, when EVA copolymers are employed, the vinyl acetate content of the EVA is somewhat important. Generally, to optimize the impact properties, the EVA polymers comprise at least about 2, preferably at least about 3, more preferably at least about 5, weight percent vinyl acetate. Correspondingly, the EVA polymers typically comprise less than about 50, preferably less than about 30, more preferably less than about 20 weight percent vinyl acetate. Similarly, when substantially random interpolymers are employed as the impact additive, the monomer content of the vinyl or vinylidene aromatic component is somewhat important as the glass transition temperature of the substantially random interpolymers will increase with increasing vinyl or vinylidene aromatic content. Typically, to optimize the impact properties the substantially random interpolymers comprise at least about 1, preferably at least about 3, more preferably at least about 5 mole percent vinyl or vinylidene aromatic component. Correspondingly, the substantially random interpolymers typically comprise less than about 30, preferably less than about 25, more preferably less than about 20 mole percent vinyl aromatic component. A particularly preferred |
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