PROCESSING AND TOUGHENING OF ETHYLENE COPOLYMER MATERIALS

Abstract: In one embodiment of the present invention there is provided a composition comprising a major amount of an ethylene alpha olefin copolymer and a minor amount of a low molecular weight ionomeric polymer.

Description: PROCESSING AND TOUGHENING OF ETHYLENE COPOLYMER MATERIALS FIELD OF THE INVENTION The present invention relates to polyolefin and polyolefin copolymer compositions. More particularly, the present invention is concerned with enhancing the toughness and processability of polyolefin polymers and copolymers that have been prepared using single-site catalysts. BACKGROUND OF THE INVENTION In recent years, a new class of polyolefin and polyolefin copolymers has been developed based on use of the so-called single site catalysts. These catalysts, which are organo-metallic coordination compounds of cyclopentadienyl derivatives of Group IVB metals ofthe Periodic Table of the Elements (56th Ed. of the Handbook of Chemistry and Physics, CRC Press (1975)), produce polyolefins that possess a more narrow molecular weight distribution than can be achieved with conventional Ziegler- Natta type catalysts. This narrow molecular weight distribution results in polymer materials that have better physical properties than that achieved with typical Ziegler- Natta type catalysts. Notwithstanding these improved physical properties however, there still remains a need to further toughen polymers prepared from single site catalysts. Additionally, because ofthe narrow molecular weight distribution of these materials, they tend to be more difficult to process. Consequently, there also is a need to provide a method for enhancing the processability of polyolefins and polyolefin copolymers prepared with single site catalysts. SUMMARY OF THE INVENTION The present invention is based on the discovery that ethylene alpha olefin copolymers that are prepared in the presence of a single site catalyst have their toughness and processability enhanced by including in the copolymer an effective amount of a low molecular weight ionomeric copolymer. Thus, in one embodiment ofthe present invention there is provided a composition comprising a major amount of an ethylene alpha olefin copolymer and a minor amount of a low molecular weight ionomeric polymer. These and other embodiments of the present invention will become apparent upon reading of the Detail Description of the Invention which follows. DETAILED DESCRIPTION OF THE INVENTION The polymers useful in the present invention include ethylene alpha olefin copolymers that have been prepared using single site catalysts, especially those catalysts described in U.S. Patent 5,391,629 which is incorporated herein by reference. Typically, the copolymers useful in the present invention will have weight average molecular weights of between about 10,000 to about 2 million and preferably between about 50,000 to about 300.000. Also, these ethylene alpha olefin polymers generally will contain 30 to 90% ethylene with the balance being an alpha olefm of from about 3 to 12 carbon atoms. Preferrably, the alpha olefin has 3 or 4 carbon atoms. The compositions of the present invention will also include a minor amount of a low molecular weight ionomeric polymer or copolymer, that is, one having a weight average molecular weight of between about 1,000 to 20.000 and most preferably between 2,000 to 10,000. In general the ionomeric polymer will have from about 0.1 to about 200 milli-equivalents of pendant ionomeric groups per 100 grams of polymer and preferably from about 1.0 to 100 mili-equivalents of pendant ionomeric groups. Examples of useful ionomeric groups are carboxylate, phosphate, and sulfonate. Preferably the ionomeric groups will also be about 50% neutralized with Group IA, IIA, IB or IIB metal (see the previously cited Table of Elements), an amine or ammonia. The amount of ionomeric polymer or copolymer will be used in amounts ranging below about 20 weight % based on the total weight of the composition and typically in the range of about 0.5 to about 10.0 weight %. Ionomeric polymers and copolymers especially suitable in the practice ofthe present invention include sulfonated polystyrene, sulfonated t-butyl polystyrene, sulfonated ethylene copolymers, sulfonated propylene copolymers, sulfonated styrene- aciylonitrile copolymers, sulfonated styrene-methyl methacrylate copolymers, sulfonated polyisobutylene, sulfonated ethylene-propylene terpolymers, sulfonated polyisoprene, and sulfonated elastomers and their copolymers. A preferred carboxylate ionomeric is ethylene-acryilic acid copolymer. The compositions ofthe present invention can be prepared by any convenient method. For example, the compositions can be prepared by mixing in a suitable blender such as a Brabender mixer. The following examples illustrate the invention. Examples 1 to 5 An ethylene-butene copolymer prepared using a single site catalyst and having a melt index of 4.5, a density of 0.873 g/cc and a polydispersity of about 2.2 was melt blended with varying amounts of an ethylene-acrylic acid copolymer having a weight average molecular weight of 2000 g/mole which were sodium and zinc neutralized, respectively. The melt processing was performed in a Brabender mixer heated at 193°C. The materials were mixed for 5 minutes at 100 RPM. The material was cooled to room temperature, cut into small pieces and subsequently compression molded (193°C) into tensile specimens. The blends were formed into final form via compression molding into approximately 2" x 2" x 0.02" pads using the following conditions; 2 minute preheat at 193°C, followed by 3 minute press cycle at 29 tons (193°C) and finally 4 minute cooling to room temperature (again at 29 tons pressure). The appropriate size sample for the tensile testing measurements are cut from these pads. The mechanical properties were obtained from an Instron® Tensile Tester with a clamp speed of 0.2 cm/min. Table 1 which follows lists typical mechanical property values for the copolymer into which varying amounts ofthe low molecular weight ionomers (sodium and zinc salts) were melt blended. Also included in the table for comparison purposes are the mechanical properties of unblended polymer. TABLE 1 MECHANICAL PROPERTIES AND TORQUE REDUCTION MEASUREMENTS lonomcr Modulus Energy to Break Torque Elongation at Tensile Additive (%) (PSI) (in lbs) Reduclion (%) Break (%).) Strength (PSI) Comparative 1 Sodium Salt 0.0 301 0 12 70 0.0 1059.0 1905.0 Example 2 Sodium Salt 1.0 680 0 13 50 20.0 1074.0 1657.0 Example 3 Sodium Salt 5 0 1091.0 I I 50 18.0 1018.0 1396.0 Example 4 Zinc Salt 1.0 701.0 18 0 14.0 1099.0 1776.0 Example 5 Zinc Salt 3 0 918 0 17 9 17.0 1099.0 1728.0 Example 6 Zinc Salt 5 0 1078 0 15 8 16.0 1069.0 1677.0 The data confirms that addition of a low molecular weight ionomer to the ethylene copolymer product markedly reduces the torque and, therefore, enhanced processability is observed. In addition, the solid state properties show an enhancement in mechanical properties, i.e., toughness.

Claims: CLAIMS: 1. A polymer composition of improved toughness comprising a major amount of an ethylene alpha olefin copolymer prepared using a single site catalyst of a cyclopentadienyl derivative of a Group IVB metal; and a minor amount of a second polymer or copolymer having a weight average molecular weight in the range of about 1 1,000 to about 20,000 and from about 0.1 to about 200 milli-equivalents of pendant ionic groups selected from carboxylate, phosphate and sulfonate groups that are about 50% metal, amine or ammonia neutralized, the composition having improved toughness over that ofthe ethylene alpha olefin copolymer. 2. The composition of claim 1 wherein the second polymer has a weight average molecular weight in the range of about 11,000 to about 20,000. 3. The composition of claim 1 wherein the second polymer or copolymer is present in an amount ranging from 0.5 to 20 wt.% based on the total weight ofthe composition. 4. The composition of claim 3 wherein the ionic group is a carboxylate group. 5. The composition of claim 4 wherein the ionic group is metal neutralized. 6. The composition of claim 5 wheren the alpha olefm of the ethylene alpha olefin polymer has from 3 to 12 carbon atoms. 7. The composition of claim 6 wherein the second polymer is an ethylene-acrylic acid copolymer.

Inventors: CHLUDZINSKI JAMES JOSEPH, ERDERLY THOMAS CRAIG, LUE CHING-TAI, PEIFFER DENNIS GEORGE, CHLUDZINSKI, JAMES, JOSEPH, ERDERLY, THOMAS, CRAIG, LUE, CHING-TAI, PEIFFER, DENNIS, GEORGE
Applicants: EXXON RESEARCH ENGINEERING CO, EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1996
Main classification: C08L23
IPC codes: C08L23