Thermoplastic polymer blends of an EPDM polymer having a high ethylene length index with polyethylene

#Polymer blends of ethylene-propylene-diene (EPDM) polymers with poly-.alpha.-monoolefin polymers, particularly with polyethylene, are known to the art (see U.S. Pat. Nos. 3,176,052; 3,328,486; 3,361,850; and 3,751,521; and Canadian Pat. No. 798,416). Such blends are useful to prepare a broad range of molded products such as tubing, toys, and household and automotive items. For many applications, the item must have high structural integrity and good tensile strength. Unfortunately, polymer blends of EPDM polymers with polyethylene often exhibit low tensile strength.

#To achieve higher tensile strengths, curing or crosslinking agents have been added to such polymer blends to effect chemical changes in the blend (see U.S. Pat. Nos. 3,256,366; 3,564,080; 3,758,643; and 3,806,558). For example, polymer blends described in U.S. Pat. Nos. 3,785,643 and 3,806,558, which are stated to be thermoplastic in nature, are prepared by partially crosslinking the polymers, particularly the EPDM polymers. The polymer blends of the present invention, i.e., physical blends of EPDM polymers having a high ethylene length index (ELI) and polyethylene (PE) polymers, are thermoplastic in nature, yet do not use curing or crosslinking agents in their preparation. Additionally, the tensile strengths of the polymer blends of the invention are far superior to that predicted from the additive individual effects of the polymer components.

#Reference is made to commonly assigned U.S. Pat. No. 3,919,358 which discloses thermoplastic polymer blends of (1) an EPDM polymer having a high degree of unstretched crystallinity with (2) polyethylene. The unstretched crystalline content of the EPDM polymer employed therein was between about 10 percent and about 20 percent as determined by an X-ray diffraction technique. Unexpectedly, it has now been discovered that an EPDM polymer having little or no unstretched crystallinity, but having a high ethylene length index (ELI) can be advantageously used with polyethylene to prepare thermoplastic polymer blends that exhibit superior tensile strengths.

#The following examples are presented to further illustrate the invention. Unless otherwise stated, the ingredients recited in the recipes are used in parts by weight.

#The polymeric components of the blends, along with compounding ingredients, if used, were mixed together using a two-roll mill. The roll ratio was 1.2 to 1 and the front roll had a roll speed of 21 rpm. Roll temperature was about 162.degree. C. The EPDM was banded on the mill and the polyethylene and compounding ingredients (if used) added to the banded polymer. Total mill time was about 5 minutes.

#The mixing conditions and temperatures outlined above were employed to get uniform dispersion of the polymers and ingredients in the thermoplastic blend. This can be accomplished using other equipment, such as a banbury mixer, by mixing at other temperatures and for other times, and the like; all of which conditions and procedures are well known to the artisan. The above conditions were used to achieve good, thorough mixing, and are outlined to illustrate the preparation of the physical blends of the Examples.