The class of rubbery ethylene-propylene copolymers, conventionally referred to as EPR polymers, is well known and has gained substantial commercial acceptance. The copolymers are known to have good properties such as weatherability, ozone resistance and thermal stability and the polymers have accepted utility in automotive applications, as construction materials and as wire and cable coatings, among others. However, conventional ethylene-propylene rubbery copolymers are often difficult to process unless compounded by relatively large amounts of other materials. In many instances the ease of processing the EPR (ethylene-propylene rubber) copolymer depends upon how "rubbery" the copolymer is. In general, the more elastomeric the copolymer is, the more easily it will be processed.
A number of proposals have been made to improve the processability of the ethylene-propylene rubbery copolymer. In Yamamoto et al, U.S. Pat. No. 4,125,699, there are disclosed ethylene-propylene copolymers having a relatively high ethylene content produced in the presence of vanadium-containing polymerization catalysts. The copolymers of Yamamoto et al are said to have improved processability because of a relatively high molecular weight distribution. Vanadium catalysts, however, are of relatively low activity and many, if not most, of the more recent commercial ethylene-propylene rubbery copolymers are produced with a titanium-based catalyst because of the higher catalytic activity available through the use of such catalysts.
In determining the elastomeric character of an ethylene-propylene rubbery copolymer, a probable very important factor is the distribution of the monomeric moieties throughout the copolymer. Without wishing to be bound by an particular theory, it appears likely that each monomer, ethylene for example, can serve to disrupt the crystallinity of the portion of polymerized other monomer, e.g., propylene, through the prevention of blocks of either monomer. This disruption results in less crystallinity in the copolymer molecule and increased elastomeric character. If the ethylene and/or propylene polymerized predominantly in blocks, the structure of the resulting copolymer would be "blocky" and the elastomeric character would be relatively low. Alternatively, a highly random structure would lead to greater elastomeric character and an improvement in properties such as processability.
In published Japanese Patent Application 58217507-A there is disclosed the use of a catalyst complex derived from titanium trichloride, an organoaluminum compound and a phosphorus compound containing a P=O moiety, the catalyst preparation being conducted in the presence of an ether. The product is said to have random character and good processability. A related copolymer produced with the use of a titanium tetrahalide-derived catalyst is disclosed by Makino et al, U.S. Pat. No. 4,506,061. The copolymer is also said to have a high degree of randomness in the copolymerization. It would be of advantage, however, to provide additional ethylene-propylene rubbery copolymer compositions of improved random polymerization character and improved processability.
USPTO Backgrounds
USPTO Backgrounds