Process of producing high molecular weight ethylene-.alpha.-olefin elastomers with an indenyl metallocene catalyst system

A process for producing an ethylene/.alpha.-olefin elastomeric copolymer in slurry polymerization, comprising the steps of:

• adding an .alpha.-olefin monomer to a reaction vessel in an amount and under a pressure sufficient to allow utilization of said .alpha.-olefin in a liquefied state as a polymerization diluent;
• adding ethylene to said .alpha.-olefin polymerization diluent in an amount sufficient to maintain a desired ethylene/.alpha.-olefin ratio in the liquid phase in the reaction vessel, and;
• adding to the mixture of monomers a supported metallocene/alumoxane catalyst complex which has been prepolymerized with ethylene or an .alpha.-olefin to a weight increase of at least 50% based on the total weight of the catalyst and support material wherein the catalyst support is an alumoxane treated inorganic oxide and the metallocene component of the catalyst is of the formula:
• ##STR5## where M is zirconium, titanium, or hafnium;
• each R.sup.1 and R.sup.2 is independently a C.sub.1 to C.sub.20 linear or branched alkyl;
• each X independently is a halide, hydride, alkyl, or aryl;
• and "y" and "z" are independently integers of 0, 1 or 2;
• reacting the mixture of olefin monomers for a time sufficient to permit copolymerization of said ethylene and .alpha.-olefin monomers to an ethylene/.alpha.-olefin elastomeric copolymer, wherein said process has less agglomeration and fouling than the process using bridged metallocene catalysts.