Process of producing thermoplastic polymer blends

Abstract

A process is described for producing a polymer blend comprising (a) a first polymer component comprising a crystalline propylene polymer and (b) a second polymer component comprising a copolymer of propylene with at least one comonomer, wherein the copolymer comprises between about 7 wt % and about 28 wt % of comonomer and the copolymer has a heat of fusion of 0.5 to 70 J/g and an mm triad tacticity of 75% or greater. The process comprises polymerizing propylene under first polymerization conditions in a polymerization reaction zone to produce a first effluent comprising a crystalline propylene polymer containing no more than 10% by weight of other monomers, the first polymerization conditions comprising a first reaction temperature between about 50° C. and about 100° C. Propylene is then copolymerized with at least one comonomer under second polymerization conditions in the presence of a metallocene catalyst and at least part of said first effluent in a slurry polymerization reaction zone to produce the second polymer component as a blend with the first polymer component, the second polymerization conditions comprising a second reaction temperature at least 7° C. less than the first reaction temperature.