<p>The copolymerization of an olefin with styrene or of ethylene with propylene or with 1-octene is conducted using catalyst compositions comprising a combination of (i) transition metal complex; (ii) a co-catalyst; and a (iii) polymerization modifier that has been identified by combinatorial analysis to improve polymer or process properties. In one embodiment, ethylene and styrene are copolymerized using (i) (1H-cyclopenta[ l ]phenanthrene-2-yl)dimethyl(t-butylamido)silanetitanium dimethyl; (ii) tris(pentafluorophenyl)boron or a trialkylammonium salt of tetrakis(pentafluorophenyl)borate; and (iii) ethylaluminum bis(N,N-diphenylamide) or di(2,7-dimethyl-6-octene-1-yl)-aluminum N,N-diphenylamide.</p>
