Ethylene-styrene (or 4-methylstyrene) co-oligomerization using various bis(diphenylphoshino)amine ligands in combination with chromium is discussed. GC analysis of the reaction mixture shows that various phenyl-hexene and phenyl-octene isomers are formed either through cotrimerization or cotetramerization. It seems that the more bulky ligands display lower selectivity to co-oligomerization and favor ethylene homo-oligomerization. Subsequent copolymerization of the oligomerization reaction mixture using a metallocene polymerization catalyst results in a copolymer with a branched structure as indicated by Crystaf and C-13 NMR analysis. Assignments of the C-13 NMR spectrum are proposed from an APT NMR experiment combined with calculated NMR chemical shift data using additivity rules. An indication of the ability of the different co-oligomerization products to copolymerize into the polyethylene chain could be established from these assignments. Unreacted styrene and the more bulky isomers, 3-phenyl-1-hexene and 3-phenyl-1-octene, are not readily incorporated while branches resulting from the other isomers present in the co-oligomerization reaction mixture are detected in the NMR spectrum. (c) 2008 Wiley Periodicals, Inc.