Styrene-ethylene co-oligomerization with bis-(diphenylphosphino)-amine/ chromium catalysts and the use of the co-oligomerization products in copolymerization reactions with metallocenes
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 13C NMR analysis. Assignments of the 13C 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. © 2008 Wiley Periodicals, Inc.