Influence of Type and Content of Various Comonomers on Long-Chain Branching of Ethene/R-Olefin Copolymers Florian J. Stadler, † Christian Piel, § Katja Klimke, ‡ Joachim Kaschta, † Matthew Parkinson, ‡ Manfred Wilhelm, ‡,⊥ Walter Kaminsky, § and Helmut Mu 1 nstedt* ,† Institute of Polymer Materials, Department of Materials Science, UniVersity Erlangen-Nu ¨rnberg, Martensstr. 7, D-91058 Erlangen, Germany; Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany; Institute of Technical and Macromolecular Chemistry, UniVersity Hamburg, Bundesstr. 45, D-20146 Hamburg, Germany; and Institute of Mechanics, Technical UniVersity Darmstadt, Hochschulstr. 1, D-64289 Darmstadt, Germany ReceiVed June 29, 2005; ReVised Manuscript ReceiVed NoVember 29, 2005 ABSTRACT: One polyethylene and nine ethene/R-olefin copolymers differing in amount (0.4-2.9 mol %) and molar mass of the comonomer were characterized by NMR, SEC-MALLS, and rheology. Samples were polymerized using a [Ph 2 C(2,7-di-t-BuFlu)(Cp)]ZrCl 2 /MAO catalyst, with octene, octadecene, and hexacosene as comonomers, resulting in polymers of M w ≈ 190 kg/mol. The comonomer content was determined by melt- state NMR. For the homopolymer 0.37 and 0.30 LCB/molecule were found by NMR and SEC-MALLS, respectively. Rheological quantities, such as the zero shear rate viscosity (η 0 ), increased with LCB as compared to linear samples of the same M w . The shape of the viscosity function and the linear steady-state elastic compliance (J e 0 ) showed a dependence on comonomer content and length. These findings are used to elucidate the various long-chain branching architectures. The highest comonomer content samples behaved like typical linear polymers in rheological experiments, while those with less comonomer contents were found to be long-chain branched. Besides the comonomer content, the type of comonomer has an influence on the branching structure. Introduction The synthesis and characterization of polyolefins, especially polyethylenes (PE) and ethene/R-olefin copolymers synthesized using metallocene catalysts, have gained great interest in recent years. This is due to several major advantages of these systems over those produced by Ziegler-Natta (Z-N) catalysis. With metallocene catalysis, the molar mass is adjustable over a broad range, 1 and the polymers show a narrow molar mass distribution (MMD). 2,3 Because of the stereo- and regiospecific nature of the catalysts, highly tactic and tailored copolymers may be produced. 4-6 Metallocene catalysts also have a high affinity to incorporate R-olefins into growing chains and are even able to produce homopolymers of these higher R-olefins. 7-9 In contrast, copolymerization of R-olefins with more than eight carbon atoms by Z-N catalysts proves difficult. Polymer chains containing a terminal vinyl group, created in situ, can also act as macrocomonomers, leading to the formation of long-chain branched (LCB) polymers. Single-site catalysts produce a novel structure combination for LCB-PE with narrow molar mass distribution being first reported in patent literature in the mid-1990s. 10,11 The first scientific papers covering this topic were published a few years later. 12-14 Evidence for long-chain branching in metallocene PE (mPE) was published by Wood-Adams et al. 15 using a combina- tion of NMR, SEC, and shear rheology. However, for the quantification of the small amount of LCB by NMR extremely long measurement times, of up to 2 million scans, were needed. Most constrained geometry catalysts found to produce LCB are either half-metallocenes 10,16 or ansa-metallocenes. 17-19 The non-ansa-metallocene Cp 2 ZrMe 2 system, activated with either B(C 6 F 4 ) 3 or methylalumoxane (MAO), was also reported to produce long-chain branches. 1,11,12,19,20 Long-chain branching in metallocene-catalyzed polymerizations is believed to take place via a copolymerization route, with the incorporation of a vinyl-terminated polyethylene chain into a growing polymer chain. 12,21,22 Investigation into the polymerization behavior of several metallocene catalysts revealed that the termination mechanisms were catalyst specific. Depending on the catalyst structure, the termination of chain growth occurred via either -H elimination, hydrogen transfer to the monomer, or chain transfer to the cocatalyst. Further research indicated that catalysts with high vinyl selectivity and good copolymerization ability were the most prominent for producing polymers with modified rheological properties. 23,24 The formation of LCB depends on many different factors, including the presence of comonomers. If R,ω-dienes are incorporated, the additional terminal vinyl groups act as starting points for long-chain branching and thus result in a higher degree of LCB. 24 Initial investigations indicated that R-olefin comono- mers decrease the amount of LCB, as they tend to terminate the growing chain. 25 The resulting vinylidene group at the end of a macromer is believed to be sterically hindered from reintroduction into a growing chain by the short-chain branch residing at the 2-position. Additionally, vinyl-terminated poly- mer chains are sterically hindered from incorporation as LCB due to the short-chain branches in the growing chain and macromonomer. Thus, the degree of LCB tends to decrease with increasing comonomer content. It was shown by Kokko et al., 19 for the catalyst system rac- [Et(Ind) 2 ]ZrCl 2 /MAO, that both the temperature dependence of the viscosity and the viscosity (at an angular frequency of ω ) 0.02 s -1 ) itself decreased when introducing up to 3.4 mol % hexadecene. This finding was explained by a decreasing amount † University Erlangen-Nu ¨rnberg. ‡ Max Planck Institute for Polymer Research. § University Hamburg. ⊥ Technical University Darmstadt. * Corresponding author: e-mail helmut.muenstedt@ww.uni-erlangen.de, Fax +49 9131 852 8321. 1474 Macromolecules 2006, 39, 1474-1482 10.1021/ma0514018 CCC: $33.50 © 2006 American Chemical Society Published on Web 01/19/2006