Catalytic 1,3-Cyclohexadiene Homopolymerization and Regioselective Copolymerization with Ethylene Dirk E. Heiser, 1 Jun Okuda, 2 Sandro Gambarotta, 3 Rolf Mu ¨lhaupt* 1 1 Freiburger Materialforschungszentrum und Institut fu ¨r Makromolekulare Chemie der Albert-Ludwigs-Universita ¨t Freiburg, Stefan-Meier-Str. 21, D-79104 Freiburg i. Br., Germany Fax: 0049 (0)761 203 4709; E-mail: rolf.muelhaupt@makro.uni-freiburg.de 2 Rheinisch-Westfa ¨lische Technische Hochschule Aachen, Professor-Pirlet-Str. 1, D-52056 Aachen, Germany 3 Department of Chemistry, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada Received: September 15, 2004; Accepted: October 25, 2004; DOI: 10.1002/macp.200400384 Keywords: catalysis; 1,3-cyclohexadiene polymers; cycloolefin copolymers; ethylene copolymerization; half-sandwich complexes; polyolefins Introduction During the past fifteen years the remarkable progress in single-site catalyst technology has offered new opportu- nities for designing advanced polyolefin materials. [1] As a function of defined coordination complex structure of metallocene and post-metallocene catalysts it is possible to tailor new polymer architectures based upon ethylene, pro- pylene, styrene and norbornene. [2–4] Ethylene/cycloolefin copolymers are prepared either by single-site catalysts or by means of catalytic hydrogenation of homo- and copoly- mers, prepared by ring opening metathesis polymerization (ROMP). [4,5] In addition to norbornene and other multicy- clic olefin monomers [4,6] also cyclopentene [7] was applied successfully to prepare cycloolefin copolymers (COC). COC exhibit excellent optical and mechanical properties combined with high dimensional stability and very low water uptake. Since the optically transparent COCs are also barrier resins, preventing permeation of moisture and of polar compounds, they are attractive materials for medical packaging applications. [8] In comparison to COC containing five membered rings, much less is known about polyethylenes containing six- membered rings in the backbone. In contrast to cyclopen- tene, cyclohexene fails to homo- and copolymerize in polyinsertion reactions. As alternative synthetic route, 1,3- cyclohexadiene (CHD) can be polymerized to obtain repeat units comprising six-membered rings. Early research in CHD polymerization includes free-radical, anionic and Ziegler-type catalysis yielding amorphous products with low molecular weights, broad molecular weight distribu- tions and poor regioselectivities. [9] Innovations in anionic polymerization techniques in the late 1990s improved the molecular weights of soluble cyclohexadiene homo- and Summary: 1,3-Cyclohexadiene (CHD) was homo- and copolymerized by means of diimine nickel complexes and various substituted titanium based half-sandwich complexes activated with methylaluminoxane (MAO). Soluble polycy- clohexadienes were produced with the constrained geometry catalyst [Me 2 Si(N t Bu)(Me 4 Cp)]TiCl 2 (CBT) (Cp ¼ cyclopen- tadienyl, Me ¼ methyl). Only in the presence of CBT/MAO soluble high molecular weight CHD copolymers with ethylene were obtained. The CHD incorporation was varied between 0 and 12.3 mol-%. According to NMR analysis the CHD/ ethylene copolymerization is highly regioselective, account- ing for exclusive formation of 1,4-cyclohexene units randomly distributed in the polyethylene backbone. 13 C NMR spectra of 1,4-poly(1,3-cyclohexadiene-co-ethy- lene) with 6.8 mol-% CHD content in the copolymer. Macromol. Chem. Phys. 2005, 206, 195–202 DOI: 10.1002/macp.200400384 ß 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Full Paper 195