Articles Highly Efficient Ti-Based Catalyst Systems for Vinyl Addition Polymerization of Norbornene Tariqul Hasan, † Tomiki Ikeda, † and Takeshi Shiono* ,‡ Chemical Resources Laboratory, Tokyo Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama 226-8503, Japan, and Graduate School of Engineering, Hiroshima University, Kagamiyama 1-4-1, Higashi-Hiroshima 739-8527, Japan Received March 18, 2004; Revised Manuscript Received July 22, 2004 ABSTRACT: Norbornene polymerization via “vinyl addition” proceeded with (t-BuNSiMe 2Flu)TiMe2 (1) in the presence of various cocatalysts [methylaluminoxane (MAO), modified methylaluminoxane (MMAO), and Ph 3CB(C6F5)4/Oct3Al] at wide range of temperatures (20-80 °C) with high activity. The 1-Ph3CB- (C6F5)4/Oct3Al system produced 4.8 × 10 3 kg of polymer per mole of Ti per hour at 20 °C. All the catalyst systems produced high molecular weight (Mn) polymers. In the 1-MMAO system, the yield and Mn values increased linearly keeping narrow molecular weight distribution against the Al/Ti ratio, suggesting that MMAO should take part not only in the initiation but also in the propagation reaction. The rate enhancement with higher Al/Ti ratio was also observed in the Ph 3CB(C6F5)4/Oct3Al system. The activity of the 1-dried MAO and 1-MMAO systems increased with raising reaction temperature up to 60 °C, whereas that of 1-Ph3CB(C6F5)4/Oct3Al decreased. The polynorbornenes obtained with 1 were amorphous, soluble in halogenated aromatic solvents, and stable up to 420 °C. The film of polynorbornene prepared by solvent casting was highly transparent in the UV-vis region. Introduction Norbornene can be polymerized via three different mechanisms, i.e., cationic, 1 ring-opening metathesis, 2 and vinyl addition. 3 Among these mechanisms, the “vinyl addition” gives the polynorbornene that possesses special properties with high thermal stability, high glass transition temperature (T g ), high transparency, and low birefringence due to its constrained structure of satu- rated carbon skeleton. Such polymeric materials have placed a greater demand on optical plastics in data storage and microelectronics technology. The research on norbornene polymerization with early transition metal single-site catalysts has been directed to ring-opening metathesis polymerization (ROMP) rather than vinyl addition polymerization because bis- (cyclopentadienyl)titanacyclobutane conducts the ROMP of norbornene in a living manner. 4 A variety of transi- tion metal complexes give polynorbornene with the ROMP mechanism. 1,2 The products obtained by ROMP have been commercialized with further modification through vulcanization or hydrogenation of double bond in polymer chain. 5 On the other hand, cationic polym- erization of norbornene gives oligomeric product. 1,3b The polynorbornene obtained via vinyl addition has several advantages because of the bicyclic structure retained in the main chain. Vinyl addition polymeriza- tion of norbornene was studied with TiCl 4 /R 3 Al in the early 1960s 6 and a number of zirconocenes since 1980s. 7 All of them showed very low catalytic activity, and the products produced were insoluble in common solvents. Recently, the monocyclopentadienyltitanium catalyst system, CpTi(OBz) 3 /MAO, was reported to show better activity than the other metallocene catalysts. 8 Late transition metal catalysts were reported to be highly active for vinyl addition polymerization of norbornene. 9-11 In the practical point of view, the improvement of catalytic activity and the precise control of product structures are the targets of polymerization catalysts. In olefin polymerization by group IV single-site cata- lysts, the catalytic activity and the structure of polymer produced depend on the nature of active species, which is the ion pair formed from a metal complex precursor and an activator. Cyclopentadienylamido (CpA) group IV complexes show high performance in olefin polym- erization due to their open coordination sites. 12 We have previously reported that (t-BuNMe 2 SiFlu)TiMe 2 (1) activated with Me 3 Al-free methylaluminoaxane (dried MAO) produced polynorbornene in a living manner at 20 °C with moderate activity. 13 In this paper, we conducted norbornene polymeriza- tion with 1 using various activators to find the most suitable polymerization conditions and investigated the physical properties of the produced polymers. † Tokyo Institute of Technology. ‡ Hiroshima University. * Corresponding author: fax +81-82-424-5494, e-mail tshiono@ hiroshima-u.ac.jp. Scheme 1. Methods of Norbornene Polymerization 7432 Macromolecules 2004, 37, 7432-7436 10.1021/ma049455p CCC: $27.50 © 2004 American Chemical Society Published on Web 09/04/2004