Controlled Vinyl-Type Polymerization of Norbornene with a Nickel(II) Diphosphinoamine/Methylaluminoxane Catalytic System GEORGIOS C. VOUGIOUKALAKIS, 1 IOANNIS STAMATOPOULOS, 1 NIKOLAOS PETZETAKIS, 1 CATHERINE P. RAPTOPOULOU, 2 VASSILIS PSYCHARIS, 2 ARIS TERZIS, 2 PANAYOTIS KYRITSIS, 1 MARINOS PITSIKALIS, 1 NIKOS HADJICHRISTIDIS 1 1 Department of Chemistry, University of Athens, Panepistimiopolis Zografou, Athens 15771, Greece 2 Institute of Materials Science, NCSR ‘‘Demokritos’’, Agia Paraskevi Attikis, Athens 15310, Greece Received 10 June 2009; accepted 12 June 2009 DOI: 10.1002/pola.23573 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: A novel nickel-based complex coordinated with an asymmetric diphosphi- noamine ligand was synthesized and fully characterized. Single crystals of good qual- ity were also obtained, and the solid-state structure of the complex was studied via X-rays diffraction. The catalytic activity of this Ni(II) complex in the vinyl-type poly- merization of norbornene was studied with methylaluminoxane (MAO) as the cocata- lyst/activator. The influence of the reaction time, the equivalents of MAO used, and the concentration of the monomer on: (i) the activity of the catalytic system; (ii) the isolated yield of the polymer; and (iii) the molecular weight and molecular weight distribution of the polymer were investigated. The isolated polynorbornene (PNB) yields are significantly higher compared with those reported for other similar nickel- based systems. The as-obtained PNBs are characterized by high molecular weights and relatively narrow and monomodal molecular weight distributions (amongst the narrowest reported in the literature). The linear dependence of the molecular weight of the obtained PNB on the concentration of norbornene points toward a controlled polymerization reaction. V V C 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5241–5250, 2009 Keywords: catalysts; gel permeation chromatography; methylaluminoxane; NMR; norbornene; vinyl polymerization INTRODUCTION The development of the transition metal-based Ziegler-Natta olefin polymerization catalysts, in the early 1950’s, 1 has served as the foundation for an amazing research field that still attracts a vast amount of interest both in industry and aca- demia. 2 By the utilization of these transforma- tions, a wide variety of high-performance polyole- fin materials has been developed. 3 In this context, polycycloalkenes derived from vinyl- (or addition) type polymerization or copolymerization repre- sent a fascinating family of materials due to their very interesting properties and potential applica- tions. 4 Bicyclo[2.2.1]hept-2-ene, better known as nor- bornene (NB), is perhaps the most popular Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 47, 5241–5250 (2009) V V C 2009 Wiley Periodicals, Inc. Additional Supporting Information may be found in the online version of this article. Correspondence to: N. Hadjichristidis (E-mail: hadjichristidis@chem.uoa.gr) and P. Kyritsis (E-mail: kyritsis@ chem.uoa.gr) 5241