Oligomers and soluble polymers from the vinyl polymerization of norbornene and 5-vinyl-2-norbornene with cationic palladium catalysts

Oligomeric vinyl polynorbornene (2 to similar to 12 monomer units) was obtained via hydrooligomerization of norbornene (NB) using the cationic palladium complexes [Pd(PPh3)(n)(NCCH3)(4-n)](BF4)(2) [n = 0(1), 3(2)] at different hydrogen pressures. The vinyl polymerization of norbornene (NB) in the ionic liquid N-butyl-N-trimethylammonium bis(trifluoromethylsulfonyl)imide (BtMA(+)NTf(2)(-)) with [Pd(NCCH3)(4)](BF4)(2) led to soluble polynorbornenes (with several hundred monomer units) at different temperatures and molar NB:Pd ratios. The norbornene derivative 5-vinyl-2-norbornene (VNB) was oligomerized in high yield with 1 in CH3NO2 primarily through the (endocyclic) norbornene double bond but also through both the norbornene and (exocyclic) vinyl double bond for about every second monomer (by H-1 NMR). A 2D H-1,C-13-HSQC NMR analysis suggests a beta-hydrogen elimination after insertion of a norbornene double bond as chain-termination mechanism. The conversion of NB or VNB increased with temperature and a lower NB:Pd and VNB:Pd ratio, respectively. The vinyl double bond in VNB slowed down the insertion rate drastically when compared with NB (activity decrease by a factor of 10(2)). (C) 2010 Elsevier B.V. All rights reserved.