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

Oligomeric vinyl polynorbornene (2 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+NTf2−) 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 1H NMR). A 2D 1H,13C-HSQC NMR analysis suggests a β-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 102).

Hydrooligomerization, an ionic liquid as solvent and a norbornene derivative with an α-olefin functionality leads to oligonorbornene, soluble polynorbornene (PNB), and oligo(5-vinyl-2-norbornene) (oligo-VNB), respectively, with cationic palladium catalysts.Figure optionsDownload high-quality image (160 K)Download as PowerPoint slide