Characterization of Norbornene Oligomers

Using metallocene catalysts, characterization of oligomers has been used successfully to facilitate the microstructural analysis of poly(cyclic olefins) [45], in the cases of both cyclopentene and norbornene. In these cases hydrogen was applied as chain transfer agent and the resulting products were christened hydrooligo-mers . 

From mass spectral data alone it is difficult to determine molecular structure or to distinguish between different isomers of the same mass. Therefore, the two norbornene dimers representing 96% of the total were separated and collected by preparative GC and subjected to NMR analysis. The C NMR spectrum of a mixture of the two dimers is shown in Fig. 4.17, along with the spectra of the dimers after separation. 

From the spectra, it is clear that the dimer with m/z 216 is a norbornene dimer terminated with a vinyl group (dimer-4, 113.36 and 141.91 ppm). The compound with m/z 244 is a norbornene dimer with an ethyl and a vinyl group at the head (14.11 and 22.18 ppm) and the tail (113.72 and 142.87 ppm) of the molecule (di-mer-5), respectively. Assignments have been made based on analysis of a C 2D-INADEQUATE spectrum and are presented in Fig. 4.18. Both dimers are enchained in the 2,3-fashion consistent with the proposal based on the NMR analysis of the norbornene polymer made with naked nickel . 

The GC/MS of the trimers shows that, just as with the dimers, there are two isomeric trimers observed with an ethyl head group and a vinyl tail (m/z=338) and two isomeric trimers observed with a hydrogen head group and a vinyl tail (m/z=310). However with the trimers, the relative concentrations of the isomers are more equal than with the dimers. 

The lower molecular weight trimers (m/z=310) were separated and isolated using HPLC techniques. Based on their mass and the structures of the dimers, isomeric forms of vinyl-terminated trimers of norbornene were proposed for these two trimers. This was confirmed by extensive NMR analysis. The H and C 

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