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LC-NMR Analysis of Phenylsilane Polymers
Pinkas, Jiří ; Merna, J. ; Sýkora, Jan
We report the analysis of dehydrocoupling polymerization reactions of phenylsilane via on-flow LC-NMR experiment. The successful separation was achieved by isocratic elution of acetonitrile and aceton (80:20). The separation was solely monitored by 1H NMR detection. The properties of the polymeric product depend on the catalytical system. The products can differ in the molar weight distribution, degree of branching and amount of cyclic and rearranged products. In our particular cases, the weight average molar mass (Mw) varies from several silane units up to 4100 g.mol-1. The branching of polysilanes is monitored by 29Si{1H} INEPT experiment with the polarization transfer from the ortho hydrogen (J~7 Hz). The connectivity within branched unit was established via 1H à 29Si-29Si INEPT-INADEQUATE experiment.
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Detection of Signed Homonuclear Couplings between Low Abundant Nuclei
Blechta, Vratislav ; Schraml, Jan
The subject of this lecture is a modification of CSEc method for detection of signed homonuclear couplings. The new sequence is neither trivial nor simple application of the CSEc but some tricks are used to design broadband pulse sequence without selective pulses. The sequence was proved on a few samples by measuring carbon-carbon two- and three-bond couplings. For the first time signs of 2J(Si-O-Si) couplings were measured on a set of siloxane oligomers with different bond maps. The results will be presented.
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