CONJUGATED IONIC POLYACETYLENES .7. OLIGOMERIZATION OF N-METHYL-2-ETHYNYLPYRIDINIUM (TRIFLUOROMETHYL)SULFONATE IN METHANOL AND PYRIDINE

Ionic oligomerization of the acetylenic bond in N-methyl-2-ethynylpyridinium (trifluoromethyl)sulfonate (triflate) monomer initiated by nucleophiles was investigated in methanol and pyridine at room temperature. Pyridine and pyridine derivatives were used as initiators, and the resulting reactions were monitored by FTIR, UV-visible, and NMR spectroscopy. The monomer is stable in the absence of nucleophiles. In methanol the reaction between the monomer and the solvent is very slow. There is no reaction between the initiator and the monomer if the heteroatom in the initiator cannot be quaternized. After initiation by an appropriate nucleophile, termination by protonation takes place followed by chain transfer to solvent, and the primary zwitterion is converted into 1-pyridiniumyl-2-(N-methylpyridiniumyl)ethylene triflate methoxide. Methoxide anions react also with the monomer and form methoxyvinyl(N-methylpyridinium) triflates. The initiation was found to be of first order with respect to the initiator and apparent zero order with respect to the monomer in the studied concentration range. Dissolving the monomer in pyridine results in a rapid formation of a black solid. The products are linear zwitterionic polyacetylene oligomers (yield = 96%). Formation of some cyclized byproducts can also be detected. The rate-determining step is the initiation. No obvious mechanism of termination has been identified in pyridine. A general reaction mechanism is proposed for the polymerization of acetylene triple bond activated by the N-methylpyridinium group.