CONJUGATED IONIC POLYACETYLENES .9. POLYMERIZATION OF N-METHYL-2-ETHYNYLPYRIDINIUM TRIFLUOROMETHANESULFONATE IN APROTIC POLAR-SOLVENTS

Ionic polymerization of the acetylene bond in N-methyl-2-ethynylpyridinium trifluoromethanesulfonate (triflate) monomer (HMTf) was investigated at room temperature in aprotic polar solvents such as acetonitrile, DMF, and DMSO. Polymerization was initiated by pyridine and pyridine derivatives and the resulting reactions were monitored by lR, UV-visible, and NMR spectroscopy. Polymerization of HMTf in aprotic polar solvents resulted in incomplete conversions. Conversions were strongly affected by the [monomer]/[initiator] ratio. Reaction rates when initiated with pyridine were not influenced by the polarity of the solvent at the same monomer concentration. Reactivity of initiators decreased in the order alkyl > alkenyl > alkynyl substitution. Ortho-substituted pyridine derivatives were found to be less reactive than the para derivatives. There was no substantial difference with respect to reaction rates and conversions of polymerizations when substituted pyridines were used or the pyridine molecules were linked by ethane, ethylene, or acetylene units. Polymerization of N-methyl-2-ethynylpyridinium triflate proceeds according to a complex zwitterionic/anionic mechanism. Two different kinds of chain growth were found and a general reaction scheme was proposed to account for the experimental findings.