Polymerization of 2-ethynylthiophene by $WCI_6$ and $MoCl_5$-based catalysts

Abstract

2-Ethynylthiophene(2-ET) was prepared by the reaction of n-Buthllithium with 2-(2,2-dichloro-1-fluorovinyl) thiophene which was obtained from the reaction of lithiothiophene with, 1,1-dichloro-2,2-difluoroethylene($CF_2 = CCl_2$). The polymerization of 2-ethynylthiophene was attempted by $WCl_6$ and $MoCl_5$ associated with cocatalyst such as organotin and organoaluminum compounds under various reaction conditions. The polymer yield and inherent viscosity were found to be strongly dependent on the mole ratio of monomer to catalyst, and $Ph_4$ Sn and $n-Bu_4Sn$ were very effective cocatalyst in the polymerization of 2-ethynylthiophene using $WCl_6$. The catalytic activity of $WCl_6$-based catalyst was greater than that of $MoCl_5$-based catalyst. The structure of polymer was identified by $^1H-NMR$, IR spectroscopy and elemental analysis. A broad peak appeared at 5.5-7.5 ppm is the $^1H-NMR$ spectrum which was assigned to the protons on conjugated chain and thienyl substituent. IR spectra showed the vinyl C-H stretching band at $3080 cm^{-1}$ and C=C stretching band at $1600 cm^{-1}$. The elemental analysis agreed with theoretical value. From these results, it is concluded that the polymer involves a conjugated linear polyene structure containing thienyl substituent. And also, this polymer showed a broad, weak $π → π^*$ absorption appeared in the range of 300-500 nm and strong emission spectrum, the feature of conjugated polymer. TGA and DSC exhibited that poly(2-ethynylthiophene) retained 95% of its original weight at 345-358℃ and it showed high softening point(227-250℃). From the consequence of copolymerization with phenylacetylene, it was found that the reactivity of 2-ET was slightly greater than that of phenylacetylene in the copolymerization using $WCl_6$.