Synthesis and properties of poly (N-methyl-3-ethynyl carbazole)

Abstract

N-methyl-3-ethynylcarbazole(NMEC) was synthesized by the reaction of n-BuLi with N-methyl-3-(2,2-dibromovinyl) carbazole which was obtained from the Wittig reaction of N-methyl-3-formylcarbazole. The polymerization of N-methyl-3-ethynylcarbazole was attempted by $WCl_6$ and $MoCl_5$ -based catalysts under various reaction conditions. It was also attempted by Ziegler-Natta catalysts. The polymer yield and inherent viscosity were found to be dependent on the polymerization time. The catalytic activity of $WCl_6$ was greater than that of $MoCl_5$. In the polymerization of N-methyl-3-ethynylcarbazoel by Ziegler-Natta catalysts, it was found that the activity of catalysts containing $Ti(OBu)_4$ was very low. The structure of obtained polymer was identified by IR, $^1H$-NMR spectroscopy. The infrared spectrum of poly(NMEC) showed characteristic absorption bands at $3080 cm^{-1}\; (\nu=C-H)$ and $1620 cm^{-1} (\nu C=C)$. In the $^1H$-NMR spectrum, an aliphatic proton peak of N-$CH_3$ appeared at around 3.8ppm, and the proton on conjugated chain and aromatic proton of carbazole at 5.8-8.2ppm. And also, this polymer showed a broad, weak $\pi \rightarrow \pi^*$ absorption appeared in the range of 300-500 nm, the feature of conjugated polymer. From these results, it is concluded that the polymer involves a linear conjugated polyene structure containing carbazolyl substituent. TGA exhibited that poly(NMEC) retained 90\% of its original weight at 375-395$^\circ$C.