Living Anionic Polymerization of 2-Isopropenylthiophene Derivatives

High Resolution Image Download MS PowerPoint Slide The anionic polymerization of 2-isopropenylthiophene ( 1 ), 2-(1-adamantyl)-5-isopropenylthiophene ( 2 ), 5-phenyl-2-isopropenylthiophene ( 3 ), and 2-cyano-5-isopropenylthiophene ( 4 ) was performed in tetrahydrofuran (THF) with various initiators including sec -BuLi, oligo(α-methylstyryl)lithium, potassium naphthalenide, and diphenylmethylpotassium at −78 °C. The anionic polymerization of 2 – 4 proceeded quantitatively to provide novel polymers with the predicted molecular weights and narrow molecular weight distributions ( M w / M n < 1.2), whereas the polymerization of 1 often suffered from side reactions, probably due to proton abstraction on the thiophene ring. After the complete polymerization at −78 °C, the propagating carbanion of the resulting polymers of 2 – 4 can be depolymerized to give the starting monomer by elevating the temperature to 0 °C. In particular, 3 showed a reversible equilibrium polymerizability similar to that of α-methylstyrene by varying the temperature of the polymerization system. From the plot of logarithm of equilibrium monomer concentration, ln[M] e, against reciprocal temperature, the thermodynamic parameters, Δ H and Δ S, and the ceiling temperature ( T c ) of the anionic polymerization of 3 in THF were estimated to be −8.09 ± 0.22 kcal mol –1, −27.3 ± 0.9 cal mol –1 K –1, and 24 °C, respectively.