Sterically hindered active centres in cationic polymerization: Tertiary aromatic amines in the polymerization of 1,3-pentadiene initiated by aluminum trichloride in non-polar solvent

Previous work on the polymerization of 1,3-pentadiene initiated by aluminum trichloride (AlCl₃) in non-polar solvent at 20 °C in the presence of triphenylamine (NPh₃) has highlighted a stabilization of the active centres and a solubilization of AlCl₃ induced by NPh₃ Delfour M, Bennevault-Celton V, Anh Nguyen H, Cheradame H, Macedo A. Macromol Chem Phys 2004;205:2312-26]. This paper reports the effect of 9-phenylcarbazole, the structure of which is close to that of NPh₃. The results showed a strong decrease of the insoluble fraction (IF), however this electron donor (ED) was a transfer agent alike NPh₃ (alkylation of aromatic rings by the growing polymer chains). To reduce transfer reaction, the influence of two para-substituted triphenylamines—tribromophenylamine (N(PhBr)₃) and tri-p-tolylamine (N(PhCH₃)₃)—on the polymerization of 1,3-pentadiene was studied in the same conditions. Although the presence of Br substituents has no effect on IF, it induced a decrease in the termination reactions with the counter-ion and the transfer reactions. Concerning methyl groups, it has been shown a strong decrease of IF and a negligible amount of alkylation reaction. Moreover the quantity of grafted molecules was reduced and tri-p-tolylamine reduced both the reactions of cyclization and isomerization. Thanks to the stabilization of the active centres by N(PhCH₃)₃ and probably the solubilization of aluminum trichloride, it was possible to obtain a more precisely defined polypentadiene than ever by cationic polymerization in a non-polar medium.