Abstract
Hexamethylcyclotrisiloxane (D~3~), octamethylcyclotetrasiloxane (D~4~), and decamethylcyclopentasiloxane (D~5~) were equilibrated with potassium tert‐butoxide or triflic acid in bulk at 100 °C to elaborate the ^1^H NMR and ^13^C NMR spectra, SEC elution curve, and MALDI‐TOF (MT) mass spectrum of a fully equilibrated poly(dimethylsiloxane). Surprisingly, triflic acid did not effect complete equilibration (even after 360 h), seemingly because cleavage of Si–C bonds eliminates the acidic proton. Large amounts of D~4~ and D~5~ together with small amount of D~6~ were formed in the early stage of the polymerization in contrast to potassium alkoxide‐catalyzed polymerizations. The usefulness of numerous metal triflates as polymerization catalysts of D~3~ was explored, and only the most acidic ones were active. Bismuth and hafnium triflate catalyzed a polymerization mechanism similar to that of triflic acid but were more active despite their poor solubility. BiCl~3~ and HfCl~4~ were considerably less reactive and the polymerization kinetics were quite different from those of the metal triflate catalyzed polymerizations. The decisive role of acidic protons was revealed by addition of a proton scavenger. Bismuth triflate proved to be an interesting and useful catalyst because it combines the highest activity with poor solubility and low toxicity.
magnified image