Synthesis of high‐molecular‐weight poly(dimethylsiloxane) of uniform size by anionic polymerization, 1. Initiation by a monofunctional lithium siloxanolate

An improved procedure for the anionic polymerization of hexamethylcyclotrisiloxane (D 3 ) initiated by a monofunctional lithium derivative is reported. The initiator seeding solution is preferably prepared in benzene, and tetrahydrofuran is used as a cosolvent which makes the presence of additional promoters useless. The main advantage of this procedure is that it delays the appearance of bimodality which is believed to result from a sudden change in aggregate molecularity during the course of the reaction. Applying this method, poly(dimethylsiloxane) samples having a single functional endgroup and possessing high molecular weights and narrow molecular weight distributions (1,03 ≤ M̄ w /M̄ n ≤ 1,06) were prepared on the 100 g scale.