Kinetics of the anionic ring-opening polymerization of octamethylcyclotetrasiloxane initiated by potassium isopropoxide

Kinetics of the anionic ring-opening polymerization of octamethylcyclotetrasiloxane (D-4) in bulk initiated by potassium isopropoxide was studied. Several promoters including N-methyl-2-pyrrolidinone (NMP), N,N-dimethylformamide (DMF), and diglyme were used. It is indicated that the reactions are first-order in D-4 during the initial stage of polymerization. The polymerization rate of D-4 is influenced by a number of factors, such as the nature of promoters, the molar ratio of promoter to initiator (C-p/C-i ratio), and the reaction temperatures. With the use of NMP as promoter, the polymerization rate constant at 30 degrees C is 10.482 h(-1) with the C-p/C-i ratio equal to 3.0. As the C-p/C-i ratio increases, the polymerization rate constant increases sharply and the cyclic oligomers content in polymer decreases evidently. The back-biting reaction that leads to the formation of decamethylcyclopentasiloxane (D-5) occurred in the polymerization of D-4. The rate of the D-5 formation relatively to the rate of D-4 conversion increases with the conversion of D-4. (c) 2006 Wiley Periodicals, Inc.