Nonequilibrium Anionic Ring-opening Polymerization of Tetraphenyltetramethylcyclotetrasiloxane (D₄^Me,Ph) Initiated by Sodium Isopropoxide

GRAPHICAL ABSTRACT

Abstract

The nonequilibrium anionic ring-opening polymerization (NAROP) of tetraphenyltetramethylcyclotetrasiloxane (D₄^Me,Ph) in the presence of initiator (sodium isopropoxide) and promoters including 12-crown-4, N-methyl-2-pyrrolidinone (NMP), N,N-dimethylformamide (DMF), and diglyme was investigated. It was found that the polymerization could be accelerated sharply by the increase of reaction temperature, as well as the mole ratio of promoter to initiator ([p]/[i] ratio). The NAROP rate of D₄^Me,Ph decreased in the order of promoters: 12-crown-4>> NMP >DMF >diglyme. In the presence of NMP and sodium isopropoxide ([p]/[i] ratio = 3.0, 10 h at 70°C), the polydispersity index (PDI) of the poly(methylphenylsiloxane) obtained is 1.52, and the conversion rate of the monomer can reach over 90%. The byproduct pentaphenylpentamethylcyclopentasiloxane (D₅^Me,Ph), which encountered in the 12-crown-4 promoted system upon prolonged reaction time, was not observed according to the ²⁹Si NMR of the reaction mixtures. In conclusion, NMP turned out to be the best choice among those promoters to realize the NAROP of D₄^Me,Ph.

Keywords:

• Anionic polymerization
• kinetics
• backbiting reaction
• promoter