Anionic polymerization of octamethylcyclotetrasiloxane in aqueous emulsion I: Preliminary results and kinetic study

The synthesis of poly(dimethylsiloxane) (PDMS) by anionic polymerization of octamethylcyclotetrasiloxane (D 4 ) in aqueous emulsion using an emulsifying agent acting also as initiator (benzyldimethyldodecylammonium hydroxide) is described. Stable emulsions of α,ω‐dihydroxy PDMS with an easily controlled molar mass (up to 15 000), a low polydispersity index and high yields were obtained. The amount of cyclics formed (essentially D 4 to D 7 ) is lower than that observed in bulk. Kinetics analysis and computerized simulations are in good agreement with a reaction scheme involving simultaneous polyaddition/polycondensation processes. At high monomer consumption, polycondensation predominates leading to a broadening of the molecular weight distribution (MWD). The apparent rate constants of initiation, propagation and condensation at various temperatures and the corresponding activation energies were determined.