Study On Anionic Ring-opening Polymerization Of D₄ In Miniemulsion

As a new technique, miniemulsion polymerization is attracting more and more concerns for its nucleation mechanism, emulsification system and process. Up to the present most researches of miniemulsion polymerization focus on radical reactions while few has been done on D4 anionic ring-opening miniemulsion polymerization. Based on the background of siloxane cationic polymer emulsions used mainly for fabric softening, miniemulsion polymerization of octamethylcyclotetrasiloxane (D4) by anionic ring-opening reaction was achieved in this work. Scientific researches such as the preparation and stability of D4 cationic miniemulsions, reaction mechanism, nucleation mechanism and kinetics of anionic ring-opening miniemulsion polymerization about this system were carried out.As monomer droplet nucleation predominates during the miniemulsion polymerization, the droplet sizes determine both the reaction mechanisms and the stability of miniemulsion. Preparation of D4 cationic miniemulsions were studied. The results indicate that dissolve and diffuse of cosurfactant, coating of droplet covered by surfactant, cooperation between cosurfactant and surfactant, and intensity of homogenize influence the miniemulsion stability remarkably. Some stable D4 miniemulsions with narrow droplet sizes distributions and small average sizes less than 100nm have been synthesized for D4 ring-open anionic miniemulsion polymerization by homogenization under the condition of surfactant and cosurfactant in small amount.After stable monomer miniemulsions had been prepared, anionic ring-opening polymerization of D4 in miniemulsion was studied, including reaction mechanism, polymerization rules and nucleation mechanism. According to the relations of polymerization velocity and viscosity average molecular weight versus conversion, the mechanism of D4 anionic ring-opening polymerization in miniemulsion was developed. Effects of variations on the rate of polymerizationwere investigated, including reaction temperatures, concentrations of catalyst, surfactant and cosurfactant. Different feature 'between miniemulsion polymerization and conventional emulsion polymerization was proved that monomer droplet nucleation predominates during anionic ring-opening miniemulsion polymerization of D4.On the kinetics study preliminarily, the number of polymer chainsmodel - = kl[D4]t -k'cNf and the propagation velocity model were established. Kinetics analysis and computerizedsimulation are in good agreement with a reaction scheme. The apparent rate constants of initiation, propagation and condensation at various temperatures and the corresponding activation energies were determined.In conclusion, some stable polydimethylsiloxane cationic miniemulsions with narrow droplet size distributions and small average sizes were synthesized through D4 anionic ring-opening miniemulsions polymerization. On such a notable industry background, the study on anionic ring-opening miniemulsion polymerization of D4 including preparation and stability of D4 cationic miniemulsions, reaction mechanism, nucleation mechanism of latex particles and kinetics are valuable to the application and development of this polymerization technique.