The nucleation study on the cationic miniemulsion polymerization of octamethylcyclotetrasiloxane (D4)

The nucleation of the cationic miniemulsion polymerization of octamethylcyclotetrasiloxane (D₄) has been investigated in detail in this work. The particle size was traced by dynamic laser scattering in the polymerization process using different concentration of dodecylbenzenesulfonic acid (DBSA) as both the initiator and surfactant. The results reveal the progressively decreasing particle sizes with the steadily increasing monomer conversion. The descending particle sizes can be explained by the existence of homogeneous nucleation of hydroxyl-terminated polydimethylsiloxane (PDMS) oligomers in addition to the primary droplet nucleation. A linear relationship between the natural logarithm of the average particle diameter (lnd(t)) and the natural logarithm of the monomer conversion (lnf(t)) is then deduced based on the theory, which has been validated by the experimental data. The slope of lnd(t)~lnf(t) line relies on the parameter of K which is the ratio of PDMS oligomers entering water phase to all PDMS oligomers produced. The influence of DBSA concentration on the K and the fraction of homogeneous nucleation (F(H)) has been then obtained. Both of the values of K and F(H) increase with the increasing DBSA concentrations.