| Nano-sized polymers have received increasing attention because of their attractive characteristics and potential applications in many fields, such as catalysts, drug delivery carriers, plastic impact modifiers, composite materials, high quality adhesives, paints, and coatings, etc.; A differential microemulsion polymerization was developed in this work for the synthesis of nanosize polymer particles. Compared to the conventional microemulsion polymerization methods, the differential microemulsion polymerization method requires much less surfactant and the reactions can be carried out at much milder conditions, and it is controllable and flexible in obtaining nanoparticles of less than 20 nm, which is difficult to be realized in the conventional methods.; Using the differential microemulsion polymerization method, experimental investigation for nano-sized particles of poly(methyl methacrylate) (PMMA) and polystyrene (PS) was carried out. The particle size of PMMA could be reduced to less than 15 nm (z-average diameter) with a solid content of about 13 wt% and a surfactant/monomerweight ratio of 0.1. The PS particles could be prepared with a size of 23 nm with a solid content of 13 wt% and a surfactant/monomer weight ratio 0.33. These significant differences between these two systems were well interpreted in this thesis by nucleation mechanisms. It is proposed that the homogeneous nucleation mechanism is the dominant mechanism in the differential microemulsion polymerization of methyl methacrylate (MMA), whereas, the heterogeneous nucleation prevails in the process for nano-sized polystyrene.; Based on the understanding of the particle nucleation mechanisms, a two-stage differential microemulsion polymerization was further developed and the experimental results confirmed that it was a very effective method for improving the polymerization performance in making smaller polymer particles. For example, PMMA/PS nanoparticles with PMMA nanoparticles as the seeds were prepared with a size of smaller than 20 nm at very mild conditions.; Modeling and simulation of the differential microemulsion polymerization was investigated and the various nucleation mechanisms were also considered for the synthesis of nano-sized PMMA and PS. The model developed in this thesis can predict the growth trends of the particle size of PMMA or PS during the polymerization process; however, it slightly overestimated it. The model also can provide useful information on the fractional conversion, the monomer conversions in the water phase and in the polymer particle, as well as the average number of free radicals per polymer particle. (Abstract shortened by UMI.)... |
