Synthesis and characterization of monodisperse functionalized micron-size polymeric microspheres by two-stage dispersion polymerization.

摘要

This thesis describes the synthesis and characterization of functionalized micronsize particles with a narrow size distribution. Most of these particles were prepared by dispersion polymerization. Some larger particles were prepared by seeded swelling suspension polymerization.; Many research groups have used dispersion polymerization in alcohol to prepare micron-size polymer particles. Unfortunately, this approach fails when various comonomers are included in the reaction. The problems encountered include loss of control of particle size, broadening of the size distribution, odd-shaped particles, and, in the extreme, coagulation of the polymer produced in the reaction. I developed a new process, which I call two-stage dispersion polymerization to synthesize these kinds of particles. My hypothesis was that most of the problems encountered in the past were due to the sensitivity of the nucleation stage. From a mechanistic perspective, the dispersion polymerization process can be separated into two stages, a "nucleation stage" (first stage) and a "particle growing stage" (second stage). The nucleation stage is short but very complex and sensitive, whereas the particle growth stage is long and relatively robust. To avoid the difficulties described above, I designed syntheses in which the problematic reagents (the functional comonomers) were added to the reaction after the nucleation stage was complete. I found that some comonomers added after this point became incorporated into the particles without disturbing the final particle size and size distribution. In this way we prepared dye-labeled, cross-linked or functional group-containing micrometer-size particles with a very narrow size distribution. By varying the amount of monomer added in the second stage, we could control the final particle diameter precisely without changing the narrow size distribution.; Applying this two-stage dispersion polymerization, I also carried out living radical dispersion polymerization with both a degenerative chain transfer agent and a RAFT agent. I could control both the particle composition and the polymer molar mass at the same time.; Oligomeric microspheres obtained in this way were used for seeded swelling suspension polymerization.