Monodisperse Polymeric Microspheres Synthesized By Photoinitiated RAFT Dispersion Polymerization

Dispersion polymerization is a facile method to synthesize monodisperse microspheres with diameters ranging from 1 to 15 μm However, the nucleation stage is so sensitive which is difficult to prepare monodisperse functional microspheres by dispersion polymerizatioa. Reversible addition-fragmentation (RAFT) polymerization has been widely used in dispersion polymerization due to its mild reaction conditions and wide monomer range. However, low yields of polymeric microsphere were usually observed in RAFT dispersion polymerization due to its low polymerization rate. Photo initiated polymerization is a technique that can be carried out at room temperature with a high polymerization rate. In this thesis, photoinitiated polymerization and RAFT polymerization were introduced in dispersion polymerization. Different types of monodisperse microspheres were synthesized by photoinitiated RAFT dispersion polymerization.1. Monodisperse poly(methyl methacrylate) (PMMA) microspheres were synthesized by photoinitiated RAFT dispersion polymerization in an ethanol/water mixture. According to the results of SEM images and yields at different irradiation times, we found that the nucleation of photoinitiated RAFT dispersion polymerization was at around 60 min. The concentrations of photo initiator and stabilizer had little-to-no effect on the particle uniformity. Monodisperse microspheres were obtained with the concentration of RAFT agent ranging from 0.25-0.75 wt%. We found that the diameter of microspheres became larger as the monomer concentration or the content of ethanol in the medium increased.2. Highly monodisperse carboxyl-functionalized PMMA microspheres were prepared by photoinitiated RAFT dispersion polymerization by adding methacrylate acid (MAA) at the beginning. The results showed that monodisperse carboxyl-functionalized microspheres were obtained with 2 wt%,6 wt% or even 10 wt% MAA in the presence of 0.5 wt% BDMAT However, only polydisperse PMMA microspheres were obtained using DDMAT as the RAFT agent. In addition, the effects of reaction conditions on the carboxyl-functionalized PMMA microspheres were investigated in detail. According to the results of particle yields, we found that the polymerization rate increased first and then decreased as the MAA concentration increased. The content of carboxyl groups on the surface of microspheres was determined by conductivity titration, and Ag/PMMA composite microspheres were prepared by taking advantage of carboxyl groups on the surface of PMMA microspheres. TEM images showed that silver nanoparticles were covered on the surface of the PMMA microspheres, and Ag/PMMA composite micropsheres exhibited catalytic activity for the decomposition of methylene blue.3. Monodisperse poly(glycidyl methacrylate) (PGMA) microspheres have been synthesized by photo initiated RAFT dispersion polymerization The polymerization exhibited a fast reaction rate with 95% yield being reached within 2 h of UV irradiation. The mechanism of photoinitiated RAFT dispersion polymerization was investigated and the effects of photoinitiator concentrations, RAFT agent concentrations and reaction medium on polymeric microspheres were studied. PGMA-NH2 microspheres were prepared by treating PGMA microspheres with ethylene ethylenediamine (EDA), and the obtained product was characterized by FT-IR and XPS. Au/PGMA composite microspheres or gold plates were obtained by using PGMA-NH2 microspheres as the template. In addition, covalently cross-linked colloidosomes were formed by cross-linking of the primary amino group on the particle surface using (tolylene 2,4-diisocyanate-terminated poly(propylene glycol) (PPG-TDI) as a cross-linker. We found that the particle size of colloidsomes decreased as the concentration of PGMA-NH2 microspheres increased.