Tailored Surfactant-ligand Design For Emulsion Atom Transfer Radical Polymerization

Emulsion polymerization undoubtedly plays an important role in polymer industry. The combination of emulsion polymerization and controlled radical polymerization (CRP) presents a new exciting direction for modern polymer reaction engineering.Atom transfer radical polymerization (ATRP) is one of the most versatile CRP techniques, with its implementation in emulsion polymerization system being investigated since 1990’s. However, its development towards industrialization is severely hindered due to several challenges. First, Cu catalyst complex is usually highly hydrophobic, thus preventing the micellar nucleation in emulsion ATRP. Second, a poor control over polymerization and unstable emulsion occur because of Cu catalyst leak to the aqueous phase. Third, residual Cu catalyst is toxic and has negative impacts on the resulting product properties.In order to resolve the aforementioned challenges, we combine surfactants with catalyst ligands based on a novel surfactant-ligand design and summarized our works in this dissertation. The new surfactant-ligand (SL) is well-defined and can be employed in emulsion ATRP to synthesize polymers with sophisticated architecture.The works in this dissertation includes:(1) The synthesis of four well-defined SLs, namely TEDETA-undecylene-PEG1000 (SL-1),TEDETA-undecylene-PEG750(SL-2),PEG 1900-b-P(MMA15-co-GMA12)TE DETA (SL-3), and PEG5000-b-P(MMA38-co-GMA30)TEDETA (SL-4). The emulsification and catalysis abilities of these SLs are evaluated. All of them can help to stabilize MMA emulsion and provide a better control in solution ATRP of MMA.(2) The investigation of emulsion ATRP of BMA with SL-1. The polymerization kinetics is investigated under different initiation conditions, i.e., in aqueous phase or in oil phase. The polymerization loses control when only SL-1 is used, which is located on the surface of the particles. Good control over polymerization with PDI<1.4 is obtained when SL-1 and 1-10% of dNbpy as free ligand are added together. In addition, initiation efficiency of oil-soluble initiators is much higher than that of water-soluble initiators. The micellar nucleation mechanism of emulsion ATRP with SL is also ascertained in this work.(3) The enhancement strategies developed to achieve better control over emulsion ATRP. The deactivation of growing chains is promoted when the particle size decreases to 75 nm, since it compresses the polymerization sites. SL-3 and SL-4 have longer hydrophobic chains and more catalytic sites, thus providing higher possibilities for the reactions between active chains and catalyst, resulting in better control over polymerization.(4) The double role of SL as a Cu capture agent (CA). CA is located on the interface between particles and aqueous phase to prevent Cu migration to the aqueous phase, thus suppressing both the formation of unstable emulsion and the loss of control in polymerization. The role of SL as CA greatly improves the emulsion polymerization stability, latex storage stability, and polymerization control in emulsion ATRP of MMA.(5) The removal of Cu catalyst from PMMA latex synthesized using the designed SL via electrolysis. The efficiency of electrolysis to remove residual Cu from latex particles under various voltages, particle sizes, and Cu catalyst concentrations is investigated. The Cu removal efficiency is more than 99% and the residual Cu is about 10 ppm. We also confirmed the morphology of latex particles, polymer structures, and properties of latex to not be affected by the electrolysis process. In addition, the storage stability of the latex and the aging resistance of polymers after the Cu removal are greatly improved.