Preparation of CO2-Switchable and Water-Redispersible Latexes Using Nitroxide-Mediated Surfactant-Free Emulsion Polymerization
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The main objective of this research project was synthesizing CO2-responsive latexes by nitroxide-mediated polymerization (NMP). Therefore, 2-(diethylamino)ethyl methacrylate (DEAEMA) as a CO2-responsive monomer was chosen for the synthesis poly(DEAEMA) macroinitiator that can be used as a stabilizer for the preparation of poly(methyl methacrylate), PMMA, latexes. NMP of DEAEMA was performed in bulk with excellent control and livingness. The synthesized poly(DEAEMA) was then used in the protonated form as a macroalkoxyamine and stabilizer for the preparation of pH-responsive and CO2-switchable latexes with surfactant-free emulsion polymerization. The resultant latex particles were stable with small particle size and narrow size distribution. To simplify the process, PMMA latexes were prepared by one-pot two-step nitroxide-mediated surfactant-free emulsion polymerization. First, DEAEMA was polymerized for the first time in water and then at high conversions, MMA was added to the reaction media and amphiphilic diblock copolymers were formed, which converted to the latex particles when the hydrophobic block reached to the critical chain length based on polymerization-induced self-assembly (PISA) mechanism. However, the synthesized nanoparticles with poly(DEAEMA) shell and PMMA core were not redispersible after coagulation. It was figured out that the main reason for the irreversible coagulation of latex particles was the low glass transition temperature (Tg) of poly(DEAEMA) which causes the diffusion of the particles shell into each other. Also, it was demonstrated that DEAEMA is hydrolyzed very fast in the basic conditions and high temperatures suitable for NMP. To address these issues, dimethaminopropyl methacrylamide (DMAPMA) was used as another CO2-responsive monomer with higher Tg and also hydraulic stability in the synthesis of MMA and styrene latexes. In this case, the synthesized nanoparticles were redispersible by the stimulation of CO2.