Synthesis Of Polymers And Polymeric Particles By RAFT Aqueous Polymerization And Their Applications

As one emerging polymerization method, RAFT polymerization has been widely used in the last decade. During polymerization process, thiocarbonyl compound is introduced as a small molecule chain transfer agent(CTA). This provides the dynamic reversible equilibrium process to the reaction, and equals the polymer degree of free radical growth chain to make the polymerization reaction controlled effectively. How to overcome the disadvantages which the RAFT polymerisation in organic media brings, interests the researchers. RAFT aqueous polymerization, using environmentally-friendly solvents- water as the dispersed media, ensures the controlled molecular weight and molecular weight monodisperse. Therefore, RAFT aqueous polymerization appeals the science researchers of polymerization method. Here, we prepared several different types of polymers or polymer particles using RAFT aqueous polymerization. At the same time, we characterized the polymers in detail and explored their applications. The main contents are as follows:1. We have developed one-step approach for the synthesis of core cross-linked star(CCS) polymers via RAFT-mediated emulsion polymerization in aqueous media. The method is called emulsion polymerization just because the hydrophobic cross-linker is used. In this approach, commercial macromonomers(polyethylene glycol methyl ether methacrylates) are used as the arms and employs small molecular chain transfer agent(CTA), hydrophobic cross-linker(HDDMA), and optional hydrophobic spacing monomer(BMA) as the polymerization recipe to synthesize CCS polymers via direct one-step polymerization in aqueous buffer solution. When we tuned the various polymerization parameters, including buffer concentration, molar ratio of macromonomer/cross-linker/spacing monomer relative to CTA, CCS polymers of high yield and low dispersity were obtained within 4 h. Analysis of polymerization kinetics and macromolecular parameters of the generated polymeric species during the polymerization process led to insights on the mechanistic aspects of the CCS formation process, which was proposed to involve three stages, i.e., polymer chain growth, cross-linking to form CCS, and CCS growth. These CCS polymers could apply in the emulsifier, imaging and drug delivery field.2. The functional CCS polymers were synthesized, using GMA as the comonomer to prepate the arms. Change the GMA percent to prepare two kind of CCS star polymers with different proportional functional groups. The ring-opening reaction and esterification were used to functionanlize the CCS star polymers. In order to broaden the star polymer applications as an emulsifier, star polymers were functionalized by dodecyl mercaptan of different proportions to prepare a series of star polymers with different polarities and different emulsification properties. During emulsifying toluene and n-octanol with the CCS star polymers, we found that CCS star polymers show better emulsifying properties for toluene which get strong polarities. These tuning emulsifiers make great sense.3. At a temperature well above the UCST, cationic polyelectrolytes showing upper critical solution temperature(UCST) were synthesized by reversible addition-fragmentation chain transfer(RAFT) polymerization in water. Analysis of polymerization kinetics, we prove it is excellent pseudo-first-order kinetics RAFT process. The polyelectrolyte concentration, molecular weight and presence of added electrolyte highly affect the cloud point. We also develop another way to obtain polyelectrolytes with different hydrophobic groups, alkylation of a neutral polymer, which were shown to increase the cloud point. The UCST polyelectrolytes would be widely applied in the chemistry, environmental technology and medical science.4. We successfully synthesized new magnetic microspheres grafted with poly(N,N-dimethylacrylamide)(PDMA) that resist nonspecific protein adsorption. Monodisperse macroporous poly(2-hydroxyethyl methacrylate)(PHEMA) microspheres, were synthesized by multiple swelling polymerization method. Iron oxides were precipitated inside the microsphere pores to render the microspheres magnetic. Carboxyl groups were introduced by hydrolysis of 2-(methacryloyl)oxyethyl acetate(HEMA-Ac) comonomer, followed by reacting with propargylamine and coupling of a chain transfer agent via azide-alkyne click reaction. PDMA was grafted from the PHEMA microspheres using RAFT-mediated aqueous polymerization, resulting in surfaces with more than 81 wt.% PDMA attached. XPS spectroscopy showed the successful modification of the microspheres. Tested in bovine serum protein solutions, the microspheres grafted with PDMA showed excellent antifouling properties. This makes the magnetic PHEMA-PDMA microspheres very promising for the specific capture of target biomolecules, such as circulating tumor cells, markers of neurodegenerative diseases such as Alzheimer’s and Parkinson’s.