Application Of Liquid/liquid Biphasic Catalysis In ATRP For Transition Metal Catalyst Removal And Recycling

Atom transfer radical polymerization(ATRP) has become a highly efficient method to synthesize various polymers with different controlled topologies and architectures due to its powerful molecular designing ability, facile operation and wide ranges of applicable monomers. However, it usually utilizes large amounts of transition metal complexes as the catalysts which may inevitably contaminate the polymers, or even limit its application and result in waste of the catalysts. Thus, how to separate and recycle the ATRP catalysts simply and effectively has always been a hot research topic for this field. In this thesis, two types of liquid/liquid biphasic catalysis system were successfully introduced into ATRP for in situ catalyst isolation, recovery and recycling. First of all, the strategy of diffusion regulated phase-transfer catalysis(DRPTC) was successfully established in ICAR ATRP(Initiators for Continuous Activator Regeneration for ATRP) in aqueous/organic biphasic system based on the selective solubility behaviors of Cu Br2/TPMA complex in water and organic solvent. All the polymerization components for this specific system are commercially available without tedious and time-consuming synthesis procedures, the polymerization was triggered via diffusion of ppm level catalyst, meanwhile, highly efficient catalyst isolation, recovery and recycling were achieved in situ. In the next place, We introduced polyethylene glycol(PEG) into ATRP and established a green, cheap and robust iron catalyzed AGET ATRP(Activators Generated by Electron Transfer for ATRP). On the basis of this and combing with the typical characteristic “Homogeneous system at elevated temperature, Phase separation at ambient temperature” between PEG-200 and PX(p-xylene), we achieved in situ iron catalyst separation and recovey in ATRP for the first time.System I: The concept based on diffusion regulated phase-transfer catalysis(DRPTC) in aqueous-organic biphasic system was successfully developed for the first time in copper-mediated ICAR ATRP(termed DRPTC-based ICAR ATRP here), using methyl methacrylate(MMA) as a model monomer, ethyl α-bromophenylacetate(EBr PA) as the initiator, Cu Br2 as the catalyst, tris(2-pyridylmethyl)amine(TPMA) as the ligand and AIBN as the reducing agent. The feature for this system was that when polymerization was conducted at polymerization temperature(75 oC), the catslyst together with the ligand in aqueous phase would transfer and diffuse into the organic monomer phase(though only ppm level catalyst diffused successfully) through intensive stirring to trigger ppm level catalyzed ICAR ATRP. Nevertheless, after cooling to ambient temperature, the catalyst automatically separated in situ from the resultants, thereby green and highly efficient catalyst separation, recovery and recycling was realized.System II:Green solvent polyethylene glycol(PEG) was introduced into iron catalyzed ATRP, combining with the advantage of cheap, easily available and biocompatibile nature of iron catalyst, iron catalyzed AGET ATRP system was successfully constructed in PEG-400 without any additional ligands, using MMA as a model monomer, ethyl α-bromophenylacetate(EBr PA) as the initiator, Fe Cl3·6H2O as the catalyst, and As Ac-Na as the reducing agent. This specific system overcomes the shortcomings of high toxicity and price for iron-based ligands, making it an environmentally-benign, cheap and highly efficient polymerization system. Since there exists the characteristic “Homogeneous system at elevated temperature, Phase separation at ambient temperature” between polar solvent PEG-200 and nonpolar solvent p-xylene(PX), whereas PEG can serve as both solvent and ligand as mentioned, the concept of iron catalyzed AGET ATRP in PEG-200/PX biphasic system was established, when the polymerization temperature was elevated to 90 oC, a(pseudo) homogeneous phase was formed, while two phases reformed after cooling to ambient temperature(25 oC). Due to the fact that the catalyst complexes existed in PEG-200, but the resultants remained in PX, catalyst separation and recycling can be easily achieved in situ via simple decantation.