Thermoregulated phase transfer catalysis in aqueous/organic biphasic system: facile and highly efficient ATRP catalyst separation and recycling in situ using typical alkyl halide as initiator

Abstract

Developing a highly efficient and facile method for catalyst separation and recycling from an ATRP system facilitates wide application of atom transfer radical polymerization (ATRP). In this work, an important development of thermoregulated phase transfer catalysis (TRPTC)-based initiators for continuous activator regeneration (ICAR) ATRP for transition metal catalyst separation and recycling in a water/p-xylene biphasic system was achieved using alkyl halide (ethyl-2-bromo-2-phenyl acetate, EBPA) as the initiator for the first time. Herein, poly(poly(ethylene glycol) methyl ether methacrylate)-supported dipicolylamine (PPEGMA-BPMA) was designed as the thermoregulated ligand, CuBr₂ as the catalyst, 1,1′-azobis(cyclohexanecarbonitrile) (ACHN) as the azo-initiator and methyl methacrylate (MMA) as the model monomer, respectively. The polymerization kinetics was investigated in detail, and the “living” feature of this novel polymerization system was confirmed by chain-end analysis and chain extension experiments for the resultant PMMA. It is noted that the catalyst complex (PPEGMA-BPMA/CuBr₂) existed only in an aqueous phase at room temperature, and it transferred to an organic phase and subsequently catalyzed the ICAR ATRP of MMA when the temperature increased to 90 °C. After polymerization the catalyst complex successfully transferred to the aqueous phase almost completely from the organic phase again while the resultant PMMA existed in the p-xylene phase once the temperature cooled down to room temperature. Therefore, the process described above combined the advantages of homogeneous catalysis in the organic phase and heterogeneous catalyst separation in situ in the aqueous/organic biphasic phase system by just changing the reaction temperature. Importantly, the catalyst complex in the aqueous phase could be recycled easily, and the catalyst retained high catalytic activity even after eight recycling times.