The Synthesis Of Hydrophilic/Amphiphilic Polymers Via Continuous RAFT Polymerization

Compared with other living radical polymerization?LRP?methods,reversible addition-fragmentation chain transfer?RAFT?polymerization has become a more effective strategy to prepare polymers with controlled molecular weight and low polydispersity,due to its mild reaction conditions,simple components,high tolerance to functional groups,and wide applicability.However,it is difficult to achieve large-scale synthesis of controllable polymers in conventional tank reactor because of the existence of some shortcomings such as intermittent operation,heterogeneous material mixing,and uneven heat/mass transfer,especially for photopolymerizations.In contrast,tubular reactor can be applied to mass production while maintaining or even improving the controllability of polymerization with its large specific surface area and efficient heat/mass transfer.Based on the above factors,a series of hydrophilic/amphiphilic polymers were synthesized in continuous tubular reactors via RAFT polymerization,with an aim to provide the theoretical basis and application examples for continuous RAFT polymerization.System I:The in Situ Formation of Nanoparticles via RAFT Polymerization-Induced Self-Assembly in a Continuous Tubular Reactor.The amphiphilic poly?poly?ethylene glycol?methyl ether methacrylate?-b-poly?methyl methacrylate??PPEGMA-b-PMMA?block copolymer nanoparticles were successfully synthesized via polymerization-induced self-assembly?PISA?at 70°C in a continuous tubular reactor with a mixed solvent of water and ethanol,using 4-cyano-4-?thiobenzoylthio?pentanoic acid?CPADB?as the chain transfer agent and 2,2'-azobis[2-?2-imidazolin-2-yl?propane]dihydrochloride?AIBI?as the initiator.It was found that the addition of a high amount of water?56%v/v?hindered the transition of the copolymer morphology with only spheres being obtained.In addition,different mixers were used to investigate the effect of the mixing intensity on the evolution of the copolymer morphology with the increasing degree of polymerization?DP?of the PMMA.For the PPEGMA₄₀-b-PMMA₅₀₀formulation,the use of T-mixer led to an approximately constant particle diameter?about 33.0 nm?during the polymerization process.In contrast,the use of static mixer resulted in kinetically-trapped spheres?11.8 nm⁴1.6nm?.System II:Visible Light Controlled Aqueous RAFT Continuous Flow Polymerization with Oxygen Tolerance.A fast visible light controlled reversible addition-fragmentation chain transfer?RAFT?polymerization of poly?ethylene glycol?methyl ether methacrylate?PEGMA?was successfully achieved in water in a continuous tubular reactor.Polymerizations were conducted under extremely mild reaction conditions:visible light,room temperature,no deoxygenation and water as a green solvent.Herein,4-cyano-4-?ethylthiocarbonothioylthio?pentanoic acid?CETPA?was used as the chain transfer agent,and 2,2'-azobis[2-?2-imidazolin-2-yl?propane]dihydrochloride?AIBI?was used as the initiator.The flow photoreactor allows the speed up of the polymerization under visible light irradiation without loss of controllability.In the cases of purple LED light,the high conversions were reached in a relatively short time?less than 0.5 h?with a narrow molecular distribution?M_w/M_n=1.10¹.30?.The removal of deoxygenation process greatly simplified the implementation and reduced the requirements of experiment devices for leakproofness.