Controllable Polymerization Of Perfluoroepoxy Oligomer-based Methacrylate In Supercritical CO₂

Due to the unique advantages,such as excellent hydrophobility,stain resistance,weatherability,chemical resistance and good optical electronic properties,surface properties,fluorinated（meth）acrylate polymer（s）is a kind of high performance and value-added functional materials,and has been applied in the fields of high performance coating materials,functional membranes,medical materials,optical devices and fibers.In recent years,supercritical carbon dioxide（scCO₂）has been paid great attention and is gradually recognized as an environmentally benign medium.Therefore,its distinct physicochemical properties give itself with advantages in the synthesis and processing of polymers.Reversible addition-fragmentation chain transfer（RAFT）polymerization is increasingly accepted as a type of typical living/controlled radical polymerization techniques,combining the superiorities of both radical and living polymerization.Owing to the special properties of good applicability to monomers,relatively mild polymerization conditions,RAFT polymerization has been extensively employed for design and synthesis of polymer materials with precise structures and good properties.Based on this cognition,substituting the traditional organic solvents for scCO₂,synthesizing the polymers with specific structure,precise molecular weight and low polydispersity index by RAFT polymerization and exploring the mechanism and polymerization kinetics of fluoromonomers,have become a hot topic in the research of chemical engineering.This thesis concentrates on the study of living/controlled radical polymerization of perfluoroepoxy oligomer-based methacrylate in scCO₂.A model monomer with high-fluorine content（namely FP3MA）and three novel fluorinated RAFT agents were designed and synthesized,the detailed solvation behaviors and RAFT polymerization process of FP3MA were monitored via high-pressure in-situ FT-MIR/NIR spectrum system,the intermolecular interaction and polymerization kinetics of FP3MA mediated by the fluorinated RAFT agents were investigated/revealed.Moreover,the homogeneous controlled polymerization of FP3MA was achieved.The three aspects are mainly shown as follows.（1）Synthesis of perfluoroepoxy oligomer-based methacrylate and exploration of its solvation behavior in scCO₂.Firstly,based on the understanding of monomer structures,intermolecular interactions and phase behaviors of homogeneous solution polymerization of fluoro-organics in scCO₂.The end-functionalized perfluoroepoxy oligomer was introduced into the methacrylate unit.In this way,a novel perfluoroepoxy oligomer-based methacrylate（namely FP3MA,molecular weight is 550.17 g.mol-1,fluorine content is 58.71%）was successfully synthesized and firmly characterized.Secondly,the detailed solvation process along with the phase behavior was monitored via the high-pressure in-situ FT-MIR spectrum system.Besides,the intermolecular interactions in the FP3MA + CO₂ binary system and the impact of temperature were systematically studied.Also,transition pressure（PT）of FP3MA + CO₂ binary system were obtained.The results showed that the introduction of F atoms/fluorinated groups enhanced the intermolecular interactions in the FP3MA + CO₂ binary system,which made FP3MA exhibit excellent solubility in scCO₂.Therefore,it was verified that the idea of introducing perfluoroepoxy oligomer as the solubilizing chain.Furthermore,the maximal value PT of FP3MA + CO₂system did not exceeded 12.4 MPa with the increase of temperature from 40 to 70 ℃,which meant that FP3MA can be miscible completely with CO₂ and can form a homogeneous system under relatively mild conditons.（2）Synthesis and characterization of novel fluorinated RAFT agents.Based on the understanding of the structures of RAFT agents and the intermolecular interactions of fluoromonomers + CO₂ required for the living/controlled radical polymerization of fluoromonomers in scCO₂,F atoms/fluorinated groups were intentionally introduced into the traditional RAFT agents.In this way,three novel fluorinated RAFT agents were designed,synthesized and characterized by NMR,FT-IR and X-ray single crystal diffraction.In addition,this work helps to broaden the species of RAFT agents,enrich the study of the living/controlled radical polymerization and lay a solid foundation for green production and controllable synthesis of fluoropolymer materials.（3）Investigation of RAFT polymerization of perfluoroepoxy oligomer-based methacrylate in scCO₂ system.The RAFT polymerization of FP3MA in scCO₂ was successfully monitored via high-pressure in-situ FT-NIR spectrum system,and the polymerization kinetics of FP3MA in scCO₂ system was obtained.It is confirmed that fluorinated RAFT agents had good controllability to the free radical polymerization of highly fluorinated monomers in scCO₂.Moreover,it was verified that the fluorinated RAFT agents had good controllability to the radical polymerization of FP3MA.Although there was a inhibition period in the polymerization process,FP3MA was polymerized in the first order under the conditions selected.Moreover,the concentrations of RAFT agent and polymerization temperature had a significant influence on the polymerization reaction rate and inhibition period,it was clear that the polymerization reaction rate increased and the inhibition phenomenon reduced with the decline of concentrations of RAFT agent or increase of temperature.Furthermore,it seemed that the fluorinated RAFT agents had a better controllability than the non-fluorinated RAFT agents.Consequently,it was found that the controllability of these RAFT agents to the polymerization of FP3MA was presented in the order of PFDBFB>PFBDB>PFBDMOB>BDB.This work provides an effective experimental basis for the further study of homogeneous controlled polymerization of high fluoromonomers in scCO₂,and lays a theoretical foundation for realization industrial green production of fluoropolymer materials.