Synthesis Of Perfluoroepoxy Oligomer-based Styrene And Its Polymerization In Supercritical CO₂

Fluorinated polymers,especially fluorinated styrene polymers,have attracted much attention due to their high thermal stability,low dielectric constant,excellent hydrophobicity and other outstanding performances.However,mainly because of the great difficulty/challenge in the preparation of the corresponding fluorinated styrene(s)along with their poor commercial availability,very few reports can be seen on the polymerization of the fluorinated styrene monomers so far,resulting that the research as well as the application of such fluorinated polymers has been limited to a great extent.Recently,supercritical carbon dioxide(scCO2)has been increasingly accepted as the best environmentally benign medium for the synthesis of the fluorinated poymers owing to its unique advantages over the traditional organic solvents.ScCO2 is low-cost,non-toxic,non-inflammable,inertness to chain transfer reaction,low viscosity,easily accessible supercritical conditions,adjustable physicochemical properties and high solubility for various amorphous fluorinated poymers.Many researchers have focused their interests on the intermolecular interactions among the fluorinated monomers/polymers+scCO2 systems,based on which proper fluorinated monomers,initiators,chain transfer agent and other fluorinated functional materials are expected to be well designed and prepared,along with that the homogeneous polymerization can been successfully achieved.Reversible addition-fragmentation chain transfer radical polymerization(RAFT polymerization)is a typical living/controllable radical polymerization strategy.In view of the relatively mild reaction conditions and the wide monomers applicability,RAFT polymerization is of great significance to the controllable preparation of novel fluorinated polymeric functional materials.In the present thesis,a controllable polymerization system of novel perfluorinated epoxy oligomer-based styrene monomer(FEOnSt)and scCO2 is eagerly expected to be established based on the understanding/recognition of the solvation behaviors and the intermolecular interactions of fluorinated monomer/polymer+scCO2 system.The contents mainly include the following three aspects.First,a series of novel FEOnSt monomers were intentionally designed and synthesized.Second,the detailed solvation behaviors and the homogenous free radical polymerization of FEOnSt+scCO2 system have been systematically investigated.More importantly,three novel fluorinated RAFT agents were intentionally synthesized and introduced to polymerization of FEOnSt in scCO2,via which the controlled free radical polymerization system was achieved.The details are mainly shown as follows.(1)Study on the design,synthesis of FEOnSt monomers and their solvation behaviors in scCO2.On the basis of our previous studies,especially the prediction of the hypothesis on the intermolecular-interaction dynamically induced solvation effects in scCO2,and aiming at the requirements of the research on the controllable preparation of the fluorinated polymeric functional materials,novel highly fluorinated styrene monomers,namely FEOnSt(n=2,3,4...15)were designed,in which a series of fluorinated epoxy oligomers with different degree of polymerization were introduced as efficient solubilizing chain,and implanted to styrene molecule.Choosing the end-functionalized perfluorinated epoxy oligomers((FEO)nCOF)and p-bromostyrene as the reactants,three novel fluorinated styrene monomers FEOnSt(n=2,3,4)were successfully synthesized via metallicorganic reagent methods.The prepared FEOnSt monomers were characterized and confirmed via FT-IR,1H NMR,13C NMR and high resolution mass spectrometry.The highest yield and fluorine content of the FEOnSt are obtained as 80%and 58.50%.The detailed solvation behaviors of FEOnSt in gaseous and supercritical CO2 were in situ monitored via a set of HP FT-MIR spectrum system,via which the intermolecular interactions between FEOnSt monomer and scCO2 were explored and revealed.It is shown that,under the experimental conditions(0.1?38.0 MPa,40.0?70.0?),the transition pressure(PT)of FEOnSt+scCO2 system not only increased with the increase of the temperature,but also slightly increased with the increase of the n in FEOnSt.However,it is clear that even at the highest temperature(70?)and/or the biggest n value(n=4,Mn=770.98 g·mol-1),the obtained PT is found to be surprisingly modest(less than 14.0 MPa).It is indicated that the solubility of FEOnSt in scCO2 is really excellent.In this way,the rationality/validity of the introducing and implanting of solubilizing chain to the styrene monomer is well verified.(2)Exploration of the free radical polymerization of FEOnSt in scCO2The free radical polymerization of FEOnSt was systematically explored via a set of HP FT-NIR spectrum system,in which FEO3St was employed as the model monomer.The impacts of reaction conditions on the polymerization process and the polymerization activity of FEOnSt were evaluated.Firstly,the impacts of polymerization medium were studied.The homogeneity as well as the polymerization results of FEOnSt in two supercritical fluids(scCHF3 and scCO2)and two organic solvents(1-methoxynonafluorobutane and toluene)were studied.It was found that scCO2 was the most suitable medium for the homogeneous or solution polymerization of FEOnSt.Secondly,the free radical homopolymerization of FEOnSt in scCO2 was explored.It is shown that the initiation performance of the azo initiator of AIBN was better than that of the peroxide one of BPO in the free radical homopolymerization of FEO3St,though the two initiators are both able to initiate the prepared FEO3St monomer.When the mole ratio of FEO3St to AIBN is 100:1,the polymerization rate of FEO3St is seemed to be faster.Last but not least,the free radical copolymerization of FEOnSt in scCO2 was also investigated.It is found that the proposed FEOnSt could successfully copolymerize with four non-fluorinated monomers(namely,styrene,acrylonitrile,butadiene and maleic anhydride).The molecular weight of the obtained random copolymers varied from 40,000 to 150,000.(3)Investigation of RAFT polymerization of FEOnSt in scCO2Firstly,in order to overcome the defects existing in the previous study on the controlled radical polymerization of fluorinated(acrylate)monomers in scCO2,three fluorinated RAFT agents,namely,DPFBTTC,PFBDB and PFBDFB,were designed,synthesized and characterized via FT-IR,1H NMR,13C NMR.It is believed that the pentafluorophenyl in the target RAFT agents can not only provide excellently stable high-fluorinated end group to the prepared fluorinated polymers,but also well match with the fluorinated styrene monomer of FEOnSt.Secondly,the RAFT polymerization of FEOnSt in scCO2 was systematically studied by using the HP FT-NIR method combined with the high pressure sampling technique,via which the polymerization kinetics was also investigated.It is shown that the prepared fluorinated RAFT agents can effectively regulate/control the free radical polymerization process of FEOnSt in scCO2,through which the novel fluorinated styrene polymers(PFEOnSt)with controllable structures and expected molecular weights were successfully prepared.It is also found that PFBDB may be the best among the prepared 3 RAFT agents to the controlled polymerization of FEOnSt in scC02.Finally,based on the initially constructed controllable polymerization system of FEOnSt+scCO2,a series of novel fluorinated styrene polymers were successfully prepared as expected by adjusting the dosage of RAFT reagent and/or the monomer conversion,which molecular weights of PFEOnSt ranged from 4,000 to 140,000.It is firmly believed that the present work may greatly promote the design and synthesis of novel fluorinated styrene monomers,and provide a solid experimental foundation to the further investigation and application of the controllable polymerization of highly fluorinated monomers in scCO2.The present work will be of great significance to the green industrialized production of fluorinated functional materials.