Quantum Chemical Calculations On The Synthesis And Polymerization Of Perfluoroepoxy Oligomer-based Styrene

Fluorinated polymers are a kind of important high performance functional materials.Due to the unique advantages,such as high thermal stability,good photoelectric performance and excellent surface hydrophobicity,fluorinated styrene polymer(s)has been applied in the fields of optical devices,electronicparts and components.However,there are very few kinds of fluorinated styrene monomers,and the synthesis process is complex and costly at present.It is urgent to explore new and effective ways to design and prepare fluorinated monomers so as to meet the increasing needs in research and application.Fluorinated monomers can be initiated by azo or peroxide free radical initiators.After polymerization,the free radicals produced by the initiators are usually connected to the end of the polymer chain.However,it is known that the stability of these non-fluorinated end groups is much lower than that of the fluorinated groups in the polymer chains,resulting in the weakness in the stability of the fluorinatedpolymers.Therefore,if a novel fluorinated initiator can be designed,synthesized and applied to the synthes is of fluorinated polymers,the performance of target fluorinated polymers will be effectively improved to meet the requirements of a wider range of applications.In recent years,supercritical carbon dioxide(scCO2)has attracted much attention in fluoropolymer research due to its unique advantages over traditional organic solvents(such asnon-toxic,non-polluting,non-flammable andnon-explosive).And more importantly,scCO2 has special affinity and excellentsolubility to fluorinated organics(monomers/polymers/initiators).Therefore,it is expected that scCO2 may replace the organic solvents which were widely used in polymerization,and thus is regarded as an environmentally benign medium.Exploring the construction of the free radical polymerization systemof fluorinated monomer-scCO2 is of great significance to the green preparation of fluorinated polymeric materials.In the present thesis,quantum chemical calculation method was mainly employed,via which the initiation performance of a fluorinated initiator(namely,PFBPO),and the best strategyto synthesize the target fluorinated monomer(namely,perfluorinated epoxy oligomer based styrene(FEOnSt))were systematically investigated so as to lay a theoretical foundation for exploring and constructing the free radical polymerization systemof fluorinated monomer-scCO2.The main contents include the following two aspects.(1)Study on the initiation performances of(fluorinated)free radical initiatorsFirstly,benzoyl perfluorperoxide(PFBPO),which possesses high fluorine content as well as high stability pentafluorophenyl group,was selected as the modelof fluorinated free radical initiator.The bond energy,thermodynamic energy of bond breaking reaction and charge distribution of primary free radicals were studied by using density functional theory(DFT)method at B3LYP/6-311+G(d)level.And then,the thenmal decomposition of the target fluorinated initiator PFBPO was studied and compared with three non-fluorinatedfree radical initiators(namely,AIBN,ABVN and BPO).Secondly,styrene was used as the model monomer.The chain initiation behaviors of PFBPO was further studied at the level of M06-2X/6-311+G(d,p)and compared to the other three free radical initiators.In this way the initiation performance of PFBPO was evaluated.It is found that PFBPO has higher thermal decomposition activity and faster chain initiation speed as compared to AIBN,ABVN and BPO.Therefore,it seemed that PFBPO is more suitable to initiate monomer under lower temperature and milder conditions,and thus is expected to be the most promising free radical initiator in the free radical polymerization of fluorinated monomer(s)in scCO2.(2)Study on thepreparation of pertluorinated epoxy oligomer-based styreneStyrene,o-methylstyrene,p-methylstyrene,methoxystyrene and ethylbenzene were selected as the substrates,and acyl fluoride group terminated hexafluoropropylene oxide dimer(FEO2COF)was used as the model electrophilic reagent.The structural characteristics(charge distribution)of these four substrates and the electrophilic substitution of FEO2F with the substrateswere studied at B3LYP/6-31G(d,p)level by DFT method.By comparing the reactivity of the different substrates,the most reasonable way to prepare the target fluorinated monomer,namely,FEO2St,was obtained since the best substrate was selected.It was found that the most active substrate among the five ones was methoxystyrene in the electrophilic substitution,followed by p-methylstyrene,styrene,and then ethylbenzene.The last one was o-methylstyrene.The calculation results show that the electrophilic substitution of methoxystyrene with FEO2COF may be the best route to prepare the target monomer of FEO2St.The present work will provide a theoretical basis for the further design and preparation of novel fluorinated monomers,and is of great significance to the construction of the controlled polymerization system of fluorinated monomer-scCO2 and the realization of the green production of fluorinated polymeric functional materials.