Study On Aqueous Cationic Polymerization Initiated By B（C₆F₅）₃ And Its Mechanisms

The production of chemical materials is always a heavy pollution source to the environment.As a solution,green chemistry gradually attracts attention in society.Water,as a clean,cheap,and environmentally friendly green resource,should play a more pivotal role in the green chemical industry in the future.Cationic polymerization was an important synthetic method in polymer chemistry.Traditional cationic polymerization co-initiators systems were extremely sensitive to water.Thus,aqueous cationic polymerization is hard to achieve.In 1999,ytterbium trifluoromethanesulfonate[Yb（OTf）₃],the first water-resistant co-initiator,had been successfully developed.It broke through the traditional concept that cationic polymerization must be carried out under water-free conditions.In this thesis,the aqueous cationic polymerization of p-methylstyrene,cyclohexyl vinyl ether,and hydroxy vinyl ether was successfully initiated by the CumOH/B（C₆F₅）₃/Et₂O initiator system.The reaction details were studied by density functional theory（DFT）.The polymerization mechanism was proposed.In the first part of the thesis,the CumOH/B（C₆F₅）₃/Et₂O initiator system was used to achieve the aqueous cationic suspension and emulsion polymerization of p-methylstyrene,respectively.The molecular weight in suspension polymerization reaches 2700 g/mol.The molecular weights of emulsion polymerization products were greatly affected by the type of surfactants.The molecular weights were between 1000 g/mol to 2200g/mol.The terminal structures of the polymer were analyzed by hydrogen nuclear magnetic spectrum（¹H-NMR）.The elementary reactions of the aqueous cationic polymerization of p-methylstyrene were revealed.The mechanism of diethyl ether promoting the dissolution of B（C₆F₅）₃ was proposed.In the second part of the thesis,the aqueous cationic suspension polymerization of cyclohexyl vinyl ether used the above-mentioned initiator system was characterized.The properties of emulsion polymerization under three different surfactants were investigated.Aqueous cationic polymerization was achieved at-15℃ for the first time with a molecular weight of 13000 g/mol.The study revealed that the polymerization induction period was prolonged correspondingly to the decrease of the polymerization temperature.The corresponding homopolymerization mechanism was proposed.The aqueous copolymerization of cyclohexyl vinyl ether,isobutyl vinyl ether,and n-butyl vinyl ether at room temperature was investigated.The influences of temperature,main initiator concentrations,surfactant types,and surfactant dosages on copolymerization were explored.The copolymerization reaction mechanism was proposed.In the third part of the thesis,the CumOH/B（C₆F₅）₃/Et₂O initiator system successfully initiated the polymerization of three types of hydroxyl-containing monomers,2-hydroxyethyl vinyl ether,4-hydroxybutyl vinyl ether,and diethylene glycol monovinyl ether by one-step synthesis to produce polyhydroxy oligomers.The influence of temperature,reaction time,feed ratio,water-oil ratio,and main initiator concentrations on the polymerization were investigated.By applying an even time interval feeding protocol,a continuous exotherm phenomenon in the system was found.Indicating that B（C₆F₅）₃ has the ability to continuously initiate polymerization,but the polyhydroxy polymer has a certain surface activity.After the degree of polymerization reaches a certain level,it would embed its own active end,and the unstable Pn-OH end of the dormant species would be converted into a Pn-CHO end.The aldehyde group cannot be reversibly activated by B（C₆F₅）₃ Et₂O.It resulted in the molecular weight of the polymer being less than 1500 g/mol.