Characteristics And Mechanism Of Styrenes And Vinyl Ethers Cationic Polymerization In Aqueous Media

Aqueous cationic polymerization is a new green polymerization technology in recent years,which not only reduces the cost but also protects the environment.Traditional cationic polymerization must be carried out in anhydrous organic solvents because Lewis acid,as a co-initiator,loses its activity in water.With the development of water-tolerant Lewis acid by Sawamoto,aqueous cationic polymerization has been extensively studied.However,there are still many shortcomings in this new technology,which need to be further studied,such as incomplete mechanism of aqueous cationic polymerization and uncontrolled polymerization in aqueous media,et al.In this paper,characteristics of styrene and its derivatives,and vinyl ethers aqueous cationic polymerizations in an air atmosphere at room temperature.The mechanism of aqueous cationic polymerization was proposed by studying the kinetics of polymerization,terminal structure of polymers and computer simulation.The main work is as follows.1.Water,ethanol,isopropanol and cumyl alcohol were used as initiators to form active centers with water-tolerant tris(pentafluorophenyl)boron,respectively.Aqueous cationic polymerizations of styrene and p-methylstyrene were successfully conducted at 20?.Polymerization rate varied with different initiators:Water<ethanol<isopropanol<cumyl alcohol.Molecular simulation indicated that there was a competition in the formation of active centers in the process of co-initiator tris(pentafluorophenyl)boron with alcohol and water.The results showed that tris(pentafluorophenyl)boron was more likely to form active centers with alcohols in aqueous media in the presence of alcohols,what's more,tertiary alcohols was more likely to form active centers than secondary alcohols and primary alcohols.In suspension polymerization,the increase of initiator concentration led to the increase of conversion(up to 60%)and molecular weight(up to 3220 g/mol).Polymerization rate,conversion and molecular weight decreased with the addition of salt(LiCl/NaCl/H2O=23%/1.2%/75.8%)or lower environmental temperature.The Cl ion in solution could disperse positive charge of active centers.In emulsion polymerization,the addition of anionic surfactants could inhibit the positive charge of active centers around the monomers,thus reducing the conversion.The steric hindrance of nonionic surfactants reduced the contact probability between active sites and monomers,and also inhibited the polymerization.All main reactions(initiation,,and termination)in aqueous media occurred at organic/water surface.Four terminal structures of polymers were determined by 1H NMR.The propagatipropagationng polymer chains would transfer to water,monomer and polymer when they reach critical length.On this basis,we proposed a complete mechanism for aqueous cationic polymerization of styrene and its derivatives.2.Aqueous cationic polymerizations of isobutyl vinyl ether,n-butyl vinyl ether,and 2-chloroethyl vinyl ether were successfully conducted by alcohols/tris(pentafluorophenyl)boron/Ether initiating systems.It was found that cumyl alcohol had the effects of stabilizing the polymerization and reducing the exotherm.The highest conversion of isobutyl vinyl ether polymerization was 53%,and the highest molecular weight of polymer can reach 7360 g/mol.The conversion of n-butyl vinyl ether and 2-chloroethyl vinyl ether polymerization was higher than that of isobutyl vinyl ether.By adding co-solvent n-hexane or toluene,sodium chloride solution diluent and surfactants,the polymerization rate was effectively reduced,and the polymerization proceeded in a mild manner.When the environmental temperature decreases,aqueous cationic polymerization rate with tris(pentafluorophenyl)boron as co-initiator decreases,which is contrary to the traditional cationic polymerization.All main reactions(initiation,propagation,and termination)in aqueous media occurred at organic/water surface.Molecular weight of polymers was still controlled by the "critical DP" effect.The terminal structures of polymers were analyzed by 1H NMR.It was found that many chain transfer reactions(to water,monomer and polymer)of vinyl ether monomers occurred in aqueous cationic polymerization.However,the hydroxyl end group obtained by chain transfer to water was unstable,which was easily converted into aldehyde end group.The mechanism of vinyl ether cationic polymerization with tris(pentafluorophenyl)boron as co-initiator in aqueous media was proposed for the first time.3.Controlled cationic solution polymerization of 2-hydroxyethyl vinyl ether in aqueous media was successfully achieved by cumyl alcohol/tri(pentafluorophenyl)boron/ether as initiating system.2-Hydroxyethyl vinyl ether can dissolve in water,and polymerization is not affected by the"critical DP" effect.The molecular weight of the polymer increases linearly with the increase of conversion.The molecular weight of polymer increases proportionally with the increase of monomer concentration,and the highest molecular weight of polymer could reach 15000 g/mol.1H NMR spectroscopy indicated that chain transfer reaction did not occur,and the GPC curves were single peak distribution.No branched polymers were found.The pendant groups of polymer chains contain a large amount of hydroxyl groups,which resulted in hydrogen bonding with water during aqueous cationic polymerization,thus maintaining the activity of polymer terminals.When the monomer reacts completely,it can still be polymerized by adding monomers after a period of rest.4.Cationic soap-free emulsion polymerization of 4-hydroxybutyl vinyl ether in aqueous media was successfully achieved by cumyl alcohol/tris(pentafluorophenyl)boron/ether as initiating system.4-Hydroxybutyl vinyl ether could form emulsion and inverse emulsion without surfactant.In emulsion polymerization,the highest monomer conversion was 58.7%and the highest molecular weight of polymer could reach 2420 g/mol.In inverse emulsion polymerization,the highest conversion of isobutyl vinyl ether polymerization was 88%,and the highest molecular weight of polymer could reach 14500 g/mol.The molecular weight increased linearly with the increase of conversion in the early stage of polymerization.In the late polymerization stage,both the emulsion and inverse emulsion polymerizations were affected by the "critical DP" effect,and the chain transfer reaction occurred.In emulsion polymerization,the critical length was about 15?20 monomer units.In inverse emulsion polymerization,the critical length was about 120?138 monomer units.1H NMR spectroscopy indicated that chain transfer reaction occurred to monomer.The mechanism of cationic soap-free emulsion polymerization of 4-hydroxybutyl vinyl ether in aqueous media was proposed by studying polymerization characteristics and elementary reactions.