Synthesis and Application of Amphiphilic Star Polymers

Author:Liu Wei Wei

Supervisor:wang hai qiao

Database:Doctor

Degree Year:2018

Download:216

Pages:172

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Amphiphilic star polymers possess not only the micro phase separation features of amphiphilic linear polymers,but also the unique spatial structures and special properties of star polymers.Recently,the important application values of the amphiphilic star polymers,which are emerged in the fields of patterned thin film materials,vivo therapeutic and diagnostic vehicles,interfacial stabilizers and nanoreactors for catalysis,have attracted immense interests of many chemists and materials scientists.Therefore,study of the molecule design and synthesis,properties and applications of the amphiphilic star polymers has been a hot research in domestic and abroad.In this dissertation,a series of organic-inorganic hybrid amphiphilic star polymers with cyclotriphosphazene core and well-defined molecule structures were designed and synthesized via thiol-ene click chemistry and reversible addition-fragmentation chain transfer(RAFT)radical living polymerization.Simultaneously,a kind of linear amphiphilic macro-RAFT agents was designed and synthesized,and then used as media to prepare methyl methacrylate/butyl acrylate(MMA/BA)copolymer latex via RAFT emulsion polymerization.This dissertation was mainly studied on the applications of the novel RAFT agents in surfactants and self-assembly,as well as the relationship between the structures and properties of the obtained amphiphilic polymers.The main contents of the dissertation are as follows.1.A series of cyclotriphosphazene derivatives were prepared via thiol-ene click reaction,and the controlled-synthesis rule of the reaction and the thermal stability of the corresponding products were investigated.The results showed as follows.The thiol-ene click reactions were almost conducted based on the anti-Markovnikov’ rule under the experimental conditions.Besides,the reactions were well controlled and the functional terminal groups could be introduced quantitatively.This strategy for preparing cyclotriphosphazene derivatives possessed many advantages,such as fast reaction times(≤30 min),high reaction yields(≥95%)and easy to mass-produced.The results of the thermogravimetric analysis demonstrated that the introduced C-S bond reduced the thermal stability of targeted products,but the onset decomposition temperature still kept on above 300℃,indicating that thiol-ene click reaction is an ideal method to prepare high performance star cyclotriphosphazene derivatives.2.Twelve kinds of PEG-based star polymers with cyclotriphosphazene core and controlled number and length of PEG arms were prepared via simple thiol-ene click reaction combining esterification under very mild experimental conditions.Effects of the number and length of PEG arms on the critical micelle concentration(CMC),surface tension and the emulsification of xylene/water system were systematically studied.The results showed that these new PEG-based star polymers had good surface activities,and when used as surfactants,a very low surfactant concentration(0.01 wt.%)was sufficient to form xylene-in-water emulsions with long-term stability more than 6 months.It should be noted that PEG-based star polymers with two arms had low surface tension and good emulsification ability due to their structural features similar to Gemini surfactants.Whereas,the PEG-based star polymers with more than two arms exhibited very low CMC values,therefore they could be utilized as surfactants to form high internal phase emulsions.The application of the PEG-based star polymers using as surfactants in styrene-acrylic emulsions was also studied and the results showed that the PEG-based star polymers with two and four arms could improve the latex stability,the water resistance and mechanical properties of the latex films.What’s more,the cross-linking degree of the latex films was also increased while the glass transition temperature kept low,indicating that the PEG-based star polymers with two and four arms had the functions of reactive plasticizers.3.Amphiphilic star macro-RAFT agents were prepared via Z-group RAFT polymerization on the base of design and synthesis of one kind of hexa-functional RAFT agents with cyclotriphosphazene core,and then fluorinated polyacrylate elastomers were successfully prepared via RAFT emulsion polymerization.The CMC values and surface tension of the amphiphilic star macro-RAFT agents,and the properties of the fluorinated polyacrylate films obtained with these star macro-RAFT agents as surfactants were investigated.The results showed that the utility of this kind of star macro-RAFT agents,which had good surface activities,could not only be used as surfactants to prepare fluorinated polyacrylate latexes with well stability,but also improve the mechanical performance and water resistance of the fluorinated polyacrylate films by introducing the "cross-linking points" in the final products.In addition,by adjusting the poly(acrylic acid)(PAA)chain length of the macro-RAFT agent,the P(2,2,2-trifluoroethyl acrylate)(PTFEA)chain length and 2,2,3,4,4,4-hexafluorobutyl acrylate/butyl acrylate(HFBA/BA)mole ratio in the emulsion polymerization,the films with hydrophobic surfaces could be obtained by directly casting the fluorinated polyacrylate latexes at room temperature without any tedious heating post-treatment.Effects of PAA and PTFEA chain length,and HFBA/BA mole ratio on the film-forming performance were studied in detail,and possible film-forming mechanisms were proposed.4.Another kind of hexa-functional RAFT agents with cyclotriphosphazene core was designed and synthesized,and then amphiphilic star fluorinated block polymers S-PHFBA-PAA were prepared via R-group RAFT polymerization.Study of the polymerization process and the analysis of the product structure characterization demonstrated that the polymerization was under control of the RAFT mechanism.Effects of different hydrophiic/hydrophobic chain lengths,solvents and polymer topology structures on the self-assembly morphologies of the amphiphilic fluorinated block polymers were investigated.Results showed that the micro phase separation morphologies on the film surfaces could be transformed from globular to ringlike,to wormlike under certain conditions,and thin films with the patterned surfaces at macro level could be realized in specific solvents.In addition,S-PHFBA100-PAA100 could firstly self-assembled into nanoparticles with the diameters of about 30 nm in the mixed solvents of 1,4-dioxane and water,and then these nanoparticles further assembled into raspberry-like spheres with the diameters of about 200 nm.That is to say,the self-assembly process could be controlled and different self-assembly morphologies could be obtained by adjusting solvents ratio.5.Stable MMA/BA copolymer latex was prepared via RAFT emulsion polymerization mediated by the linear amphiphilic macro-RAFT agents.Effects of pH values of the latexes and degree of polymerization(DP)of the PAA hydrophilic segments on the polymerization process,latex particle size and molecular weight and its distribution of the products were investigated.The solid content,temperature,pH value,and DP of the hydrophilic segments all affected the rheological behavior of the latexes associated with particles packing,hydrophobic association,hydration layer and hydrodynamics volume,respectively,thus changed the rheological properties of the latexes.In addition,the results of differential scanning calorimetric measurement,atomic force microscopy characterization and the water resistance test of latex films demonstrated that pH values and the DP of PAA chain length had a different degree influence on the glass transition temperature of the products,as well as the surface morphology,contact angle and water absorption of the latex films.