Preparation Of Eight-Arm Star-Shaped Styrenic Thermoplastic Elastomer Copolymers Via Living Anionic Polymerization

Thermoplastic elastomer(TPE)is a kind of polymeric materials with crosslinked rubber properties at room temperature and processing characteristics of thermoplastic resin at high temperature.Since its birth,various types of TPEs have been developed and broadly used in different areas.Among them,the most typical one is styrenic thermoplastic elastomers(STPEs),in which the hard blocks are generally styrenic polymers while the soft blocks are commonly conjugated diolefin polymers.The molecular structures of STPEs are mainly linear triblock structure,star-shaped block structure and other complex topologies.Thereinto,the star-shaped block structure has attracted wide attention and star-shaped STPEs show remarkable performances compared to their linear analogues.In this thesis,living anionic polymerization(LAP)was firstly used to synthesize living block copolymer chains,which were then used to react with octavinyl polyhedral oligomeric silsesquioxane(OVPOSS)to successfully achieve the rapid and efficient preparation of eight-arm star-shaped block copolymer elastomers.Moreover,the selective hydrogenation of unsaturated double bonds in the PI block of star-shaped block copolymers was also conducted to improve their properties.The chemical structures and related properties of all polymers have been systematically characterized.The detailed research contents are shown as follows:(1)Synthesis and characterization of eight-arm star-shaped block copolymers based on polystyrene-b-polyisopreneFirstly,living polystyrene-b-polyisoprene block copolymer chains(PS-PI-Li)with different block ratios were synthesized via LAP by sequentially feeding different amounts of St and Ip monomers;Subsequently,several eight-arm star-shaped block copolymers(PS-PI)8POSS were conveniently prepared by the reaction between PS-PI-Li and OVPOSS.The chemical structures and molecular information of(PS-PI)8POSS and their precursors were characterized by proton nuclear magnetic resonance spectroscopy(1H-NMR),gel permeation chromatography(GPC)and Fourier transform infrared spectroscopy(FT-IR).In addition,the thermal properties,mechanical properties and surface morphology of(PS-PI)8POSS were studied by differential scanning calorimetry(DSC),thermogravimetric analysis(TGA),mechanical test,linear viscoelasticity test,as well as atomic force microscope(AFM).(2)Synthesis and characterization of eight-arm star-shaped block copolymers based on poly(styrene-co-diphenylethylene)-b-polyisopreneIn order to enhance the service temperature of elastomer copolymer(PS-PI)8POSS,commercial 1,1-diphenylethylene(DPE)was applied to copolymerize with styrene to improve the glass transition temperature(Tg)of hard block in elastomer copolymers.Various living poly(styrene-co-diphenylethylene)chains(PSD-Li)with different contents of DPE unit were firstly synthesized through LAP by controlling the molar ratio of St and DPE monomers;Subsequently,PSD-Li with appropriate molecular weights and monomer compositions were selected as the macroinitiator to polymerie isoprene to obtain living poly(styrene-co-diphenylethylene)-b-polyisoprene block copolymer chains(PSD-PI-Li);Finally,several eight-arm star-shaped block copolymers(PSD-PI)8POSS were conveniently prepared by the copouling reaction between PSD-PI-Li and OVPOSS.The chemical structures,molecular weights and molecular weight distribution of(PSD-PI)8POSS and precursors were characterized by 1H-NMR and GPC analyses.The thermal and mechanical properties of(PSD-PI)8POSS were investigated by DSC,TGA,mechanical test and linear viscoelasticity test.(3)Study on the hydrogenation reaction of eight-arm star-shaped block copolymersThe unsaturated double bonds in the PI block of aforementioned star-shaped elastomer copolymers can be hydrogenated by p-toluenesulfonyl hydrazide(TSH)to obtain saturated aliphatic chains(HPI)to improve their thermal property.The effect of TSH feeding amounts and reaction time on the hydrogenation was first investigated.Subsequently,the established optimal reaction condition was used to conduct the hydrogenation of(PS-PI)8POSS or(PSD-PI)8POSS,affording new eight-arm star-shaped block copolymers(PS-HPI)8POSS or(PSD-HPI)8POSS with saturated aliphatic chain as the soft block.The chemical structures,molecular weight and molecular weight distribution of hydrogenated products were characterized by 1H-NMR,GPC and FT-IR analyses.The thermal and mechanical performances of eight-arm star-shaped block copolymers before and after hydrogenation were also characterized by DSC,TGA,mechanical test and linear viscoelasticity test.In summary,this thesis focuses on the rapid preparation of eight-arm star-shaped block copolymers containing both hard and soft blocks.The service temperature was enhanced by the introduction of DPE in the hard block,and the thermal property was improved by transforming the unsaturated polydiene block into saturated aliphatic chain via hydrogenation reaction.Simultaneously,the chemical structures of all polymers were characterized in detail and the effects of different compositions on the properties of polymers were preliminary explored.This kind of novel star-shaped block copolymers containing both hard and soft segments may find potential application in thermoplastic elastomers.