Study On Regulating Of The Nanophase Structures And Performances Of Epoxy Nanocomposites

Epoxy is one of most important thermoset resins and widely applied in many areas owing to its superior performance.However,traditional modification methods encounter challenge how to overcome its brittleness,to enhance its thermo mechanical properties,and endow it with novel functions.In this study,amphipathic branched polymers are used as template polymers to control the formation of order or disorder microphase structures of nanocomposites at nano-scale and optimize the comprehensive mechanical of thermosets by the micro-phase separation behavior of template polymers.The specific works are as follows:（1）Active lithiation sites were introduces onto the benzene rings of SEPS by lithiation reaction,from which PEG branches polymerized to synthesize graft copolymer SEPS-g-PEG;The–CH₂Cl groups were introduced onto the benzene rings of SEBS by chloromethylation reaction They were coupled with–OH groups of PEG chains to synthesize SEBS-g-PEG.GPC,FT-IR,¹H-NMR,DSC,SAXS and AFM were utilized to investigate the development of the crystalline structure and micro-phase separation structures of these two kinds of branched copolymers changing with their molecular topological structures.The results shows that the domain size and crystallinity of PS-g-PEG phase increase as more PEG are introduced in SEPS-g-PEG;But,no crystalline texture is formed in SEBS-g-PEG due to its short PEG chains with a molecular weight of 350.（2）After curing agents and preparation technologies were optimized,epoxy thermosets nanocomposites were prepared using SEPS-g-PEG and SEBS-g-PEG as template copolymer,respectively.Their morphology and size of micro/nano-phase,and fractured surfaces were researched by DSC,SAXS,AFM,and AFM respectively.Furthermore,their mechanical properties were also tested,such as impact toughness and flexural strength.The results show that the low partial drag force due to the low branching degree of SEPS-g-PEG can’t produce good compatibilization with epoxy matrix.Compared with SEPS-g-PEG,SEBS-g-PEG has much high branching degree,which drag force in a relative longer region in PS phase can improve its compatibilization with epoxy matrix.Besides,the residual benzyl chloride groups can react with curing agent,which can further improve the compatibilization and stability of their components.As the content of PEG increases,the impact toughness of nanocomposites is enhanced and the loss of flexural strength decrease due to the increased compatibility between the epoxy resin and SEBS-g-PEG.When SEBS-g-PEG has 42 wt%of PEG branches,its toughed nanocomposites have worm-like nanophases with a width of 20nm,impact toughness of 111%higher than pure epoxy and less than 3%of loss of flexural strength due to their best compatibilization and immersion.Thus,this case can maintain good strength with significantly improved toughness.（3）The formation and toughening mechanism of nanostructured composites were investigated according to the relationship between molecular topological structures of SEBS-g-PEG and nano/microphase separation structures of nanocomposites.The hydrogen-bond interaction between compatible PEG chains and epoxy matrix could stabilize the nanophase of incompatible EB block in epoxy matrix.Under external force,crazing might be produced in the matrix and extended to elastic EB phase,which could prevent further extension of crazing.Besides,the stronger the interaction force between nano/microphase and matrix was,more energy would be consumed during stripping,and therefore,it could improve toughness of nano/microphase epoxy composite;Meanwhile,less cross-linked networks were damaged and the strength of composites could be maintained.