| Hyperbranched epoxy resins(HERs)have played an important role in the fields of aerospace,automotive industry and electronic packaging materials due to their excellent electrical insulation,mechanical properties,chemical resistance and adhesion.Many kinds of HERs with different structures have been obtained by various methods,but it is still an important problem to precisely control the microstructure of HERs.Thiol-ene click reaction is a high efficiency,high selectivity and mild synthesis method.In this paper,Thiol-ene click reaction was used to effectively control the degree of branching of HERs,and latent cationic curing agent was used to prepare HERs/DGEBA hybrid resin.The effects of the degree of branching and content of HERs on the mechanical and thermal properties of hybrid resin were studied,and the microstructure of the resin was characterized and analyzed to explore the reinforcing and toughening mechanism of HERs on DGEBA.The research contents are as follows:(1)Synthesis and characterization of hyperbranched epoxy resin with controllable degree of branching.The trifunctional unsaturated monomer THMPM was prepared by using trimercapto nitrogen heterocyclic monomer(THMP)and binary olefin monomer(DPPM)as raw materials;N-benzyl-N-(2-hydroxy-ethyl)-3-Mercaptopropionamide(AB)and N,N-bis-(2-hydroxypropyl)-3-mercaptopropiona-mide(AB2)are respectively used as linear monomers and branched monomers,prepared by reacting with THMPM in different proportions The hydroxyl-terminated hyperbranched polymer NMHOH-n(n=0,0.33,0.5,0.67 and 1)with different degree of branching was prepared;and NMHOH-n and mercaptopropionic acid(MPA)were used to prepare the mercapto-terminated hyperbranched by esterification NMHSH-n;finally NMHSH-n and allyl glycidyl ether(AGE)were prepared by the Thiol-ene click reaction to prepare hyperbranched epoxy resin NMHEP-n with a nitrogen-phosphorus skeleton with different degree of branching.The molecular structure of each step was characterized by ~1H NMR and FT-IR.The degree of branching of the hyperbranched epoxy resin was calculated by the ~1H NMR of the hydroxyl-terminated hyperbranched polymer NMHOH-n,which was basically consistent with the theoretical branching degree.The molecular weight of the product in each step was determined by GPC,which was close to the theoretical molecular weight.The structure and morphology of hyperbranched epoxy resin NMHEP-n in tetrahydrofuran were studied by dynamic and static light scattering.It was found that the hydrodynamic radius Rh,root mean square radius of gyration Rg and shape factor all decreased with the increase of branching degree.(2)The performance of hyperbranched epoxy resin film with controllable branching degree.NMHEP-n was cured with methylnadic acid anhydride to obtain film materials,and the mechanical and thermal properties of the cured film of NMHEP-n were studied.Studies have shown that the pencil hardness can reach 4 H,the adhesion and flexibility are 1 and 1mm,respectively,showing excellent hardness,toughness and abrasion resistance.As the branching degree of NMHEP-n increases,the glass transition temperature(Tg)and thermal decomposition temperature of the cured film show an increasing trend.(3)The properties of hyperbranched epoxy resin/bisphenol A epoxy resin.NMHEP-n/DGEBA hybrid resin was prepared with cationic curing agent,and the influence of branching degree and NMHEP-n content on the mechanical and thermal properties of NMHEP-n/DGEBA hybrid resin was studied.The mechanical properties of the hybrid resin first increase and then decrease with the increase of the NMHEP-n content and branching degree,and reach the maximum when 12 wt%NMHEP-0.5 is added;the Tg of the hybrid resin increases with the branching degree of NMHEP-n And the content increases and decreases;the thermal decomposition temperature of the composite material is slightly lower than that of pure DGEBA.The dynamic thermomechanical properties,crosslinking density and free volume of the resin were discussed using DMA and TMA,and the reasons for the improvement of the mechanical properties of hybrid resins were studied in detail;The compatibility and morphology of the curing system were analyzed by Raman,AFM and SEM.It is found that the addition of NMHEP-n significantly increases the Young’s modulus and crosslinking density of the hybrid resin,and reduces the free volume;NMHEP-n is evenly distributed in the matrix resin DGEBA and has a homogeneous structure,which confirms that the NMHEP-n pair The reinforcing and toughening of DGEBA is an in-situ reinforcing and toughening mechanism. |
