Study On Homogeneous Epoxy Resin System Modified By Hyperbranched Polymers

Epoxy resin is common in daily life due to its great abilities such as adhesive property and thermal property.However,the poor toughness limits the application of the epoxy resin.Recently,many researches are foucesed on the toughening epoxy resin modified by hyperbranched polymers(HBPs)due to their unique physical and chemical properties.However,the reported HBP-modified epoxy resin is micro-phase separated after curing,which leads the reduction of modulus and glass transition temperature(T_g).Therefore,a misjudgment of the modification effect on improving toughness by HBP occurrs frequently owing to the occurrence of micro-phase separation.To confirm the effect of HBPs on the modification of epoxy resin,the homogenous phase system is expected to be designed.Herein,to improve toughness,modulus and T_g of epoxy resins and eliminate the influence of phase separation,both chemical and physical methods are used to get homogenous HBP-modified epoxy resin.The main results and conclusions are as follows:1.Epoxy-terminated hyperbranched polyether was used to react with the curing agent in the epoxy resin blending system.Hperbranched polyether was prepared through the 1,2,7,8-diepoxyoctane reacting with trimethylolethane,and then the polymerized product was added into epoxy resin.Subsequently,coating,adhesive and sheet samples of neat epoxy resin and modified resin were prepared for testing.Compared with neat epoxy resin,the mechanical properties of modified resin including impact strength,flexural strength,tensile strength and storage modulus were enhanced and there was an optimal content of the hyperbranched polyether in the modified network.The differential scanning calorimetry(DSC)as well as thermal gravimetric analysis(TGA)results proved that the thermal performance of epoxy resin treated with hyperbranched polyether was reduced slightly,as compared with the neat epoxy resin.The micro-phase structure was studied by scanning electronic microscopy(SEM).The SEM images showed that the network of hyperbranched polyether and epoxy resin was homogeneous.All the results demonstrated that toughness and modulus of epoxy resin were improved simultaneously by epoxy-terminated hperbranched polyether without the effect of micro-phase separation.2.Aromatic hyperbranched polyurethane(M-HBPU)and aliphatic hyperbranched polyurethane(H-HBPU)were prepared through the aromatic diisocyanate(MDI)and aliphatic diisocyanate(HDI)reacting with diethanolamine respectively.Then,hyperbranched polymers were further added into epoxy resin as modifiers to make samples for testing.The mechanical properties including flexural strength,impact strength,tensile strength and storage modulus of modified epoxy resin were improved after the treatment with both M-HBPU and H-HBPU,and there was an optimal amount of the hyperbranched polyurethanes in the modified epoxy resin systems.Meanwhile,DSC and TGA results revealed that the thermal performance of epoxy resin treated with the M-HBPU was enhanced markedly,as compared with the pure epoxy resin.The micro-phase structures were studied by SEM.The SEM images showed that the blending of M-HBPU and epoxy resin was homogeneous after curing,while the blending of H-HBPU and epoxy resin was phase-separated.All results indicated that the mechanical properties and thermal performances of the modified epoxy resin could be improved directly by M-HBPU without the effect of micro-phase separation.