Microphase Separation Behavior And Properties Of Epoxy Networks With Flexible Side Chains

Epoxy resin has excellent mechanical and processing properties,but the epoxy network has large crosslinking density during the curing process,which makes it strong but the brittle.It is the most important problem to expand its use range and improve the toughness of epoxy resin.In.this paper,first,we selected bisphenol F epoxy resin and 4,4'-diaminodiphenylmethane(DDM)with a large number of benzene rings as curing agents.A series of epoxy resin systems with different content and different length flexible side chains were prepared by the reaction of single end fatty amine and epoxy group.The results of the introduced side chain were characterized by FTIR,and the mechanical and thermal properties of the introduced side chain were tested by universal testing machine and DSC.AFM test results show that the flexible side chain can't form micro phase structure in DGEBF/DDM system.We speculated that the occurrence of microphase separation structure was not only related to the compatibility between the main chain and the side chain,but also limited by the rigidity and flexibility of the main chain.Second,in order to study the reasons for the formation of the microphase separation structure,we designed and prepared a series of rigid flexible and controllable epoxy resin systems[DGEBF/DDM/4,4 '-diaminodicyclohexylmethane(H-DDM)/octylamine system].By means of XRD,nano-IR and the microscopic morphology of AFM test,it was conjectured that the formation of the microphase separation structure is not only related to the incompatibility between the main side chains,but also limited by the stiffness of the main chain.Last,in order to study the influence of microphase separation structure on the thermodynamic properties and mechanical properties,we designed and prepared resin systems(DGEBF/DDM/H-DDM/single end amine system)with a series of flexible side chains with different lengths and contents.Thermomechanical and mechanical properties were characterized by DMA,DSC and universal testing machine.The results of the mechanical properties showed that the microphase separation structure can greatly improve the mechanical properties of the epoxy resin.It was proved that all the nano-,submicro-sized bump structures had a significant effect on the toughness of epoxy resins and enhanced themodulus dramatically.When the curing agent system is changed to H-DDM/DDM=45/55 and the flexible side chain is 5%of the epoxy resin mass ratio,the mechanical properties reach the extreme value.The tensile strength was 88.4MPa.The elongation at break was 6.6%.The tensile modulus is 3.5GPa.Compared with the DGEBF/DDM/H-DDM system,the strength of the system was increased by 16.2%,the elongation at break was increased by 43.5%and the modulus was increased by 29.6%.