Enhancing the toughness of epoxy resin by using a novel hyperbranched benzoxazine

In this study, a novel hyperbranched benzoxazine (HB-PED230) was synthesized from the reaction of Jeffamine D230, 1,1,1-tris(4-hydroxyphenyl)ethane and paraformaldehyde through the simple one-step Mannich condensation reaction. The characteristic structure of oxazine ring in HB-PED230 was confirmed by FTIR, 1H and 13C NMR and the corresponding degree of branching (DB) was calculated to be 0.51. The effects of HB-PED230 on the copolymerization behavior, thermal stability and mechanical properties of epoxy resin were studied. Compared with the neat epoxy resin, the flexural modulus of modified thermosets decreased obviously by increasing the amount of HB-PED230, indicating that the HB-PED230 had plasticization effect on epoxy resin and reduced its brittleness. Simultaneously, the flexural strength of copolymer was enhanced. More importantly, the impact strength of modified thermoset with the incorporation of 12 wt% HB-PED230 was improved by 247.4%, implying the great improvement of toughness for epoxy resin. Scanning electron microscope (SEM) imagines showed that no phase separation appeared in the thermosets, also revealing the evidence of increased toughness after addition of HB-PED230.