Preparation And Research Of High Performance Polybenzoxazine Toughened By Hydrogen Bond

Polybenzoxazine is a new type of phenolic resin because it has a structure similar to phenolic resin after curing.Polybenzoxazine not only maintains the good mechanical properties,thermal properties and dielectric properties of traditional phenolic resin,but also has the characteristics of high char yield and low water absorption.It has been used in electronic packaging materials,aerospace industry,flame retardant materials,high temperature resistant materials and other fields.However,the high brittleness and low impact strength of benzoxazine resin restrict their further application as high-performance structural materials.Therefore,it is of great significance to toughen polybenzoxazine.The current toughening methods often sacrifice the thermal properties or processing properties of benzoxazine,so it is necessary to find new modification methods.In this paper,the idea of introducing dynamic hydrogen bond into polymer to construct“sacrificial bond”was used to toughen polybenzoxazine.Firstly,two low molecular weight compounds with hydrogen bond structure were synthesized,respectively has Zigzag hydrogen bond structure poly（ether-thiourea）（TUEG₃）and dimer form quadruple hydrogen bond structure of 2-urea-4[1H]pyrimidinone（UPy）.They were introduced into bisphenol a-aniline benzoxazine（BA-a）respectively.The resin was toughened by changing the type and number of hydrogen bonds in the cured resin,at the same time,the resin was toughened by reversible hydrogen bond fracture and effective energy dissipation.The main research contents and conclusions are as follows:1.Different proportions of TUEG₃ were added to BA-a,and the curing behavior of TUEG₃/BA-a system was studied by DSC and FTIR tests.The results showed that the addition of TUEG₃ significantly reduced the curing temperature of benzoxazine,and formed intermolecular-OH···N hydrogen bond between TUEG₃ and benzoxazine,which promoted the increase of cross-linking density of the resin.The thermal property of the TUEG₃/BA-a system was studied through DMA and TGA tests.The results showed that the addition of TUEG₃further improved the thermal performance of the benzoxazine resin.When the content of TUEG₃ was 15 wt%,the T_g of blend increased to 209℃.The mechanical properties of the TUEG₃/BA-a system were tested,and the results show that when the content of TUEG₃ is 5wt%,the system has the highest impact strength and flexural strength,which were 15.45 k J·m^-2 and 140.2 MPa,respectively,they were 156%and 35%higher than that of pure benzoxazine.SEM test on the impact fracture surface of the resin showed that the roughness of the fracture surface was obviously enhanced and fibrous cracks appeared,but there was no phase separation phenomenon.The viscosity of TUEG₃/BA-a system was studied by rheological test.The results showed that when the content of TUEG₃ was 5 wt%,the lowest viscosity of the resin could reach 0.12 Pa·s,which had good processability.With the introduction of TUEG₃,the balance among toughness,thermal properties and processability of benzoxazine resin was achieved.2.Different proportions of UPy were added to BA-a,and the curing behavior of UPy/BA-a resin was studied by DSC and FTIR.The changes of hydrogen bond type and quantity in the system were analyzed by fitting the peaks of hydroxyl stretching vibration region in FTIR spectra.The results show that the curing temperature of benzoxazine can be reduced by the addition of UPy,and-OH···N hydrogen bond is formed between UPy and benzoxazine.The thermal properties of UPy/BA-a resin were studied by DMA and TGA tests.The results showed that the addition of UPy could significantly improve the T_g of the system.When the content of UPy was 5 wt%,the T_g of the system increased to 222℃,but the thermal stability decreased,and the char yield at 800℃decreased.The mechanical properties of UPy/BA-a resin were tested.The results show that when the content of UPy is only 3 wt%,the system has the highest impact strength and flexural strength,which are 16.39 k J·m^-2 and 128.4 MPa,respectively,which are 172%and 24%higher than that of polybenzoxazine,respectively.The toughening effect is better than that of TUEG₃/BA-a system.SEM test on the impact fracture surface of the resin shows that fiber,ridge and gully cracks appear after adding UPy,and there is no phase separation phenomenon,which is corresponding to DMA test result.The rheological test results showed that the processing window of UPy/BA-a blends was about 120℃,and the blend system had shorter gel time,lower curing temperature and better processability.