Preparation And Study Of High Performance Polybenzoxazine Resin Matrix Toughened By Cyclic Compound

As a new type of high performance phenolic resin,benzoxazine has many unique advantages,such as flexible molecular design,near zero volume shrinkage and no small molecule release during curing,low water absorption,high mechanical strength,modulus,high heat resistance and high carbon residue.Because of these characteristics,benzoxazine can be widely used in electrical and electronic engineering and aerospace fields.However,the further development of benzoxazine resin is limited by its brittleness and poor impact resistance.The aim of this paper is to improve the toughness of benzoxazine resin without sacrificing its heat resistance.In this paper,a cyclic compound?-cyclodextrin(?-CD)was selected and modified(?-CD-MAH)was blended with benzoxazine to balance the strength,modulus,toughness and heat resistance of the resin.Secondly,in order to further improve the toughness of benzoxazine,2,4-dinitrofluorobenzene encapsulated polyrotane(PR)was synthesized and blended with benzoxazine to toughen and modify it.The main work of this paper is as follows:(1)?-CD and?-CD-MAH in different proportions were blended with bisphenol A-type benzoxazine(BA-a),and the mechanical properties of the castable mixture were investigated.The results showed that the impact strength of the mixture system reached 12.24 k J·m^-2 and14.29 k J·m^-2,respectively,when the addition amount of?-CD and?-CD-MAH was 1.0 wt%,which increased by 53%and 86%,respectively,compared with that of pure PBA-a.The curing reaction,possible chemical structures,and fractured surface were examined using differential scanning calorimetry,Fourier transform infrared spectroscopy,and scanning electron microscopy techniques to understand the mechanism of generation of toughness.The results revealed that the sea-island structure and the presence of hydrogen bonds between polybenzoxazine and?-cyclodextrin and?-cyclodextrin-MAH resulted in the generation of toughness.Furthermore,the curves generated during thermogravimetric analysis did not significantly change,revealing the good thermal properties of the system.The phase-separated structure and the hydrogen bonds present in the system can be exploited to prepare synergistically tough polybenzoxazine exhibiting excellent thermal properties.This can be a potential way of modifying the thermoset resins.(2)In this paper,2,4-dinitrofluorobenzene terminated Polyrotaxane(PR)was synthesized,and then the Polyrotaxane was added to benzoxazine resin by solution blending method.The modified resins with different adding amounts were prepared.The effects of the addition amount of Polyrotaxane on the curing behavior,static mechanical behavior,dynamic mechanical behavior,thermal behavior and rheological properties of the curing system were investigated.The impact strength of the modified resin increased first and then decreased with the addition of Polyrotaxane.The impact strength of the modified resin reached 18.74 k J·m^-2,which was 134%higher than that of pure PBA-a.The results of FTIR,SEM and DMA show that the reason why the toughness of polybenzoxazine can be improved is that the PR is evenly intersperted in the cross-linking network of polybenzoxazine.And The-OH of?-CD on PR forms intermolecular hydrogen bonds with benzoxazine.At the same time,due to the unique topological structure of PR,the?-CD on it can slide and rotate on the axis,which can play a good stress relaxation effect.The thermogravimetric analysis results showed that the thermal properties of the blends were retained,which was similar to that of pure PBA-a.