Study On Modification Of Bismaleimide Resin By Bio-based Allyl Compounds

Bismaleimide（BMI）resin has better properties than epoxy resin（EP）.At present,it has attracted extensive attention in the field of stringent working conditions.However,the inherent brittleness of cured BMI resin greatly limits its application.After a series of studies,modifying with allyl compounds has become one of the most commonly used modification methods.In particular,BMI resin modified by 2,2’-diallyl bisphenol A（DBA）,named BD resin,has promoted the development of BMI resin.The processability and thermal properties have reached a relatively excellent level,and the toughness has also been improved.Therefore,BD resin is widely used in high-end applications such as aerospace,new energy and microelectronics.However,with the development of science and technology,the working conditions in more and more advanced technology fields has become increasingly strict.This puts forward higher performance requirements for cured BD resin,especially the flame retardant modification and further improvement of toughness.In this context,it is urgent to synthesize new allyl compounds instead of DBA to modify BMI resin,so as to obtain materials with excellent flame retardancy and toughness,and other excellent comprehensive properties.This paper focuses on the relationship between structure and properties,and prepares cured BMI resin with excellent comprehensive properties by changing the chemical structure of modifier.The main research work is as follows:Firstly,resveratrol allyl ether（AER）was synthesized by one-step method as a modifier of BMI resin.Then,a series of BMI/AER resins（BA resins）were prepared by changing the molar ratio of BMI to AER.Compared with BD resin widely used in industry,BA resins can be cured at lower temperature,and cured BA resins show better thermal properties and flame retardancy.When the molar ratio of maleimide to allyl functional groups in the system is 1:0.8,the glass transition temperature（T_g）,thermal decomposition temperature(T_d5%)with weight loss of 5%and char yield(Y_800℃)under nitrogen atmosphere of 800℃ reach 388℃,415℃ and 48.6%respectively.At the same time,the vertical combustion test and limit oxygen index（LOI）test show that BA-0.8 resin has excellent flame retardancy,reaching V-0 level in UL-94 fire rating and value of LOI reaches 37.7%.Compared with DBA,AER with three functional groups and stable stilbene skeleton gives the cured resin higher crosslinking density,excellent thermomechanical properties,thermal stability and flame retardancy.Secondly,eugenol allyl ether polysiloxane（PMES-Allyl）was synthesized from eugenol and polysiloxane.Using the reactive allyl functional groups on the terminal and side chains,PMES-Allyl can successfully modify BD resin as the second phase to obtain BMI/DBA/PMES-Allyl resin（BDPA resin）.The toughening modification and other comprehensive properties of the cured resin were studied by changing the addition amount of PMES-Allyl.Cured BDPA resin has better toughness than cured BD-0.8 resin.Especially when the addition amount of PMES-Allyl is 15 wt%,the impact strength and flexural strength reach 17.9 kJ/m² and 177.1MPa respectively.In addition,PMES-Allyl uniformly dispersed in BDPA15%resin also brings to higher crosslinking density and excellent T_g（303.6℃）.Polysiloxane with hydrophobicity and higher bond energy can significantly improve the hydrophobic performance and thermal stability of cured resins.Because cured BAPA15%resin is easy to form an expanded and dense carbon layer during heating,it also shows excellent flame retardant performance.Compared with cured BD-0.8 resin,the peak heat release rate（PHRR）,total heat release（THR）and total smoke production（TSP）of cured BDPA15%resin are reduced by 58.6%,33.1%and 41.9%respectively.Thirdly,based on the above work,two allyl compounds which are AER and PMES-Allyl,were used to modify BMI resin together.BMI/AER/PMES-Allyl system（BAPA resin）was prepared by maintaining the molar ratio of maleimide to allyl at 1:0.8 and controlling the addition of 15 wt%PMES-Allyl.The effects of AER and PMES-Allyl on the comprehensive properties of BMI resin were systematically studied.The results show that the cured BAPA resin has excellent thermal properties,and T_g is more than 380℃.In the thermogravimetric analysis（TGA）test,the T_d5%,maximum thermal decomposition temperature(T_dmax)and Y_800℃of the cured BAPA resin reached 424.8℃,458.0℃ and 46.4%respectively.Compared with BD-0.8 resin,the values increased by 20.5℃,8.3℃ and 22.3%respectively.In addition,due to the flexibility of PMES-Allyl,the mechanical toughness of the cured resin has also been improved to a certain extent.BAPA resin also shows excellent fire safety,especially in inhibiting smoke release.Specifically,in the cone calorimetry test,the TSP of cured BAPA resin is only 35.6%of that of cured BD-0.8 resin,which greatly improves the fire safety of the resin.In the common industry performance characterization,cured BAPA resin shows lower water absorption and aging weight loss,which provides reliability for the material to adapt to the harsh working environment.