Abstract:Polymethacrylimide(PMI)foams were prepared by the casting process using methacrylic acid(MAA)and methacrylonitrile(MAN)as monomers.The structure and properties of the PMI foams were analyzed by infrared adsorption spectrum(FTIR),optical microscope,differential scanning calorimeter(DSC)and thermogravimeter(TG).The results show that the foamable MAA/MAN copolymers were prepared at 40-60℃ by polymerizing the mixture of 50phr MAA,50phr MAN,1-5phr magnesium oxide,2-8phr butanol and tert-butanol,0.2-0.3phr dibenzoyl peroxide and tert-butyl perbenzoate and 0.1-0.2phr DMF.Then the resulting copolymers were expanded at 200-220℃ for 2-3h,subsequently treated at 160℃ for 5-6h,generating PMI foams with excellent mechanical properties and heat-resistance.Molecular rearrangement reaction occurs during the foaming and post-treatment forming hexahydric imide ring.The prepared PMI foams have closed cell structure with the cell size ranging from 0.5mm to 0.7mm and have a good thermostability with the characteristic degradation temperature at about 221.5℃.