Abstract：Polymethacrylimide foams were prepared by free radical bulk polymerization with butyl methacrylate (BMA), acrylamide (AM) as the reactive monomer, acrylic acid (AA) as the third monomer and crosslinker at different heat treatment time. The structure and properties were characterized by FTIR, SEM, TGA and DSC. The results show that with the increase of heat treatment time of BMA/AM/AA copolymer, the rearrangement reaction between molecular chains produces a six-membered imide ring. After cross-linking and solidification, PMI foam is obtained. The characteristic absorption peaks are in good agreement with the literature values. After heat treatment for 5 h, a dense closed cell foam with a pore diameter of 100-200 μm is obtained, which has good mechanical properties, compressive strength of 8.160 MPa and tensile strength of 12.95 MPa. The glass transition temperature (Tg) of the foam is 255℃, the thermal decomposition temperature Td10 is as high as 280℃ when the thermal mass loss is 10%, and the foam still retains more than 80% at 345℃, and the thermal conductivity is 0.05424 W/(m·K). It is indicated that the foam with excellent high temperature resistance and thermal insulation properties is obtained after heat treatment of the copolymer for 5 h.
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