Abstract: Polymethylacrylimide (PMI) foam is a kind of rigid foam with excellent thermodynamic properties, widely used in aerospace, sports equipment, and medical equipment. The foam properties of PMI foam are affected by the blowing agent. The type and amount of gas produced by the decomposition of blowing agent during heating have an effect on the size, morphology, and properties of PMI foam. The thermodynamic properties of self-foaming PMI foam using copolymerizable foaming monomers are directly affected by the foaming monomers. Therefore, in this work, acrylonitrile (AN) and methacrylic acid (MAA) were used as polymerization monomers, acrylamide (AM) as crosslinking agent, azodiisobutyronitrile (AIBN) as initiator, and tert-butyl methacrylate (tBMA) as copolymerizable foaming monomers. Lightweight and high strength PMI foam was prepared by free radical polymerization and free thermal foaming. The tert-butyl ester group in tBMA would thermally decompose into carboxyl groups and isobutene during the foaming stage, and the release rate of isobutene determined the physical structure of PMI and then affected its performance. Therefore, the effects of different foaming temperatures on the microstructure and thermodynamic properties of PMI foam were investigated. The physicochemical structure and properties of PMI foam were analyzed by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (SEM), thermogravimetric analyzer (TGA), differential scanning calorimeter (DSC), and universal testing machine. The results showed that with the increase of foaming temperature, the imimization degree of PMI increased, which improved the thermal stability of foam. At the same time, the high foaming temperature also increased the size of the bubble, resulting in a decrease in the density and mechanical properties of the foam. When foamed at 200℃, the foam had a low apparent density of 63 kg/m3, and exhibited excellent thermal stability and mechanical properties, with a glass transition temperature (Tg) of 216.1℃ and a compressive strength of 1.08 MPa.

Key words: PMI foam, self foaming, foaming temperature, thermal properties, mechanical properties

摘要： 聚甲基丙烯酰亚胺(PMI)泡沫是一种具有优异热力学性能的硬质泡沫，广泛应用于航空航天、体育器械及医疗器械等领域。其性能受发泡剂影响，发泡剂在加热过程中分解产生气体的种类及总量均对PMI泡沫的泡孔大小、形貌、性能有显著影响。自发泡PMI泡沫的热力学性能受可共聚发泡单体的直接影响。本工作以丙烯腈(AN)、甲基丙烯酸(MAA)为聚合单体，丙烯酰胺(AM)为交联剂，偶氮二异丁腈(AIBN)为引发剂，甲基丙烯酸叔丁酯(tBMA)为可共聚发泡单体，通过自由基聚合和自由热发泡工艺制备了轻质高强的PMI泡沫。tBMA分子中的叔丁酯基在发泡阶段受热分解成羧基和异丁烯，其中异丁烯的析出速率决定了PMI的物理结构，进而影响其性能。基于此，系统考察了不同发泡温度对PMI泡沫微观结构及宏观热力性能的影响。通过傅立叶转变红外光谱仪(FTIR)、场发射扫描电镜(SEM)、热重分析仪(TGA)、差示扫描量热仪(DSC)及万能试验机对PMI泡沫塑料的物理化学结构和性能进行分析。结果表明，随着发泡温度升高，PMI亚胺化程度升高，提升了泡沫的热稳定性；同时高的发泡温度也增大了泡孔尺寸，致使泡沫的密度和力学性能呈下降趋势。在200℃下进行发泡，泡沫具有较低的密度，为63 kg/m3，同时表现出优异的热稳定性和机械性能，玻璃化转变温度(Tg)为216.1℃，压缩强度达1.08 MPa。

关键词: PMI泡沫, 自发泡, 发泡温度, 热性能, 力学性能