Research On Preparation, Structure And Properties Of Polymethacrylimide Foams

With the rapid development of aerospace and other special areas,core materials must have higher strength, stiffness and heat resistance. Atpresent, the general foams’(such as PE, PP etc.) heat-resistant strengthis poor, the high temperature deformation of them will destroy thedimensional stability of core sandwich structure. They can not meet theusing requirements of above areas. Polymethacrylimide (PMI) foam asone of the new high performance foams, its strength and heat resistanceare highest in the existing foams. PMI foam currently used in above fieldsare mainly imported from Germany with high price. In order to break thelong-term dependence on imports and reduce costs, research anddevelopment PMI foam with independent intellectual property rightsbrooks no delay.PMI foam was prepared by free radical prepolymerization. Theeffects of each component on quality of PMI foam were researched. Thedosage range of each component and the basic precription of PMI foamwere defined. Thermal transition on molecular structure of PMI foam wasanalyzed by using fourier transform infrared spectroscopy analysis(FTIR), differential scanning calarimetry (DSC) and thermogravimetric(TG). Microstructure of PMI foam was observed by scanning electronicmicroscopy (SEM) and optical microscopy. The mechanical propertiesand thermal properties of PMI foam were tested. The effects of foamingtechnique and density on the molecular structure and properties of PMIfoam were studied.The results demonstrated that the precription with acrylonitrile (AN)58~50phr., methacrylic acid (MAA)42~58phr.,2,2-azobisisobutyronitrile (AIBN)0.25~0.45phr., acrylamide (AM)2phr.,formamide2~8phr. and carbonamide0.5phr. can be prepared light PMIfoam with high properties. Within the permissible range, adjusting thecontent of foaming agent and foaming temperature can produce light PMIfoams with different densities. Moreover, with the content of foamingagent and foaming temperature increasing, the density of PMI foamdecreases. BMI can be used as density control agent for preparing PMI foam with high density, density increases significantly with the content ofBMI increasing. A small amount of crosslinking agent can make PMIfoam produce a certain cross-linked structure, as a result, they caneffectively improve some of the physical mechanical properties of PMIfoam. Carbonamide has excellent nucleation effect, it can effectivelyreduce the cellular dimension and make them distribute more evenly, it’ssuitable for using as nucleating agent to prepare PMI foam. During thefoaming and heat treatment under the high temperature, molecularstucture of PMI foam changed significantly and formed cyclic structureand crosslinking structure. The obturator rate of PMI foam is up to100%;it’s a isotropic material and has excellent mechanical properties, heatresistance and process ability; it can be used as the ideal core material ofthe core sandwich structure.