Polyurethane‐imide (PUI) foams, in combination with the mechanical performance of polyurethane and flame retardancy of polyimide, were prepared by polyimide prepolymer method. Expended vermiculite (EV), with a wider layer spacing than vermiculite, was used as the filler to further enhance the mechanical and thermal properties of the PUI foams. The effect of filler content on the morphology of foams was also investigated. The results showed that the mean cell diameter of foams became smaller and the cell size distribution was more uniform at low filler content. The addition of EV resulted in a substantial increase in thermal stability. The compression strength increased from 0.024 to 0.065 MPa with an increase in EV content from 0% to 9.6%. The limited oxygen index values increased from 24% to 30.8% with an increase in filler content from 0% to 9.6%. Hence, PUI foams could significantly enlarge its application range with the addition of EV.

Polyurethane‐imide (PUI) composite foams with expandable graphite (EG) of different sizes were prepared by a polyimide prepolymer method. EG particles were treated with a silane coupling agent to improve compatibility with the foam. The effect of EG particle size on cell morphology, thermal degradation, flame‐resistance and mechanical properties of PUI foams was investigated. Results showed that the mean cellular diameter of foams with EG particle was much higher than that of foams with surface‐modified EG particle at the same filler loading. When filler particle diameter increased from 20 to 90 μm, the compressive strength, density and closed‐cell ratio of foams increased, and then decreased when filler particle diameter further increased from 90 to 150 μm. Thermal stability of foams increased with the increasing filler particle diameter from 20 to 50 μm, and decreased with the increasing filler particle diameter from 50 to 90 μm. The limited oxygen index (LOI) value of foams with surface‐modified EG increased from 24.8% to 32.1% when EG particle diameter was below 90 μm. Foams with surface‐modified EG exhibited enhanced mechanical properties, thermal stability and flame resistance than foams with neat EG at the same loading.

A series of rigid polyimide (PI) foams were prepared by the prepolymer method with pyromellitic dianhydride and polyaryl polymethylene isocyanate as the starting materials and dibutyltin dilaurate (DBTDL), and triethanolamine (TEOA) as catalysts. The effect of the two kinds of catalysts on the structure and properties such as molecular structure, cell morphology, density, mechanical properties, thermal properties, and flame retardancy of the resulting foams were characterized in detail. The experimental results showed that the PI foams prepared in this work possessed low density, good mechanical properties, outstanding thermal stability, and excellent flame retardancy. The thermal stability and flame retardancy were improved obviously with the increase of DBTDL content. While with the increase of the content of TEOA, the mechanical strength and apparent density of PI foams increased significantly. Therefore, different structure and performance of PI foams can be prepared by adjusting the content of these two catalysts. J. VINYL ADDIT. TECHNOL., 25:385–395, 2019. © 2019 Society of Plastics Engineers