Enhanced thermal stability and flame resistance of rigid polyurethane-imide foams by varying copolymer composition

Polyurethane-imide (PUI) foams were prepared from polyphenyl polymethylene isocyanate (PAPI), pyromellitic dianhydride (PMDA) and castor oil. As a copolymer, the ratio of polyurethane/polyimide segment of the resulting materials was varied by changing the ratio of starting materials (castor oil/PMDA). Thus, the structure and properties, especially thermal stability and flame resistance were regulated in related to the copolymer composition. With the increase of PMDA content, average cellular diameter decreased, while density and compressive strength of PUI foams increased. In addition, the thermal stability and flame retardant of PUI foams greatly improved with the increase of PMDA. The LOI value of PUI foams increased from 17.5 to 23.8 vol % compared with that of polyurethane foam and the degradation temperature as well as carbon residue of PUI foams increased with increase of PMDA content. Therefore, it is viable to control the copolymer segment composition by varying the starting material ratio, and PUI foams with enhanced thermal properties and flame resistance were obtained through enhancing the polyimide segment content.