Polyimide Nanofoams via Phase Separated Block Copolymers: Labile Block Considerations

A means of generating foams of high temperature polymers, polyimides, has been developed for use in dielectric layers in microelectronics. In these systems, the pore sizes generated are in the tens of nanometer range, thus the term nanofoams. The foams are generated by preparing phase separated block copolymers with the majority phase comprised of polymide and the minor phase consisting of a thermally labile block. Films are cast, solvent removed and the copolymers are cured, causing phase separation of the two blocks. The labile blocks are subsequently removed via thermal treatments leaving pores the size and shape of the original copolymer morphology. A very important factor in the generation of nanofoams is the choice of labile block used. The synthesis and characterization of a number of labile blocks such as poly(propylene oxide), poly(methylmethacrylate), styrenic polymers, aliphatic polyesters and polycarbonates have been studied, with emphasis on their utility as labile blocks for polymide nanofoam formation.