Sub-10 nm domains in high-performance polyetherimides

Dielectric polyetherimide (PEI) thin films require ultra-small air voids to reduce the dielectric constant and maintain the structural integrity. Conventional synthesis of dielectric PEI uses thermally labile high-molecular-weight polymers to create air voids. The air voids, however, range from hundreds of nanometers to several micrometers, which limits the use of PEI in ultrathin films. Herein we present the synthesis of polystyrene-b-polyetherimide-b-polystyrene (PS-b-PEI-b-PS) triblock copolymers with ultra-low molecular weights. The molecular weights of the thermally labile polystyrene (PS) blocks are controlled to be as low as 1.5 kDa. By tuning the molecular weight of the PEI block to be 8, 10, and 12 kDa, the volume fractions of PS are 30.4%, 26.4%, and 23.4%, respectively. The triblock copolymers exhibit PS nanostructures of <8 nm in size. Such small domains will potentially enable the preparation of ultra-small air voids in PEIs.