Nanoporous low-κ polyimide films prepared from poly(amic acid)s with grafted poly(methylmethacrylate)/poly(acrylamide) side chains

Copolymers of poly[N,N'-(1,4-phenylene)-3,3'4,4'-benzophenonetetra-carboxylic amic acid] (PAmA) with grafted poly(methylmethacrylate) (PMMA) and poly(acryamide) (PAAM) side chains (PMMA-g-PAmA and PAAM-g-PAmA, respectively) were synthesized by thermally-induced graft copolymerization of methylmethacrylate (MMA) and acrylamide (AAM) with the ozone-pretreated PAmA in N-methyl-2-pyrrolidone (NMP) solutions. The graft copolymers were characterized by elemental analysis, X-ray photoelectron spectroscopy (XPS), thermogravimetric (TG) analysis, and differential scanning calorimetry (DSC). Nanoporous low dielectric constant (low-kappa) polyimide (PI) films were obtained by thermal imidization of the PAmA graft copolymers under reduced argon pressure, followed by thermal decomposition of the side chains in air. The nanoporous PI films were characterized by density, scanning electron microscopy (SEM) and dielectric constant measurements. Nanoporous PI films with porosities in the range 4-15% and pore sizes in the range 30-60 nm were obtained. Dielectric constants as low as 2.3 and 2.5 were obtained for the nanoporous PI films prepared from the PMMA-g-PAmA and PAAM-g-PAmA copolymers, respectively.