Nanoporous Polyimides Derived from Highly Fluorinated Polyimide/Poly(propylene Oxide) Copolymers

Abstract

Porous, low dielectric constant polyimide films have been made by a “nanofoam” approach. The pore sizes generated in the polymer films are in the tens of nanometers range, hence the term “nanofoams”. The nanoporous foams are generated by preparing triblock copolymers with the majority phase comprising polyimide and the minor phase consisting of a thermally labile block. Films of the copolymers are cast and then heated to effect solvent removal and annealing, resulting in microphase separation of the two dissimilar blocks. The labile blocks are selectively removed via thermal treatments, leaving pores the size and shape of the original copolymer morphology. The polyimide derived from 2,2-bis(4-aminophenyl)hexafluoropropane (6FDAm) and 9,9-bis(trifluoromethyl)xanthenetetracarboxylic dianhydride (6FXDA) was used as the matrix material for the generation of nanofoams, and specially functionalized poly(propylene oxide) oligomers were used as the thermally labile constituent. The synthesis and characterization of the copolymers were performed and the process for obtaining nanofoams was optimized. The foams were characterized by a variety of techniques including thermal gravimetric analysis (TGA), transmission electron microscopy (TEM), dynamic mechanical thermal analysis (DMTA), density, small-angle X-ray scattering (SAXS), refractive index, and dielectric constant measurements. Thin-film, high-modulus nanoporous films with good mechanical properties and dielectric constants ∼2.3 have been synthesized by the copolymer/nanofoam approach.

Nanoporous polymeric materials: A new class of materials with enhanced properties

“…In this case, the thermal stability of nanoporous PI was higher than 250°C, and the mechanical response was improved (n = 1.4 for the Young's modulus) with respect to the results obtained by Lee et al [130]. Carter et al [132] also produced closed-pore nanoporous PI films with an average thickness from 1 to 40 lm, an average pore size around 10 nm, a porosity around 20%, and a dielectric constant of 2.27…”

“…Polyimides (PI) are a favored material because of their high thermal stability, low stress coefficient of thermal expansion, low dielectric constant, high resistivity, and high dielectric breakdown [120,[130][131][132][133][134][135]. For instance, Lee et al [130] managed to develop a nanoporous PI films (thickness: 200 lm) with pore sizes from 10 to 40 nm, a porosity around 20%, and a dielectric constant of 2.25 (a reduction of 31% with respect to the solid).…”

“…17. Dielectric constant values of the foams normalized by the dielectric constant of the solid and divided by the relative density versus pore size for different nanoporous materials [118,120,122,[124][125][126]130,132,135,[137][138][139][140].…”

Synthesis and characterization of flexible and high-temperature resistant polyimide aerogel with ultra-low dielectric constant

“…By this methodology, various ultra low-k PIs have been reported [10][11][12][13][14]. However, the attempts further reducing the k values of PIs below 1.5 seem to be more challenging because the conventional methods could only achieve a very limited air loading (<60%, volume ratio).…”

Nanoporous Polymer Thin Films via Polyelectrolyte Templating

“…[15] Other approaches to preparing nanoporous polymer materials include CO 2 foaming, [16] templating around supramolecular liquid crystals, [17] self-assembly of modified polypeptides, [18] reactive encapsulation of a solvent, [19] and removal of a thermally labile phase. [20] In this paper, we report the use of removable polyelectrolytes in layer-by-layer assembled polyelectrolyte multilayer (PEM) thin films [21,22] as a versatile approach to the production of nanoporous polymer films. The significance of this new method is that, in principle, it can be generalized to any PEM system where two components are fixed and a third can be removed.…”