Thermal decomposition of labile poly(acrylic acid) (PAAc) side chains grafted onto fluorinated polyimide backbones (see Figure) is used to prepare nanoporous ultra‐low‐κ fluorinated polyimide films. The dielectric constant of the nanoporous fluorinated polyimide film can be varied by altering the graft concentration of the labile side chains.

Thermally-initiated living radical graft polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA) with ozone-pretreated fluorinated polyimide (FPI) via the reversible addition–fragmentation chain transfer (RAFT)–moderated process was carried out. The chemical composition and structure of the copolymers were characterized by nuclear magnetic resonance (NMR), thermogravimetric analysis (TGA), and molecular weight measurements. The "living" character of the grafted PEGMA side chains was ascertained in the subsequent extension of the PEGMA side chains. Nanoporous ultra-low dielectric constant (κ) fluorinated polyimide films were prepared by solution casting of the graft copolymers, followed by thermal decomposition of the labile PEGMA side chains in air. The nanoporous FPI films obtained from the RAFT-moderated graft copolymers had well-preserved FPI backbones, porosity in the range of 2–10% and pore size in the range of 20–50 nm. These films also had more well-defined pores, more uniform pore size distribution, and better-retained mechanical properties than those of the corresponding nanoporous FPI films obtained from the graft copolymers prepared by the conventional free-radical process. Dielectric constants approaching 2.0 were obtained for the nanoporous FPI films prepared from the RAFT-moderated graft copolymers.

Electroless plating of copper via a tin-free activation process was carried out effectively on two types of fluorinated polyimide (FPI) films modified by UV-induced surface graft copolymerization with N-containing monomers, such as 1-vinylimidazole (VIDz) and 4-vinyl pyridine (4VP). The graft copolymerization of VIDz and 4VP was carried out on the argon (Ar) plasma-pretreated FPI films via a solvent-free process under atmospheric conditions. X-ray photoelectron spectroscopy (XPS) results showed that the VIDz graft-copolymerized FPI surface (the VIDz-g-FPI surface) and 4VP graft-copolymerized FPI surface (the 4VP-g-FPI surface) were much more susceptible to the electroless deposition of metals via the Sn-free process than the pristine FPI surfaces, and the FPI surfaces modified by Ar plasma pretreatment alone. T-peel adhesion strengths above 9 N/cm were achieved for the electrolessly deposited copper on both VIDz-g-FPI surfaces (the Cu/VIDz-g-FPI assemblies) and 4VP-g-FPI surfaces (the Cu/4VP-g-FPI assemblies). These adhesion strength values were much higher than those obtained for assemblies involving electrolessly deposited copper on pristine or on Ar plasma pretreated FPI films. The high adhesion strength of the Cu/VIDz-g-FPI and Cu/4VP-g-FPI assemblies was attributed to the synergistic effect of spatial interactions of the grafted VIDz or 4VP polymer chains with the copper atoms, and the fact that the VIDz or 4VP polymer chains were covalently tethered on the FPI surfaces. XPS results also revealed that the Cu/VIDz-g-FPI and Cu/4VP-g-FPI assemblies delaminated by cohesive failure inside the FPI films.

Photo-induced reduction of gold and platinum metal salt solutions was carried out using viologen graft copolymerized on low-density polyethylene (LDPE) films and viologen-containing poly(vinylidene fluoride) (PVDF-PVBV) microporous membranes. The effects of the UV irradiation time and concentration of the metal salt solutions on the metal ion reduction process and the resultant metal deposition on the polymeric substrates were investigated. The metal-polymer composites were characterized using X-ray photoelectron spectroscopy (XPS), scanning and transmission electron microscopy (SEM and TEM), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and UV-visible absorption spectroscopy. The amount of metal uptake, the state of the metal, and the size of the metal particles were found to be strongly dependent on the UV irradiation time and the type and concentration of the metal salt solution. The microporous structure and the high viologen content of the PVDF-PVBV membrane constitute an effective matrix for metal ion reduction and preparation of metal nanoparticles.

Molecular modification of the ozone-pretreated fluorinated polyimide (FPI) via thermally induced graft copolymerization with either acrylic acid (AAc) or 4-vinylpyridine (4VP) in an N-methyl-2-pyrrolidone solution was carried out. The resulting FPI copolymers with grafted AAc and 4VP side chains (the PAAc-g-FPI and P4VP-g-FPI copolymers, respectively) were characterized by Fourier transform infrared spectroscopy, elemental analysis, thermogravimetric analysis, and differential scanning calorimetry. In general, the graft concentration increased with the monomer concentration used for graft copolymerization. Microfiltration (MF) membranes were prepared from the PAAc-g-FPI or P4VP-g-FPI copolymers by phase inversion in aqueous media with pH values ranging from 1.0 to 6.4. The surface composition of the membranes was characterized by X-ray photoelectron spectroscopy. A substantial surface enrichment of the grafted AAc and 4VP polymer was observed for the copolymer membranes. The morphology of the MF membranes was studied by scanning electron microscopy. The pore sizes of the MF membranes were measured using a Coulter porometer. The flux of aqueous solutions through the PAAc-g-FPI and P4VP-g-FPI MF membranes exhibited a pH-dependent behavior but in an opposite manner, with the most drastic change in the permeation rate being observed at solution pH values between 1 and 4.

Molecular modification of a fluorinated polyimide (FPI), 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride + 4,4‘-bis(4-aminophenoxy)diphenyl sulfone, via ozone pretreatment and thermally induced graft copolymerization with N-isopropylacrylamide (NIPAAm) in a N-methyl-2-pyrrolidone solution, was carried out. The resulting FPIs with grafted NIPAAm polymer side chains [FPI-g-P(NIPAAm) copolymers] were cast into microfiltration membranes by phase inversion in water at temperatures ranging from 4 to 55 °C. The surface composition of the membranes was characterized by X-ray photoelectron spectroscopy. The surface composition, mean pore size, and morphology of the membrane varied with the temperature of the aqueous coagulation bath. For the copolymer membrane cast below the lower critical solution temperature of the NIPAAm polymer (∼32 °C), the rate of water permeation increased substantially at a permeate temperature above 32 °C. For the flux of 2-propanol through the membrane cast above 32 °C, a rever...

Thermally-induced molecular graft copolymerization of acrylic acid (AAc) or methoxy poly(ethylene glycol) monomethacrylate (PEGMA) with the ozone-pretreated poly(amic acid) precursor, poly(N,N'-(1,4-phenylene)-3,3'4,4'-benzophenonetetra-carboxylic amic acid] or PAmA, in N-methyl-2-pyrrolidone (NMP) solution was carried out. Nanoporous low-K polyimide (PI) films were obtained after thermal imidization of the PAmA backbones under reduced argon pressure and the subsequent thermal decomposition of the side chains in air. The nanoporous PI films were characterized by scanning electron microscopy (SEM), mechanical and dielectric properties measurements. SEM images revealed that the pore size was in the range of 30-100 nm. Dielectric constants as low as 2.1 and 2.4 were obtained for the nanoporous PI films prepared form PAmA with grafted AAc polymer and PEGMA polymer side chains, respectively.

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-κ) 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.

Surface modification of argon plasma-pretreated polyimide (PI, Kapton® HN) films by plasma graft copolymerization with 4-vinylpyridine (4VP) was carried out. The effects of glow discharge conditions on the chemical composition and structure of the plasma-polymerized 4VP (pp-4VP) films were analyzed by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy, respectively. The XPS and FTIR results revealed that the pyridine groups in the pp-4VP layer could be preserved to a large extent under proper glow discharge condition. The topography of the modified PI surface was investigated by atomic force microscopy (AFM). The pp-4VP film with well-preserved pyridine groups was used not only as the chemisorption sites for the palladium complexes (without the need for prior sensitization by SnCl2) during the electroless plating of copper, but also as an adhesion promotion layer to enhance the adhesion of the electrolessly deposited copper with the PI film. The T-peel adhesion strength of the electrolessly deposited copper to the pp-4VP grafted PI (pp-4VP-PI) film could reach about 7N/cm. This adhesion strength was much higher than that of the electrolessly deposited copper to the pristine or the Ar plasma-treated PI film.

Argon plasma-pretreated poly(tetrafluoroethylene) (PTFE) films were solution coated with a thin layer of poly(4-vinyl pyridine) (P4VP). Subsequent exposure of the films to argon plasma resulted in the grafting of P4VP on the PTFE films. Electroless plating of copper could be carried out effectively on the P4VP-grafted PTFE (P4VP-g-PTFE) surface after PdCl 2 activation and in the absence of SnCl 2 sensitization (the Sn-free process). The catalytic processes of the electroless plating of copper in the presence and absence of sensitization by SnCl 2 were also compared. The effect of glow discharge conditions on the P4VP concentration and the adhesion strength of the electrolessly deposited copper was investigated. The T-peel adhesion strength of the electrolessly deposited copper with the graft-modified PTFE film was improved in the absence of SnCl 2 sensitization and could reach about 3 N/cm. PdCl 2 activation and electroless deposition of copper could not be carried out on the pristine or the Ar plasma-treated PTFE surface in the absence of prior sensitization by SnCl 2 . X-ray photoelectron spectroscopic (XPS) analysis revealed that the electrolessly deposited copper delaminated from the P4VP-g-PTFE film by cohesive failure inside the PTFE film.