A general route to organic–inorganic hybrids with nanophase morphologies has been elaborated with the objective of ultimately generating nanoporosity in organosilicates. Hyperbranched block ...copolymers prepared by either the sequential or concurrent polymerization of an ABC monomer ( γ-( ∊-caprolactone) 2-bromo-2-dimethylpropionate) with a BCD monomer (2-hydroxyethyl methacrylate) were used as the macromolecular templates. The two monomers, each polymerizing by different chemistries, for example ring-opening polymerization and atom transfer radical polymerization, bear initiating centres that are targeted for the functionality located on the accompanying monomer. Consequentially, a branched polymer is obtained which avoids the traditional multistep procedures. The branching density was altered simply by the addition of the appropriate AB ( ∊-caprolactone) and/or CD (methyl methacrylate) comonomers. These polymers were readily soluble initially in the organosilicate prepolymer (methyl silsesquioxane), however, upon the onset of crosslinking, both the solubility parameters and molecular weight of the organosilicate (polymethylsilsesquioxane) change, causing the hyperbranched polymer to phase separate by a nucleation and growth process. The organic polymer was selectively removed by thermolysis, producing a nanoporous inorganic structure. The size and shape of the pores are identical to those of the initial hybrid morphology. A significant reduction in the dielectric constant was achieved by simply replacing a portion of the glass matrix with air, which has a dielectric constant of 1.0.
The synthesis of unique miktofunctional μ-initiators, combining initiator sites for both controlled ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP) arranged in an ...alternating fashion, is described. This initiator was used to prepare miktoarm star block copolymers in a core-out approach utilizing consecutive ATRP and ROP processes. NMR and GPC studies on the block copolymers comprising poly(methyl methacrylate) (PMMA) and poly(caprolactone) (PCL) confirm the versatility of this approach which is independent of the order of polymerization. Furthermore, amphiphilic alternating arm block copolymers containing poly(caprolactone) and poly(acrylic acid) blocks were also prepared by this method.
Nanopores created by micellar star polymers in amorphous organic silsequioxane thermosets produce morphologically controlled porous materials for semiconductor chip applications (see picture). Pore ...size is independent of concentration and processing conditions, but depends solely on the size of the polymer molecule.
Dendrimers between the sheets: Environmentally responsive dendritic‐linear block copolymers, based on poly(ethylene oxide) and a dendron derived from 2,2′‐bis(hydroxymethyl)propionic acid (see ...structure), were used to organize organosilicate vitrificates into nanostructured lamellar morphologies. Upon thermolysis of the template, a perforated porous lamellar structure (4 nm) between organosilicate sheets (6–9 nm) was obtained.
Materials with nanometer size heterogeneities are commonplace in the chemical and biological sciences (e.g, polymer blends, microemulsions, gels) and often exhibit complex morphologies. Although this ...morphology has a dramatic effect on the materials' properties, it is often difficult to accurately characterize. We describe a method, using small-angle X-ray scattering data, of generating representative three-dimensional morphologies of isotropic two-phase materials where the morphology is disordered, and we apply this to thin films containing nanometer sized pores with a range of porosities (4−44%). These representations provide a visualization of the pore morphology, give the pore size scale and extent of interconnection, and permit the determination of the transitions from closed pore to interconnected pores to bicontinuous morphology.
Bridged oxycarbosilane monomers are excellent precursors for the formation of spin on porous low-k materials using sacrificial pore generators. The measured Young's modulus numbers for the ...as-synthesized thin films without any post porosity toughening are the highest by far of any that we have observed for porous films generated using the sacrificial porogen route. For a given dielectric constant, the Young's modulus of these oxycarbosilane films are 4-5 times higher than available organosilicates and at least 2 times higher than UV treated organosilicate materials.
The sorption behavior of nanoporous poly(methyl silsesquoxane), PMSSQ, thin films was investigated using a quartz crystal microbalance (QCM) combined with reflectance infrared spectroscopy (IR). The ...nanoporous PMSSQ films are intrinsically hydrophobic and show highly selective sorption behavior. With organic liquids having surface tensions below the critical value (38−48 dyn/cm), the extent of sorption increased with porosity of PMSSQ films. Extremely low amounts of sorption were measured with liquids having a surface tension higher than the critical value. The selective sorption behavior can be interpreted by capillary condensation resulting from the lowered vapor pressure in the nanoscopic pores.
Patterns of thin films of nanoporous poly(methylsilsesquioxane) (PMSSQ) were generated using a lithographic method coupled with reactive ion etching. Surface hydrophilicity of the nanoporous films ...was modulated using a simple UV/O
3 treatment. A fluorescent dye, 6-carboxyfluorescein (6-FAM), was attached using a linker, bis(hydroxyethyl) aminopropyltriethoxysilane (HE-APTS), to the patterns. An approximately 10× increase in the green light intensity in the porous regions relative to flat silicon wafer surface was observed, which suggests that the patterned nanoporous PMSSQ thin film has a potential as a high density substrate for tethering bioprobe molecules.
The dielectric properties are reported for nanoporous thin films of poly(methyl silsesquioxane) (MSSQ) for use as an ultralow, dielectric intermetal insulator. Direct experimental conformation is ...provided that the films have low dielectric constants with low loss up to 10 GHz. Low-frequency measurements are also reported.
Ultramicrotomy, the technique of cutting nanometers-thin slices of material using a diamond knife, was applied to prepare transmission electron microscope (TEM) specimens of nanoporous ...poly(methylsilsesquioxane) (PMSSQ) thin films. This technique was compared to focused ion beam (FIB) cross-section preparation to address possible artifacts resulting from deformation of nanoporous microstructure during the sample preparation. It was found that ultramicrotomy is a successful TEM specimen preparation method for nanoporous PMSSQ thin films when combined with low-energy ion milling as a final step. A thick, sacrificial carbon coating was identified as a method of reducing defects from the FIB process which included film shrinkage and pore deformation.
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