Structure of Arylene-Bridged Polysilsesquioxane Xerogels and Aerogels

Abstract

Arylene-bridged polysilsesquioxanes are an interesting class of porous materials prepared by sol−gel processing of ethoxysilane monomers in which there are two or more trialkoxysilyl groups positioned about an arylene bridging group. The majority of these materials are highly porous with surface areas as high as 1880 m2/g. In an effort to understand the nature of porosity in these materials, small-angle X-ray and neutron scattering were employed to characterize phenylene-, biphenylene-, and terphenylene-bridged polysilsesquioxanes. Phenylene-bridged polysilsesquioxane xerogels and aerogels were also compared to understand the effect of drying protocol on pore structure. The effect of catalyst concentration is also reported for the base-catalyzed system. In all cases studied here, we find evidence for domains in the nanometer range with distinct fractal character. We associate these domains with porosity rather than microphase separation of organic and inorganic moieties. The nature of this porosity depends on the bridging group in a systematic way, but is only weakly dependent on other synthetic parameters such as catalyst type, catalyst concentration, and drying protocol.

Luminescent Triazine‐Containing Bridged Polysilsesquioxanes Activated by Lanthanide Ions

“…In this work, the luminescent bridged polysislsesquioxanes were obtained by hydrolysis and condensation of the urea-based tris(silylated) monomer containing large organic bridging groups under acidic conditions. [26] The FTIR spectra of the monomer and the monomer with Eu 3+ (Eu 3+ /monomer ratio = 0.5) are shown in Figure 1. For the monomer, the ν(Si-C) and ν(Si-OEt) absorption bands characteristic of trialkoxysilyl functions appear at 1194 and 1080 cm -1 , respectively.…”

Organic-inorganic hybrid aerogels with high mechanical properties via organotrialkoxysilane-derived sol-gel process

“…54), 55) Since the surface of the gels derived from these precursors is highly hydrophilic, the organic bridging groups are deduced to be embedded inside the rigid siloxane networks resulted from hexafunctionality, and do not contribute to the mechanical properties and hydrophobicity. Flexible networks with low crosslinking density, low residual silanol groups density, and the presence of dangling hydrophobic groups are highly important factors to increase the mechanical properties and hydrophobicity of siloxane-based aerogels.…”

Mixed Silica Titania Materials Prepared from a Single-Source Sol−Gel Precursor: A Time-Resolved SAXS Study of the Gelation, Aging, Supercritical Drying, and Calcination Processes

“…7,8 Schaefer et al have shown that the scattering profile of gels obtained from arylenebridged alkoxysilanes (EtO) 3 Si(C 6 H 4 ) n Si(OEt) 3 (n ) 1-3) was similar to that prepared from Si(OR) 4 . 9 Thus, the morphology is not qualitatively changed by the bridging organic groups which are integrated in the network. However, the case of 1 is different from that of (RO) 3 Si-X-Si(OR) 3 precursors because two different metal alkoxide moieties are involved.…”