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Organic Substituents (organic + substituent)

Distribution by Scientific Domains

Polymers and Materials Science	75%

Selected Abstracts

Synthesis of Organosilica Films Through Consecutive Sol/Gel Process and Cationic Photopolymerization

MACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2010
Davy-Louis Versace
Abstract The cationic photopolymerization of epoxy polysilsesquioxane resins synthesized through a acid-catalyzed sol/gel process is studied. To elucidate the effect of the organic substituent on sol/gel reaction kinetics, two organotrimethoxysilanes with different organic groups were employed. Effects of UV irradiation on the microstructure of the epoxy-functional polysilsesquioxanes were also studied. 29Si solid-state MAS NMR proved that UV-generated Brönsted acids favored a work-up of the silicate network by promoting new sol/gel condensation reactions. There was a significant slowdown of epoxy conversion rates with increasing sol aging, which may be due to a competition between an active chain end and an activated monomer mechanism for the epoxy cationic polymerization. [source]

Ultralow Dielectric Constant Tetravinyltetramethylcyclotetrasiloxane Films Deposited by Initiated Chemical Vapor Deposition (iCVD)

ADVANCED FUNCTIONAL MATERIALS, Issue 4 2010
Nathan J. Trujillo
Abstract Simultaneous improvement of mechanical properties and lowering of the dielectric constant occur when films grown from the cyclic monomer tetravinyltetramethylcyclotetrasiloxane (V4D4) via initiated chemical vapor deposition (iCVD) are thermally cured in air. Clear signatures from silsesquioxane cage structures in the annealed films appear in the Fourier transform IR (1140,cm,1) and Raman (1117,cm,1) spectra. The iCVD method consumes an order of magnitude lower power density than the traditional plasma-enhanced CVD, thus preserving the precursor's delicate ring structure and organic substituents in the as-deposited films. The high degree of structural retention in the as-deposited film allows for the beneficial formation of intrinsically porous silsesquioxane cages upon annealing in air. Complete oxidation of the silicon creates ,Q' groups, which impart greater hardness and modulus to the films by increasing the average connectivity number of the film matrix beyond the percolation of rigidity. The removal of labile hydrocarbon moieties allows for the oxidation of the as-deposited film while simultaneously inducing porosity. This combination of events avoids the typical trade-off between improved mechanical properties and higher dielectric constants. Films annealed at 410,°C have a dielectric constant of 2.15, and a hardness and modulus of 0.78 and 5.4,GPa, respectively. The solvent-less and low-energy nature of iCVD make it attractive from an environmental safety and health perspective. [source]

Sol-gel derived C-SiC composites for re-entry structures

MATERIALWISSENSCHAFT UND WERKSTOFFTECHNIK, Issue 4 2003
Y. Haruvy
Abstract Composites of carbon fibers, fabrics, or their precursors as reinforcement, and sol-gel-derived silicon carbide as matrix, have been developed, aiming at high-temperature stable ceramics that can be utilized for re-entry structures. These composites are produced via the sol-gel process, starting with a sol-gel reaction of a mixture of silane precursors. The sol-gel-derived resin is cast onto the reinforcement fibers/fabrics mat (carbon or its precursors) to produce a ,green' composite that is being cured. The ,green' composite is converted into a C-SiC composite via a gradual heat-pressure process under inert atmosphere, during which the organic substituents on the silicon atoms undergo internal oxidative pyrolysis via the schematic reaction: (SiRO3/2)n , SiC + CO2 + H2O The composition of the resultant silicon-oxi-carbide is tailorable via modifying the composition of the sol-gel reactants. The reinforcement, when made of carbon precursors, is converted into carbon during the heat-and-pressure processing as well. The C-SiC composites thus derived exhibit superior thermal stability and comparable thermal conductivity, combined with good mechanical strength features and failure resistance, which render them greatly applicable for re-entry shielding, heat-exchange pipes, and the like. No abstrat [source]

Synthesis, structure and biological activity of triorganotin 1H -tetrazolyl-1-acetates: cyclic hexamer and linkage coordination polymers

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 1 2010
Yun-Fu Xie
Abstract Reaction of 1H -tetrazolyl-1-acetic acid (CHN4CH2CO2H) with (R3Sn)2O or R3SnOH yields triorganotin 1H -tetrazolyl-1-acetates [CHN4CH2CO2SnR3, R = Ph (1), p -tolyl (2), cyclohexyl (3), n -Bu (4) and Et (5)]. 1H -tetrazolyl-1-acetates in these triorganotin derivatives display remarkably different coordination modes, depending on the properties of the organic substituents bonded to the tin atoms. Complex 1 displays a rare cyclohexameric structure by the assembly of the SnN coordination bond, while complex 2 forms a linkage coordination polymer through the intermolecular Sn···N interactions. The structure of complex 3 is similar to that of complex 2, but the intermolecular Sn···N interactions are weaker in the former. However, in complex 4, the tetrazolyl nitrogen atoms do not coordinate to the tin atoms. This complex forms a polymeric chain by the unsymmetric bridging carboxylate group. All these complexes exhibit good antifungal activities in vitro against Alternaria solani, Cercospora arachidicola, Gibberella zeae, Physalospora piricola and Botrytis cinerea. The corresponding EC50 values of these complexes were tested. Copyright © 2009 John Wiley & Sons, Ltd. [source]