Crosslinking of epoxy-polysiloxane system by reactive blending

(PAMS) containing pendant amino groups and diglycidyl ether of Bisphenol A (DGEBA). The initially immiscible blend is compatibilized during the reaction and crosslinked. Network formation, dynamics of the system and evolution of morphology were determined by dynamic mechanical analysis and light scattering techniques. The grafting epoxy-amine reaction involves a high extent of cyclization resulting in a high fraction of the sol in the networks. Dynamic light scattering data analysis reveals fast and slow relaxation modes of reacting species in the pregel and one single mode in the post-gel state. The network with a stoichiometric composition shows the most homogeneous morphology with a single glass transition temperature. On the contrary, the networks with excess of PAMS are strongly phase-separated exhibiting the unreacted PAMS-rich phase, PAMS phase partly grafted with epoxide and PAMS-DGEBA crosslinked phase.The authors acknowledge financial support of the European Commission through a Marie Curie Training Site contract No. HPMT-CT-2001-00396 and of the Grant Agency of Academy of Sciences of the Czech Republic (A4050008).Publicad

Photoluminescence of Bridged Silsesquioxanes Containing Urea or Urethane Groups with Nanostructures Generated by the Competition between the Rates of Self-Assembly of Organic Domains and the Inorganic Polycondensation

The aim of this study was to investigate the changes produced in the nanostructures and the photoluminescence spectra of bridged silsesquioxanes containing urea or urethane groups, by varying the relative rates between the self-assembly of organic domains and the inorganic polycondensation. Precursors of the bridged silsesquioxanes were 4,4‘-[1,3-phenylenebis(1-methylethylidene)]bis(aniline) and 4,4‘-isopropylidenediphenol, end-capped with 3-isocyanatopropyltriethoxysilane. The inorganic polycondensation was produced using either high or low formic acid concentrations, leading to transparent films with different nanostructures as revealed by FTIR, SAXS, and ²⁹Si NMR spectra. For the bridged silsesquioxanes containing urea groups the self-assembly of organic domains was much faster than the inorganic polycondensation for both formic acid concentrations. However, the arrangement was more regular and the short-range order higher when the rate of inorganic polycondensation was lower. The photoluminescence spectra of the most ordered structures revealed the presence of two main processes:  radiative recombinations in inorganic clusters and photoinduced proton-transfer generating NH₂⁺ and N⁻ defects and their subsequent radiative recombination. In the less-ordered urea-bridged silsesquioxanes a third process was present assigned to a photoinduced proton transfer in H-bonds exhibiting a broad range of strengths. For urethane-bridged silsesquioxanes the driving force for the self-assembly of organic bridges was lower than for urea-bridged silsesquioxanes. When the synthesis was performed with a high formic acid concentration, self-assembled structures were not produced. Instead, large inorganic domains composed of small inorganic clusters were generated. Self-assembly of organic domains took place only when employing low polycondensation rates. For both materials the photoluminescence was mainly due to radiative processes within inorganic clusters and varied significantly with their state of aggregation.The financial support of the National Research Council (CONICET, Argentina), the National Agency for the Promotion of Science and Technology (ANPCyT, Argentina, PICT 14738-03), the University of Mar del Plata, the Grant Agency of the Czech Republic (Project 203/05/2252), and Project Nanoter (Project MAT2004/01347, MEC-DGI, Spain) is gratefully acknowledged. INTEMA and the Institute of Macromolecular Chemistry acknowledge the support of the European Network of Excellence Nanofun-Poly for the diffusion of their research results

The ASBA service and the use thereof in Czechoslovakia

The ASBA service was already referred to and briefly described in World Patent Information 2 (3), 116-119 and 3 (3), 100-102. The present article gives a more complete description of this service and the use thereof in Czechoslovakia, stressing the partly centralised, partly decentralised character of the service. Also, some expected future developments of the ASBA service are indicated.

Use of patent information at a Czechoslovak research institute

This article describes the patent information services in Czechoslovakia and the use made of patent information in applied research and in patent practice. The various possibilities which exist centrally, regionally and in industry are discussed.

A thesaurus to supplement the international patent classification in the field of biomedical engineering

The International Patent Classification, in spite of its clear advantages, does not meet the requirements of research and development in biomedical engineering. This article presents a descriptor thesaurus system providing finer classification of patent information for research and development needs, developed at the Chirana Research Institute of Medical Engineering. The article describes in detail the arrangement of the thesaurus, the data storage and retrieval using the computer facility of the Institute, and various outputs available from the storage and retrieval system for various purposes.

Tunable reinforcement of epoxy-silica nanocomposites with ionic liquids

Imidazolium ionic liquids (ILs) have the capacity to exert multiple functions as additives for the formation of epoxy-silica nanocomposites, via the simultaneous sol–gel process and epoxy network build-up. This study addresses the effect of ILs on the reinforcement of tensile properties in rubbery epoxy-silica nanocomposites, allowing property tailoring. The use of ILs together with the coupling agent 3-glycidyloxypropyltrimethoxysilane (GTMS) created a synergic action between physical and chemical interfacial bonding, enabling an increase in toughness without a considerable loss of stiffness. The best tensile property balance was obtained with IL 1-triethylene glycol monomethyl ether-3- methylimidazolium methanesulfonate and GTMS. The rubbery nanocomposite produced was remarkably both stiffer and tougher than the unmodified epoxy-silica system, displaying ca. 6 times higher modulus and tensile strength as well as more than 10 times higher energy to break

Tunable reinforcement of epoxy-silica nanocomposites with ionic liquids

Imidazolium ionic liquids (ILs) have the capacity to exert multiple functions as additives for the formation of epoxy-silica nanocomposites, via the simultaneous sol–gel process and epoxy network build-up. This study addresses the effect of ILs on the reinforcement of tensile properties in rubbery epoxy-silica nanocomposites, allowing property tailoring. The use of ILs together with the coupling agent 3-glycidyloxypropyltrimethoxysilane (GTMS) created a synergic action between physical and chemical interfacial bonding, enabling an increase in toughness without a considerable loss of stiffness. The best tensile property balance was obtained with IL 1-triethylene glycol monomethyl ether-3- methylimidazolium methanesulfonate and GTMS. The rubbery nanocomposite produced was remarkably both stiffer and tougher than the unmodified epoxy-silica system, displaying ca. 6 times higher modulus and tensile strength as well as more than 10 times higher energy to break

Reactivity of the tin homolog of POSS, butylstannoxane dodecamer, in oxygen-induced crosslinking reactions with an organic polymer matrix: Study of long-time behavior

International audienceThe chemical activity of the heavier POSS homolog, n-butylstannoxane dodecamer cage, in an epoxy matrix containing polopropylene oxide (PPO) chains was studied in detail, especially the long-time development of the effect and its limits in time at different concentrations. A multi-method investigation was carried out, employing spectrometric analysis of chemical composition (NMR, IR), TEM, thermogravimetry, weight loss analysis during isothermal oxidation at 180 degrees C, as well as dynamic-mechanical thermal analysis (DMTA) of intact and of oxidized epoxy/stannoxane hybrids. The PPO segments of the matrix were found to be preferentially degraded by oxidation or by anaerobic pyrolysis, while at the same time these segments are the sites of crosslinldng reactions with stannoxane, which counteract matrix degradation. It was demonstrated, that the cages undergo repeated reactions on the Sn atoms, and remain finely dispersed and well-accessible even after long oxidation times. The repeated reactions also explain the observed very strong stabilizing effect of stannoxane at very low concentrations. Efficient stabilization against the degradation of the mechanical properties was found to require higher but still very low concentrations, than the stabilization against weight loss. Interestingly, certain amounts of stannoxane caused simultaneously enhanced weight losses and a mechanical reinforcement due to a higher amount of radical reactions