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

Progressive Deterioration of Thermal Stability of Nanofilled Polypropylene

Publikace je zaměřena na stabilitu PP matrice plněné nano-plnivem. Morfologicka charakterizace takovéto matrice byla provedena pomoci rentgenografie a TEM. Jako hlavní charakteristika byla zkoumána teplotní stabilita pomocí TGA. Vzorky byly připraveny mísením práškového PP s práškovým plnivem a dalšími komponenty. Takto připravená směs byla poté zpracována na dvoušnekovém vytlačovacím stroji. Z výsledků lze pozorovat prudky pokles teplotní stability vzorků po přidání nano-plniva.The paper concentrates on polypropylene stability from the point of structural and thermal characterisation of PP/nanocomposites through mechanical testing, X-ray diffraction, TEM and thermogravimetric analysis. Composites were prepared from powdered polypropylene, stabiliser and nano-clays both natural and organophilic using a twin-screw extruder. The results showed that the type of nano-clay affects the morphology, mechanical and thermal properties of the composite, but not only in the expected way. An extreme decrease of PP durability under isothermal load was observed. This paper is presented as the first part of obtained PP/nanocomposites degradation investigation

Self-assembly of a bridged silsesquioxane containing a pendant hydrophobic chain in the organic bridge

The aim of this study was to synthesize and characterize the self-assembly of a new family of bridged silsesquioxanes containing a pendant hydrophobic chain in the organic bridge. The precursor of this hybrid was obtained by the reaction of glycidoxypropyl(trimethoxysilane) (GPMS) (2 mol) with dodecylamine (1 mol). Polycondensation was produced with formic acid, either in mass or using tetrahydrofuran or isopropanol as solvents. The resulting bridged silsesquioxane was characterized by the presence of both ordered and disordered domains. Experimental evidence obtained from SAXS, WAXS, 29Si NMR, FTIR, HRTEM, and SAED techniques suggested that the basic structure of ordered domains consisted of hybrid organic-inorganic multilayers separated by hydrophobic regions with a thickness equal to the length of a tail-to-tail association of dodecylamine chains in all-trans conformations. To our knowledge, this is the first example of the presence of this kind of structure in a cross-linked hybrid material. A hierarchical organization of ordered domains into semicylindrical shells was observed in a microscopic scale. Because of the presence of pendant hydrophobic chains, the precursor of this hybrid material may be used for the dispersion of hydrophobic molecules or of nanoparticles stabilized by hydrophobic chains.Fil: Romeo, Hernan Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Fanovich, Maria Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Williams, Roberto Juan Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Matějka, Libor. Czech Academy of Sciences; República ChecaFil: Pleštil, Josef. Czech Academy of Sciences; República ChecaFil: Brus, Jiří. Czech Academy of Sciences; República Chec