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

Structure and swelling behaviour of epoxy networks based on α,ω-diamino terminated poly(oxypropylene)-block-poly(oxyethylene)-block-poly(oxypropylene)

Structure and swelling behaviour of hydrophilic epoxy networks prepared from α,ω-diamino terminated poly(oxypropylene)-block-poly(oxyethylene)-block-poly(oxypropylene) and diglycidyl ether of brominated Bisphenol A in dependence on the initial molar ratio of reactive amino and epoxy groups has been investigated by small- and wide-angle X-ray scattering (SAXS and WAXS), differential scanning calorimetry (DSC) and dynamic mechanic analysis (DMA). Anomalous swelling behaviour of the networks in water has been found. The anomaly is attributed to the changing microphase separation in the networks controlled by their composition and crosslinking density, and inhomogeneous swelling on nanometer space scale

Structure and properties of hydrophilic epoxy networks

Two series of the networks were prepared by end-linking reaction of α, ω-diamino terminated poly(oxypropylene)-block-poly(oxyethylene)- block-poly(oxypropylene) α, ω-diamino terminated poly(oxypropylene) (POP) and diglycidyl ether of Bisphenol A propoxylate (PDGEBA). In the first series, prepared using functionalized POP-POE-POP and PDGEBA, hydrophilicity of the networks was controlled via cross-linking density of the networks, changing the initial ratio of reactives. In the second series, POP-POE-POP was gradually substituted by POP of the same molecular weight, enabling a control of hydrophilicity of the networks at essentially constant crosslinking density. Microphase separated structure of the networks swollen in deuterated water with variations of neutron scattering length density on nanometer scale was found by SANS. Thermal behaviour of the networks in dry and swollen state was investigated by DSC