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A polyhedral oligomeric silsesquioxane (POSS) containing one epoxy group and seven isobutyl groups per molecule was incorporated into an epoxy network following a two-stage process. In the first stage, POSS was reacted with an aromatic diamine, employing a 1:1 molar ratio of both reactants. The distribution of species at the end of reaction, determined by size exclusion chromatography (SEC), was close to the ideal one. In a second step, this precursor was reacted with the stoichiometric amount of an aromatic diepoxide to generate an organic-inorganic hybrid material containing 51.8 wt % POSS. A primary liquid-liquid phase separation process occurred at the time of adding the diepoxide to the POSS-diamine precursor. This led to a macrophase separation into epoxy-rich and POSS-rich regions, possibly derived from the incompatibility of the isobutyl groups attached to the POSS with the aromatic epoxy-amine network. A secondary phase separation occurred in the epoxy-rich phase in the course of polymerization, producing a dispersion of small POSS domains. Both modulated local thermal analysis (LTA) and differential scanning calorimetry (DSC) showed that most POSS-rich domains were amorphous. A small fraction of POSS crystals was also detected. A postcure cycle led to an increase in the glass transition temperature and the disappearance of crystallinity. A reference network was synthesized by replacing POSS by phenyl glycidyl ether (PGE) in equimolar amounts. The resulting network was homogeneous but exhibited a lower glass transition temperature than the POSS-modified network. As both networks had the same topology, the higher T g observed for the POSS-modified epoxy may be associated with the hindering of polymer chain motions by their covalent bonding to POSS clusters. The most important concept arising from these results is that a phase separation process may take place when employing a POSS bearing organic groups that are not compatible with the epoxy network.

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Composite materials were prepared by mixing fly ash obtained from biomass combustion as filler and isotactic polypropylene (PP) as matrix. Three silane‐type coupling agents mainly differing in the size of their functional groups were used to improve the compatibility between both components. Uniaxial tensile tests showed that the incorporation of untreated ash into PP led to stiffer but also more brittle and weaker materials, as Young's modulus significantly increased and tensile strength and elongation at break decreased. Furthermore, an enhancement in storage and loss moduli as well as in composite viscosity was observed with the addition of fly ash. Hardness tests and thermal and fracture surface analyzes revealed tensile test results similar to those mentioned earlier. In summary, after analyzing the effects of the three silanes on mechanical, thermal, morphological, and rheological properties, the silane containing the vinyl functional group (XL10) was selected as the most appropriate for the PP/ash composites investigated. POLYM. COMPOS., 31:1722–1730, 2010. © 2010 Society of Plastics Engineers.

There is need for developing novel conductive polymers for Digital Light Processing (DLP) 3D printing. In this work, photorheology, in combination with Jacobs working curves, efficaciously predict the printability of polyaniline (PANI)/acrylate formulations with different contents of PANI and photoinitiator. The adjustment of the layer thickness according to cure depth values (Cd) allows printing of most formulations, except those with the highest gel point times determined by photorheology. In the working conditions, the maximum amount of PANI embedded within the resin was ≃3 wt% with a conductivity of 10−5 S cm−1, three orders of magnitude higher than the pure resin. Higher PANI loadings hinder printing quality without improving electrical conductivity. The optimal photoinitiator concentration was found between 6 and 7 wt%. The mechanical properties of the acrylic matrix are maintained in the composites, confirming the viability of these simple, low-cost, conductive composites for applications in flexible electronic devices.

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