Polysiloxanes were modified by (co-)hydrosilylation with γ-cyanopropyl and hexyl groups, to finely tune their composition and properties, especially dielectric permittivity, as a way towards active components in dielectric elastomer transducers. Un-modified Si–H groups can be further used to obtain cross-linked thin films.

The dielectric permittivity (ε') of a polymeric material can be significantly increased when blended with conductive fillers at concentrations approaching percolation threshold. However, reproducible synthesis of such composites is after decades of research still a major challenge and a bottleneck for their application. Difficulties arise in controlling size and shape of the filler as well as in its homogenous distribution within the composite. These parameters strongly affect the dielectric as well as the mechanical properties of the composite. While a substantial amount of literature is dealing with the influence of conductive filler on the dielectric properties of composites, little is known about their mechanical properties. It is therefore still an important goal to synthesize materials with simultaneously high ε' and good mechanical properties. Here, we report the synthesis of dielectric elastomers that combine key properties such as high flexibility and stretchability, high thermal stability, increased ε', low dielectric loss and conductivity. Such materials were prepared by solution processing using quasi-spherical silver nanoparticles (AgNPs) of defined size in a polydimethylsiloxane matrix (M w = 692 kDa). To prevent percolation, the AgNPs were coated with a thin silica shell (<4 nm). To increase their compatibility with the silicone matrix, these core/shell nanoparticles were passivated with a silane reagent. The insulating silica shell around the particles precisely defines the minimum approach distance between the cores as twice the shell thickness. The dielectric properties of those passivated particles (filler) were measured in pellets and found to have an almost frequency independent value of ε' = 90 and a very low loss factor tan δ = 0.023 at high frequencies. When such particles were used as filler in a polydimethylsiloxane matrix, composites with low dielectric losses were obtained. A composite containing 31 vol% filler with ε' = 21 and a tan δ = 0.03 at ~1 kHz was achieved. At a AgNPs volume fraction of 20%, the composite has a ε' = 5.9 at ~1 kHz, a dielectric strength of 13.4 V/µm, elastic modulus as low as 350 kPa at 100% strain, and a strain at break of 800%. Due to the high specific energy density per volume at low electric fields, these composites are attractive materials in applications involving low electric fields.A composite of Ag/SiO 2 core/shell nanoparticles 20 vol% in polydimethylsiloxane with ε' = 5.9, E b = 13.4 V/µm, Y 100% = 350 kPa, a strain at break of 800% is presented.

Poly(siloxane‐urethane) crosslinked structures were prepared from isophorone diisocyanate, α,ω‐bis(hydroxybutyl)oligodimethylsiloxane and a new hybrid diol containing hydrolysable SiOC2H5 groups besides OH groups. The latest was synthesized by the acid‐catalyzed reaction between 1,3‐bis(3‐glycidoxypropyl)tetramethyldisiloxane and 3‐aminopropyltriethoxysilane. The formations of the urethane groups along the polymer backbone as well as the formation of the silica domains were first confirmed by the presence of the specific bands in Fourier transform infrared spectra. The resulted materials were characterized using differential scanning calorimetry, thermogravimetric analysis and scanning electron microscopy. The results of the dynamic mechanical analysis (DMA) performed at various frequencies revealed shape memory capabilities for some of the obtained structures. The silica formed because of the hydrolysis‐condensation reactions proved to have reinforcing effect upon siloxane‐urethane structure also evidenced by DMA and increasing water vapor sorption capacity as was measured by dynamic vapor sorption. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

The reaction of 2,6-diformyl-4-methylphenol with 1,3-bis(3aminopropyl)tetramethyldisiloxane in the presence of MnCl 2 in a 1:1:2 molar ratio in methanol afforded a dinuclear μchlorido-bridged manganese(II) complex of the macrocyclic [2+2] condensation product (H 2 L), namely, [Mn 2 Cl 2 (H 2 L)-(HL)]Cl·3H 2 O (1). The latter afforded a new compound, namely, [Mn 2 Cl 2 (H 2 L) 2 ][MnCl 4 ]·4CH 3 CN·0.5CHCl 3 ·0.4H 2 O (2), after recrystallisation from 1:1 CHCl 3 /CH 3 CN. The coexistence of the free and complexed azomethine groups, phenolato donors, μ-chlorido bridges, and the disiloxane unit were well evidenced by ESI mass spectrometry and FTIR spectroscopy and confirmed by X-ray crystallography. The [a] "Petru

A polydimethylsiloxane‐α,ω‐diol with molar mass Mn = 43,000 has been synthesized by cationic polymerization of octamethylcyclotetrasiloxane and reinforced with silica. Two pathways were used for incorporation of silica in the polymeric matrix: ex situ by mechanical blending of a pretreated fumed silica and in situ by adding tetraethyl‐orthosilicate (TEOS) as silica precursor in the polymer matrix followed by their hydrolysis and condensation (sol–gel technique). The procedure occurred in the absence of solvent. Composites with different contents of silica were prepared and investigated by dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The results were compared to those obtained on a model network based on the same polysiloxane without silica. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers

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