A poly(urethane-urea-siloxane) was prepared in a two-step procedure involving the synthesis of a bis-isocyanate prepolymer on the basis of 4,4′-diphenylmethane diisocyanate, a polyether glycol and dimethylol propionic acid, and its extension by reacting with 1,3-bis(3-aminopropyl)tetramethyldisiloxane. The resulted polymer was used in different percentages to prepare three series of interpenetrating networks (IPNs) with polydimethylsiloxane-α,ω-diols with molecular masses, M_n, of 70 000, 230 000 and 370 000 g mol⁻¹. A polydimethylsiloxane–polyethyleneoxide graft copolymer was added as a compatibilizing agent. The IPN precursors were mixed in solution and processed as films. During solvent evaporation, the chemical crosslinking of the polydimethylsiloxane-α,ω-diols occurs with tetraethyl orthosilicate in the presence of dibutyltin dilaurate, while in the case of poly(urethane-urea-siloxane) only physical crosslinking by hydrogen bonds is expected to occur. The morphology and thermal transitions of the resulted networks were examined by scanning electron microscopy, differential scanning calorimetry with dynamic mechanical analysis. The mechanical and dielectric characteristics (dielectric permittivity, loss, strength) of the aged films were studied. Their responsiveness to an external stimulus in the form of an increasing electric field was assessed by electromechanical measurements and expressed as lateral strain. The results were critically analyzed with respect to each other as a correlation with their composition and compared with those obtained for three common commercially available dielectric elastomers.

A new class of elastomers that simultaneously shows sensing, actuation and energy conversion functionalities is synthesized to meet the current requirements for electroactive materials. These new materials consist of a silicone network (polydimethylsiloxane-α,ω-diol crosslinked through chain ends) semi-interpenetrated with different percentages (2, 5, and 10 wt%) of polyimide derivatives stepwise modified by different strategies to improve the compatibility with the silicone core network. By addressing the right chemical pathway, the resulting semi-interpenetrated structures (S-IPNs) show noticeable dielectric permittivity, eps′ (up to 11), and breakdown strength, Ebd (up to 88 μm V⁻¹), improvements as compared with the starting polymers (silicone with eps′ = 2.9 and Ebd = 38 μm V⁻¹ and our best polyimide with eps′ = 6.2 and Ebd = 23 μm V⁻¹). The S-IPNs with 10 wt% polyimide are able to gain energy up to 132 mJ cm⁻³ at 100% strain and up to 164 mJ cm⁻³ at maximum strain to develop large actuation strain (up to 8.7%) and show very good piezo-response (up to 44 pm V⁻¹), making them highly suitable for cutting-edge electromechanical applications. For a better evaluation, S-IPNs are compared with one of the commercially available dielectric elastomers, most often used for this purpose.

Two polysiloxanes, a polydimethylsiloxane-α,ω-diol (PDMS) with M_n = 370 000 g mol⁻¹, and α,ω-bis(vinyl)polydimethylsiloxane (Vi₂PDMS) with M_n = 34 500 g mol⁻¹, and appropriate crosslinking systems for each of them (tetraethyl orthosilicate–dibutyltindilaurate and α,ω-bis(trimethylsiloxy)poly(dimethylmethyl-H-siloxane)–Speier's catalyst, respectively), were mixed together in various weight ratios (1 : 0.1, 1 : 0.2, 1 : 0.3, 1 : 0.5) and cast into films. These were sequentially crosslinked by different mechanisms. A determined pre-stretch was applied to the first network after its formation followed by thermal treatment for curing the second network. Non-prestreched networks were also prepared in parallel for comparison. The aged films were characterized from the point of view of the soluble fraction content, and analysed by differential scanning calorimetry, water vapour sorption in dynamic regime, dielectric spectroscopy and tensile tests. Dielectric strength and actuation strain were measured to estimate the suitability of the samples for electromechanical applications. The results revealed that through this approach one can relatively easily obtain very simple and homogeneous materials suitable for use as dielectric elastomer transducers.