Silicones with enhanced permittivity for dielectric elastomer actuators

The research efforts for silicone based elastomers with high dielectric permittivity (Ɛ') intensified significantly in the last years since such materials would allow the construction of dielectric elastomer actuators (DEA) with low operation voltages. Polar groups can be introduced to elastomers to adjust their permittivity. The results obtained regarding the functionalization of silicones with polar nitrile (CN) and trifluoropropyl (CF₃) groups are presented. Those with CN groups were synthesized via anionic polymerization of nitrile containing cyclosiloxanes or via a post-polymerization modification of functional polysiloxanes. Polysiloxanes containing CF₃ groups were prepared by anionic copolymerization of 1,3,5-tris(3,3,3-trifluoropropyl)-1,3,5-trimethylcyclosiloxane with octamethylcyclotetrasiloxane. Importantly, we have found that all polysiloxanes have glass transition temperatures (Tg) well below room temperature (<-50°C). This ensures that the materials turn into true elastomers after cross-linking. In addition to this, a linear increase in Ɛ' with increasing content of polar groups was observed with maximum values of Ɛ' = 18 and Ɛ' = 8.8 for polysiloxanes modified at every repeating unit with either CN or CF₃ groups, respectively.