Fine-tuning of the dielectric properties of polysiloxanes by chemical modification

Abstract

A series of novel polysiloxanes is presented, the glass transition temperatures and dielectric properties of which are systematically fine-tuned by utilizing thiol-ene post-polymerization reactions. The pendant vinyl groups of a high molecular weight polymethylvinylsiloxane P1 were exhaustively reacted with the thiol compounds 1-butanethiol (2) and 3-mercaptopropionitrile 3 both separately to give polymers P2 and P3, respectively, as well as in various ratios x, y so as to create materials P2_xP3_y with greatly differing contents of the polar nitrile group (y). All modifications proceeded quantitatively as was confirmed by ¹H NMR spectroscopy. Because of the presence of the polarizable thioether and nitrile groups, the resulting siloxane polymers exhibit permittivity ranging from ε′ = 4.7 to 18.4 for P2 and P3, respectively. The ε′ values of all polymers P2_xP3_y carrying more than one kind of thiolether group lie within this range. Additionally, broadband dielectric spectroscopy measurements of P2, P2₁P3₁ and P3 have been conducted in the temperature range from −150 °C to 60 °C and the frequency range from 0.1 Hz to 1 MHz. Due to their high permittivity, polymers P2, P2_xP3_y and P3 are attractive candidates for dielectric elastomer actuators and flexible electronics.