Metal-free thiol-Michael addition for hydrogen bond-rich poly(dimethyl siloxane) networks with improved electromechanical properties and self-healing capabilities

Thiol-maleimide conjugation is a well-established coupling method in biochemistry but with little reported use within silicone materials. A facile synthetic route of functionalised poly(dimethyl siloxane) (PDMS) to a prepolymer species capable of non-metal-catalysed cross-linking via thiol-Michael addition is presented. Two systems are compared: maleimide (MI) terminated PDMS and its precursor, maleamic acid amide (MA) terminated PDMS. Despite the traditional view of maleamic acid amide functionalities as being of inferior value to their maleimide counterparts, we argue for their potential. The increased relative concentration of polar groups in a robust MA network matrix can be exploited for better electrical properties for self-healable dielectric elastomer actuators, as demonstrated by the MA networks with their quadruple hydrogen bonding centres, self-healing capabilities, increased polarity, good electrical breakdown strength, and increased dielectric permittivity over both commercial and MI PDMS networks. Novel use of thiol-Michael addition enables metal-free cross-linking of PDMS, enhancing self-healing and dielectric properties.