The Study On Homogeneous Dielectric Elastomers With Dramatically Improved Electromechanical Properties By Using Thiol-Ene Click Chemistry

Dielectric elastomers fall into the category of electroactive polymers which expand in area and shrink in thickness when a voltage is applied. These elastomers have been receiving much attention because of these surprisingly large deformation by applying an electric field. By virtue of the light weight, high efficiency and high energy density, DEAs find applications in many fields. However one limit is the need of high votage to drive them. The conventional approach to achieve high performance DE is to introduce fillers into elastomer matrix to prepare composites. However there exist some intrinsic drawbacks of dielectric elastomer composites. A promising direction for research of dielectric elastomers is to synthesis a homogeneous dielectric elastomer with intrinsic high electromechanical properties, meaning high dielectric constant as well as low modulus, through molecule design or grafting modification. Normally when subjected to electric field dipoles of polar elastomers could orient adjusting to the electric strength which leads to a better polarizability compared to nonpolar elastomers. As a result the chemical synthesis method mainly concentrate on the introduction of polar groups into elastomer networks. However, limited by the synthesis method the polar groups that can be introduced are confined in both variety and quantity. Herein, we report the design and preparation of an intrinsic "green" styrene-butadiene-styrene triblock copolymers (SBS) dielectric elastomer (DE) with dramatically improved electromechanical properties by using a photochemical thiol-ene click reaction. Different dipoles (ester group and cyano group) are grafted onto the backbone double bonds or pendant vinyl groups.(l)After the grafting of ester groups on SBS, the compatibility between PB and PS block of SBS increases, leading to the phase mixing and the large decrease in size of PS domains. The tensile strength and elastic modulus of modified SBS obviously decreases. However, the modified SBS still shows good mechanical strength (>3Mpa). The dielectric constant (k) largely increases from 4.3 for stock SBS to 12.2 for modified SBS. The maximum actuated strain largely increase from 0.42 for stock SBS to 5.5% for modified SBS, and the actuated strain at low electric field (15kv/mm) largely increases from 0.01% for stock SBS to 3.0% for modified SBS.(2)After the grafting of ester groups on SBS, the tensile strength and elastic modulus of modified SBS obviously decreases. The dielectric constant (k) largely increases from 4.3 for stock SBS to 7.32 for modified SBS. The maximum actuated strain largely increase from 0.79 for stock SBS to 2.12% for modified SBS, and the actuated strain at low electric field (15kv/mm) largely increases from 0.01% for stock SBS to 1.06% for modified SBS.Our study provides a simple, effective and controllable chemical method to prepare "green" DE with high k, large actuated strain at low electric field, good mechanical strength, easy processibility, and recyclability.