The Study On The Preparation Of Intrinsic Dielectric Elastomers Based On Thiol-Ene Chemistry

Dielectric elastomers(DE) is one of the electroactive polymers(EAPs) which is taken as a new generation of actuators, it can expand in area and convert electrical energy into mechanical energy under applied voltage.It has been widely used as small miniature robots, artificial muscles, plane loudspeaker, cd-rom drives, and other fields due to their excellent property of light weight, large strain, fast response, reliability, well efficiencies and high energy density. But the traditional DE often has low dielectric constant and the high driving voltage is often dangerous to humans and equipements. The traditional methods are add the fillers like the ceramic with high dielectric constant or conductive fillers, but the addition of fillers tend to cause the increase of modulus, the decline of design flexibility and the decline of breakdown strength due to the defect, this greatly limits its application in dielectric elastomer actuator. Limited by the preparation process, the introduction of functional groups is very limit by the chemical systhesis methods. This study aims to introduce polar groups(ester and carboxyl) to styrene-butadiene-styrene copolymer(SBS) and high vinyl content silicone rubber(MVQ) base on thiol-ene click chemistry to increase the orientation polarization ability and the dielctric properties, the creative work and results are as follows:(1)We successfully grafted the carboxyl groups on the PB domains of SBS based on the thiol-ene click chemistry. The tensile strength of modified SBS significantly decreases due to the miscibility of PS and PB domains but still greater than 1MPa, and the elastic modulus of the modified SBS slightly increased because of the strong intermolecular interactions by hydrogen bonding of carboxyl groups in PB domains. What's more, the ?r largely increased from 2.2 for pristine SBS to 7.2 for modified SBS ascribed to the increase in the polar orientation polarizability by the carboxyl groups on PB block. The maximum actuated strains increased to 1.75% for grafting degree of 52%, which is almost a 4-fold increase over that of pristine SBS (0.47%). This provided us a simple, effective and controllable method to synthesis reusable processing and homogeneous dielectric elastomers without any addition of ingredients.(2)We successfully prepared the high vinyl content silicone rubber(MVQ) whose vinyl content is 34% by anionic ring opening polymerization, afterwards we grafted the easter and carboxyl groups onto the side chain of MVQ. The ?r incrased to 5.3 and 5.1 from 2.6 for pristine MVQ due to the incresed orientation polarization when grafted MT and TGA, individually. It is interesting that the two polar groups behaved two different contribution to the modulus of MVQ. The space free volume effect results in the decrease of modulus when grafted MT, and the hydrogon bonding of carboxyl groups results in the increase of modulus when grafted TGA. The effective electromechanical factor(?') increased to 22.1 for MVQ-MT and 11.3 for MVQ-TGA, a 2.5-fold and 1.3-fold increase over that of pristine MVQ (8.7), respectively. The maximum actuated strains increased to 14.2% for MVQ-MT-34% and 6.5% for MVQ-TGA-15%, a 2.5-fold and 1.2-fold increase over that of pristine MVQ (5.6%), respectively. It is worth noting that the modified MVQ's actuated strains increased significantly under low voltage, this provides us a new methods to prepare dielectric elastomers which are homogeneous and large deformation under small voltage.