Preparation And Properties Of High Dielectric Constant Polyrotaxane Elastomer Based Composites

As a kind of electroactive polymer,the dielectric elastomer can produce a certain deformation in the electric field so that can convert electrical energy into mechanical energy.Thus,it has wide prospect of applications in the fields of sensors,electromechanical transducers,robots,actuators and artificial muscles.Under certain condition of electric field,the factors that affect the electrostriction of dielectric elastomer are the dielectric constant and the elastic modulus of the polymer.Therefore,improving the dielectric constant of polymer is the purpose of this paper while keeping elastic modulus as the same level.Based on the pseudopolyrotaxane that self-assembled by the alpha-cyclodextrin and polyethylene glycol,2,4-dinitrofluorobenzene was used as the end capping agent,and supramolecular polyrotaxane was synthesized in this paper.After the hydroxypropylation modification of polyrotaxane,polycaprolactone was grafted onto the side chains to obtain the polyrotaxane derivative HyPR-PCL.The successful synthesis of polyrotaxane and its derivatives was confirmed by 1H-NMR.And through crosslinking HyPR-PCL using two kinds of crosslinking agents,and meanwhile adding different fillers,two types of high dielectric constant polyrotaxane elastomer materials were prepared.(1)Through crosslinking the polyrotaxane derivative with isophorone diisocyanate(IPDI)and grafting copper phthalocyanine oligomers(CuPc)simultaneously,the organic nanocomposite(HyPR-PCL)-g-CuPc was fabricated.The results of FT-IR and ICP showed the success of grafting reaction.TEM analysis showed that the CuPc molecules agglomerated to form particles and were dispersed uniformly in the matrix.The size of most particles was only in the range of 10-20 nm.DSC and TGA analysis showed that the addition of CuPc improved the thermal stability of the crosslinked matrix.The dielectric constants and losses of the grafted composite films all increased with the CuPc content increasing,and the dielectric constant of the composite film with 8 wt% CuPc reached to 135 at 100 Hz,which was 13 times than that of pure crosslinked matrix(about 10).And the dielectric loss was just 0.34,which was only 2.6 times than that of matrix.In addition,the elastic modulus of the grafted composite film did not increase too much with the CuPc content increasing,only from 7.31 MPa of cross-linked matrix to 9.24 MPa of composite film with 8 wt% CuPc.(2)Through crosslinking the polyrotaxane derivative with hexamethylene diisocyanate(HDI)and adding the filler of graphene at the same time and polyvinyl pyrrolidone(PVP)which was to improve the dispersibility of graphene in the matrix,the composite(HyPR-PCL)/PVP-GR was fabricated.FT-IR proved the success of the cross-linking reaction.SEM analysis showed that the dispersion of graphene in crosslinked matrix was better than that of unmodified one.DSC and TGA analysis also showed that the thermal stability of crosslinked matrix was enhanced due to the addition of conductive graphene filler.The percolation threshold of PVP modified composite film was 2.46 vol.%,while the unmodified composite film was 2.20 vol.%.And with the increase of graphene content,the dielectric constants of two composites were improved greatly and the dielectric loss slightly before reaching the percolation threshold.For the PVP modified composite films,the dielectric constant increased from 11.6 of pure cross-linked matrix to 289.8 with the graphene content of 2.35 vol.% at 100 Hz.The dielectric loss only increased from 0.19 to 0.46.And for unmodified composite films,the dielectric constant reached to 198.2 with the graphene content of 2.02 vol.%,while the dielectric loss was as high as 1.36.In addition,the elastic modulus of the two composites was pretty small,but the elastic modulus of the PVP modified composite was a little higher than that of the unmodified one.