Design, Preparation And Properties Of Highly Conductive Thermo-Reversible Silicone Elastomer Based On Diels-Alder Reaction

Conventional methods for preparing conductive silicone rubbers by blending the conductive filler with silicone rubbers have many problems,such as poor compatibility between the filler and the rubber matrix,the conductivity is affected in many ways.As a result,the material cost is high because the conductive filler is expensive and the prepared conductive silicone rubber is often difficult to recycle.In order to solve the above problems,we use a reversible covalent cross-linked network constructed between the conductive filler and the rubber matrix to prepare a kind of conductive silicone rubber having both high conductivity and thermo-reversible properties.The prepared material can not only improve the compatibility between conductive filler and the rubber matrix,it also can be recycled and reused,thereby effectively reducing resource waste and cutting material costs.The study mainly including the following two parts in our work:1)Firstly,we prepare a series of methyl vinyl silicone rubbers with different vinyl contents;then modify the silicone rubber via click chemistry reaction to introduce the furan functional group on the side chain of the silicone rubber.After analyzing the influence of the vinyl contents in the silicone rubber and the reaction time of the click chemistry on the furan grafting ratio,the optimum vinyl contents and reaction time were selected.Finally,the Diels-Alder reaction occurs between the carbon nanotubes as the dienophiles and the silicone rubber containing pendant furan functional groups as the dienes.The structure,morphology,mechanical properties,electrical properties,and thermal reversible properties of the silicone rubber by adding different mass fractions of carbon nanotubes were studied,then the effect of the carbon nanotube contents on the reversible properties of the conductive silicone rubber via Diels-Alder reaction was analyzed.When the vinyl content is different,the grafting ratio first increases and then decreases as the vinyl content increases from 20%to 30%and 50%.When the vinyl content is 50%,it is easy to produce gel during the reaction,resulting in the grafting ratio reduced.When the vinyl content is 30%,the grafting ratio of the modified silicone rubber tends to increase with the increase of the reaction time,and the grafting ratio of 39.06%is obtained after 30 minutes of reaction.The carbon nanotubes,as dienophiles in Diels-Alder reaction,can form a thermally reversibly covalent crosslinked network with the silicone rubber containing pendant furan functional groups and the obtained material has a good thermal reversible propert,the compatibility between carbon nanotubes and silicone rubber becomes better due to the Diels-Alder reaction between them.Diels-Alder reaction occurred at 60? and retro-Diels-Alder reaction occurred at above 150?,when the materials can be dissolved in good solvent.After secondary molding of the prepared conductive silicone rubber,the tensile strength was restored 77%,the elongation at break was restored 88%,the electrical conductivity was restored 86%compared with the original sample,which shows the recyclability of the materials.Meanwhile,the carbon nanotubes have good electrical conductivity,when 10%mass fraction of carbon nanotubes is added,the conductivity of the silicone rubber is 0.9091 S/cm.In addition,carbon nanotubes have a large length-diameter ratio,which has a significant effect on the reinforcement of the material,the strength can increase from 0.2 MPa to 2.3 MPa to the silicone rubber with the addition of 10%mass fraction of carbon nanotubes.Therefore,a conductive silicone rubber having good conductivity,interface compatibility,and recyclability was prepared by using carbon nanotubes as dienophiles in Diels-Alder reaction.2)Firstly,we prepare the pedant amino silicone rubber with different amino group content,then modify the silicone rubber with maleic anhydride to introduce the maleimide functional group on the side chain of it;silver nanoparticles with good dispersibility were prepared and modified to make the silver nanoparticles complex with furan functional groups;finally,the Diels-Alder reaction occurs between the silicone rubber containing the maleimide functional group in the side chain as the dienophiles and the modified silver nanoparticles containing the furan functional group as the dienes to prepare the conductive silicone rubber.The pedant amino silicone rubber with 4.3%,8.9%and 16.8%amino groups were prepared by changing the ratio of experimental materials.Through the FT-IR and NMR tests on the grafted silicone rubber,it was found that the maleimide functional group was introduced on the side chain of the molecular chain,indicating that the grafting experiment was successful.The prepared silver nanoparticles are uniformly dispersed and have a size of 40-50 nm,after the modification reaction,the size increases to 125 nm-160 nm.