Preparation And Application Of Super Soft Self-healing Elastomer Based On Polymer Molecular Brush

Super-soft elastomers,which are defined as networks with a modulus value at the level of kilopascals,are also in demand in a number of emerging applications including high-sensitivity capacitive pressure sensors,biomimetic materials and efficient dieletric actuators.Gels are lightly cross-linked three-dimensioned（3D）networks with substantial amount of water or organic solvents entrapped in them and they exhibit excellent soft properties.Currently,most of the reported super-soft elastomers are based on gels,which show lower stability in practice as the softness of the materials will decrease with solvent gradually evaporating.Meanwhile,some solvents are toxic or corrosive,and the practical applications of the resultant super-soft elastomers will be limited,especially when interfacing with human body.In addition,most of the elastomers suffer from lack of self-healing capability.So,it is important to fabricate super-soft elastomers possessing self-healing capability in the absence of additives.In this research subject,three different kinds of bottlebrush polymers were designed and synthesized via“grafting through”method of ring-opening metathesis polymerization（ROMP）,and super-soft elastomers were obtained as the synthesized bottlebrush polymer were crosslinked.The targeted bottlebrush copolymers and their intermediates were well characterized by ~1H NMR,FT-IR and GPC.The results demonstrated that the prepared elastomers had lower T_g and exhibit super-soft proper and self-healing capability.The contents are as following:（1）Two macromonomers NB-P（LLA-co-CL）with different monomer ratios were first synthesized using 5-norbornene-2-methanol initiating the copolymerization of LLA and CL.Then,the bottlebrush polymers were prepared via“grafting through”method by ROMP of NB-P（LLA-co-CL）.Finally,the networks composed of dynamic ester bonds were obtained by cross-linking the bottlebrush polymers.The effect of LLA and CL monomer ratio on the mechanical properties of the elastomers were investigated.In addition,the self-healing behavior of the elastomers was also studied in the presence of Sn（Oct）₂catalyst at70℃.The application of the resultant elastomers as the sensor to detect human health was explored.（2）Bottlebrush polymers was fabricated via“grafting through”method using the copolymers of LLA and CL containing norbornene group as the macromonomer.The networks containing hydrogen bonds and dynamic disulfides covalent bonds were obtained by cross-linking the resultant bottlebrush polymer,proving the elastomers with rapid self-healing capability at ambient temperature.Moreover,the obtained elatomers exhibited excellent adhesive performance toward different substrates（e.g.,glass,rubber,and steel）.The sensors based on the prepared elastomers could make stable response to human motion quickly.（3）Networks containing dynamic boronic ester bonds was fabricated as the bottlebrush polymer was crosslinked via the bromo-thio“Click”reaction between the end bromo groups and the thio groups on BDB.The resultant elastomers exhibited excellent adhesive performance toward many substrates due the unique supersoft and adhesive properties of poly（n-butyl acrylate）（Pn BA）.The strain sensor made of the elastomer coating with carbon nanotubes exhibited low detection limit and high sensitivity,which can be utilized to monitor human motions under various strains.When the sensor was damaged,the conductive path can be repaired during only 120 milliseconds.Overall,different kinds of supersoft elastomers with the self-healing and adhesive capabilities were successfully fabricated from the bottlebrush polymers.Wearable sensors with high stability was developed,which can be used to monitor various body activities.