Shape Memory Properties Of Polycaprolactone Diacrylate/n-Butyl Acrylate Copolymers And Their Applications

Shape memory polymers have a wide application in various fields due to their controllable responsive shape changing behavior.Among them,reversible dry adhesives enabling surface shape memory effect are capable of switching their adhesion strength upon stimuli,which have shown important potential in the transfer printing process for the assembly procedure of soft electronics.However,current material systems are based on shape memory epoxy that provides excessive modulus both above and below the glass transition,which would easily break the brittle devices.Moreover,the materials enable only one way shape memory behavior,which is a significant restriction.In this thesis,(Polycaprolactone diacrylate/butyl acrylate)copolymers are synthesized via free radical polymerization.By adjusting the composition,material with low modulus(both at the crystalline and rubber states)and excellent shape memory property(both shape fixity and recovery ratios are higher than 96%)is obtained.With surface microstructuring,reversible adhesive is prepared.At the strong adhesion state,the adhesive is capable of stably adhering a object for days when the surface structures have been temporarily flattened..Once heated,it will immediately switch to the weak adhesion state and release the object upon the recovery of the surface structures.The adhesion strength will not lose in repeated use.Such a shape memory dry adhesive owes a promising application in transfer printing as a stamp.By incorporating a transesterification catalyst,the PCLDA/BA copolymers show a two-way reversible shape memory capability since the dynamic ester bond exchange in the network aligns the crystalline PCL chains under mechanical deformation.The mechanism of the reversible shape changing is studied by changing the composition,the programming strain and the annealling time.A maximun reversible strain of 10%can be obtained.A programmable two-way reversible shape memory towards complex shapes is achieved,which may expectedly contribute to the design of dry adhesive.