Liquid Crystal Elastomers With Dynamic Covalent Bonds:Molecular Design,Preparation And Property Study

The shape control of soft materials is of great importance in reality.Liquid crystal elastomer(LCE)is smart shape-changing polymer.The reversible shape-changing ability of LCE mainly comes from the reversible phase transition of oriented LCE(which is called monodomain LCE)triggered by external stimuli.Thus,the preparation of monodomain LCE demands the orientation of the mesogens.In order to obtain crosslinked polymer network and oriented mesogens at the same time,researchers developed several methods that either aligning the material before or in the middle of crosslinking,including the well-know “two-step” crosslinking method.However,the network topology of thermoset like LCE could not be altered after crosslinking,therefore,the preparation of monodomain LCE has always been a bottle-neck problem.By introducing dynamic covalent bonds into LCE,we found that it is possible to obtain monodomain LCE from randomly ordered polydomain LCE,by utilizing “postcrosslinking” method.LCE with dynamic covalent bonds are reprocessible at high temperature,even by light irradiation under certain circumstances.What's more,the introduction of dynamic covalent bonds makes it much easier to construct materials with more complex shape-changing behaviors from LCE,in order to realize the regional and sequential shape control of materials.The main results of this thesis are:(1)Crosslinked liquid crystal epoxy based on dynamic reversible transesterification is prepared.The reprocessibility and the recyclability are studied.Then,the polydomain to monodomain transition is further investigated,based on which,mouldable LCE actuators with different shapes are prepared.Finally,the shape memory properties are also studied.(2)Shape memory building blocks with different thermal transitions are prepared based on the mouldable LCE with transesterification.The shape memory effects of individual building block are studied.Then,the construction of novel multishape memory assemblies and their shape control are further investigated.Finally,the recyclability and the shape reconfigurability are also characterized.(3)Mouldable LCE with dynamic reversible disulfide exchange is prepared.The "post-crosslinking" method for LCE with dynamic covalent bonds is verified.Then,the polydomain to monodomain transition is studied with light instead of temperature.Photo-weldable and partially photo-healable mouldable LCEs are prepared.Finally,the recyclability is proved.