Thermadapt Shape Memory Polymers With Two Crystalline Phases

Shape memory polymers(SMPs)can undergo programmable shape recovery under specific stimuli.Due to their good processability,high recoverable strain,tunable operation temperature,and multiple functionalities,SMPs have brought unique benefits for advanced manufacturing,soft robotics,medical devices,and aerospace applications Recently emerged two-way shape memory effect in crystalline shape memory polymers,which allows reversible shape-shifting between two predefined shapes without repeated programming,opens up more opportunities for future device applications.In respect of the molecular design of SMPs,covalent bonds and crosslinks are commonly used to construct the network.By introducing dynamic covalent bonds to the network,thermoset polymers exhibit thermoplastic-like properties such as reprocessability as well as unique self-healing capability and solid-state plasticity.Such materials are entitled thermadaptsIn this thesis,dynamic covalent network with dual crystalline phases was synthesized to explore the influence of bond exchange on the two-way shape memory performance and the network topological isomerization.We propose a new method for the construction of two-way shape memory effect by combining both chemical and physical mechanisms in a synergetic wayFirst,a permanent shape was chemically reconfigured in a three-dimensional form by ester bond exchange.Then the shape was physically programmed(flattened)to achieve reversible shape-shifting between a three-dimensional shape and a two-dimensional plane(an apparent zero-strain state like the original shape).Previous reversible SMP systems require deformation of the original two-dimensional shape to establish the network anisotropy,which determines that they can only switch between two nonzero strain states.Reprogrammability of the physical mechanism and cumulative effect of the chemical mechanism also provide more opportunities for making customized materials.Dynamic bond exchange in the above process enables solid-state plasticity,but it doesn't make notable influence on material properties.With a proper network design,the bond exchange between different polymer chains can be achieved for network topological isomerization.How molecular changes affect the macroscopic physical properties of the material was investigated by DSC characterization.If supported by further optimization and spatio-selective control,it is possible to achieve localized programmability on physical properties,and enable complex shape shifting with shape memory effect.