Exploration On Plasticity And Functional Applications Of Classical Chemical Crosslink Networks

Thermoset polymers crosslinked by covalent bonds(including epoxy polymer,polyurethane,and silicone rubber)represent an important branch of polymers.Compared with thermoplastics,they exhibit robust networks with good stability.However,the chemical crosslink nature generally makes their permanent shapes simple,constrain to the mold and non-redefinable,which severely limit their performance in high-value added applications.Amongst,the epoxy polymer has been reported to achieve reprocessing via bond exchange(transesterification).In contrast,chemical crosslink polyurethane and silicone rubber still suffer from compromised shape reconfigurability.Thus,how to explore the new properties and applications of these two classical chemical crosslink networks becomes a big challenge.In short,this work mainly focuses on the plasticity behavior of classical chemical crosslink polyurethane and silicone rubber,in order to endow the new performance and functional applications.Thermoset polyurethanes as a vital class of shape memory polymers possess superior thermomechanical properties.This work discovered that the chemical crosslink polyurethane itself exhibits ability in permanent reshaping(plasticity)via transcarbamoylation.The highly sophisticated shapes and intriguing shape changing behaviors can be further achieved by combining with shape memory properties.Despite the discovery,ensuring the plasticity severely limits the polymer network design,which will adversely affect the ability to tune classical shape memory properties.To deal with that,this work designed an amorphous polyurethane network and its cross-linking density can be adjusted in a wide range.This catalyst free system possessed tunable recovery stress and shape memory transition temperatures,without compromising plasticity behavior.Besides,this network can achieve triple shape memory performance.Silicone rubber as an important thermoset polymer can be used as engineering materials directly or as preceramic polymers.This work discovered that the commercialized silicone rubber can achieve siloxane bond exchange via rational choice of catalysts,which led the polymer with complex hierarchical structural features spanning from macroscopic to submicron scales.The following pyrolysis allowed unparalleled freedom in manipulating 3D complex shapes of ceramics.Overall,this work discovered that the permanent shape of chemical crosslink polyurethane and silicone rubber is redefinable,which will broaden the applications of these two classical chemical crosslink networks.These findings will have significant benefits in dynamic covalent polymers.