Epoxy Based Vitrimer Composites

As coatings,adhesives electronic materials and so on,epoxy resins have been used in various fields,including electronics,aerospace,chemical industry,ship building,car,military industry,metallurgy,daily life,etc.As the epoxy resins are a kind of thermosetting polymers,they can not be reprocessed or reshaped due to their infusible and insoluble nature,which not only causes the waste of resources,but also brings about the disposal problem.To solve it,Leibler and co-workers developed a dynamic covalent network by introducing transesterification catalyst into epoxy/acid or epoxy/anhydride crosslinked networks,which were defined as“Vitrimers”.Thermally induced transesterification leaded to the rearrangement of the permanent crosslinked network at high temperature,which made it possible to reprocess and weld the epoxy thermosets.This reprocessing was triggered by direct heating.But on many occasions,direct heating is not practical?e.g.,when the material is used in electronic devices,or when only a small part of the material needs shape change?.To replace direct heating,light is preferred,because light can be rapidly switched on and off,precisely focused on a desired area,and remotely controlled.To this end,in this thesis,we introduced two kinds of photo-thermal agents?carbon nanotubes and perovskites?into the epoxy Vitrimers.The resultant networks are able to be reprocessed?reshaped,welded,healed?by light and are responsive to sunlight.More importantly,using liquid crystalline Vitrimers,we provide a new method to make dynamic 3D structures with many excellent properties.This will expand the application of epoxy resin,decrease the waste of resources and simplify the disposal procedures.The main topics in this thesis are presented below:?1?We present a very simple but highly efficient method to manipulate the transesterification reaction in epoxy Vitrimers using the photothermal effect of carbon nanotubes?CNTs?.The carbon nanotube dispersed Vitrimer epoxy can be welded,reshaped and healed by light remotely and locally.?2?By introducing transesterification and carbon nanotubes?CNTs?into liquid crystaline epoxy,combining the reversible actuation of liquid crystalline elastomer and the photo-thermal effect of CNTs,the resultant networks are capable of the light-controlled fabricaiotn,actuation,restoration,shaping,healing,welding and low-temperature resistance of dynamic 3D structures.?3?We found a new kind of light-absorber with excellent photo-thermal effect——organic-norganic hybrid perovskite CH₃NH₃PbI₃,which can effectively convert solar energy into heat.Coating a CH₃NH₃PbI₃ layer onto the surface of shape memory polymers?here is epoxy Vitrimer?,the composites are sunlight-responsive and their shape memory behavior can be controlled by direct sunlight.The CH₃NH₃PbI₃layer can be easily washed off by water.So coating-erasing CH₃NH₃PbI₃ can be repeated for many times to make the shape memory polymers photo-responsive and photo-inert alternatively.