Design Of Recyclable Polymer Based On Dynamic Urea Bond Capable Of Photocuring 3D Printing

Thermosets polymers are insoluble,infusible,and stable in nature due to their chemical crosslinking structure,but they can only be solidified once,causing problems such as inconvenient processing and waste of resources.The topological rearrangement of the cross-linked network composed of reversible dynamic covalent bonds will occur under thermal stimulation,so that the material has both the stability of thermosetting and the processability of thermoplastic,and is expected to be applied to the field of 3D printing as a multifunctional material.3D printing technology,also known as additive manufacturing,is a new type of molding processing which obtains target products by stacking layers.Among them,digital light processing(Digital light processing,DLP)3D printing technology is currently one of the mainstream 3D printing technologies due to its advantages of fast production efficiency and high printing accuracy.At present,the selection range of DLP raw materials is small and most of them have single properties.The application of cross-linked polymers containing dynamic covalent networks in DLP printing will greatly promote the development and application of DLP.In this paper,we synthesize dynamic vinylogous urea bond(Vinylogous urea bonds,VU-a)and integrate it with commercial monomer polymethyl methacrylate.In this system,VU-a showed good dynamic reversibility and thermal stability.The tensile strength of the material at room temperature is 40.9MPa.After 3 repeated hot-pressing cycles,the system material still maintains good mechanical properties and stability.VU-a is easy to synthesize without catalyst,has good dynamic performance and high designability.Potential for applying DLP.Through reasonable structure design,the crosslinked polymethyl methacrylate(VU-A-PMMA)photosensitive resin solution containing VU-a was configured and could be3 D printed by DLP.When the cross-linking ratio is 10:1,the maximum tensile strength is26.6MPa,the elongation at break is 50.9%,and the maximum tensile strength recovery efficiency is 84.2%.The mechanical properties of the DLP printing materials with this system are excellent and can be recycled repeatedly.In addition,Acrylate system materials containing dynamic steric hindered urea bonds(Hindered urea bond,HUB)are printed by DLP.Heat will be released during the DLP photocuring molding process,while HUB has excellent high-temperature dynamic performance,and its reaction activation energy is 60.11KJ/mol.The heat can promote HUB.exchange reactions between them.Based on this,the normal temperature self-healing and powder DLP printing recovery of the system material were explored.The HUB repair fluid is exchanged and combined with the HUB reaction point at the interface under heat,so that the gap of the material can be completely repaired under the light for 5 minutes without changing its mechanical properties,and the complete self-repair of the rigid material at room temperature is realized.At the same time,20wt% material powder directly mixed with photosensitive liquid for DLP printing,and the performance of the product has not changed.After 3 repeated powder recycling and printing,the mechanical properties and thermomechanical properties of the material are consistent.It is a dynamic exchange based on DLP printing.A more convenient and efficient way to recycle polymers.