Study On Interpenetrating Network Toughened Shape Memory Cyanate And Its Photocurable 4D Printing

Shape memory cyanate ester（SMCE）is a common thermosetting resin with a high glass transition temperature（T_g）,high modulus,thermal stability,irradiation resistance,and low dielectric constant,and has obvious superiority in aerospace.Due to the existence of a large number of 1,3,5-triazine rings in cyanate esters,the molecular structure is symmetrical and the network structure is regular,which leads to the high brittleness and low toughness of cyanate resin.Moreover,the structure prepared by traditional manufacturing technology is simple and the deformation mode of the structure is simple,which limits the application of cyanate ester in engineering.Compared with traditional manufacturing technologies,4D printing has obvious advantages,which can be integrated into the rapid processing of personalized products with complex structures and large individual differences.However,very few types of thermosetting polymers can be printed at present.Therefore,it is necessary to study the printable SMCE resin with high toughness,T_g,and modulus as well as irradiation resistance.The thermosetting bisphenol A cyanate ester was toughened by two kinds of linear toughening agents,polyethylene glycol（PEG）and polyethylene glycol diglycidyl ether（PEGDGE）.Because of the high activity of epoxy groups,PEGDGE can react with cyano groups in cyanate ester monomer,which can effectively reduce the cross-linking density of triazine rings.PEG is a straight-chain molecule with hydroxyl end-capped and does not participate in the polymerization reaction.It tangles in the network structure formed by CE and PEGDGE as a molecular form forming semi-interpenetrating network structure.The T_g（164.3～219.7℃）,storage modulus（1883.0～2138.1 MPa）and fracture strain（3.6～6.9%）of SMCE resin were adjusted by changing the mass ratio of each component.The shape fixation ratio（R_f）and shape recovery ratio（R_r）of SMCE resin was99.6%and 99.6%,respectively.To study the space stability,the SMCE resin was irradiated by different doses ofγ-rays,which had little effect on the thermodynamic and shape memory properties,showing that SMCE resin has good tolerance toγ-rays.PEG and PEGDGE can toughen SMCE resin to a certain extent,but the toughness does not reach the expected effect.We proposed to construct an IPN structure in CE to toughen CE.The prepolymer CE was mixed with photosensitive resin,and they are cured via two different curing methods.The IPN structure was formed by light curing and then heat curing.The oligomer epoxy acrylate（EPAC）was synthesized from epoxy and acrylic acid by an addition esterification reaction catalyzed by triethylamine.The oligomer EPAc,the diluent polyethylene glycol dimethacrylate（PEGDMA）,and the photoinitiator 2,4,6-trimethyl benzoyl-diphenyl phosphine oxide（TPO）were mixed in a certain proportion.The cured resin with low T_g（65.7℃）,high modulus（3124.3 MPa）,and high toughness was successfully prepared,and its strain at break was 18.4～28.5%.The photosensitive resin can be used for 3D printing to realize integrated molding of complex structures,which solves the problem of manufacturing complex structures with traditional manufacturing technology.After irradiation with 10⁶ Gyγ-rays,the molecular structure of the prepared resin was destroyed and the thermodynamic properties decreased.The printable cyanate-based ink was composed of oligomer EPAc,cyanate ester prepolymer,diluent PEGDMA,and photoinitiator TPO.In the process of DLP printing,EPAC and PEGDMA crosslink to form a photoinitiation network structure,and cyanate ester prepolymer forms a thermal initiation network structure during heating.The two networks are nested together to form an interpenetrating polymer network（IPN）.The two network structures have different thermodynamic properties,SMCE resin has two T_g and triple shape memory properties,T_g1 is 94.1～102.1℃,T_g2 is 164.4～221.0℃,R_f is87.1%,R_r is 92.0%.The results of the mechanical tensile test show that the fracture strain at room temperature is 7.4～10.9%and the fracture stress is 62.4～72.1 MPa,indicating that the SMCE resin has good toughness.Cyanate composite inks were prepared by adding 0.2 wt%SCFs and 0.2 wt%SGFs into the cyanate inks.The SCFs and SGFs enhanced cyanate composite was successfully printed and had good triple-shape memory performance.The fracture strain and fracture stress of SMCE resin irradiated with different doses ofγ-rays are stable,and the thermal properties of the polymers are also less affected.The results show that the prepared tri-shape memory cyanate has goodγ-ray tolerance.