Mechanically Robust and Reprocessable Acrylate Vitrimers with Hydrogen-Bond-Integrated Networks for Photo-3D Printing

Abstract

Reprocessable acrylate vitrimer needs to enhance its strength to expand the application in photo-three-dimensional (photo-3D) printing. However, the methods for improving mechanical properties by the addition of nanofillers or a multifunctional resin into acrylate vitrimers are inappropriate for photo-3D printing due to the low curing speed of photopolymerization induced by weakening light transmittance or reduction of dimensional accuracy caused by large shrinkage. At present, we demonstrate a new strategy for developing a kind of mechanically robust and reprocessable 3D printing thermosets by combining hydrogen bonds and exchangeable β-hydroxyl esters into acrylate vitrimers. To realize this purpose, diacrylate prepolymer containing β-hydroxyl esters was first synthesized from glycidyl methacrylate and suberic acid. Then, the resin formulations for 3D printing comprising the synthesized diacrylate prepolymer together with acrylamide generate exchanged β-hydroxyl ester and pendent amide in cross-linked networks. Here, hydrogen bonds resulting from the amide group as sacrificial bonds dissipate vast mechanical energy under an external load. With the inclusion of 20 wt % acrylamide, the average tensile strength and Young’s modulus are up to 40.1 and 871 MPa, which increased by about 4.4 and 3.85 times, respectively. The network rearrangement of cross-linked vitrimers can be achieved through the dynamic ester exchange reactions with gradual disappearance of hydrogen bonds at elevated temperatures, imparting reprocessability into the printed structures. Various photo-3D printing or UV irradiation shapes were successfully produced, and these dissolved in ethylene glycol could be remolded again.

Relaxation of Vitrimers with Kinetically Distinct Mixed Dynamic Bonds

“…Developed over the past decade, vitrimers have been designed from many different chemistries and for many different applications. Vitrimers can provide an ideal platform for designing the viscoelastic properties of a polymer via changes in the chemistry of the polymer backbone − or the type of dynamic bond. ,− These materials have been investigated in applications including shockwave dissipation, three-dimensional (3D) printing, creep resistant plastics, thermally conductive materials, solid battery electrolytes, and ultrathin coatings, where the viscosity and modulus contribute substantially to the resultant performance. In most cases, vitrimers show an Arrhenius temperature dependence of viscosity and a storage modulus, which increases with the cross-link density. ,,, The modulus of vitrimers has also been shown to increase upon heating in contrast to most dissociative dynamic networks. ,, Through a combination of multiple dynamic bonds, the goal of precise control over the temperature-dependent viscoelasticity of a polymer may be possible.…”

Amine-Cured Glycidyl Esters as Dual Dynamic Epoxy Vitrimers

“…A single type of dynamic covalent bond has been widely used in the synthesis of conventional epoxy vitrimers via the reaction between glycidyl ether and carboxylic acid (Scheme b). − However, a single dynamic vitrimer takes a long reprocessing time to rearrange the network topology at high temperatures, which easily leads to polymer network degradation. Incorporating multiple dynamic noncovalent or covalent bonds into polymer systems can provide an attractive and effectual method to achieve multifunctional response, , typical including hydrogen bonds and coordination bonds into polymers that are endowed with high-strength and self-healing properties. − A gentle approach has been developed to merge dual or triple dynamic covalent bonds into elastomeric networks with different multiplicities of exchangeable units . The combination of two different dynamic bonds based on disulfide exchange and carboxylate transesterification into epoxy vitrimers exhibits rapid stress relaxation and remarkably elevated malleability …”

Toughening shape-memory epoxy resins via sacrificial hydrogen bonds

“…The two broad peaks at 3413 and 3285 cm −1 at 30 °C before heating were attributed to -OH and -NH, respectively. 31 Upon heating, these two characteristic peaks were observed below…”