Tuning Mechanical Properties of Dual-Wavelength Thiol-Methacrylate Resins via Orthogonal Photoreactions

Polymers that are able to undergo curing by light exposure offer a lot of advantages in various application fields such as 3D printing, coatings and biomedical applications. These materials can be processed under mild conditions without the need for elevated temperatures or toxic solvents. However, it is very difficult to change the mechanical properties of these materials after polymerization. This master¿s thesis addresses this challenge by developing a dual-wavelength responsive thiol-methacrylate-based photoresin system capable of locally tuning mechanical properties through orthogonal photoreactions. The resin system utilizes 450 nm light to initiate radical thiol-methacrylate polymerization, forming a solid polymer network. Post-crosslinking is achieved by triggering the [4¿4] photocycloaddition of covalently bound anthracene through 365 nm UV exposure, resulting in localized stiffening of the network. Methacrylate-functionalized anthracene was incorporated into the methacrylate backbone as the reactive component for this wavelength-selective crosslinking process. To optimize the resin formulation, functional group conversion kinetics were examined using FTIR and UV-Vis spectroscopy. Dynamic mechanical analysis was performed to evaluate the storage modulus and the glass transition temperature (Tg) over a wide temperature range, while tensile testing was carried out to evaluate the Youngs¿s modulus and tensile strength of the cured and the additionally post-cured material at room temperature. The optimized resin formulation demonstrated a significant increase in mechanical properties after post-curing, as the Young¿s modulus increased from 7.4 MPa to 19.9 MPa, and the tensile strength increased from 1.4 MPa to 1.9 MPa. The glass transition temperature was found to be at around 12 °C, with the post-cured sample showing a broader loss factor distribution, indicating the formation of a heterogenous network. In conclusion, the successful development of a thiol-methacrylate-based photoresin with orthogonal photoreactions enables local and selective modification of mechanical properties. The resin system shows great potential for applications in multi-wavelength 3D printing, particularly in the fabrication of structures with spatially varying mechanical properties, such as soft robotics, adaptive mechanical components, and photopatterned materials.