Evaluation of Vinyl Cinnamate for 4D printing of light-induced Shape Memory Polymers by digital light projection

Abstract

Light-induced Shape Memory Polymers (SMP) exhibits shape memory effect via photodimerization by forming cyclobutane crosslinkage between a determined wavelength when exposed to ultraviolet (UV) light. For the above to occur, monomers that contain Cinnamate acid (CA) groups allow these temporary crosslinks to be formed under UV light. The most used monomer that contains CA groups are synthesized Polyvinyl Cinnamate (PVCinn). However, they exist in powder form which is not adequate for digital light processing (DLP). In this report, the feasibility of using Vinyl Cinnamate (VCinn) through DLP technique to create a light induced SMP was demonstrated. A resin formulation with integration of VCinn allows for photodimerization and photocleaving to occur between 260nm. The resin formulation was 3D printed successfully via DLP. It was subsequently subjected to Tensile Testing, Fourier-transform Infrared Spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) to evaluate the mechanical properties, the number of cyclobutane crosslinks and the effects on glass transition temperature after photodimerization and photocleaving respectively. The addition of VCinn increased the tensile strength, young’s modulus and reduced tensile strain, more so after photodimerization because of the formation of cyclobutane crosslinks. FTIR measurements also showed a decrease in % transmittance at 1635cm-1 indicating that cyclobutane crosslinks were formed after exposure to UV wavelength >260nm. Also, DSC results showed that VCinn increases the glass transition temperature.