We investigate the impact of the non-uniform spatio-temporal conversion, intrinsic to photopolymerisation, in the context of light-driven 3D printing of polymers. The polymerisation kinetics of a series of model acrylate and thiol-ene systems, both neat and doped with a light-absorbing dye, is investigated experimentally and analysed according to a descriptive coarse-grained model for photopolymerisation. In particular, we focus on the relative kinetics of polymerisation with those of 3D printing, by comparing the evolution of the position of the conversion profile (z_f) to the sequential displacement of the object stage (∆z). After quantifying the characteristic sigmoidal monomer-to-polymer conversion of the various systems, with a combination of patterning experiments, FT-IR mapping, and modelling, we compute representative regimes for which z_f is smaller, commensurate with, or larger than ∆z. While non-monotonic conversion can be detrimental to 3D printing, for instance in causing differential shrinkage of inhomogeneity in material properties, we identify opportunities for facile fabrication of modulated materials in the z-direction (i.e., along the illuminated axis). Our simple framework and model, based on directly measured parameters, can thus be employed in photopolymerisation-based 3D printing, both in process optimisation and in the precise design of complex, internally stratified materials by coupling the z-stage displacement and frontal polymerisation kinetics.

A unified patterning strategy via frontal photopolymerization (FPP) that is robust to a wide range of radical photopolymerizing systems, including thiol–ene and acrylic monomers is reported. The factors governing the spatiotemporal solidification process, including front position, profile shape, and thermal effects, are investigated and modeled theoretically, resulting in the predictive FPP patterning of polymer networks with prescribed dimensions.

A cationic photo-curable cycloaliphatic epoxy resin has been investigated as reactive monomer in blue light crosslinking process. We have demonstrated that camphorquinone is able to abstract labile hydrogen from the epoxy monomer, giving rise to the formation of carbon-centered radicals that are oxidized by the onium salt; a complete epoxy group conversion was reached after 50 s of irradiation. The presence of water up to 1 wt% was tolerated without any important detrimental effect on the kinetics of light-curing. The presence of the inorganic filler up to 65 wt% did not significantly influence the curing process.