Additive manufacturing and the quest for novel, smart and renewable materials for 3D
printing and light-based applications has become a major focus in polymer science. The
aim of this thesis was the further development of 3D printing resins with regard to these
characteristics, as well as the development of a novel multifunctional resin system by
implementation of orthogonal photoreactions into the 3D printing process.
In a first approach the introduction of network disparity through the use of two orthogonal
photoinitiators was investigated. In a thiol-acrylate resin with excess acrylate a photo base
(PB) and a radical photoinitiator (PI) are used in combination with a visible light source
(405 nm) and UV light (365 nm). Activating the PB at 405 nm forms crosslinks between
thiol and acrylate units, consuming both groups equally. The step-growth manner of
the polymerization produces a well defined network with a late gel-point and a low glass
transition temperature (Tg), as the uncured acrylate in the system acts as plasticizer. Further
curing the sample with 365 nm activates the radical PI, the remaining acrylate is cured and
the Tg is increased significantly. Very similar material properties can be achieved by solely
curing the resin with UV light, activating both photoinitiators and proceeding in a mixedmode
polymerization consuming all monomers simultaneously. While a stepwise curing with
a relatively large difference in thermo-mechanical properties could be demonstrated, the
hypothesis of the molecular structure having a significant effect on the material properties
could not be confirmed.
In a second, more comprehensive study, a dual-cure, single-vat resin was developed, based
on radical polymerization of a thiol-methacrylate monomer system containing covalently
bound chalcone units as dimerizable crosslinkers. Thermo-mechanical properties can be
spatially and temporally controlled via the λ-orthogonal [2+2] cycloaddition reaction of the
chalconyl groups during printing or post-processing. Using defined doses of light (405 nm)
after polymerization (450 nm), the Tg and elastic modulus can be altered in a continuous
way, generating not only two but numerous distinct material properties. Shape memory
experiments as well as multi-wavelength 3D printing was shown on macro- and micro-scale
to present the vast opportunities for this novel 3D-printable material. Further functional
groups were investigated upon their reactivity upon irradiation with the most common
wavelengths creating a library of photo-crosslinkable moieties. Notably, the reactivity did
not always align with the recorded ultraviolet-visible absorption spectrum, confirming a
reactivity analysis crucial for all light-induced processes especially if orthogonality is desired.
In all studies photo-DSC and FTIR kinetics were used as a tool to investigate and characterize
curing behavior. These methods were used to contribute to detailed investigations on a
number of novel photoinitiators and biobased molecules for advanced applications in future
additive manufacturing were additionally evaluated. Thereby, two bio-based methacrylates,
eugenyl methacrylate (EM) and vanillyl alcohol methacrylate (VAM) were investigated
upon their curing behavior along a range of temperatures to optimize processing conditions
in paper coating. Finding VAM to be the more reactive of the two bio-based alternatives,
exhibiting a water contact angle (106°) comparable to existing coatings if PDMS-ECEMS
is used as an additive (10 wt%). This makes vanillyl alcohol methacrylate a suitable sustainable alternatives for hydrophobic paper coatings. Additionally, Novel type I radical
photoinitiators, based on tin or germanium, were investigated upon their curing behavior.
They can be used in future applications as an alternative to state-of-the-art phosphorous PIs
with reduced toxicity and pronounced reactivity in the energy-efficient, innocuous visible
light region. Lastly, bio-based monomers with methacrylate, vinyl and alkyne functionalities
were evaluated for their applicability in novel resins for 3D-printable biological scaffolds or
coatings.
Finally, a literature review is given as a comprehensive overview on single-molecule
(type I) radical photoinitiators. The focus is put on visible light activation, comprising not
only phosphorous but also silicon, germanium and tin compounds, as a way to more benign
and energy-conscious curing.
The three main topics of this thesis are photoinitiators and their characterization, bio-based monomers for radical photo-polymerization and molecules for the implementation
into dual-cure 3D printing resins for smart materials. They all contribute to a better
understanding of all constituents used, their reaction mechanism, curing behavior and
influence on the final material properties, crucial for sophisticated material development
towards advanced 3D printing of smart materials.