Creation of a script for efficient and productive training for heterogeneous types of learners

Vor dem Hintergrund der Mitarbeiterentwicklung ist es schwierig unterschiedliche Mitarbeiter gleich effizient zu schulen. Die vorliegende Diplomarbeit behandelt eingangs die Theorien um das Lernen und die unterschiedlichen Lerntypen, sowie die Grundlagen der Kommunikation. Anhand des 4 Mat Designs wird eine Beispielsschulung erstellt, welche auf heterogene Lerntypen gleichermaßen eingeht. Durch das Ergebnis ist ein effizientes und ergiebiges schulen Teilnehmer unterschiedlichster Lerntypen möglich

Microstructural PALS study of regulated dimethacrylates: Thiol- versus β-allyl sulfone-based networks

The final publication is available via https://doi.org/10.1002/polb.24240.Radical photocuring of multifunctional (meth)acrylates is lacking control over the irregular chain growth process yielding highly crosslinked, inhomogeneous networks. Chain transfer agents (CTAs, e.g. thiols or β-allyl sulfones) have been widely used to modify this curing process, thus reducing shrinkage stress and increasing the toughness of the formed photopolymers. Resulting photopolymer networks exhibit higher bulk density, lower crosslinking density and narrow glass transitions. Consequently, a more homogeneous network structure was postulated for those networks. Whereas macroscopic properties of the modified final materials have already been studied, herein the microstructural arrangement of such modified networks has also been evaluated with the help of positron annihilation lifetime spectroscopy (PALS). A more homogenous network structure with a decreased free-volume void size was confirmed for CTA-based dimethacrylate networks. A sharper distribution of the orthopositronium (o-Ps) lifetime, mainly for the β-allyl sulfone-based photopolymers, hints towards a more regulated network structure. Moreover, the combination of PALS, DMTA, density and swelling experiments elucidates relations between void formation, crosslinking density and macroscopic characteristics such as shrinkage stress and mechanical properties.Austrian Science Funds (FWF

Light-triggered radical silane-ene chemistry using a monoalkyl substituted bis(trimethylsilyl)silane

The final publication is available via https://doi.org/10.1002/macp.201600563.Chain transfer agents (e.g., thiols) enrich radical photopolymerization for use in advanced applications such as stereolithography, optical materials, and biomedicine. Resulting thiolene-based photopolymers exhibit numerous benefits such as tunable thermomechanical properties, and give access to spatially resolved functional materials. Silane-ene chemistry could serve as alternative to this popular thiol-ene approach. A monosubstituted bis(trimethylsilyl)silane (MSiH) is synthesized by a simple one pot procedure. Photoinitiated radical silane-ene chemistry has been performed with multiple enes and the conversions are assessed by 1H NMR spectroscopy. Compared to the most reactive silane from literature, tris(trimethylsilyl)silane (TTMSSiH), the radical reactivity of MSiH is reduced in all tested formulations, but the possibility for further functionalization and accessibility of multifunctional MSiH-derivatives is upheld. A silane-acrylate formulation is found to be most promising. In comparison to a thiolacrylate system, a more uniform conversion of the chain transfer agent and acrylate is shown for the silaneacrylate formulation with MSiH. The promising results for the silane-acrylate system are confirmed by further tests (i.e., NMR spectroscopy, GPC, and MALDI MS), giving additional information on molecular weight regulation and radical mechanism. First MSiH-based photopolymer networks have been fabricated and analyzed via DMTA, thus paving the way for future silane-acrylate networks.Austrian Science Funds (FWF

Low volatile monofunctional reactive diluents for radiation curable formulations

In the last decades the importance of UV curable formulations has increased continuously. Their fast curing speed, solvent-free polymerization conditions, and the formation of hard and highly crosslinked photopolymer networks represent major benefits. Commercial UV resins generally consist of multi-functional vinyl oligomers, photoinitiators, additives, and reactive diluents. Mono- and multi-functional reactive diluents serve as thinners to lower the overall resin viscosity and to improve processability. However, many monofunctional reactive diluents like isobornyl (meth)acrylate or benzyl (meth)acrylate exhibit high volatility, often already at room temperature. This causes adverse effects such as unpleasant odor, potential health risks, and changing resin composition during processing. A new group of monomers that show high potential for replacing traditional highly volatile reactive diluents are salicylate (meth)acrylates. In this work, salicylate-based thinners are synthesized, polymerized, and characterized with respect to their viscosity, volatility, thermal stability, photoreactivity, and thermomechanical properties of their homopolymers. Additionally, a first example of their diluting effect in a highly viscous difunctional polyester urethane methacrylate is demonstrated with 30 wt% of a cycloaliphatically and an aromatically substituted salicylate methacrylate. The polymers of the diluted resin exhibit similarly high glass transition temperatures of 110 and 126 °C, which are in the range of the polymers of the undiluted resin.</p

Regulated acrylate networks as tough photocurable materials for additive manufacturing

In lithography-based additive manufacturing, mostly crosslinking monomers with acrylate functionality are applied, which yield brittle materials with inhomogeneous network architectures. The toughening of state-of-the-art materials is an integral requirement for the advancement of photopolymer-based three-dimensional (3D) products. Here we show that the final material properties of acrylate networks can be adjusted through regulation of the radical curing mechanism using difunctional vinyl sulfonate esters to obtain toughened 3D structured materials. A substantial improvement of the thermomechanical behavior of resulting materials over materials regulated by state-of-the-art reagents (e.g. thiols) is presented and first 3D parts have successfully been printed. Resulting materials exhibit reduced shrinkage stress, reduced warpage, higher overall conversion and higher glass transition temperatures compared with the pure acrylate network.</p

Heterotelechelic poly(propylene oxide) as migration-inhibited toughening agent in hot lithography based additive manufacturing

Light-based processing techniques triggering photopolymerization are among the most promising 3D printing technologies due to their benefits regarding resolution, surface quality and build speed. However, the main challenge remains the development of strong and tough materials, since most commercially available photopolymer resins are limited in terms of their thermomechanical performance. We therefore synthesized a heterotelechelic hybrid oligomer based on poly(propylene oxide) (PPO-H), bearing one methacrylic and one addition-fragmentation chain transfer group (AFCT) as end groups. This new compound was successfully implemented as a toughening agent by regulating the network structure via the AFCT mechanism and acted as reactive diluent for highly viscous resins. Formulations containing 10-25 db% (double bond percent) of PPO-H mixed into a commercially available resin (Bomar XR-741MS) were investigated and compared to the corresponding PPO dimethacrylate (PPO-D) mixtures, representing state of the art resins. Full double bond conversion could be reached for PPO-H containing formulations, while shrinkage stress was simultaneously reduced by up to 50% compared to the PPO-D mixtures. Glass transition temperatures decreased with increasing PPO contents. Toughness was enhanced by a factor of 2 (10 db% PPO-H) to 4 (15 db% PPO-H), measured by elongation at break, while decrease in tensile strength remained low (factor of 1.2 and 1.4 for 10 and 15 db% PPO-H, respectively). Impact strength increased by 55 and 92% for 10 and 15 db% PPO-H, respectively. By employing the recently developed Hot Lithography technique, toughened and migration-free 3D printed parts were obtained with PPO-H.</p

Photo-chemically induced polycondensation of a pure phenolic resin for additive manufacturing

Bakelite© or phenoplasts are considered the first synthetic polymers in the world. These resins, produced by polycondensation, have always been known for their chemical resistance, excellent flame resistance and thermal stability. Originally, pressure and temperature are required for processing and limited the production of phenoplasts to compression and injection molding. However, with the invention of lithography and 3D printing, new desirable processing possibilities have emerged. Previous work in the area of additive manufacturing of phenoplasts has focused on thin-layer photoresists or parts that can only be printed using other polymers as a matrix. Here we report direct 3D printing of phenoplasts, without binders or matrix polymers, using Hot Lithography, a stereolithography-based 3D printing technology at elevated temperatures. In simultaneous thermal analysis and photo-DSC experiments we investigated suitable conditions for the UV-induced polycondensation of the phenolic resins. Based on these experiments, formulations are presented, which are stable under the selected printing conditions and yet reactive enough for the printing process. Direct 3D printing with Hot Lithography and post-curing gave bubble-free specimens, thus a simple production of complicated structures could be achieved without the conventional complex injection molding and more importantly the first bulk polycondensation process using this technique.</p

β‑Allyl Sulfones as Addition–Fragmentation Chain Transfer Reagents: A Tool for Adjusting Thermal and Mechanical Properties of Dimethacrylate Networks

Dimethacrylates are known to have good photoreactivity, but their radical polymerization usually leads to irregular, highly cross-linked, and brittle polymer networks with broad thermal polymer phase transitions. Here, the synthesis of mono- and difunctional β-allyl sulfones is described, and those substances are introduced as potent addition–fragmentation chain transfer (AFCT) reagents leading to dimethacrylate networks with tunable properties. By controlling the content and functionality of said AFCT reagents, it is possible to achieve more homogeneous networks with a narrow glass transition and an adjustable glass transition temperature (<i>T</i>_g), rubber modulus of elasticity (<i>E</i>_r), and network density. In contrast to dimethacrylate networks containing monomethacrylates as reactive diluents, the network architecture of the β-allyl sulfone-based dimethacrylate networks is more homogeneous and the tunability of thermal and mechanical properties is much more enhanced. The reactivity and polymerization were investigated using laser flash photolysis, photo-DSC, and NMR, while DMTA and swellability tests were performed to characterize the polymer

Debonding on Demand with Highly Cross-Linked Photopolymers: A Combination of Network Regulation and Thermally Induced Gas Formation

Photopolymerizable glues and cements that offer debonding on demand (DoD) through an external stimulus are of great interest for the fields of recycling and repair. State-of-the-art DoD solutions often require a high-energy impulse (e.g., >200 °C, strong force), which is due to the typical glassy nature of such photopolymer networks. Herein, various blocked isocyanates (BICs) that enable thermally induced gas formation at temperatures far below 200 °C are studied. Thermally induced gas bubble formation is accomplished within a linear, thermoplastic poly­(<i>N</i>-acryloyl­morpholine) matrix above glass transition temperature, introducing porosity. The resulting porosity within the material then causes mechanical failure. However, highly cross-linked photopolymer networks remain unchanged due to their glassy nature at temperatures well above 150 °C. A BIC-based thermolabile photopolymerizable cross-linker is prepared in order to create a polymer network with cleavable cross-link. Additionally, a β-allyl sulfone-based chain transfer reagent is used to tune the final cross-linking density and thermomechanical properties of the material. Above the resulting sharp glass transition (>60 °C), plastic deformation becomes possible, thus allowing formation of porosity. This introduces a covalently cross-linked, thermolabile photopolymer with a tailored network architecture as potential glue for DoD at ∼150 °C