Dagmar R. D’hooge

A Light-Activated Reaction Manifold

We introduce an efficient reaction manifold where the rate of a thermally induced ligation can be controlled by a photonic field via two competing reaction channels. The effectiveness of the reaction manifold is evidenced by following the transformations of macromolecular chain termini via high-resolution mass spectrometry and subsequently by selective block copolymer formation. The light-controlled reaction manifold consists of a so-called o-quinodimethane species, a photocaged diene, that reacts in the presence of light with suitable enes in a Diels-Alder reaction and undergoes a transformation into imines with amines in the absence of light. The chemical selectivity of the manifold is controlled by the amount of ene present in the reaction and can be adjusted from 100% imine formation (0% photo product) to 5% imine formation (95% photo product). The reported light-controlled reaction manifold is highly attractive because a simple external field is used to switch the selectivity of specific reaction channels.

Computational Study and Kinetic Analysis of the Aminolysis of Thiolactones

The aminolysis of three differently α-substituted γ-thiolactones (C4H5OSX, X = H, NH2, and NH(CO)CH3) is modeled based on CBS-QB3 calculated free energies corrected for solvation using COSMO-RS. For the first time, quantitative kinetic and thermodynamic data are provided for the concerted path and the stepwise path over a neutral tetrahedral intermediate. These paths can take place via an unassisted, an amine-assisted, or a thiol-assisted mechanism. Amine assistance lowers the free energy barriers along both paths, while thiol assistance only lowers the formation of the neutral tetrahedral intermediate. Based on the ab initio calculated rate coefficients, a kinetic model is constructed that is able to reliably describe experimental observations for the aminolysis of N-acetyl-dl-homocysteine thiolactone with n-butylamine in THF and CHCl3. Reaction path analysis shows that for all conditions relevant for applications in polymer synthesis and postpolymer modification, an assisted stepwise mechanism is operative in which the formation of the neutral tetrahedral intermediate is rate-determining and which is mainly amine-assisted at low conversions and thiol-assisted at high conversions.

Waterborne Electrospinning of Poly(N-isopropylacrylamide) by Control of Environmental Parameters

With increasing toxicity and environmental concerns, electrospinning from water, i.e., waterborne electrospinning, is crucial to further exploit the resulting nanofiber potential. Most water-soluble polymers have the inherent limitation of resulting in water-soluble nanofibers, and a tedious chemical cross-linking step is required to reach stable nanofibers. An interesting alternative route is the use of thermoresponsive polymers, such as poly(N-isopropylacrylamide) (PNIPAM), as they are water-soluble beneath their lower critical solution temperature (LCST) allowing low-temperature electrospinning while the obtained nanofibers are water-stable above the LCST. Moreover, PNIPAM nanofibers show major potential to many application fields, including biomedicine, as they combine the well-known on-off switching behavior of PNIPAM, thanks to its LCST, with the unique properties of nanofibers. In the present work, based on dedicated turbidity and rheological measurements, optimal combinations of polymer concentration, environmental temperature, and relative humidity are identified allowing, for the first time, the production of continuous, bead-free PNIPAM nanofibers electrospun from water. More specifically, PNIPAM gelation was found to occur well below its LCST at higher polymer concentrations leading to a temperature regime where the viscosity significantly increases without compromising the polymer solubility. This opens up the ecological, water-based production of uniform PNIPAM nanofibers that are stable in water at temperatures above PNIPAMs LCST, making them suitable for various applications, including drug delivery and switchable cell culture substrates.

Can the melt flow index be used to predict the success of fused deposition modelling of commercial poly(lactic acid) filaments into 3D printed materials

ABSTRACT The melt flow index (MFI) of seven commercial poly(lactic acid) (PLA) grades is investigated in view of 3D printing quality. A threshold value of 10 g (10 min)−1 (2.16 kg; ISO 1133) is put forward for a successful printing (190–220°C), enabling a fast and practical screening of PLA materials. It is however shown that a sole focus on MFI is insufficient, as the plasticiser type and crystallinity also play a role after the polymer melt deposition. The latter is supported by scanning electron micromorphology and differential scanning calorimetry measurements. In particular, blending with poly(hydroxyl butyrate) (PHB; 20 m%) allows to control both MFI and crystallinity without the need for annealing.

Facile and low-cost route for sensitive stretchable sensors by controlling kinetic and thermodynamic conductive network regulating strategies

Highly sensitive conductive polymer composites (CPCs) are designed employing a facile and low-cost extrusion manufacturing process for both low- and high-strain sensing in the field of, for example, structural health/damage monitoring and human body movement tracking. Focus is on the morphology control for extrusion-processed carbon black (CB)-filled CPCs, utilizing binary and ternary composites based on thermoplastic polyurethane (TPU) and olefin block copolymer (OBC). The relevance of the correct CB amount, kinetic control through a variation of the compounding sequence, and thermodynamic control induced by annealing is highlighted, considering a wide range of experimental (e.g., static and dynamic resistance/scanning electron microscopy/rheological measurements) and theoretical analyses. High CB mass fractions (20 m %) are needed for OBC (or TPU)-CB binary composites but only lead to an intermediate sensitivity as their conductive network is fully packed and therefore difficult to be truly destructed. Annealing is needed to enable a monotonic increase of the relative resistance with respect to strain. With ternary composites, a much higher sensitivity with a clearer monotonic increase results, provided that a low CB mass fraction (10-16 m %) is used and annealing is applied. In particular, with CB first dispersed in OBC and annealing, a less compact, hence, brittle conductive network (10-12 m % CB) is obtained, allowing high-performance sensing.

Polymers: Design and Production

This chapter gives an overview of the most frequently applied numerical methods for the simulation of polymerization processes, that is, the calculation of the polymer microstructure as a function of monomer conversion and process conditions such as the temperature and initial concentrations. It is important to note, such simulations allow one to optimize the macroscopic polymer properties and to influence the polymer processability and final polymer product application range. Both deterministic and stochastic modeling techniques are discussed. In deterministic modeling techniques, time variation is seen as a continuous and predictable process, whereas in stochastic modeling techniques, a random-walk process is assumed instead.

Advanced Theoretical Analysis in Chemical Engineering: Computer Algebra and Symbolic Calculations

The principle of critical simplification in chemical kinetics is formulated using algebraic methods. Relaxation procedures for distinguishing linear and non-linear models are described. Intersections and coincidences in kinetic dependences are analyzed.

Chapter 6 – Thermodynamics

The mathematical basis of chemical thermodynamics is presented, including the analysis of overshooting an equilibrium. Equilibrium relationships for non-equilibrium chemical dependences are constructed for some typical chemical reactions.

Stability of Chemical Reaction Systems

The concept of stability is extremely important for a wide variety of dynamical systems, ranging from purely mathematical to natural and social systems. Physical and engineering systems, such as chemical reaction systems, are usually designed to operate at an equilibrium state (closed systems) or steady state (open systems), which must be stable for successful operation. This stability depends on whether a small perturbation is damped, leading to a stable state, or amplified, which results in an unstable state.

Experimental Data Analysis: Data Processing and Regression

The Newton-Gauss method assumes that with good approximation f can be assumed to be linear over the full length of every parameter step. It is also possible, however, to search for the minimum of the objective function, Eq. (9.4) , numerically without having to make such an assumption by using algorithms derived from optimization theory.