Fd Frank Wiesbrock

Influence of different branched alkyl side chains on the properties of imidazolium-based ionic liquids

Several new branched ionic liquids were synthesized under microwave irradiation applying two different synthetic approaches. Different already known ionic liquids, both linear and branched, were added to this set of new ionic liquids to investigate the influence of the branching on the thermophysical properties to elucidate first structure–property relationships. Thermogravimetric analysis was utilized to investigate the decomposition behavior and differential scanning calorimetry was used to study the influence of the branching on the thermal behavior, e.g. the melting point, the glass transition temperature, the freezing point and the cold crystallization temperature. Moreover, the water uptake of selected ionic liquids was analyzed.

Elastic moduli for a diblock copoly(2-oxazoline) library obtained by high-throughput screening

Using depth-sensing indentation, the elastic modulus E of a diblock copoly(2-oxazoline) library was investigated in order to determine structure–property relationships. The adopted experimental procedure, dropcasting of the copolymer materials and determining the elastic modulus by depth-sensing indentation, was compatible with high-throughput experimentation. The elastic modulus of the investigated materials depended strongly on the side-group. Materials containing poly(nonyloxazoline) exhibited a lower modulus than materials without any poly(nonyloxazoline) block as poly(nonyloxazoline) was at room temperature above its glass-transition temperature Tg, while the other homopolymers in this study were glassy at room temperature. The elastic modulus also depended on the relative humidity (RH) of the testing environment; the stiffness of ethyloxazoline and methyloxazoline decreased significantly due to water absorption from the air. At lower RH, hydrogen bonding or polar interactions among the polymer chains resulted in a surprisingly high modulus for the poly(methyloxazoline). In addition, as anticipated, the elastic moduli of AB diblock copolymers were bounded by those of the A and B homopolymers, both at high and at low RH. The presented results indicate how, and to what extent, for these materials the E (and the change in E) at a given (change in) humidity can be adjusted by tailoring the composition.

Evaporation induced micellization of poly(2-oxazoline) multiblock copolymers on surfaces

The formation of micelles on surfaces by spin-coating dilute solutions of diblock, triblock, and tetrablock copoly(2-oxazoline)s in a non-selective solvent is demonstrated. The micelles are not preexistent in the initial solution but are formed during the evaporation of the solvent by precipitation of the least-soluble block. The morphology and size of the micelles vary according to the fraction of this block but are not dependent on the block order in the copolymer.

Kinetic investigations on microwave-assisted statistical terpolymerizations of 2-oxazoline monomers

The microwave-assisted statistical terpolymerization of 2-oxazolines via a living cationic ring-opening polymerization mechanism is discussed. Kinetic investigations on the terpolymerizations of combinations of 2-methyl-2-oxazoline, 2-ethyl-2-oxazoline, 2-nonyl-2-oxazoline, and 2-phenyl-2-oxazoline were performed by heating separate polymerization mixtures for different predefined times. The resulting polymer solutions were analyzed by gas chromatography and size exclusion chromatography, demonstrating the living character of the statistical terpolymerizations. In addition, the monomer distribution throughout the polymer chains is discussed based on the linear first order kinetic plots of the separate monomers in the terpolymerizations. The observed differences in monomer distribution are expected to influence the polymer properties, which will be the focus of future investigations.

Correlating the mechanical and surface properties with the composition of triblock copoly(2-oxazoline)s

The elastic moduli, surface energies, and phase morphologies of poly(2-oxazoline) triblock copolymers were investigated and compared to the corresponding homopolymers and diblock copolymers, at a constant degree of polymerization. The elastic moduli of ABA triblock copolymers were bound by those of the respective AB diblock copolymers and A homopolymers. These results show that the elastic moduli of these copolymers – obtained by instrumented indentation – depended on the interplay between phase-separation, crystallization and hygroscopicity, and can be adjusted by tailoring the composition. The surface energy strongly depended on the presence of a poly(2-nonyl-2-oxazoline) block. If such a block was present, the surface energy was reduced due to segregation of nonyl side-chains to the surface. This segregation was promoted by annealing. The crystallization of nonyl side-chains at the surface promoted the development of surface texture and an increase in surface roughness, as demonstrated by atomic force microscopy topographic imaging.

Microwave-assisted nitroxide-mediated polymerization of alkyl acrylates

Abstract Nitroxide-mediated polymerizations of methyl and tert-butyl acrylate were performed in a single-mode microwave reactor at 120°C. The polymerizations could be carried out in a controlled way in concentrated solution (approx. 50 wt.-% of monomer) up to monomer conversions of around 90%. Monomer conversion followed first-order kinetics in the case of tert-butyl acrylate. For methyl acrylate, it seems that the kinetics obeyed the persistent radical effect. The polymers obtained from this controlled radical polymerization technique exhibited narrow molecular weight distributions (indicated by polydispersity indices below 1.3).