Andreas Taden

A facile route to phosphorus-functionalized polyurethane dispersions (P-PUDs) with improved adhesion properties is presented. (Bis)phosphonic acid moieties serve as adhesion promoting sites that are covalently attached via an end-capping reaction to isocyanate-reactive polyurethane particles under aqueous conditions. The synthetic approach circumvents solubility issues, offers great flexibility in terms of polyurethane composition, and allows for the synthesis of semicrystalline systems with thermomechanical response due to reversible physical cross-linking. Differential scanning calorimetry (DSC) is used to investigate the effect of functionalization on the semicrystallinity. The end-capping conversion was determined via inductively-coupled plasma optical emission spectroscopy (ICP-OES) and was surprisingly found to be almost independent of the stoichiometry of reaction, suggesting an adsorption-dominated process. Particle charge detection (PCD) experiments reveal that a dense surface coverage of phosphonic acid groups can be attained and that, at high functionalization degrees, the phosphonic adhesion moieties are partially dragged inside the colloidal P-PUD particle. Quartz crystal microbalance with dissipation (QCMD) investigations conducted with hydroxyapatite (HAP) and stainless steel sensors as model surfaces show a greatly enhanced affinity of the aqueous P-PUDs and furthermore indicate polymer chain rearrangements and autonomous film formation under wet conditions. Due to their facile synthesis, significantly improved adhesion, and variable film properties, P-PUD systems such as the one described here are believed to be of great interest for multiple applications, e.g., adhesives, paints, anticorrosion, or dentistry.Keywords: adhesion; hydroxyapatite; phosphorus; polyurethane dispersions; quartz crystal microbalance with dissipation

Dual-compartment nanofibres: separation of two highly reactive components in close vicinity

Co-reporter:Ann-Christin Bijlard, Anke Kaltbeitzel, Yuri Avlasevich, Daniel Crespy, Marc Hamm, Katharina Landfester and Andreas Taden

RSC Advances 2015 vol. 5(Issue 118) pp:97477-97484

Publication Date(Web):09 Nov 2015

DOI:10.1039/C5RA17750B

Dual-compartment nanofibres separating two highly reactive components in close vicinity are investigated. The study is intended as a non-classical approach for the control of reaction latency in colloidal systems. An epoxide resin and a hydrophobic polyamine which react readily at low temperatures are chosen as model compounds. Colloid electrospinning with PVA as the confining matrix is used for the immobilization of both in separate compartments. Uniform fibres are produced with a matrix/colloid weight ratio of 3/1. The internal fibre morphology was investigated via dual-colour stimulated emission depletion (STED) microscopy and TEM. The results show a statistical distribution of epoxy- and amine-containing compartments and indicate average particle–particle distances of <100 nm, which is supported by computations. The fibres are highly storage stable under ambient conditions and yet allow for efficient crosslinking and self-healing. The curing reaction can be initiated via thermal or mechanical stimuli, as demonstrated by electron microscopy and electrochemical testing of fibre containing coatings. The reactivity and latency for reaction is furthermore proven by calorimetric and chromatographic methods.

Synthesis and Thermal Curing of Benzoxazine Functionalized Polyurethanes

Co-reporter:Stefan Kirschbaum, Katharina Landfester, and Andreas Taden

Macromolecules 2015 Volume 48(Issue 12) pp:3811-3816

Publication Date(Web):June 11, 2015

DOI:10.1021/acs.macromol.5b00954

Benzoxazine (BOX) functionalized polyurethanes (PU) are introduced to provide a conceptually new thermal curing mechanism for polyurethanes. 3,4-Dihydro-3-methyl-2H-1,3-benzoxazine (P-m) was carefully oligomerized through thermal treatment. In a straightforward synthesis the newly formed hydroxyl groups are used for end-capping reactions with isocyanate-terminated polyurethane prepolymers. The isocyanate reactive hydroxyl content (IRH) of the benzoxazine oligomer was investigated in detail via 1H NMR spectroscopy, HPLC-MS, indirect potentiometric titration in various solvents, and comparison with model substances and found to be strongly influenced by hydrogen bonding. The corresponding polyurethane/benzoxazine hybrid materials (PU/BOX) can cross-link at elevated temperatures and do not suffer from shelf-life issues or outgassing of blocked isocyanates. The thermally activated curing reaction was investigated via rheology and DSC. Significant improvements over state-of-the-art systems based on phenol-capped PU prepolymers are shorter curing times, increased moduli, and drastically increased glass transition temperatures.

Polyurethane Dispersions with Peptide Corona: Facile Synthesis of Stimuli-Responsive Dispersions and Films

Co-reporter:Laura Breucker, Susanne Schöttler, Katharina Landfester, and Andreas Taden

Biomacromolecules 2015 Volume 16(Issue 8) pp:

Publication Date(Web):July 9, 2015

DOI:10.1021/acs.biomac.5b00672

Peptide–polymer hybrid particles of submicron size yielding stimuli-responsive macroscopic films are presented. A thermoplastic polyurethane (PU) carrying polysiloxane and polyester soft segments serves as core material to obtain flexible, yet semicrystalline films with temperature-sensitivity. The synthesis is based on the high-sheer emulsification of isocyanate-terminated PU prepolymers, which in our model system purposefully lack any ability of colloidal self-stabilization. While emulsification in water leads to immediate coagulation, stable dispersions of polyurethane nanoparticles were formed in aqueous solutions of a hydrolyzed protein from wool. A comparison of dispersion and film properties to nonreactive, otherwise identical dispersions suggests covalent attachment of the peptide to the PU backbone. We show that the colloidal stability of the hybrid particles is completely governed by the peptide corona, and hence pH-triggered coagulation can be employed to induce particle deposition and film formation. Differential scanning calorimetry confirms partial crystallinity in the film and reveals strongly modified crystallization behavior due to the peptide.

Controlled Formation of Polymer Nanocapsules with High Diffusion-Barrier Properties and Prediction of Encapsulation Efficiency

Co-reporter:Ines Hofmeister;Dr. Katharina Lfester;Dr. Andreas Taden

Angewandte Chemie International Edition 2015 Volume 54( Issue 1) pp:327-330

Publication Date(Web):

DOI:10.1002/anie.201408393

Abstract

Polymer nanocapsules with high diffusion-barrier performance were designed following simple thermodynamic considerations. Hindered diffusion of the enclosed material leads to high encapsulation efficiencies (EEs), which was demonstrated based on the encapsulation of highly volatile compounds of different chemical natures. Low interactions between core and shell materials are key factors to achieve phase separation and a high diffusion barrier of the resulting polymeric shell. These interactions can be characterized and quantified using the Hansen solubility parameters. A systematic study of our copolymer system revealed a linear relationship between the Hansen parameter for hydrogen bonding (δ_h) and encapsulation efficiencies which enables the prediction of encapsulated amounts for any material. Furthermore EEs of poorly encapsulated materials can be increased by mixing them with a mediator compound to give lower overall δ_h values.

Alternative Pathway for the Stabilization of Reactive Emulsions via Cross-Linkable Surfactants

Co-reporter:Ann-Christin Bijlard, Svenja Winzen, Kenji Itoh, Katharina Landfester, and Andreas Taden

ACS Macro Letters 2014 Volume 3(Issue 11) pp:1165

Publication Date(Web):October 23, 2014

DOI:10.1021/mz500625w

Highly reactive emulsions were stabilized by employing a surfmer analogous concept. An interfacial reaction between an emulsion droplet and a cross-linkable reactive surfactant was used to provide colloidal stability and simultaneously maintain the majority of the reactive groups. Polyaddition-type reaction between epoxy and amine was chosen as a model system to spontaneously and covalently bond the surfactant to the emulsion droplets. The interfacial reaction was monitored via isothermal titration calorimetry analysis. With this method, the increased colloidal stability could be attributed to a reaction rather than a pure physical adsorption. The maintained reactivity of the emulsion droplets enables consecutive conversions with coreactive components, e.g., for cross-linking reactions, corrosion protection, or functional coatings.

Water-Based Adhesives with Tailored Hydrophobic Association: Dilution Resistance and Improved Setting Behavior

Co-reporter:Alexer Dundua;Katharina Lfester

Macromolecular Rapid Communications 2014 Volume 35( Issue 21) pp:1872-1878

Publication Date(Web):

DOI:10.1002/marc.201400391

Facile synthesis of tunable alkali soluble latexes

Co-reporter:Alexander Dundua, Katharina Landfester, Andreas Taden

Polymer 2014 Volume 55(Issue 16) pp:3543-3550

Publication Date(Web):5 August 2014

DOI:10.1016/j.polymer.2013.08.028

•Miniemulsion-analogous polymerization of highly water-soluble monomers is performed.•Defined copolymerization with highly water-insoluble monomers in water-based system.•Facile synthesis of hydrophobically-modified alkali soluble emulsions (HASE) explored.•HASE with unusually low acid contents and tunable properties obtained.•Adjustable dissolution behavior and control over rheological properties achieved.Highly hydrophobic and highly hydrophilic (meth)acrylic monomers were copolymerized in heterophase system via a miniemulsion analogous polymerization technique. The versatility of the approach was demonstrated by the direct synthesis of hydrophobically modified alkali soluble emulsions (HASE) without the use of otherwise commonly required specialty monomers. It was demonstrated that copolymer composition drift during the course of the free radical heterophase polymerization the can be effectively regulated by the initial monomer ratios. This feature was employed to achieve (1) a more even distribution of acid functionalities throughout the growing polymer chains and the corresponding latex particles, (2) improved dissolution behavior upon deprotonation of the acid groups and (3) the possibility to tailor rheological properties at elevated pH values. Highly soluble HASE systems with surprisingly low contents of ionogenic groups and strong thickening effect were synthesized, which can provide beneficial characteristics in the coatings and adhesive sector.

Thermoset–thermoplastic hybrid nanoparticles and composite coatings

Co-reporter:Yang Zhang, Rebecca Foos, Katharina Landfester, Andreas Taden

Polymer 2014 Volume 55(Issue 10) pp:2305-2315

Publication Date(Web):13 May 2014

DOI:10.1016/j.polymer.2014.02.052

Structured thermoset–thermoplastic hybrid nanoparticles and composite coatings were successfully synthesized through a novel one-pot approach. Both the polyaddition of epoxy curing and the free radical polymerization of various vinyl monomers were performed in sequence in miniemulsion droplets. Benefiting from the precise control of the compatibility between thermoset phase (epoxy monomer/amine curing agent) and vinyl phase (vinyl monomers/polymers), colloidally stable, core–shell structured thermoset–thermoplastic hybrid nanoparticles between 100 and 200 nm were obtained through chemically induced phase separation. The influence of the compositions on the colloidal stability and morphology of the final hybrid latexes and films was studied in detail. Meanwhile, the mechanical properties of thermoset–thermoplastic coatings and corresponding thermoplastic coatings were investigated. It is found that the thermoset–thermoplastic composite coatings showed significantly improved film properties in terms of hardness compared to the analogous thermoplastic coatings. Furthermore the thermoset–thermoplastic hybrid films were highly transparent even with 33 wt% of epoxy thermoset domains embedded.

A Facile Route toward Structured Hybrid Particles Based on Liquid–Solid Assembly

Co-reporter:Yang Zhang, Katharina Landfester, and Andreas Taden

Macromolecules 2014 Volume 47(Issue 3) pp:1030-1038

Publication Date(Web):January 23, 2014

DOI:10.1021/ma401893g

Structured hybrid particles with strongly improved colloidal stability are synthesized through a facile fabrication method based on the assembly of miniemulsion droplets containing liquid monomeric precursors onto solid nanoparticles. Classical heterocoagulation experiments between solid particles with similar compositions are performed for comparison and result in coagulated samples. A two-step mechanism is proposed which involves polymerization to fixate the final hybrid particle morphology after electrostatically driven self-assembly. Negatively charged polyacrylonitrile (PAN) nanoparticles with a high degree of semicrystallinity are utilized as solid core and combined with positively charged monomer droplets of varying compositions. A simple adjustment of miniemulsion composition enables the tailored synthesis of raspberry or core–shell structured hybrid particles. While the ζ-potential strongly affects the colloidal stability, adjusting the Tg of the polymer and/or the cross-linking degree after polymerization is an efficient tool to determine the final latex morphology. As-prepared hybrid dispersions can form transparent films with embedded PAN domains with an undisturbed high degree of semicrystallinity and thus show potentials in a wide variety of applications, e.g., for coatings and adhesives with reinforced mechanical properties and improved barrier performance.

pH-Sensitive Nanocapsules with Barrier Properties: Fragrance Encapsulation and Controlled Release

Co-reporter:Ines Hofmeister, Katharina Landfester, and Andreas Taden

Macromolecules 2014 Volume 47(Issue 16) pp:5768-5773

Publication Date(Web):August 14, 2014

DOI:10.1021/ma501388w

A facile synthesis method for polymer nanocapsules with high diffusion barrier and stimuli-responsive release properties is presented. The highly volatile fragrance α-pinene was used as hydrophobic model compound for the encapsulation process, which is based on a miniemulsion-analogous free radical polymerization process. The copolymer composition was systematically varied, and increasing contents of methacrylic acid as functional monomer in combination with high glass transition temperatures enabled unusually high encapsulation efficiencies of ≥90% for capsules with z-average diameters of <200 nm. Temperature and pH change can be used as trigger to open the capsules, and the release kinetics can be tailored depending on the polymer shell composition. In contrast to more frequently applied barrier microcapsules the nanocapsules provide drastically improved colloidal stabilities. Furthermore, the barrier nanocapsule approach is principally not restricted to fragrances and is expected to be compatible with other hydrophobic actives.

Water-based hybrid zinc phosphate–polymer miniemulsion as anticorrosive coating

Co-reporter:Nermeen Nabih, Ute Herrmann, Gunnar Glasser, Ingo Lieberwirth, Katharina Landfester, Andreas Taden

Progress in Organic Coatings 2013 Volume 76(Issue 4) pp:555-562

Publication Date(Web):April 2013

DOI:10.1016/j.porgcoat.2012.11.003

A water-based hybrid zinc phosphate–polymer miniemulsion was synthesized via a multiple miniemulsion process. In this process zinc phosphate was synthesized in situ using homogenization of two inverse miniemulsions containing suitable precursors dispersed within a polymerizable continuous phase. Converting the resultant inverse miniemulsion into a direct miniemulsion, followed by polymerization, resulted in a water-based hybrid zinc phosphate, organic solvent free, which was used to coat steel panels via autodeposition. The coated panels were subjected to salt spray testing which showed better anticorrosion performance in comparison to an equivalent polymer coated panel prepared with a separate corrosion resistance step.The results show that combination of inorganic and organic properties in one synthesis, combining also their properties and performance, is promising for new generation coatings, functional coatings, barrier coatings, electrodeposition coatings as well as other industrial applications.The miniemulsion was characterized using dynamic light scattering (DLS) and scanning electron microscopy (SEM). Elemental analysis was carried out using X-ray fluorescence (XRF), as well as inductively coupled plasma-optical emission spectroscopy (ICP-OES). The film coating cross-section was investigated using SEM and energy dispersive X-ray analysis (EDX).Graphical abstractHighlights► Synthetic route devised for water-based zinc phosphate–polymer miniemulsion. ► Autodeposition carried out from miniemulsion on cold rolled steel substrates. ► Salt spray test results show hybrid particle possesses anticorrosion properties. ► Investigation of film cross section using SEM and EDX suggests mechanism. ► Mechanism dependent on zinc phosphate mobility at high temperatures across film.

Advanced chemically induced phase separation in thermosets: Polybenzoxazines toughened with multifunctional thermoplastic main-chain benzoxazine prepolymers

Co-reporter:Christian Sawaryn, Katharina Landfester, Andreas Taden

Polymer 2011 Volume 52(Issue 15) pp:3277-3287

Publication Date(Web):7 July 2011

DOI:10.1016/j.polymer.2011.04.064

Multifunctional thermoplastic main-chain benzoxazine prepolymers were synthesized and systematically varied in their structure in order to function as high-performance toughener additives. Their unique chemical composition allows multiple covalent crosslinking with many thermoset network systems including benzoxazines and epoxides in conjunction with a defined chemical induced phase separation (CIPS) upon curing. This was successfully shown using a benzoxazine-based thermoset resin matrix as an example. The corresponding morphologies were addressable in a predictable manner and brought into context with the obtained macroscopic mechanical and thermal properties. In this relationship the CIPS process was classified and compared with the literature in more general means for advanced morphology control by differentiating between covalently attached and so-called gradient domain structures. The prepolymers were characterized by 1H NMR, FT-IR, DSC and TGA. The thermoset morphologies were investigated by TEM and AFM. The fracture toughness (KIc) and the elastic modulus (E) were measured by fracture and three point bending experiments. Thermal properties of the resulting films have been tested by DMA.

Water-based inorganic/polymer hybrid particles prepared via a multiple miniemulsion process

Co-reporter:Nermeen Nabih;Katharina Lfester

Journal of Polymer Science Part A: Polymer Chemistry 2011 Volume 49( Issue 23) pp:5019-5029

Publication Date(Web):

DOI:10.1002/pola.24963

Abstract

A universal method for the synthesis of water-based inorganic–polymer hybrid particles was developed in which no organic solvent is required. To demonstrate the versatility of this process, zinc phosphate, calcium carbonate, and barium sulfate were chosen as different pigment examples which additionally can be utilized for functional coating applications. Furthermore, a complex polymeric composition based on epoxy–acrylic–styrene was chosen to illustrate the versatility from a soft matter point of view. The overall synthesis process was carried out by coemulsification of two inverse miniemulsions, containing two precursors, surrounded with a polymerizable continuous phase. This was then transferred to a direct miniemulsion by addition to a surfactant solution and subsequent homogenization followed by radical polymerization of the vinylic monomers. To our knowledge, this is the first work where a polymerizable continuous phase has been used in an inverse miniemulsion formation followed by transfer to a direct miniemulsion, followed by polymerization, so that the result is a water-based dispersion. The resultant dispersion was characterized by dynamic light scattering; the particles were investigated via transmission electron microscopy with insitu determination of crystallinity using electron diffraction. Elemental analysis was also performed for the particles and the polymerized miniemulsions using X-ray fluorescence and inductively coupled plasma-optical emission spectroscopy, respectively. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011