Klaus Tauer

Functional hollow carbon nanospheres by latex templating.

A facile and sustainable synthesis of hollow carbonaceous nanospheres is presented, offering a scalable and multifunctional route to the generation of useful nanocontainers, which critically possess the stability not offered by polymeric equivalents and functionality not afforded by other nanocarbons. Carbonization temperature provides a subtle but elegant mechanism to control structure and thereby hydrophobicity, nanopartitioning, and permeation between the inner and outer space.

Reactive surfactants in heterophase polymerization. VI. Synthesis and screening of polymerizable surfactants (surfmers) with varying reactivity in high solids styrene—butyl acrylate—acrylic acid emulsion polymerization

Several polymerizable surfactants (surfmers) have been used in the semi-continuous emulsion copolymerization of styrene, butyl acrylate, and acrylic acid. Three of the (anionic) surfmers (sodium 11-crotonoyl undecan-1-yl sulfate, sodium 11-methacryloyl undecan-1-sulfate, and sodium sulfopropyl tetradecyl maleate) were prepared in house with purities between 53 and 82%. Physicochemical properties such as the critical micelle concentration, the adsorption isotherm, and the specific adsorption area were determined. The surfmers were then used with constant addition profiles in semicontinuous reactions, and the instantaneous conversions of the main monomers determined. The particle size, amount of coagulum, surface tension, and stability against electrolyte solutions of the latices were evaluated. Films were cast of some of the latices, and the visual appearance and water adsorption were assessed.

Towards a consistent mechanism of emulsion polymerization - new experimental details

The application of atypical experimental methods such as conductivity measurements, optical microscopy, and nonstirred polymerizations to investigations of the ‘classical’ batch ab initio emulsion polymerization of styrene revealed astonishing facts. The most important result is the discovery of spontaneous emulsification leading to monomer droplets even in the quiescent styrene in water system. These monomer droplets with a size between a few and some hundreds of nanometers, which are formed by spontaneous emulsification as soon as styrene and water are brought into contact, have a strong influence on the particle nucleation, the particle morphology, and the swelling of the particles. Experimental results confirm that micelles of low-molecular-weight surfactants are not a major locus of particle nucleation. Brownian dynamics simulations show that the capture of matter by the particles strongly depends on the polymer volume fraction and the size of the captured species (primary free radicals, oligomers, single monomer molecules, or clusters).

Surfactants in heterophase polymerization: A study of film formation using atomic force microscopy

Film formation of three different latices was studied using atomic force microscopy. The latices were made from a mixture of butyl acrylate, styrene, and acrylic acid using either a polymerizable or an unreactive anionic surfactant as an emulsifier. Sodium 11-crotonoyloxyundecan-1-ylsulfate and sodium 3-(sulfopropyl)tetradecylmaleate were used as a reactive surfactant and the unreactive surfactant was sodium dodecylsulfate (SDS). The conventional surfactant was found to migrate to the surface of the latex film to a much greater extent than did the reactive surfactants; however, also, the latter were incompletely anchored to the particle. The maleate surfactant was bound to a higher degree than was the crotonate, a finding which is in line with the relative reactivities of the two surfactants.

Core–shell particle interconversion with di-stimuli-responsive diblock copolymers

Core-shell reversible particle precipitation from aqueous di-stimuli-responsive diblocks is demonstrated as also is the interconversion from one core-shell combination to the other.

Structural control in radical polymerization with 1,1 diphenylethylene: 2. Behavior of MMA-DPE copolymer in radical polymerization

Abstract Copolymers of 1,1-diphenylethylene (DPE) behave in a very special way in radical polymerization. Particularly, the behavior of MMA–DPE copolymers in radical polymerization is investigated. The results reveal that the semiquinoid structure of the precursor polymer identified in a previous contribution is activated by the attack of free radicals and thus, in a second stage polymerization with a second monomer, block copolymers are formed. The block copolymer yield depends strongly on the ratio between the amount of DPE-containing precursor polymer and the initiator and monomer concentration used in the second stage. The mechanism proposed is able to explain at least qualitatively all experimental results including the restriction of this mode of control of radical polymerization to the formation of diblock copolymers only.

π-Conjugated polyHIPEs as highly efficient and reusable heterogeneous photosensitizers

π-Conjugated microporous polyHIPEs are synthesized via Suzuki cross-coupling. The polymeric backbone consists of electron donor and acceptor moieties with suitable energetic characteristics to promote the efficient photosensitizing ability for the activation of singlet oxygen, showing extraordinarily high stability. The reaction can be carried out in a continuous flow reaction set-up, realizing complete conversion of α-terpinene into ascaridole.

Structural control in radical polymerization with 1,1-diphenylethylene. 1. Copolymerization of 1,1-diphenylethylene with methyl methacrylate

Abstract The role of 1,1-diphenylethylene (DPE) in radical emulsion polymerization of methyl methacrylate is investigated. The presence of DPE causes a strong decrease in both the rate of polymerization and the molecular weight. According to the results of structure analysis by means of MALDI-TOF mass spectrometry, UV–vis spectroscopy, and 1H–NMR spectroscopy, DPE is incorporated in the copolymer chain exclusively as a reactive recombinant α,p-dimer, underlining the peculiar role of DPE in radical polymerizations.

Initiators based on poly(ethylene glycol) for starting heterophase polymerizations - generation of block copolymers and new particle morphologies.

Radical heterophase polymerizations with poly(ethylene glycol) radicals lead to the formation of block copolymer particles where the block copolymer architecture and the particle morphology depend on the number of radicals per poly(ethylene glycol) chain, the radical termination mode, and the polarity of the monomer, respectively. The thermal decomposition of symmetrical poly(ethylene glycol) azo-initiators following the classical recipes of Heitz results in one radical per poly(ethylene glycol) chain whereas the number of radicals can be adjusted between one or two in the redox system poly(ethylene glycol)/cerium ions. The polymerization of styrene results in latex particles with an almost spherical morphology, consisting of block copolymers, only. In case of a methyl methacrylate polymerization the latex morphology depends on the architecture of the block copolymers formed. Heterophase polymerization with poly(ethylene glycol) azo-initiators in oligo(ethylene glycol) (average molecular weight 200 g mol -1 ) instead of in water results in particles with random shape and a strongly indented interface which is explained by the surface tension between polymers and solvent being close to zero.

Polymerized Ionic Liquid as Stabilizer in Aqueous Emulsion Polymerization Enables a Hydrophilic–Hydrophobic Transition during Film Formation

Polymerized ionic liquid (PIL) nanoparticles are for the first time applied as sole stabilizers in aqueous emulsion polymerization and reveal an astonishing and unexpected behavior. In a well-dispersed state, the PIL nanoparticles serve as an unexpectedly effective stabilizer for polystyrene dispersions, enabling solids content of greater than 40%. However, the same PIL as dry powder is hydrophobic and, in accordance with Bancrofts rule, unable to stabilize aqueous dispersions. This ambivalent behavior of PIL is extremely beneficial for the application of aqueous dispersions because, as desired for decades, the hydrophilic dispersed state during synthesis turns hydrophobic in the dried state during application of the polymer.