Claus D. Eisenbach

Protection of iron against corrosion with polyaniline primers

The corrosion protection of iron with polyaniline primer was investigated. It was found that the protection takes place in three consecutive phases: conversion of original iron oxides, the active corrosion protection action of a conductive polyaniline form due to the separation of partial cathodic and anodic corrosion processes, and the action of a non-conductive form of polyaniline. The features of these separate phases and the role of a top coat were especially considered.

Isomerization of aromatic azo chromophores in poly(ethyl acrylate) networks and photomechanical effect

Abstract The photochemical and thermal cis-trans isomerization of azo chromophores which were either dissolved, a pendant group or part of a crosslink in rubbery poly(ethyl acrylate) networks has been investigated. The thermal relaxation behaviour of the azo compound in the networks depends on the crosslinking density and can be described by a WLF-equation with the same parameters as found for non-crosslinked polymers. For stretched polymer films with azo-aromatic crosslinks, a photomechanical effect, i.e., a reversible contraction and expansion was observed, which is mainly ascribed to conformational change of the azo chromophore.

Microphase Behavior and Enhanced Wet-Cohesion of Synthetic Copolyampholytes Inspired by a Mussel Foot Protein.

Numerous attempts have been made to translate mussel adhesion to diverse synthetic platforms. However, the translation remains largely limited to the Dopa (3,4-dihydroxyphenylalanine) or catechol functionality, which continues to raise concerns about Dopas inherent susceptibility to oxidation. Mussels have evolved adaptations to stabilize Dopa against oxidation. For example, in mussel foot protein 3 slow (mfp-3s, one of two electrophoretically distinct interfacial adhesive proteins in mussel plaques), the high proportion of hydrophobic amino acid residues in the flanking sequence around Dopa increases Dopas oxidation potential. In this study, copolyampholytes, which combine the catechol functionality with amphiphilic and ionic features of mfp-3s, were synthesized and formulated as coacervates for adhesive deposition on surfaces. The ratio of hydrophilic/hydrophobic as well as cationic/anionic units was varied in order to enhance coacervate formation and wet adhesion properties. Aqueous solutions of two of the four mfp-3s-inspired copolymers showed coacervate-like spherical microdroplets (ϕ ≈ 1-5 μm at pH ∼4 (salt concentration ∼15 mM). The mfp-3s-mimetic copolymer was stable to oxidation, formed coacervates that spread evenly over mica, and strongly bonded to mica surfaces (pull-off strength: ∼17.0 mJ/m(2)). Increasing pH to 7 after coacervate deposition at pH 4 doubled the bonding strength to ∼32.9 mJ/m(2) without oxidative cross-linking and is about 9 times higher than native mfp-3s cohesion. This study expands the scope of translating mussel adhesion from simple Dopa-functionalization to mimicking the context of the local environment around Dopa.

Evaluation of the delamination of coatings with scanning reference electrode technique

On the basis of the scanning reference electrode technique (SRET), a new laboratory test for the evaluation of the delamination resistance of coatings was developed. With the optimized SRET it is possible to perform screening tests and discriminate coatings according to their delamination resistance within a relatively short period of loading time.

3-dimethylaminopropyl-lithium—An analytical and kinetic investigation of a new initiator system for polymer synthesis

Abstract The formation of 3-dimethylaminopropyl-lithium from the reaction of 3-chloro-1-(dimethylamino)-propane with powdered lithium in tetrahydrofuran (THF) at −25° and in cyclopentane (CP) at +49·5°, respectively, has been investigated. The kinetic and analytical determinations of this reaction were made by gas chromatography. The lithium compound was obtained in a > 90% yield in THF, although in this solvent its stability was limited even at low temperatures. In contrast in CP a more stable solution of the organometallic compound was formed, but lower yields (50% at most) were realized; this solution, unlike the THF solution, was contaminated with by-products.

Diisocyanato dicyclohexylmethane: structure/property relationships of its geometrical isomers in polyurethane elastomers

Abstract4,4′-Diisocyanato dicyclohexylmethane (HMDI) is a commercially available diisocyanate used as a building block for polyurethane products that require excellent light stability and hydrolysis resistance. It consists of a mixture of three geometrical isomers, the trans,trans-, cis,trans-, and cis,cis-isomers. We found that the trans,trans-isomer leads to some interesting properties in polyurethane elastomers. Surprisingly, the hardness and percent elongation (properties that usually follow an inverse relationship) both increase with increasing trans,trans- HMDI contents. We also observed dramatic increases in the ultimate tensile strength, split-tear strength, resilience, and solvent resistance. Also, the melting temperature of the elastomers increases with increasing trans,trans content. X-ray analysis of model hard segments showed that the hard segment based ont,t-HMDI is highly ordered, leading to higher melting temperatures and better separation between the hard- and soft-segment phases.

Polyurethane Elastomers with Monodisperse Segments and their Model Precursors: Synthesis and Properties

Uniform model compounds for the soft and hard segment of polyurethane (PU) elastomers and the corresponding tailormade elastomers with monodisperse segment length distribution were synthesized and characterized with the objective of getting a better understanding of the structure and morphology as well as the structure-property relationships of multiphase segmented PU elastomers from the study of such clearly defined model systems.

Mechanical and dynamic mechanical properties of polyurethane and polyurethane/polyurea elastomers based on 4,4′‐diisocyanatodicyclohexyl methane

The physical and thermal properties of hand-cast polyurethane and polyurethane/polyurea elastomers prepared from prepolymers of 20 and 97% trans,trans-4,4′-diisocyanatodicyclohexyl methane (t,t-rMDI) and C3- and C4-polyethers chain extended with either 1,4-butanediol (XB) or a commercial mixture of diethyl toluenediamine isomers (DETDA) were determined. The influence of the distribution of geometric isomers of the diisocyanate and of the chain-extender building blocks on these properties is significant. Urethane/ureas are harder and have higher modulus than polyurethanes formed from the same prepolymer. The polyurethane/polyurea elastomers all have somewhat high compression set. Dynamic Mechanical Analysis (DMA) suggests that DETDA extended systems based on 20% t,t-rMDI are phase separated, as illustrated by extended rubbery plateau regions and significantly higher softening points than the corresponding XB extended ones. Uniquely, these elastomers are transparent rather than opaque as typical with most other phase-segregated elastomers. Polyurethanes based on 97% t,t-rMDI are harder and have higher modulus than those based on 20% t,t-rMDI (Desmodur™ W). They have good phase separation and high softening points but they are opaque. Surprisingly, there is not much difference between the physical or thermal properties of polyurethane/polyureas and polyurethanes based on 97% t,t-rMDI. Replacing XB with DETDA gives only moderate improvement in properties, but it does make the elastomers optically clear.

Poling and orientational relaxation: Comparison of nonlinear optical main‐chain and side‐chain polymers

We investigated both time and temperature dependence of chromophore movements by means of in situ second‐harmonic generation (SHG) measurements. Using real‐time detection of the SHG intensities during and after poling of various nonlinear‐optical polymer films we observed differences between main‐chain and side‐chain polymers regarding the nonlinear coefficients d33 and the glass transition dynamics. We present experimental data on new main‐chain polymers with polar stilbene chromophores attached in the most common transverse position to the backbones (MC‐T) or incorporated in a linear fashion where they are a part of the main‐chain (MC‐L). The side‐chain polymer (SC) presented here has been developed for photorefractive applications and is a copolymer containing Disperse Red 1 and a photoconducting carbazole unit in the side chain. The influence of the macromolecular structure on the chromophore dynamics is striking. This is verified by means of in situ corona poling experiments and thermal experiments b...

Evaluation of corrosion and protection of coated metals with local ion concentration technique (LICT)

Abstract Local ion concentration technique (LICT) is a new method of measuring pH and ion concentration with high spatial resolution in thin electroytic layers or small volumes. LICT can be used to follow pH changes in corrosive medium during corrosion of metals and degradation of organic coatings. The data can be used to elucidate process mechanisms and to evaluate the protective action of coatings. In this paper, we present the setup and the components of the LICT instrument. Furthermore, we demonstrate the construction of a metal–metal oxide pH microsensor and we compare the effect of aging on sputtered and electrochemically formed iridium–iridium oxide electrodes. Applications for these sensors are discussed.