Improving the Corrosion Protection of Poly(phenylene methylene) Coatings by Side Chain Engineering: The Case of Methoxy-Substituted Copolymers.

This work aims to improve the corrosion protection features of poly(phenylene methylene) (PPM) by sidechain engineering inserting methoxy units along the polymer backbone. The influence of side methoxy groups at different concentrations (4.6% mol/mol and 9% mol/mol) on the final polymer properties was investigated by structural and thermal characterization of the resulting copolymers: co-PPM 4.6% and co-PPM 9%, respectively. Then, coatings were processed by hot pressing the polymers powder on aluminum alloy AA2024 and corrosion protection properties were evaluated exposing samples to a 3.5% w/v NaCl aqueous solution. Anodic polarization tests evidenced the enhanced corrosion protection ability (i.e., lower current density) by increasing the percentage of the co-monomer. Coatings made with co-PPM 9% showed the best protection performance with respect to both PPM blend and PPM co-polymers reported so far. Electrochemical response of aluminum alloy coated with co-PPM 9% was monitored over time under two "artificially-aged" conditions, that are: (i) a pristine coating subjected to potentiostatic anodic polarization cycles, and (ii) an artificially damaged coating at resting condition. The first scenario points to accelerating the corrosion process, the second one models damage of the coating potentially occurring either due to natural deterioration or due to any accidental scratching of the polymer layer. In both cases, an intrinsic self-healing phenomenon was indirectly argued by the time evolution of the impedance and of the current density of the coated systems. The degree of restoring to the "factory conditions" by co-polymer coatings after self-healing events is eventually discussed.

The Ins and Outs of 14C Dating Lead White Paint for Artworks Application.

Lead white is known as one of the oldest pigments in art and can be used as a dating material. Upon production following the Stack process, the 14C isotope of atmospheric carbon dioxide is fixed in the carbonate, and its radiocarbon dating can be used as a proxy for the age of a painting. The previously reported carbonate hydrolysis protocol reaches its limitation when confronted with samples presenting a mixture of carbonates, such as lead carbonate (cerussite or hydrocerussite), calcium carbonate (calcite), and/or calcium magnesium carbonate (dolomite). Thermogravimetric analyses indicate that decomposition of lead carbonate can be achieved at 350 °C in TGA diagrams, as other mineral carbonates only decompose to carbon dioxide at temperatures above 700 °C. Thus, a thermal approach is proposed to separate the various carbonates and isolate the specific 14C signature to the lead carbonate. In practice, however, discrepancies between the measured radiocarbon ages and expected ages were observed. FTIR analyses pointed to the formation of metal carboxylates, an indicator that the organic binder is not inert and plays a role in the dating strategy. Upon drying, oxidation and hydrolysis take place leading to the formation of free fatty acids, which in turn interact with the different carbonates upon heating. Their removal was achieved by introduction of a solvent extraction step prior to the thermal treatment, which was confirmed by GC-MS analyses, and thus, the collected carbon dioxide at 350 °C results can be assigned correctly to the decomposition of the lead white pigment. The proposed procedure was furthermore verified on mixed carbonate-bearing paint samples collected from a Baroque oil painting.

Derivatization Technique To Identify Specifically Carbonyl Groups by Infrared Spectroscopy: Characterization of Photooxidative Aging Products in Terpenes and Terpeneous Resins.

Analysis of bioorganic materials by infrared spectroscopy (FT-IR) is frequently limited due to overlapping of diagnostic bands from the various components, which poses a fundamental problem to this analytical technique. The distinction of oxidized di- and triterpenes, for example, is hindered by the superposition of similar absorption bands of carbonyl functional groups summing up to a broad, nondistinctive signal. This study presents a technique for selective fluorination of various carboxylic acids by exposure to gaseous sulfur tetrafluoride. The derivatization treatment leads to characteristic band shifts, allowing the separation of otherwise overlapping bands. Accordingly, the IR bands of primary acids, α,ß-unsaturated acids, tertiary acids, peroxy acids, esters, ketones, and α,ß-unsaturated ketones are split into distinct absorption bands. The capability of this method is demonstrated on the example of natural resins and their ingredients, which are commonly known to be susceptible to oxidation at ambient conditions. The derivatization method enables one to identify various carbonyl containing functional groups by infrared spectroscopy, even in complex mixtures of terpenes. It unveils previously hidden degradation reactions running in terpenes and natural resins exposed to artificial aging by irradiation with light. New insight is presented on the individual reaction pathways of the terpenes hydroxydammarenone and abietic acid as well as of natural resin varnishes made from dammar and colophony.

Polystannanes: processible molecular metals with defined chemical structures.

Polystannanes are a unique class of materials as those inorganic polymers (more precisely organometallic polymers) appear to be hitherto the only characterized polymers with a backbone of covalently bound metal atoms. This review reflects the synthesis, spectroscopic characterization (in particular (119)Sn NMR and UV-vis spectroscopy), physical properties and material properties of polystannanes, and their processing into (oriented) films and fiber blends.

From near hard spheres to colloidal surfboards.

This work revisits the synthesis of the colloidal particles most commonly used for making model near hard suspensions or as building blocks of model colloidal gels, i.e. sterically stabilised poly(methyl methacrylate) (PMMA) particles. The synthesis of these particles is notoriously hard to control and generally the problems are ascribed to the difficulty in synthesising the graft stabiliser (PMMA-g-PHSA). In the present work, it is shown that for improving the reliability of the synthesis as a whole, control over the polycondensation of the 12-polyhydroxystearic acid is the key. By changing the catalyst and performing the polycondensation in the melt, the chain length of the 12-polyhydroxystearic acid is better controlled, as confirmed by 1H-NMR spectroscopy. Control over the graft copolymer now enables us to make small variations of near hard sphere colloids, for example spherical PMMA particles with essentially the same core size and different stabilising layer thicknesses can now be readily produced, imparting controlled particle softness. The PMMA spheres can be further employed to create, in gram scale quantities, colloidal building blocks having geometrical and/or chemical anisotropy by using a range of mechanical deformation methods. The versatility of the latter methods is demonstrated for polystyrene latex particles as well.

Polynuclear iron(II)-aminotriazole spincrossover complexes (polymers) in solution.

Polynuclear spincrossover (SCO) complexes prepared by the combination of [Fe(DMF)6](2+) and NH2trz (NH2trz = 4-amino-1,2,4-triazole) were studied (2ns(-) = counterion 2-naphthalenesulfonate). It is demonstrated that these [Fe(NH2trz)3](2ns)2 complexes can be dissolved-contrary to common reported experience-in N,N-dimethylformamide (DMF) and, therefore, can be conveniently processed by simple means. The resulting solutions were examined with UV/vis and X-ray absorption spectroscopy (XANES and EXAFS) as well as with small-angle X-ray scattering (SAXS). At a molar NH2trz/Fe(2+) ratio of 3/1, corresponding to the stoichiometric ratio of the ideal coordination compound, [Fe(NH2trz)3](2+) in the low-spin state was found to be in equilibrium with polynuclear species in the high-spin state. The equilibrium can be shifted virtually completely to the side of low-spin Fe(2+) by an excess of the ligand. The polymer therewith formed contains 100 or more Fe(2+) ions and is of a pronounced rigid-rod structure, with Fe-Fe distances around 3.32 Å (in comparison to 3.94 Å of the polynuclear species in the high-spin state). Reversible spin crossover takes place in solution upon a temperature increase to around 60 °C; this process is associated with a shift in equilibrium toward species shorter than the initial polynuclear species.

Synthesis of Soluble High Molar Mass Poly(Phenylene Methylene)-Based Polymers.

Poly(phenylene methylene) (PPM) is a multifunctional polymer that is also active as an anticorrosion fluorescent coating material. Although this polymer was synthesized already more than 100 years ago, a versatile synthetic route to obtain soluble high molar mass polymers based on PPM has yet to be achieved. In this article, the influence of bifunctional bis-chloromethyl durene (BCMD) as a branching agent in the synthesis of PPM is reported. The progress of the reaction was followed by gel permeation chromatography (GPC) and NMR analysis. PPM-based copolymers with the highest molar mass reported so far for this class of materials (up to Mn of 205,300 g mol-1) were isolated. The versatile approach of using BCMD was confirmed by employing different catalysts. Interestingly, thermal and optical characterization established that the branching process does not affect the thermoplastic behavior and the fluorescence of the material, thus opening up PPM-based compounds with high molar mass for applications.

Application of Atmospheric-Pressure Jet Plasma in the Presence of Acrylic Acid for Joining Polymers without Adhesives.

This study investigates the treatment of surfaces with jet plasma at atmospheric pressure in the presence of acrylic acid as a resource-saving and efficient approach to joining polymers on polystyrene (PS) and polyamide 12 (PA 12) surfaces. Acrylic acid was added in order to introduce functional groups to the polymer surfaces. XPS analysis revealed a high density of oxygen-containing groups, e.g., carboxylic acid groups, on the polymer surfaces, the detailed composition depending on the polymer. The AFM measurements indicated that the modification of polyamide resulted in morphological changes and an increase in surface roughness due to polymer recrystallization. When the surface-modified polymers were brought in contact under a load, significant adhesion between the polymer surfaces was measured. In particular, PS and PA 12, which are otherwise difficult to join by gluing, could readily be connected in this way. The joint polymers could be separated intentionally by immersion in water, thus enabling the recycling of the materials. The resistance of the joint to water depends on the polymer system, with polyamide providing strikingly higher resistance than polystyrene. Accordingly, treating the joint polymers with water allows debonding on demand, particularly when PS is involved. Exposure of modified polymer surfaces to solutions of metal ions increased the resistance of joint polymers to water.

Polystannanes: synthesis, properties, and outlook.

Polystannanes are characterized by a main chain which consists of covalently bound tin atoms. Characteristic absorption maxima in UV-vis spectra of poly(dialkylstannane)s are due to σ-delocalization and of poly(diarylstannane)s to σ-π delocalization. Poly(diorganostannane)s are thermally stable with decomposition commencing above 200 °C. Poly(dialkylstannane)s can show liquid-crystalline behavior around room temperature. They can be oriented by various procedures, whereby orientation of the polystannane main chain depends on the orientation procedure and the length of the alkyl side groups. Some of the oriented systems showed a pronounced dichroism. Polystannanes degrade under the action of light, in particular when in solution.

Effect of Fibrillated Cellulose on Lime Pastes and Mortars.

The use of nanocellulose in traditional lime-based mortars is a promising solution for green buildings in the frame of limiting the CO2 emissions resulting from Portland Cement production. The influence of the fibrillated cellulose (FC) on lime pastes and lime-based mortars was studied incorporating FC at dosages of 0%, 0.1%, 0.2% and 0.3 wt% by weight of binder. The lime pastes were subjected to thermal and nitrogen gas sorption analyses to understand if FC affects the formation of hydraulic compounds and the mesoporosities volume and distribution. The setting and early hydration of the mortars were studied with isothermal calorimetry. The mechanical performances were investigated with compressive and three-point-bending tests. Furthermore, fragments resulting from the mechanical tests were microscopically studied to understand the reinforcement mechanism of the fibres. It was found that 0.3 wt% of FC enhances the flexural and compressive strengths respectively by 57% and 44% while the crack propagation after the material failure is not affected.

Studies on the Interaction of Poly(phenylene methylene) with Silver(I) and Hexacarbonylchromium(0).

Complexes of poly(phenylene methylene) (PPM) with silver(I) ions and tricarbonylchromium(0) moieties, respectively, were synthesized. 13C NMR spectra indicate interaction of phenylene groups with silver(I) and chromium(0), and peak broadening implies dynamic behavior of the silver(I) complexes, with all phenylene groups temporarily involved in coordination, in contrast to the chromium complexes. About 5-10% of the phenylene groups are coordinated to metal atoms. 1H NMR and IR spectra, in the case of chromium(0), and the solubility of silver salts in the presence of PPM provide further evidence of coordination. The complexes are soluble in chloroform, but the silver complexes decay in tetrahydrofuran (second-order kinetics were observed in an example). The photoluminescence (fluorescence) of PPM is maintained upon complexation, although coordination of silver(I) seems to favor the so-called blue phase of PPM relative to the green phase by a factor of approximately two in PL spectra. The pronounced absorption of the tricarbonylchromium(0) units interferes with the blue phase, which almost disappears at a concentration of 50 mg/mL in PLE spectra, whereas the emission maximum of the green phase is hardly affected. This leads to a confinement of the emitted wavelength range of PPM. Thus, the perceived optical emission of PPM can be modified by coordinated entities.

Copper Ions Absorbed on Acrylic-Acid-Grafted Polystyrene Enable Direct Bonding with Tunable Bonding Strength and Debonding on Demand.

Recycling adhesively bonded polymers is inconvenient due to its expensive separation and removal of adhesive residues. To tackle this problem, adhesive technologies are needed allowing debonding on demand and which do not contaminate the surface of the substrate. Direct bonding enabled by oxygen plasma treatment has already achieved substantial adhesion between flat substrates. However, debonding takes place by water, thus limiting the applications of this technology to water-free environments. The work presented in the following shows that this drawback can be overcome by grafting acrylic acid and adding copper(II) ions on the surface of polystyrene. In this process, the number of functional groups on the surface was significantly increased without increasing the surface roughness. The bonding strength between the substrates could be increased, and the process temperature could be lowered. Nevertheless, the samples could be debonded by exposure to EDTA solution under ultrasound. Hence, by combining acrylic acid grafting, variations in the bonding temperatures and the use of copper(II) ions, the bonding strength (5 N to >85 N) and the debonding time under the action of water can be tuned over large ranges (seconds to complete resistance).

Smart Anticorrosion Coatings Based on Poly(phenylene methylene): An Assessment of the Intrinsic Self-Healing Behavior of the Copolymer.

Poly(phenylene methylene) (PPM) is a multifunctional polymer featuring hydrophobicity, high thermal stability, fluorescence and thermoplastic processability. Accordingly, smart corrosion resistant PPM-based coatings (blend and copolymer) were prepared and applied by hot pressing on aluminum alloy AA2024. The corrosion protection properties of the coatings and their dependence on coating thickness were evaluated for both strategies employed. The accelerated cyclic electrochemical technique (ACET), based on a combination of electrochemical impedance spectroscopy (EIS), cathodic polarizations and relaxation steps, was used as the main investigating technique. At the coating thickness of about 50 µm, both blend and copolymer PPM showed effective corrosion protection, as reflected by |Z|0.01Hz of about 108 Ω cm2 over all the ACET cycles. In contrast, when the coating thickness was reduced to 30 µm, PPM copolymer showed neatly better corrosion resistance than blended PPM, maintaining |Z|0.01Hz above 108 Ω cm2 with respect to values below 106 Ω cm2 of the latter. Furthermore, the analysis of many electrochemical key features, in combination with the optical investigation of the coating surface under 254 nm UV light, confirms the intrinsic self-healing ability of the coatings made by PPM copolymer, contrary to the reference specimen (i.e., blend PPM).

Rhythmic crystal growth into hierarchical patterns by polymer-mediated self-assembly.

Controlled, bottom-up self-assembly of ordered and hierarchical structures remains a major challenge and increasingly attracts attention in basic and technology-driven research. A simple process is described for the generation of such structures, which is based on slow solvent evaporation of a polymer solution blended with a crystal-forming species (Krogmann's salt). Upon drying, the viscosity of the polymer-blend solution increases in a progressing solidification zone, which precisely controls crystal growth by limiting the transport of the crystallizing units through this gel-like solidification zone and gives rise to a position- and time-dependent diffusion rate. The progressing solidification zone also leads to a preferential crystallographic orientation on a centimeter scale and introduces an instability that drives spatial pattern formation and hierarchical ordering on five distinct levels, ranging from the atomic positions in crystals to the assembly on a microscale and up to a centimeter length scale. Together with a quantitative description, the presented findings are envisaged to improve the understanding and application of periodic precipitation processes.

Composites of Copper Nanowires in Polyethylene: Preparation and Processing to Materials with NIR Dichroism.

Agglomeration of copper nanowires (aspect ratios on the order of 1000) in polyethylene, commonly a major problem, could be prevented by modification of the nanowires with a surface layer of oleylamine. Nanocomposite films were prepared by mixing nanowire dispersions in organic solvents with polyethylene solutions followed by casting, drying, and sometimes hot pressing. Orientation of the copper nanowires by solid-state drawing of the composites at elevated temperatures led to preferential alignment of the nanowires in the drawing direction. This arrangement gave rise to a uniform dichroism in the near-infrared (NIR) region, which is uncommon in the case of the hitherto reported dichroic nanocomposites. The NIR dichroism is ascribed to the high aspect ratio of the metal wires. Hence, drawing of isotropic nanocomposites with metal wires may serve for the manufacture of NIR polarization filters.

Synthesis of High Molar Mass Poly(phenylene methylene) Catalyzed by Tungsten(II) Compounds.

Poly(phenylene methylene)s (PPMs) with high molar masses were isolated by polymerization of benzyl chloride catalyzed with tungsten(II) compounds and subsequent fractionation. Four different tungsten(II) catalysts were successfully exploited for the polymerization, for which a strict temperature profile was developed. The PPMs possessed roughly a trimodal molar mass distribution. Simple fractionation by phase separation of 2-butanone solutions allowed to effectively segregate the products primarily into PPM of low molar mass (Mn = 1600 g mol-1) and high molar mass (Mn = 167,900 g mol-1); the latter can be obtained in large quantities up to 50 g. The evolution of the trimodal distribution and the monomer conversion was monitored by gel permeation chromatography (GPC) and ¹H NMR spectroscopy, respectively, over the course of the polymerization. The results revealed that polymerization proceeded via a chain-growth mechanism. This study illustrates a new approach to synthesize PPM with hitherto unknown high molar masses which opens the possibility to explore new applications, e.g., for temperature-resistant coatings, fluorescent coatings, barrier materials or optical materials.

Transparent, anatase-free TiO2 nanoparticle dispersions.

Preparation of optically transparent dispersions of TiO2 nanoparticles which are free of the anatase polymorph is a challenging process which has been difficult to control to date. Here, we report and discuss the reproducible formation of such dispersions by hydrolysis of TiCl4. Clouding times of the dispersions and the finally resulting crystal modification of TiO2 was found to depend on a number of synthesis parameters, such as the temperature profile during the reaction, the ratio between the starting substances and the rate of TiCl4 addition. A low pH value and moderate reaction temperatures were required to yield rutile particles, which were established to be formed by transformation of initially amorphous particles just prior to clouding occurred. The latter phenomenon was found to be caused by agglomeration, and not by growth of primary nanosized particles.

Reversible photochromic properties of TiO2-polymer nanocomposites.

Composite films of nanosized TiO2 particles, which contained rutile as the only detected crystal modification, and poly(vinyl alcohol), poly(vinyl pyrrolidone) or poly(4-vinylpyridine) were prepared from aqueous dispersions. During exposure to UV irradiation the nanocomposites comprising poly(vinyl alcohol) or poly(vinyl pyrrolidone) turned blue as a consequence of a partial reduction of TiIV to TiIII. The color intensity increased with increasing TiO2 content and irradiation time. This color did not fade after removal of the UV source in spite of the sensitivity of TiIII to atmospheric oxygen. By contrast, exposure to water caused the nanocomposites to adopt their original colorless appearance. These colorization-decolorization cycles could be repeated more than 10 times without apparent loss of intensity. Due to the small size of the TiO2 nanoparticles (ca. 3 nm), patterned blue structures of high resolution could be created in the polymeric materials, for instance with simple masking methods.

Formation mechanism of nanotubes comprising layers of PbS nanoparticles in polymer-surfactant solutions.

The crystallization of PbS in aqueous solutions containing the surfactant sodium dodecyl sulfate (SDS) and hydrophilic polymers resulted in a novel type of metastable nanotubes, the walls of which consist of layers of ordered PbS nanoparticles, apparently separated by layers of surfactant molecules. Information on the mechanism of formation of these structures was obtained by focusing on the roles of the polymer, and of the insoluble lead dodecyl sulfate (Pb(DS)2) present in the system. TEM investigations of the early stages of crystallization revealed the coexistence of PbS and Pb(DS)2 precipitates, the latter being surprisingly important for nanotube formation, and allowed to follow the evolution of layered structures from combination of the two types of crystals. Six different hydrophilic polymers have been used, which interact with SDS with varying strengths. Surprisingly, and in contrast to previous hypotheses, layered nanostructures were observed in all polymer solutions, regardless of the strength of polymer-surfactant interactions. This indicates that, although the presence of a polymer is necessary, polymer-SDS interactions are not a driving force for the formation of the layered structures and nanotubes. On the contrary, the interactions between the polymer chains and the growing particles appear to be of the utmost importance. Results presented here can be interpreted in terms of two alternative mechanisms for layered nanostructure and nanotube formation.