Layered Silicate‐Induced Enhancement of Fracture Toughness of Epoxy Molding Compounds over a Wide Temperature Range

Summary: The fracture toughness of EMC was dramatically increased over a wide temperature range by the addition of a very low volume fraction of layered silicates to EMC filled with micro‐silica particles. Layered silicate‐EMC nanocomposites containing intercalated and the exfoliated silicates were fabricated by using o‐cresol and biphenyl type epoxy resins, respectively. It was found that exfoliated silicates were more effective than intercalated silicates at toughening EMC at temperatures above T_g of the epoxy resin. Enhanced fracture toughness of EMC over a wide temperature range, from ambient to 230 °C has been attributed to the presence of layered silicates, which induces macroscopic crack deflection and severe plastic deformation in front of the crack tip.

     

Design of a Microfluidic System to Investigate the Mechanical Properties of Layer‐by‐Layer Fabricated Capsules

A microfluidic system was designed, fabricated and implemented to study the behavior of polyelectrolyte capsules flowing in microscale channels. The device contains microchannels that lead into constrictions intended to capture polyelectrolyte microcapsules which were fabricated with the well‐known layer‐by‐layer (LbL) assembly technique. The behavior of hollow capsules at the constrictions was visualized and the properties of the capsules were investigated before and after introduction into the device.

Time series of video frames showing capsules being compressed into a constriction.     

Novel Poly(N‐isopropylacrylamide)‐graft‐poly(vinylidene fluoride) Copolymers for Temperature‐Sensitive Microfiltration Membranes

In the present work, we report on the synthesis and characterization of poly(vinylidene fluoride) (PVDF) with N‐isopropylacrylamide (NIPAAM) polymer side chains from molecular graft copolymerization in solution. The copolymer can be readily cast into temperature‐sensitive microfiltration (MF) membranes by the phase inversion technique. The copolymer approach to membrane fabrication allows a much better control of the physicochemical nature of the membrane pores through the variation in graft concentration, membrane casting temperature and concentration of the membrane casting solution.

     

Monodisperse Silica‐Polymer Core‐Shell Microspheres via Surface Grafting and Emulsion Polymerization

We describe a flexible method for preparing monodisperse silica‐polystyrene core‐shell microspheres. In this method, silica nanoparticles grafted with 3‐(trimethoxysilyl)propyl methacrylate (MPS) were employed as seeds in an emulsion polymerization. The thickness of the shells could be changed through varying the amount of the monomer. The monodispersity and diameters of the core‐shell microspheres were found to depend on the size of the grafted silica nanoparticles and the concentration of emulsifier. In addition, we investigated the formation mechanism of the core‐shell microspheres.

Schematic outline of the experimental procedure and TEM image of the monodisperse silica/PS core‐shell microspheres; inset: grafted silica nanoparticles (scale bar = 200 nm).     

Effect of the Addition of Toluene on the Structure and Properties of Styrene‐Isoprene‐Butadiene Rubber/Montmorillonite Nanocomposites

Summary: Styrene‐isoprene‐butadiene rubber/montmorillonite nanocomposites were synthesized by the addition of toluene into clay and living anionic polymerization. These silicate layers (B‐M) were exfoliated within 30 min after polymerization initiation, whereas the layers in the nanocomposites prepared without using toluene (A‐M) were only partially exfoliated and not well‐dispersed in the matrix. The results of TEM and X‐ray diffraction revealed disperse silicates and a strong interaction between the terpolymer matrix and clay in the B‐M nanocomposites. The B‐M‐exfoliated nanocomposites exhibited higher decomposition and glass transition temperatures, storage moduli, tensile strengths and elongations at the break than those of the pure terpolymer and A‐M. With an organophilic montmorillonite (OMMT) content of 3 wt.‐%, the exfoliated nanocomposite exhibited the best thermal stability and mechanical properties. In addition, GPC and ¹H NMR results showed that the introduction of OMMT caused a slight increase in the of terpolymer, but hardly affected the microstructure of the terpolymer independent of the preparation method. Thus, the addition of toluene plays an important role in enhancing the dispersion of OMMT, which leads to the improvement of the structure and properties of the B‐M nanocomposites.

TEM image of the SIBR/MMT nanocomposite.     

Analysis of Crosslinked Styrene‐Butadiene Rubbers by Liquid Chromatography and FT‐IR Spectroscopy, 1

Crosslinked styrene‐butadiene and butadiene rubbers can efficiently be analyzed by liquid chromatography and FT‐IR spectroscopy. In a first step the vulcanizate is pyrolyzed under mild conditions. The resulting high molar mass fragments are extracted from the bulk material and analyzed by size exclusion chromatography. The molar masses of the extractables are in the range of 3 000 to 25 000 g/mol. The chemical composition as a function of molar mass is visualized by coupled SEC‐FT‐IR spectroscopy. By quantitative analysis of the FT‐IR spectra the concentrations of the different structural units, including styrene, 1,4‐trans‐butadiene, 1,2‐vinylbutadiene, and 1,4‐cis‐butadiene, are determined. It is shown that the chemical composition of the original non‐crosslinked rubbers and the chemical composition of the extractables are rather identical. Therefore, this technique can be used to obtain structural information on rubber formulations even in the case when the material is already vulcanized.

SEC chromatograms of SBR 1712 and the extractables after pyrolysis, stationary phase: SDV linear, mobile phase: THF, detector: ELSD.     

Poly[(vinylidene fluoride)‐co‐trifluoroethylene] Membranes Obtained by Isothermal Crystallization from Solution

Electroactive macroporous poly[(vinylidene fluoride)‐co‐trifluoroethylene] membranes have been produced by solvent evaporation at room temperature, starting with a diluted solution of the copolymer in dimethylformamide. The pore architecture consists of interconnected spherical pores. This architecture is independent of the membrane thickness. The thickness of the membranes ranges from a few to several hundred µm, using spin coating and evaporation in static conditions, respectively. The pore structure is explained by a spinodal decomposition of the liquid/liquid phase separation and crystallization in the copolymer‐rich phase.

     

Artificial Opals as Effect Pigments in Clear‐Coatings

Summary: In this paper, we describe the use of artificial opals from polymer beads as effect pigments in transparent industrial and automotive coatings. For this purpose, we synthesized monodisperse colloids from fluorinated methacrylates by surfactant‐free emulsion polymerization. The fluorinated monomers, in combination with crosslinking, lead to a refractive index contrast, thermal stability, and solvent resistivity necessary for use as effect pigments. After crystallization of the monodisperse polymer beads, crystal flakes with iridescent colors can be obtained. The crystal flakes can act as effect pigments in various transparent industrial and automotive coatings. Due to photonic crystal behavior of effect pigments, color flops up to 100 nm are observed.

Crystal flakes of CS ‐7 as effect pigments in a transparent coating. The diameter of the tube is 5 mm.     

Improved Design of Shearing Sections with New Calculation Models Based on 3D Finite‐Element Simulations

New models for the Maddock and spiral shearing sections have been developed, employing three‐dimensional finite element analysis (3D FEA). These models describe the pressure‐throughput and power consumption behavior of the shearing sections for both the extrusion and the injection molding process and have been implemented in the REX 6.0 and PSI 4.0 simulation software. As a consequence it is now possible to describe the process behavior of these shearing sections within just a few seconds with the accuracy of FEA calculations.

Actual Maddock shearing section (left) and actual spiral shearing section (right).     

Synthesis of Poly(methyl‐co‐trifluoropropyl)silsesquioxanes and Their Thin Films for Low Dielectric Application

Poly(methyl‐co‐trifluoropropyl)silsesquioxanes (P(M‐co‐TFP)SSQs) were prepared using methyltrimethoxysilane (MTMS) and trifluoropropyltrimethoxysilane (TFPTMS). The molecular weight, microstructure of the copolymers and properties of their thin films have been changed by adjusting reaction parameters such as the molar ratio of water to silane, the molar ratio of catalyst to silane, reaction time, solvent content, and temperature. The refractive index of the copolymer thin film decreased from 1.404 to ca. 1.348 as curing temperature was increased to 420 °C. The dielectric constant of the film decreased with an increase of the molecular weight of the copolymer, and the lowest dielectric constant obtained was ca. 2.2. Hardness and elastic modulus of the thin films were 0.7 and 5 GPa, respectively. Crack velocity was measured to be 10^?11 m/s at the film thickness of around 0.9 μm under aqueous environment.

     

Elaboration of Poly(ε‐caprolactone)‐g‐TiNbO5 Nanocomposites via in situ Metal Complex Initiated Intercalative Polymerization

Summary: The preparation of poly(ε‐caprolactone)‐g‐TiNbO₅ nanocomposites via in situ intercalative polymerization of ε‐caprolactone initiated by an aluminium complex is described. These nanocomposites were obtained in the presence of HTiNbO₅ mineral pre‐treated by AlMe₃, but non‐modified by tetraalkylammonium cations. These hybrid materials obtained have been characterized by Fourier transform infrared absorption spectroscopy, wide‐angle X‐ray scattering, scanning electron microscopy, and dynamic mechanical analysis. Layered structure delamination and homogeneous distribution of mineral lamellae in the poly(ε‐caprolactone) (PCL) is figured out and strong improvement of the mechanical properties achieved. The storage modulus of the nanocomposites is enhanced as compared to pure PCL and increases monotonously with the amount of the filler in the range 3 to 10 wt.‐%.

SEM image of the fractured surface of a PCL‐TiNbO₅ nanocomposite film.     

Synthesis and Characterization of Biodegradable Poly(ε‐caprolactone)‐Polyglycolide‐Poly(ethylene glycol) Monomethyl Ether Random Copolymer

Summary: Poly(ε‐caprolactone)‐polyglycolide‐poly(ethylene glycol) monomethyl ether random copolymers were synthesized from ε‐caprolactone (ε‐CL), glycolide (GA) and poly(ethylene glycol) monomethyl ether (MPEG) using stannous octoate as catalyst at 160 °C by bulk polymerization. The copolymers with different composition were synthesized by adjusting the weight ration of reaction mixture. The resultant copolymer with a weight ratio (10:15:75) of MPEG2000, GA, and CL was characterized by IR, ¹H NMR, GPC and DSC. The new biodegradable copolymer has potential for medical applications since it is combined with properties of PCL, PGA and MPEG.

     

End‐Grained Wood‐Polyurethane Composites, 1

Summary: In order to improve the dimensional stability of end‐grained wood upon environmental humidity variations, a two‐step procedure was thoroughly studied which involved the osmotic impregnation of native poplar wood by PEG, followed by the reactive impregnation with HMDI, leading to polymer chain extension and polyurethane formation. It came out that the efficiency of PEG and/or polyurethane grafting within ligno‐cellulosic cell walls was intimately related to parameters such as concentration of the PEG impregnation bath, PEG molar mass, time and temperature of impregnation steps. Based on the different sample characterizations, Soxhlet extraction and density measurements, it came out that adequate experimental conditions are to carry out osmotic impregnation at 20 °C for 24 h starting from an aqueous solution of PEG ([PEG] = 0.5 mol · L^?1 and = 400 or 1 000) and reactive impregnation in bulk with a large excess of HMDI at 20 °C for 2 h. Combining scanning electron microscopy and mercury porosimetry demonstrated the selective impregnation of cell wall and wood rays which were collapsed in native wood and expanded in wood polyurethane composites.

SEM of an end‐grained wood transversal cross‐section after Soxhlet extractions successively with water and THF.     

Photoreversible Superhydrophobic Surfaces with Switchable Sticky‐Rolling State of Water Droplets

A photoresponsive fluorinated azobenzene homopolymer is synthesized via TERP. UV irradiation of the surface based on a fluorinated azobenzene homopolymer with micro/nanostructures induces a tunable/switchable water droplet mobility. Water droplets can easily roll off the pristine surface at a small tilt angle (≈14°). The apparent water CA changes from 150 to 135° after UV illumination of the surface. Thus, water drops stick on the surface when the substrate is turned vertically or even upside down, indicating a very high adhesion force. Interestingly, the water droplet rolls off again under visible‐light irradiation. The as‐prepared surface may be useful for applications requiring switchable mobility of water droplets.

     

Bio‐Based Rubbers by Concurrent Cationic and Ring‐Opening Metathesis Polymerization of a Modified Linseed Oil

Bio‐based rubbers prepared by tandem cationic polymerization and ROMP using a norbornenyl‐modified linseed oil, Dilulin?, and a norbornene diester, NBDC, have been prepared and characterized. Increasing the concentration of the NBDC in the mixture results in a decrease in the glass transition temperature. The new bio‐based rubbers exhibit tensile test behavior ranging from relatively brittle (18% elongation) to moderately flexible (52% elongation) and with decreasing values of tensile stress with increasing NBDC content. Thermogravimetric analysis reveals that the bio‐based rubbers have maximum decomposition temperatures of over 450 °C with their thermal stability decreasing with increasing loadings of NBDC.

     

Thermo‐Physical and Impact Properties of Epoxy Containing Epoxidized Linseed Oil, 2

Summary: Biobased neat epoxy materials containing epoxidized linseed oil (ELO) were processed with an amine curing agent. A defined amount of diglycidyl ether of bisphenol F (DGEBF) was replaced by ELO. The thermophysical properties of the amine‐cured biobased neat epoxy were measured by dynamic mechanical analysis (DMA). The Izod impact strength increased with an increase in the amount of ELO added. The change in the Izod impact strength was correlated with the thermophysical properties measured by DMA.

Relation between the Izod impact strength and loss factor for amine‐ and anhydride‐cured ELO‐containing epoxy resins.     

Copper(II)‐Catalyzed Reactions of Dimethylformamide with Phenylacetonitrile and Sulfur to Form N,N‐Dimethylthioamides

Novel copper‐catalyzed three‐component reactions of phenylacetonitrile, sulfur and DMF (dimethyformamide) for the selective preparation of N,N‐dimethylthiobenzamide and N,N‐dimethyl‐2‐phenylethanethioamides in yields of up to 96% are described.

     

Advantages of an Emulsion‐Produced Ziegler‐Natta Catalyst Over a Conventional Ziegler‐Natta Catalyst

Summary: Self‐supported and MgCl₂‐supported Ziegler‐Natta catalysts, produced by two catalyst synthesis methods are compared. Borealis Polymers OY (Finland), who supplied the catalysts, developed the catalyst synthesis methods. The first method (Method One) is based on an emulsion system and consists of an in situ single step preparation. The second method (Method Two) consists mainly of two steps: formation of the catalyst carrier particles, and their subsequent impregnation with the active material. The results showed that Method One produced catalysts of compact, spherical particles with good intra‐particle homogeneity and a narrow particle size distribution. On the other hand, Method Two produced catalyst particles whose properties depended directly on that of the catalyst carrier: they were spherical but very porous, with a broad particle size distribution. Polymer particles produced with the two catalyst systems are perfect replicas of the catalyst particles. Fines formed either during catalyst preparation or during polymerization were observed only with the catalyst prepared using Method Two. The particles of the catalysts produced using Methods One and Two had similar activities, independent of the initial particle size. Fragmentation of catalyst particles was very fast for both catalyst systems and was only observed to be 100% completed using the catalyst produced with Method One. Studies of the thermal properties showed that the catalyst prepared using Method One produced poly(propylene) of higher crystallinity and with a narrower melting peak.

SEM images of polymer particles produced by (A) Method One and (B) Method Two.     

Monomers for Adhesive Polymers 12 Synthesis and Free‐Radical Homo‐ and Copolymerization of 2‐Ethoxycarbonylallyl 5‐(1,2‐dithiolane‐3‐yl)‐pentanoate

The 2‐ethoxycarbonylallyl 5‐(1,2‐dithiolane‐3‐yl)‐pentanoate monomer (AODS) includes in its molecular structure C?C and S? S reactive bonds allowing it to behave as a bi‐functional monomer, possessing two groups, however, with different reactivity for use in polymer chain building. The polymerization‐specific features of this monomer are the absence of auto‐acceleration and polymer chain crosslinking. Polymerization proceeds readily through most free‐radical initiators. One exception, carboxy‐peroxides are rapidly decomposed without the production of free radicals. AODS is partially converted to a gel without the consumption of double bonds during monomer dissolution in certain organic solvents and after being mixed in solution with carboxy‐peroxides. The determined AODS‐co‐MMA copolymerization parameters are r₁ = 2.61, r₂ = 0.23 if Luperco peroxide is used as a polymerization initiator, and r₁ = 2.71, r₂ = 0.38 if AIBN is used.

     

Influence of Screw Speed on Electrical and Rheological Percolation of Melt‐Mixed High‐Impact Polystyrene/MWCNT Nanocomposites

The influence of screw speed on the electrical and rheological percolation of HIPS/MWCNT composites prepared via melt mixing was investigated. Microscopic examination of these composites using POM, FESEM and HRTEM revealed optimum MWCNT dispersion was achieved at intermediate screw speeds. On addition of MWCNTs to HIPS, the electrical conductivity of HIPS increased by up to 12 orders of magnitude. At screw speeds up to 100 rpm an electrical percolation of 1–3 wt.‐% was achieved. This increased to 3–5 wt.‐% when the screw speed was increased to 150 rpm. The onset of a rheological percolation was detected for an MWCNT loading of 5 wt.‐%, irrespective of screw speed employed. An up‐shift in the Raman G‐band of 24 cm^?1 was observed, implying strong interfacial interaction between HIPS and MWCNTs.