The Influence of the Irradiation Temperature on the Ratio of Chain Scission to Branching Reactions in Electron Beam Irradiated Polytetrafluoroethylene (PTFE)

Polytetrafluoroethylene (PTFE) films have been irradiated by electron beam in vacuum at various temperatures ranging from room temperature up to temperatures far above the melting temperature. Changes of the chemical structure have been analyzed by ¹⁹F solid‐state NMR and IR spectroscopy. The concentration of several structures generated by irradiation increases with increasing irradiation temperature up to the beginning of the thermal degradation. The molar ratio of >CF? branching points to ? CF₃ end groups changes with crossing of the melting temperature. The generation of >CF? branching points is accelerated if the PTFE is irradiated in the molten state, where branching reactions become more important.

     

Metallized Organoclays as New Intermediates for Aqueous Nanohybrid Dispersions,Nanohybrid Catalysts and Antimicrobial Polymer Hybrid Nanocomposites

Summary: The chemical metallization of aqueous bentonite dispersions afforded stable aqueous hybrid nanoparticle dispersions containing simultaneously dispersed sodium bentonite nanoplatelets together with bentonite supported silver, palladium, or copper nanoparticles with average metal nanoparticle diameters varying between 14 and 40 nm. Such aqueous bentonite/metal hybrid nanoparticle dispersions were blended with cationic PMMA latex to produce PMMA hybrid nanocomposites containing exfoliated polymer‐grafted organoclay together with bentonite supported metal nanoparticles. This dispersion blend formation was investigated with respect to the role of nanostructure formation and mechanical properties. Palladium/bentonite hybrid dispersions were used as catalysts for hydrogenation reactions and the electroless plating of copper. In contrast to the conventional organoclay nanocomposites, the PMMA hybrid nanocomposites, containing simultaneously dispersed organoclay nanoplatelets together with organoclay supported silver nanoparticles, exhibited high antimicrobial activity against the ubiquitous bacterium Staphylococcus aureus, even at low silver content.

Preparation of a polymer hybrid nanocomposite.     

The Solid State Postcondensation of PET, 4

Summary: A new method of polymerising PET in the solid state is proposed in either a gas phase reactor, or in hydrocarbon dispersion. It is shown that the reaction can be carried out efficiently at temperatures on the order of 200–240 °C directly from a prepolymer without the need for a melt phase step. It is shown that the crystal structure of the prepolymer plays a determining role in the kinetics of the SSP reaction.

Schema of the reactor used for gas phase SSP.     

Synthesis and Characterization of Segmented Block Copolymers Based on Hydroxyl‐Terminated Liquid Natural Rubber and α,ω‐Diisocyanato Telechelics

Summary: Segmented block copolymers, consisting of non‐polar soft segments from hydroxyl‐terminated liquid natural rubber (HTNR) and polar hard segments from α,ω‐diisocyanato telechelics obtained by “criss‐cross”‐cycloaddition, have been synthesized. The block copolymer formation took place under relatively mild reaction conditions at 80 °C in dichloroethane in the presence of dibutyltin dilaurate as a catalyst. The resulting block copolymers were characterized by spectroscopic techniques (¹H NMR, FTIR, UV‐vis spectroscopy) as well as GPC for molar mass determination. The block copolymers were compression molded in a hot stage press, and the resulting samples were characterized by DSC and stress‐strain measurement. The solubility and phase morphology of the materials have also been studied.

Segmented block copolymer from HTNR and α,ω‐diisocyanato telechelics     

Synthesis and Characterization of Epoxy/MCDEA Networks Modified with Imidazolium‐Based Ionic Liquids

Epoxy‐networked materials containing N,N'‐dioctadecylimidazolium iodide are prepared by curing a mixture of DGEBA and different ratios of the ionic liquid with MCDEA at high temperature. The presence of ionic liquid results in an increase of the storage modulus and a decrease of the glass transition temperature, as indicated by DMA. Also, the onset curing temperature decreases as the amount of IL increase indicating that IL also takes part on the curing process. DSC and FTIR analyses confirm that the imidazolium‐based ionic liquid is able to promote the crosslink of the epoxy pre‐polymer without the presence of external curing agent.

     

Effect of Cyclic Deformations on the Dynamic‐Mechanical Properties of Silica‐Filled Butyl Rubber

The effect of the chemical modification of the silica surface by the silane coupling agent (Si69) on both the real and the imaginary parts of the shear compliance (J′, J″) on silica‐filled butyl rubber vulcanizates was investigated in a wide temperature and frequency range, ?70 to 120 °C and 10^?4 to 10 Hz, respectively. In addition, the stress‐strain measurements, DSC, and TEM were carried out. Moreover the effect of stress‐strain cyclic deformation up to ten times with maximum deformation 80% of the elongation at break on J′, J″ is also studied. It was found that the filler network recovers after cyclic stress‐strain in a time scale of one year at room temperature.

Transmission electron photographs of the butyl rubber [IIR] vulcanizates: (a) IIR, unfilled, (b) IIR, filled with 20 phr SiO₂, (c) IIR,filled with 20 phr SiO₂ + 1.6 phr Si69.     

One‐Pot Double Benzylation of 2‐Substituted Pyridines using Palladium‐Catalyzed Decarboxylative Coupling of sp2 and sp3 Carbons

An efficient and practical decarboxylative double benzylation method for various 2‐picolinic acids has been established by using a bimetallic catalytic system of palladium(II) chloride (PdCl₂) and silver(I) oxide (Ag₂O), which offered a variety of diarylmethane derivatives with moderate to good yields.

     

Tensile Fracture and Failure Behavior of Thermoplastic Starch with Unidirectional and Cross‐Ply Flax Fiber Reinforcements

Thermoplastic starch (MaterBi®) based composites containing flax fibers in unidirectional and crossed‐ply arrangements were produced by hot pressing using the film stacking method. The flax content was varied in three steps, viz. 20, 40 and 60 wt.‐%. Static tensile mechanical properties (stiffness and strength) of the composites were determined on dumbbell specimens. During their loading the acoustic emission (AE) was recorded. Burst type AE signal characteristics (amplitude, width) were traced to the failure mechanisms and supported by fractographic inspection. The mechanical response and failure mode of the composites strongly depended on the flax content and the flax fiber lay‐up. It was established that the tensile strength increases until 40 wt.‐% flax fiber content but stays almost constant above this value. In the case of 40 wt.‐% unidirectional fiber reinforcement, the tensile strength of the composite was 3 times greater than that of the pure starch matrix. The flax fiber reinforcement increased the tensile modulus of the pure starch by several orders of amplitude.

SEM picture of the fracture surface of a composite with UD flax reinforcement.     

Matrimid Aerogels by Temperature‐Controlled,Solution‐Based Crosslinking

This paper reports on a temperature‐controlled, solution‐based method to prepare diamine crosslinked Matrimid aerogels. Addition of a diamine to a preheated polymer solution resulted in a well‐dispersed solution, allowing formation of a homogeneous gel upon cooling. The gels (studied by FTIR and AFM) were dried by solvent extraction with supercritical CO₂. The resulting aerogels showed surface areas of approximately 150 m² · g^?1 and porosities of 0.66–0.69 mL · g^?1 with polymer domains and pore sizes of tens of nanometers. A room temperature‐prepared, inhomogeneous aerogel gave approximately 250 m² · g^?1 and 0.31 mL · g^?1 with meso‐ and micropores. SEM images of the aerogels show similar surface features as AFM images of the Matrimid solvent gels.

     

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.     

Synthesis of Block Copolymers containing Chain‐Controlled Aramid and Fluoroethylene Segments

Summary: Novel block copolymers containing aromatic polyamide (aramid) and fluoroethylene segments were synthesized by a two‐step solution polycondensation. This synthetic method could control the chain‐length of aramid segments and these copolymers could have high structural regularity. The number‐average molecular weight ( ) of one of these polymers is over 2.0 × 10⁴. Incorporating fluoroethylene segments improves the solubility of the resulting polymer compared with conventional aramids.

The synthesis of the fluoroethylene‐aramid block copolymers.     

Preparation of Nano‐Polyethylene Fibers and Floccules by Extrusion Polymerization Under Atmospheric Pressure Using the SBA‐15‐Supported Cp2ZrCl2 Catalytic System

Summary: Nano‐polyethylene fibers and floccules were prepared under atmospheric pressure via ethylene extrusion polymerization in suit, using the SBA‐15‐supported Cp₂ZrCl₂ catalytic system. The major morphology units in the samples were fibers and floccules. The diameter of the single nano‐fibers was 120–200 nm. The single nano‐fibers could aggregate to form fiber aggregates and bundles. The number of PE floccules increased with extension of polymerization time, while the melting point of PE with nano‐fibers was little higher than that of common polyethylene.

SEM micrograph of the nano‐polyethylene fibers produced at a polymerization time of 60 min: micro‐fibers and floccule surface morphologies.     

Intercalated Polycarbonate/Clay Nanocomposites: Nanostructure Control and Foam Processing

Intercalated polycarbonate (PC)/clay nanocomposites (PCCN)s have been prepared successfully through the melt intercalation method in the presence of a compatibilizer. The internal structure and morphology of the PCCNs has been established by using wide‐angle X‐ray diffraction (WAXD) analyses and transmission electron microscopic (TEM) observations. The morphology of these nanocomposites and degradation of the PC matrix after nanocomposites preparation can be controlled by varying surfactants used for the modification of clay and compatibilizer. The intercalated PCCNs exhibited remarkable improvements of mechanical properties when compared with PC without clay. We also discuss foam processing of one representative PCCN using supercritical CO₂ as a foaming agent.

TEM bright field image of intercalated polycarbonate/synthetic fluorohectorite nanocomposite.     

Formaldehyde Resins Bearing Diaminodiphenylmethane Groups: Synthesis,Characterization and Properties

Summary: Novel formaldehyde resins bearing diaminodiphenylmethane groups were synthesized by the polymerization of a mixture of diaminodiphenylmethane (DDM), cyclohexanone (CHx) and o‐cresol (o‐Cz) with formaldehyde (FA) in the presence of an acid catalyst (HCl). The resins obtained were characterized by spectral, elemental and thermal analysis and used as a hardener for epoxy resins. The curing and temperature behavior of these epoxy resin/formaldehyde systems were investigated using differential scanning calorimetry and thermogravimetry techniques. The resins had good thermal stability and the activation energies of degradation reactions had values between 70–98 kJ · mol^?1.

The curing reaction of epoxy resins with the DDM/CHx/o‐Cz/formaldehyde resins.     

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.     

Structure‐Property Relationships of New Water‐Soluble Grafted Starches with Amphoteric Character

In an attempt to develop an environmentally friendly, multifunctional mud additive for oilfield drilling treatment, new water‐soluble grafted starches with amphoteric character were prepared by grafting the mixed monomer system of 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid (AMPS) and 2‐(dimethylamino)ethyl methacrylate (DMAEM) onto naturally occurring potato starch, and characterized by IR and composition analyses. Their structure‐property relationships with respect to the hydration suppression of the swellable clay and the control of mud rheology were studied with the help of clay hydration‐swelling test, mud rheology test, and SEM observation. It has been found that the grafting of DMAEM enhances the inhibition effectiveness of clay hydration‐swelling and that the grafting of AMPS increases the viscosity of the treated muds and the tolerance to added salt. Compared with the partially hydrolyzed polyacrylamide with a degree of hydrolysis of 16%, a typical polymeric additive used in current drilling fluids, such grafted starch with suitable grafting percentage and composition has some distinct advantages in the formulation of water‐based drilling muds.

Swelling percentage (S_p) of the clay pellets as a function of hydration time (t) in water and various sample solutions.     

Crystalline and Conductive Poly(3‐hexylthiophene) Fibers

Intrinsically conducting polymer fibers are prepared from P3HT by melt spinning. High crystallinity is achieved by drawing the fibers after the spinning process, applying a draw ratio of 1:2. DSC and XRD measurements confirm the continuous increase of crystalline phases with drawing. For comparison, poly(ethylene terephthalate) fibers are coated with P3HT and drawn as well. Again, the drawing of the coated fiber results in a significant increase in crystallinity of the P3HT coating. The high amount of crystalline phases is associated with a dramatic increase in conductivity (350 S · cm^?1) after doping with FeCl₃ in nitromethane.