A diacrylate polysulfone oligomer is synthesized and used as the acrylic oligomer for the in situ synthesis of noble metal/PSU nanocomposites through UV‐induced simultaneous radical polymerization of acrylic functionalities and NP formation by reduction of their precursors. Thus, silver or gold NPs are formed in situ during polymer network formation. FESEM analysis of the morphology of the cured systems demonstrates that the nanoparticles of the noble metals are homogeneously distributed in the network without macroscopic agglomeration.
Two novel cationic RAFT agents, PCDBAB and DCTBAB, were anchored onto MMT clay to yield RAFT‐MMT clays. The RAFT‐MMT clays were then dispersed in styrene where thermal self‐initiation polymerization of styrene to give rise to exfoliated PS/clay nanocomposites occurred. The RAFT agents anchored onto the clay layers successfully controlled the polymerization process resulting in controlled molecular masses and narrow polydispersity indices. The nanocomposites prepared showed enhanced thermal stability, which was a function of the clay loading, clay morphology, and slightly on molecular mass.
PIB/MMT nanocomposite films containing UHP are fabricated and characterized for potential applications in wounded‐skin oxygen delivery and/or tooth cleaning. The UHP acts as a source of oxygen, whereas MMT creates a pathway for water molecules penetrating the film in order to generate a controlled release of H2O2 molecules. Most UHP particles are uniformly dispersed throughout the entire thickness of the films. DMA measurements indicate that the material retains most of its structural characteristics when exposed to water. SEM measurements show that no interface exists between individually spread multilayers. SAXS measurements indicate that the clay platelets are predominantly exfoliated and randomly oriented within the film. Controlled release of H2O2 is found over a period of ≈90–100 min.
PET/PEN blends were prepared over the full composition range via a melt mixing process under various processing conditions. This resulted in transesterification reactions and formation of copolymer structures with various average sequence block lengths and degree of randomness (RD) determined by 1H NMR. It was seen that with an increase in time and temperature of mixing copolymer content (TEN%) and RD increased, whereas the , values were decreased. The differences in the extent of transreactions arising from different processing histories showed their systematic influence on rheological characteristics. Moreover due to progress of transreactions during the rheological measurements, convergence was seen in all the rheological characteristics at terminal zones in the high frequency regions. Similar convergence in the copolymer structural parameters was also obtained by NMR analysis. An increase in TEN% led to a systematic increase in viscosity of the blends. A decrease in the , values results in an increase in elasticity and relaxation time due to improvement of blend interface with increase in extent of copolymer formation.
A siloxane‐grafted new diamino monomer DBPDMS has been prepared and used as a co‐monomer in combination with the fluorinated diamine monomer TFBB to prepare siloxane‐grafted polyimides. The polymers have been characterized by means of GPC, IR, and NMR. Their thermal, mechanical, and surface properties have been evaluated and compared with the homopolyimide and with polyimides where polysiloxane is incorporated in the main chain. DSC revealed melting of the grafted siloxane chain at sub‐ambient temperature and a glass transition corresponding to the main polymer chain at high temperature. Isothermal gravimetric analysis at 350 °C indicated that grafted siloxane moiety can be removed thermally from the polymer chain without affecting the polymer backbone.
Rubbery thermosets prepared by ROMP of a modified castor oil containing norbornene moieties and cyclooctene have been synthesized and characterized. The thermosets range from 55 to 85 wt.‐% oil and are flexible, slightly transparent and have a sand‐like hue. Increasing concentration of the modified castor oil in the feed ratio results in an increase in the extracted (unreacted or oligomeric) components in the final thermoset. Thermogravimetric analysis reveals that all of the specimens have temperatures of maximum degradation around 500 °C. DMA and TGA analysis on solvent‐extracted specimens show that the presence of the soluble fractions helps to plasticize the materials and give added thermal stability.
Epoxy anhydride networks were modified with Siloxane/PMMA hybrid materials, obtained from sol/gel method. The effects of thermal annealing of the Siloxane/PMMA hybrids and of the hybrid composition on the nanostructure of the epoxy network were investigated by means of SAXS. The composites containing Siloxane/PMMA materials with low amount of MMA present a hierarchical nanostructure whose first level is made of siloxane nanoparticles spatially correlated in the matrix forming larger secondary hybrid aggregates. Small amounts of hybrid material decrease the glass temperature of the composite, but increase the storage modulus, indicating its nanoreinforcing action.
Additive processing technologies are rapidly growing in all fields of application. A large number of scientific publications were investigated in order to provide a comprehensive overview of rapid prototyping methods for polymers and their applications, of currently available materials and research concerning additive processes. The current problems of additive processes are described, together with their potential solutions. Furthermore, this article delivers an insight into possible future trends of additive technologies.
A new, nickel‐coated graphite resistance‐change‐based method for gel‐point determination for epoxy‐based thermoset resins is presented and compared with DSC and rheological methods. Gelation times determined by this new method are in very good agreement with conventional techniques; this new method is potentially simpler and less time consuming than existing ones.
Light up galectin: Photoprobes based on thiodigalactoside were prepared for galectin‐3, a lectin linked to cancer. The probes contained either benzophenone or acetophenone moieties as the photolabel for covalent attachment to the protein. One particular probe labeled galectin‐3 selectively, even in the presence of cell lysate.
An experimental correlation between the non‐linear behaviour of commercial polyethylene melts in LAOS flow, and the pressure fluctuations associated with melt flow instabilities developed in capillary rheometry are presented. Polyethylene melts with enhanced non‐linear behaviour under LAOS conditions present larger pressure fluctuations during capillary extrusion, and consequently, larger surface distortions on the extrudate. The combination of both methods can be a tool to predict the development of melt flow instabilities in the extrusion process of polyethylene melts, and can elucidate their correlation with material structural properties ( , MWD and topology).
Bio‐stereo nanocomposite polylactides are prepared by polymerization followed by stereocomplexation in scCO2/dichloromethane through in situ polymerization and master batch processes. The bio‐stereo nanocomposite polylactides show intercalated‐exfoliated and fully exfoliated nanoscale clay distribution in a perfect stereocomplex polylactide matrix. In situ polymerization proves better strategy to produce well‐exfoliated silicate layers in the stereocomplex matrix compared to the MB route that increases the melting temperature by up to ≈64 °C. The thermal properties of these materials maintain both stereocomplex and nanocomposite features simultaneously. The results open a new and versatile way to develop polylactide‐based materials.
Liquid‐crystalline epoxy thermosets were prepared by adding M1 into DGEBA/DDM blends. M2 was added to DGEBA/DDM to produce thermosets for comparison. The influences of the concentration and chemical structure on the mechanical and thermal properties were investigated systematically. The M1 /DGEBA blends possessed increased rubbery plateau modulus, higher glass transition temperatures, and lower tan δ. The use of small amounts of M1 may improve the mechanical properties greatly. Izod notched impact strength could be enhanced by 55% by addition of 2% M1 compared to unmodified DGEBA blends. Extremely rough and highly deformed fracture surface could be obtained in the M1 /DGEBA blends. M1 /DGEBA blends also exhibited excellent thermal properties.
Epoxy/BaTiO3 hybrid materials are prepared as good candidates for organic capacitors. The hybrid system is cured by using camphorquinone and a iodonium salt through a free‐radical promoted cationic polymerization using a long‐wavelength tungsten halogen lamp. The cured films are fully characterized. Morphological characterization shows a well‐dispersed inorganic phase within the organic matrix. Electrical characterization demonstrates a linear increase of the dielectric constant with increasing filler content, while low dielectric loss values are obtained.
A novel electrospinning set‐up has been developed to successfully electrospin multiple jets with controlled fiber repulsion using a plastic filter. This set‐up shows reduced fiber repulsion as compared to a multineedle set‐up, along with increased throughput. The effect of processing parameters on the fiber repulsion in a multineedle set‐up was also studied. It was found that fiber repulsion could be reduced by controlling emitter voltage and emitter/collector distance. Other important parameters studied included fiber distribution and throughput. It was found that the plastic filter set‐up produced fibers with lower mean diameters and better uniformity. This novel plastic filter design for electrospinning provides increased electrospinning rates with better fiber uniformity.
New dibenzoylgermanium derivatives are synthesized starting from various dithioacetal protected benzaldehydes by a coupling reaction with different dialkyldichlorogermanes and subsequent oxidative cleavage of the protecting group. The synthesized germanium compounds show a significantly stronger blue light absorption than camphorquinone. During irradiation, the dibenzoylgermanium derivatives undergo photodecomposition under formation of radicals. Therefore, the different dibenzoylgermanium derivatives are used as amine‐free visible‐light photoinitiators for dental cements and composites. Composites based on the different dibenzoylgermanes are storage‐stable and show a significantly improved bleaching behavior over composites with CQ/amine photoinitiators.
Hydrophobic materials were successfully prepared from SPI and NR by blending via freezing/lyophilizing. The interfacial interaction, surface properties, hydrophobicity, and mechanical properties, biodegradability as well as the biocompatibility were investigated. The blend sheets exhibited good interface adhesion and good optical transparency. Their hydrophobicity was significantly improved compared with pure soy protein sheets. XPS results proved the NR surface enrichment. Flexibility and toughness of the blend sheets were enhanced and phase inversion phenomena were observed. Furthermore, the blend sheets exhibited good biodegradability and biocompatibility capable of supporting cell adhesion and proliferation.
PVA nanofibers have been successfully prepared via an electrospinning process by optimizing the electrospinning operational parameters including applied voltage, polymer concentration, feed rate, and working distance. Inexpensive NaCl and Fe(NO3)3 are found to reduce the fiber size drastically (minimum of 157 and 169 nm, respectively) even at a low loading. The thermal stability is investigated by both thermogravimetric analysis and differential scanning calorimetry. Fourier transform infrared spectroscopy is utilized to characterize the functionality of the fibers and to investigate the interaction between PVA and inorganic additions. Glass transition and melting temperatures of the PVA fibers have slight change with the increase of the salt loading.
Surface modification of carbon black by plasma polymerization was aimed to reduce its surface energy in order to compatibilize the filler with various elastomers. A fullerenic carbon black was used for the modification process. Thermogravimetric analysis, wetting behavior with liquids of known surface tension, TEM and TOF‐SIMS were used to characterize the carbon black before and after modification. The state of plasma‐coated carbon black in rubber was studied by means of conductivity measurements. The behavior of the modified filler in rubber was studied using the Payne effect and stress/strain properties. The study shows that plasma‐coated carbon black results in a better dispersion in different rubber systems than the uncoated version.
Electrically conductive, cationically UV‐cured composites were prepared using exfoliated graphite plates (EGP) with cycloaliphatic epoxy resin and polyalcohol binder system. Exfoliated graphite (EG) was obtained from natural flake graphite through chemical and thermal treatment. Sonication of EG in solvent produced EGP. Characterization of graphite samples by XRD showed structural similarity between original graphite and EGP. UV curing behavior was characterized using photoDSC. Electrical resistivity measurements of the composites as a function of EGP concentration showed that at low filler concentration the binder system can influence the electrical percolation behavior. Some formulations showed electrical percolation at less than 1 vol.‐% of EGP filler.
