*** Editorial Corner ***
A reversible addition-fragmentation chain transfer (RAFT) agent with carbazole as Z-group was immobilized on the surfaces of the cross-linked poly (4-vinylbenzyl chloride-co-styrene) (PVBCS) nanospheres with a diameter of about 70 nm by the reaction of benzyl chloride groups in the PVBCS between carbazole and carbon sulfide. Then surface RAFT polymerization of 4-vinylpyridine (4VP) was used to modify the nanospheres to produce a well-defined and covalently tethered P4VP shell. By surface activation in a PdCl2 solution and then reduction by hydrazine hydrate (N2H4•H2O), the P4VP composite shells were obtained containing densely palladium metal nanoparticles. The chemical composition of the nanosphere surfaces at various stages of the surface modification was characterized by X-ray photoelectron spectroscopy (XPS). Transmission electron microscopy (TEM) was used to characterize the morphology of the hybrid nanospheres. The Pd/P4VP shell nanospheres were also applied to the catalytic reaction and proved to be efficient and reusable for the Heck reaction.
The present review article describes in detail the state-of-the-art of organic-inorganic hybrid materials based on polyimide/silica components. The article is divided in three parts. In the first the basic processing route for the preparation of these systems is described, i.e. the sol-gel technique, along with the strategies developed to control the final morphology. In the second part the curing characteristics, the dynamic-mechanical and the mechanical and fracture properties of hybrids with different morphologies are reviewed. Finally, the more technologically relevant applications devised for these high performance materials are discussed.
Poly(ethylene glycol) bis (methylimidazolium chloride) (PEGBMIM) with average molecular weights of 600 and 1000 g/mol and poly(ethylene glycol) bis (2-oxazoline) (PEGBOX) with average molecular weight of 600 g/mol have been prepared using microwave irradiation under solvent-free condition. The method described herein is a very good, safe, clean, economical and environmentally friendly alternative to the classical procedures. The resulted products have been characterized by common spectroscopic methods, such as FT-IR (Fourier transform infrared spectroscopy), 1H NMR (Nuclear magnetic resonance of proton) and elemental analysis. Also, the effects of power levels and irradiation time on the yield of reactions and solubility of products have been studied.
Electrospinning utilizes electric forces and hence the electrical properties of the solution have an effect the process. The study examined the effect of conductive additive and filler on the electrospinning process with polyacrylonitrile (PAN). Electrospinning trials were performed using a pure PAN solution, a salt-containing solution, and a solution containing carbon nanotubes (CNTs). Different nozzle sizes were used, and the spinning voltage and distance were also varied. The composition of the solution had a greater effect on fibre diameter than varying the process parameters. Conductivity of the solution increased the probability of process problems such as the formation of three-dimensional (3D) structures and the occurrence of larger, micro-sized fibres. When the viscosity of the solution was increased, as was the case with the PAN/CNT solution, the severity of the problems became less acute than with the PAN/Salt solution.
A series of novel oligomers with promesogenic groups on both termini were prepared by a hydrosilylation reaction between well-defined telechelic oligocarbosilazanes end-fitted with vinylsilane (SiVi) groups and promesogenic compounds containing one reactive hydrosilane (SiH) group. We investigated the correlations between the structure of the resulting mesogen end-capped oligomers and their phase behavior as examined by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM).
A prominent α' process in specifically treated nylon 66 and microcomposite samples is identified by dynamic mechanical analysis and proposed to be an amorphous phase counterpart of the Brill transition identified by synchrotron wide-angle X-ray diffraction (WAXD). It is suggested that this α' process, which marks a critical free volume change and an onset of segmental chain movement in the amorphous phase, precedes and prompts the Brill transition in the crystalline phase.
Lactic acid/ethylene terephthalate copolyesters were synthesized by the standard melt polycondensation of lactic acid (L), ethylene glycol (EG) and dimethyl-terephthalate (DMT). Effects of reaction temperatures and types of catalysts on the structures and properties of the copolymers were examined. In addition, feasibility of promoting the copolymerization process by a novel synthesis step of using thermo-stabilizers was investigated. The results show that a reaction temperature of higher than 180°C is necessary to produce copolymers with appreciable molecular weight. However, degradation was observed when the reaction temperature is higher than 220°C. Triphenyl phosphate (TPP) shows promising results as a potential thermo-stabilizer to minimize this problem. It was found that Sb2O3 and Tin(II) octoate are most effective among 4 types of catalysts employed in this study. 1H-NMR results indicate that copolymers have a random microstructure composed mainly of single L units alternately linked with ET blocks at various sequential lengths. The longer ET sequence in the chain structure leads to the increase in melting temperature of the copolymer. TGA results show that the resulting copolymers possessed greater thermal stability than commercially-available aliphatic PLA, as a result of the inclusion of T (terephthalate) units in the chain structure.