All issues / Volume 10 (2016) / Issue 9 (September)
This is an editorial article. It has no abstract.
The polycyclotrimerization reaction of dicyanate ester of bisphenol E (DCBE) in the presence of varying amounts (from 0.5 to 5 wt%) of 1-octyl-3-methylimidazolium tetrafluoroborate ([OMIm][BF4]) ionic liquid has been investigated using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) techniques, after a curing stage at 150 °C for 6 h. It is noteworthy that an amount of [OMIm][BF4] as low as 0.5 wt% accelerates dramatically the thermal curing process leading to the formation of a polycyanurate network. The conversion of DCBE increased with increasing [OMIm][BF4] content in the temperature range studied. A reaction mechanism associated with the ionic liquid-catalyzed DCBE polycyclotrimerization is newly proposed via the involvement of a [CN]δ+–[OMIm]δ– complex as a key intermediate.
Three-dimensional nanoporous graphene monoliths are utilized to prepare graphene-poly(vinylidene fluoride) nanocomposites with enhanced mechanical and electro-mechanical properties. Pre-treatment of the polymer (poly(vinylidene fluoride), PVDF) with graphene oxides (GOs) facilitates the formation of uniform and thin PVDF films with a typical thickness below 100 nm well coated at the graphene nano-sheets. Besides their excellent compressibility, ductility and mechanical strength, the nanoporous graphene-PVDF nanocomposites are found to possess high sensitivity in strain-dependent electrical conductivity. The improved mechanical and electro-mechanical properties are ascribed to the enhanced crystalline β phase in PVDF which possesses piezoelectricity. The mechanical relaxation analyses on the interfaces between graphene and PVDF reveal that the improved mechanical and electro-mechanical properties could result from the interaction between the –C=O groups in the nanoporous graphene and the –CF2 groups in PVDF, which also explains the important role of GOs in the preparation of the graphene-polymer nanocomposites with superior combined mechanical and electro-mechanical properties.
The authors report that during tensile stress relaxation test of a polyurethane crosslinked by catechol-iron coordination bonds, the stress gradually increases with time after the initial drop, which differs from the documented behaviors of other materials. Based on model experiment and structural characterization, water triggered rapid increase of dynamic crosslinkages accompanied by Poisson’s contraction is found to be responsible for the stress intensification effect. In addition, the influential factors are carefully discussed. The findings might help to develop novel polymeric materials with improved application performance under loading conditions.
Evaluation of the release characteristics of covalently attached or electrostatically bound biocidal polymers utilizing SERS and UV-Vis absorption
G. N. Mathioudakis, A. Soto Beobide, N. D. Koromilas, J. K. Kallitsis, G. Bokias, G. A. Voyiatzis
Vol. 10., No.9., Pages 750-761, 2016
Vol. 10., No.9., Pages 750-761, 2016
In this work, biocidal polymers with antimicrobial quaternized ammonium groups introduced in the polymer biocidal chains either through covalent attachment or electrostatic interaction have been separately incorporated in a poly (methyl methacrylate) polymer matrix. The objective of present study was to highlight the release characteristics of biocidal polymers, primarily in saline but also in water ethanol solutions, utilizing UV-Vis absorption and Surface Enhanced Raman Scattering (SERS). It is shown that through the combination of UV-Vis and SERS techniques, upon the release process, it is possible the discrimination of the polymeric backbone and the electrostatically bound biocidal species. Moreover, it is found that electrostatically bound and covalently attached biocidal species show different SERS patterns. The long term aim is the development of antimicrobial polymeric materials containing both ionically bound and covalently attached quaternary ammonium thus achieving a dual functionality in a single component polymeric design.
A series of carbazole-based polymers were synthesized via Suzuki polymerization between N-(2-ethylhexyl)carbazole-3,6-bis(ethyleneboronate) (Cbz) and dibromobenzazole unit. Three different polymers, PCBN, PCBS and PCBSe were obtained from 4,7-dibromo-2-hexyl-2H-benzotriazole (BN), 4,7-dibromo-2,1,3-benzothiadiazole- (BS) and 4,7-dibromo-2,1,3-benzoselenadiazole (BSe), respectively. It is observed that, the variation of heteroatoms (N,S and Se) on the benzazole unit have most important effect on electro-optic properties of the PCBX polymers. Neutral state color of the polymer films and their electrochromic performances are also influenced. Among the synthesized polymers, the PCBS bearing 2,1,3-benzothiadiazole as acceptor units has a broad absorption and 50% of ΔT in the near-IR regime at the oxidized state. This property of PCBS is a great advantage for near-IR electrochromic applications.
Natural fibre reinforced polylactic acid (PLA) foams, as potential green replacements for petroleum-based polymer foams, were investigated. Highly porous (ε > 95%) microcellular PLA foams were manufactured by supercritical CO2 assisted extrusion process. To overcome the inherently low melt strength of PLA, epoxy-functionalized chain extender was applied, while talc was added to improve its crystallization kinetics. The combined application of chain extender and talc effectively promoted the formation of uniform cell structures. The effect of cellulose and basalt fibre reinforcement on the foamability, morphology, structure and mechanical properties of the PLA foams were investigated as well. The addition of 5 wt% natural fibres promoted the cell nucleation, but caused non-uniform distribution of cell size due to the microholes induced by local fibre-matrix debonding. The compression strength of the manufactured basalt fibre reinforced PLA foams reached 40 kPa.
Polyaniline (PANI) is the most important conducting polymer with excellent electrochemical properties. So PANIbased biosensors may find wide applications in medical diagnostics. We report here a ternary nanocomposite of gold nanoparticle-decorated single- walled carbon nanotubes (SWCNTs) embedded in sulfonated polyaniline matrix, prepared using a simple solvothermal chemical route. The structural and morphological characteristics have been determined by electron microscopy, X-ray diffraction and Raman spectroscopy. Optical characteristics of the nanocomposite have been determined by ultraviolet (UV)-visible absorption spectroscopy and photoluminescence spectroscopy. The direct current (DC)-conductivity measurement of the material shows a significant increase in electrical conductivity at 353 K from 7.80·10–2 S/m for pure SPANI to 10.91 S/m for the 3-phase nanocomposite as synthesized in the present investigations. Thus the incorporation of SWCNT/Au nanohybrid fibers in the PANI matrix enhanced its electrical properties. Sulfonation increased the processability of the material, as the samples have now been found to be soluble in water and common organic solvents like DMSO. Such a functional nanocomposite will make an excellent biosensor electrode material.