Telechelic polymers by living and controlled/living polymerization methods

Telechelic polymers, defined as macromolecules that contain two reactive end groups, are used as cross-linkers, chain extenders, and important building blocks for various macromolecular structures, including block and graft copolymers, star, hyperbranched or dendritic polymers. This review article describes the general techniques for the preparation of telechelic polymers by living and controlled/living polymerization methods; namely atom transfer radical polymerization, nitroxide mediated radical polymerization, reversible addition-fragmentation chain transfer polymerization, iniferters, iodine transfer polymerization, cobalt mediated radical polymerization, organotellurium-, organostibine-, organobismuthine-mediated living radical polymerization, living anionic polymerization, living cationic polymerization, and ring opening metathesis polymerization. The efficient click reactions for the synthesis of telechelic polymers are also presented.     

Relaying methods with high coding rate for wireless communications

A cooperative wireless relaying communication system usually consists of a source node, a destination node and one or more relay nodes. In this work Amplify-and-Forward/Decode-and-Forward relaying techniques are discussed in order to improve the performance of a wireless relaying communication system under the case of high code rate. As a performance metric, the outage probability of the proposed Amplify- and-Forward/Decode-and-Forward relaying structure is compared with and without coding issue. Results from the proposed modeling and simulations illustrate that our Amplify-and-Forward/Decode-and-Forward relaying method with high code rating enables robust cooperative wireless communication.     

Dynamics of overall swelling profile of multiresponsive ionic dimethylacrylamide-based hydrogels and cryogels: Diffusion characteristics evaluation of salt-dependent swelling

Due to the importance of ion–polymer interactions in many technological applications, systematic measurements have been investigated on a variety of ionic poly(N,N-dimethylacrylamide) (PDMAAm) hydrogels and cryogels to determine the effect of mono- and multivalent ions on their dynamic properties. Using uniaxial compression, the influence of counter-ion valency on flexibility of charged polymer chains was investigated and the results were discussed as a function of ionic comonomer. To estimate the general swelling features, diffusion process and oscillating swelling–deswelling kinetics of ionic PDMAAm gels in salt solutions have been explained by model equations using early-time approximation as a function of characteristic response time.     

Spectral characterisation and computational studies of some novel phenylazoindol‐2‐one dyes

A series of novel phenylazo disperse dyes were prepared by coupling selected diazotised 3‐ or 4‐anilines with indol‐2‐one. The structures of the synthesised dyes were determined by spectroscopic and analytical methods. Solvent effects on the ultraviolet–visible absorption spectra of these novel dyes were studied. The colour of the dyes was evaluated with respect to the substituent therein. Acid and base effects on the visible absorption maxima of the dyes were also reported. The tautomerism of 3‐(phenyldiazenyl)indol‐2‐one was modelled by density functional theory at the B3LYP level. The ultraviolet–visible absorption spectra for the tautomers were reproduced with the time‐dependent density functional theory and semi‐empirical Zerner’s intermediate neglect of differential overlap/spectroscopic (ZINDO/S) method. The predominance of the keto–hydrazone tautomer was confirmed experimentally and theoretically.     

Study of poly(vinyl chloride) nanofiber structured assemblies as oil sorbents

The most significant feature of Nanofiber electrospinning is its capability of producing very fine Nanofiber mats which can be suitable as oil absorbent. This paper presents an investigation of oil adsorption and retention of poly(vinyl chloride) (PVC) Nanofiber mat absorbent. The emphasis is on the numerical modeling of the oil sorption capacity and the factors affecting it such as the packing density and the Nanofiber diameter. Finally, the mechanism of absorbent property enhancement and the ways to improve performance and fracture toughness for oil sorption are discussed. To enhance the oil sorption, it was suggested to add a low percentage of cellulose acetate (CA) and assess the performance of various Nanofibers as absorbent material. When the results of these studies were compared to results that of PVC Nanofiber mat, it was shown that PVC/CA 8% blend absorbs oil more efficiently.     

A liquid diffusion model for thin-layer drying of rough rice

In this study, the drying behavior of single-layer rough rice with a moisture content of between 22 and 24% on the dry basis was simulated by means of a liquid diffusion model, based on a prolate spheroid geometry. For this purpose, the solution of liquid diffusion equation was fitted to the experimental moisture ratios for drying air temperatures between 40 and 60 °C and velocity 1.5 m s⁻¹. In order to make a comparison, the predictions of liquid diffusion equations for a spherical and finite cylindrical geometry were also fitted to the experimental results. Modeling was performed by selecting the diffusion coefficients in diffusion equations in such a manner as to minimize the sum of the squared differences between the experimental results and the theoretical predictions. It was found that the liquid diffusion model, based on a prolate spheroid geometry, explains single-layer drying behavior of rough rice well. It was also found that the model, based on a prolate spheroid geometry, has better agreement with the experimental results than the other geometries.     

Reentrant phase transition of poly(N‐isopropylacrylamide) gels in polymer solutions: Thermodynamic analysis

The swelling behavior of poly(N‐isopropylacrylamide) (PNIPA) gels in polymer solutions, particularly in aqueous solutions of poly(ethylene glycol)s, was investigated using the theory of equilibrium swelling. The volume of the PNIPA gel and the partition parameter of the macromolecules between the gel and the solution phases were calculated for various extents of the energetic interactions between the components. The simulation results were compared with the experimental data reported in the literature. It was shown that the PNIPA gel has a tendency to a reentrant phase transition in an aqueous solution of low molecular weight linear polymers. In such a transition, the gel first collapses, then reswells, if the linear polymer concentration is continuously varied. The necessary condition for the reentrant behavior of PNIPA gels was predicted in terms of the interaction parameters among the PNIPA network, the linear polymer, and water. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 801– 813, 2002     

Manipulating Estrogenic/Anti-Estrogenic Activity of Triphenylethylenes towards Development of Novel Anti-Neoplastic SERMs

Selective estrogen receptor modulators (SERMs) act as estrogen receptor (ERα) agonists or antagonists depending on the target issue. Tamoxifen (TAM) (a non-steroidal triphenylethylene derivative) was the first SERM approved as anti-estrogen for the treatment of metastatic breast cancer. On the hunt for novel SERMs with potential growth inhibitory activity on breast cancer cell lines yet no potential to induce endometrial carcinoma, we designed and synthesized 28 novel TAM analogs. The novel analogs bear a triphenylethylene scaffold. Modifications on rings A, B, and C aim to attenuate estrogenic/anti-estrogenic activities of the novel compounds so they can potentially inhibit breast cancer and provide positive, beneficial estrogenic effects on other tissues with no risk of developing endometrial hyperplasia. Compound 12 (E/Z-1-(2-{4-[1-(4-Chloro-phenyl)-2-(4-methoxy-phenyl)-propenyl]-phenoxy}-ethyl)-piperidine) showed an appreciable relative ERα agonistic activity in a yeast estrogen screen (YES) assay. It successfully inhibited the growth of the MCF-7 cell line with GI₅₀ = 0.6 µM, and it was approximately three times more potent than TAM. It showed no potential estrogenicity on Ishikawa endometrial adenocarcinoma cell line via assaying alkaline phosphatase (AlkP) activity. Compound 12 was tested in vivo to assess its estrogenic properties in an uterotrophic assay in an ovariectomized rat model. Compared to TAM, it induced less increase in wet uterine wet weight and showed no uterotrophic effect. Compound 12 is a promising candidate for further development due to its inhibition activity on MCF-7 proliferation with moderate AlkP activity and no potential uterotrophic effects. The in vitro estrogenic activity encourages further investigations toward potential beneficial properties in cardiovascular, bone, and brain tissues.     

CTAB-assisted hydrothermal synthesis of NiFe2O4 and its magnetic characterization

A simple hydrothermal route is demonstrated for the synthesis of nickel ferrite nanocrystals, NiFe₂O₄, using cetyltrimethylammonium bromide (CTAB) as the surfactant and NH₃ and NaOH as hydrolyzing agents. Synthesized materials have been characterized by XRD, FTIR, ESR, and TEM techniques. It was found that crystallization in both hydrolyzing agent led to nanometric in size. Average particle size of prepared samples was calculated from TEM micrographs and varied significantly between samples prepared using different hydrolyzing agents; it was 12 nm when conc. NH₃ was used and 50 nm when 2 M NaOH was used. Crystallite size obtained using Scherrer equation agreed well with the TEM observations with the respective values of 15 and 55 nm. ESR analysis showed single broad bands which might indicate the phase homogeneity of the materials. Furthermore, linewidths were observed to differ due to the difference in magnetization that depends on the particle size; NiFe₂O₄ sample hydrolysed with NH₃ has a larger linewidth revealing its smaller particle size as confirmed by XRD and TEM techniques.