The synthesis of highly strained [5]cycloparaphenylene ([5]CPP), a structural unit of the periphery of C60 and the shortest possible structural constituent of the sidewall of a (5,5) carbon nanotube, was achieved in nine steps in 17% overall yield. The synthesis relied on metal-mediated ring closure of a triethylsilyl (TES)-protected masked precursor 1c followed by removal of the TES groups and subsequent reductive aromatization. UV-vis and electrochemical studies revealed that the HOMO-LUMO gap of [5]CPP is narrow and is comparable to that of C60, as predicted by theoretical calculations. The results suggest that [5]CPP should be an excellent lead compound for molecular electronics.

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Cyclic precursors of cycloparaphenylenes (CPPs) containing 1,4-dihydroxy-2,5-cyclohexadien-1,4-diyl units are prepared by modifying a synthetic method developed by Jasti and co-workers for the synthesis of corresponding 1,4-dimethoxy derivatives. Reductive aromatization of the diyl moieties by SnCl2/2 HCl takes place under mild conditions and affords the CPPs in good yields, incorporating 5 or 7-12 phenylene units. Highly strained [5]CPP is synthesized in greater than 0.3 g scale. (119)Sn NMR spectroscopy clarifies the in situ formation of an ate complex, H2SnCl4, upon mixing a 2:1 ratio of HCl and SnCl2, which serves as a highly active reducing agent under nearly neutral conditions. When more than 2 equivalents of HCl, in relation to SnCl2, are used, acid-catalyzed decomposition of the CPP precursors takes place. The stoichiometry of HCl and SnCl2 is critical in achieving the desired aromatization reaction of highly strained CPP precursors.

A modelagem de equaes estruturais (Structural Equation Modeling -SEM) cada vez mais usada como um mtodo para a conceituao e desenvolvimento de aspectos tericos nas cincias sociais aplicadas, em particular na rea de marketing, pois mais e mais h a necessidade de avaliar vrios constructos e relaes latentes complexas. Tambm, constructos de segunda ordem podem ser modelados fornecendo uma melhor compreenso terica de relaes com boa parcimnia. Modelagens do tipo SEM so, em particular, bem adequadas para investigar as relaes complexas entre os vrios constructos. Os dois mtodos analticos SEM mais prevalentes so os baseados em covarincia SEM (CB-SEM) e os baseados em varincia SEM (PLS-SEM). Embora cada tcnica tenha suas vantagens e limitaes, neste artigo vamos nos concentrar no CB-SEM com o AMOS para ilustrar sua aplicao na anlise das relaes entre orientao para o cliente, a orientao para os funcionrios e desempenho da empresa. Tambm ser demonstrado como constructos de segunda ordem so teis para modelar os componentes de pr-atividade e responsividade dessas relaes.DOI: 10.5585/remark.v13i2.2718

Well-defined amphiphilic poly(ε-caprolactone)-b-poly(N-vinylpyrrolidone) (PCL-b-PNVP) block copolymers were successfully prepared via the combination of ring-opening polymerization (ROP) and xanthate-mediated reversible additionÀfragmentation chain transfer (RAFT) polymerization. Well-defined poly(ε-caprolactone) (PCLÀOH) was synthesized by ROP in bulk at 110 °C using benzyl alcohol as initiator and stannous octate [Sn(Oct) 2 ] as catalyst . The ÀOH end group was then converted into its corresponding xanthate (PCLÀX) via the conversion to its corresponding bromide (PCLÀBr). These are verified by 1 H NMR spectroscopy. PCL-b-PNVP block copolymers were synthesized via RAFT polymerization in tetrahydrofuran (THF) at 80 °C using PCLÀX as macro-chain transfer agent and characterized by 1 H NMR spectroscopy and gel permeation chromatography (GPC). The amphiphilic diblock copolymer PCL 63 -b-PNVP 90 forms spherical micelles of ∼34 nm diameter in water as shown by transmission electron microscopy (TEM), supported by 1 H NMR spectroscopy, and light scattering. The critical micellar concentrations were determined by fluorescence spectroscopy using pyrene as probe. The critical micelle concentration (cmc) value of the block copolymers increases with the increase in the chain length of PNVP block. The overall hydrodynamic radius (R h ) of the micelles remains almost constant over the concentration range above the cmc value and over the angles of scattering measurement.

Macroporous poly(N-isopropylacrylamide) (PNIPAM) hydrogels have been prepared in methanol-water (1:1, v/v) mixture in the presence of 0, 0.05, 0.1, 0.15, and 0.2 M Y(OTf)(3) Lewis acid concentrations. Synthesis of the corresponding linear PNIPAM homopolymers in the absence of a cross-linker keeping all other conditions the same shows that the isotacticity (meso dyad, %) and the cloud point temperature of the resulted in polymers increases and decreases, respectively, with the increase in the concentration of the Lewis acid. SEM micrographs reveal that the resulted hydrogels are highly porous. Swelling ratios of all the hydrogels in water decrease with the increase in the temperature. Moreover, swelling ratios of all the hydrogels in different methanol-water mixtures pass through a minimum in the co-nonsolvency zone, and the co-nonsolvency zone shifts toward the lower methanol-content solvent mixture with gradual increase in the Lewis acid concentration. Deswelling rate of the hydrogel prepared in methanol-water (1:1, v/v) mixture is much faster than that of the conventional hydrogel prepared in water. Moreover, the deswelling rate slightly increases with the hydrogels prepared with the increasing concentrations of Lewis acid. But, the reswelling rate of the hydrogels follows almost the reverse order. All these results have been explained on the basis of the formation of highly porous hydrogels with higher isotactic PNIPAM chain segment owing to the faster polymerization rate in the methanol-water mixture in the presence of Lewis acid and the co-nonsolvency behavior of the methanol-water (1:1, v/v) mixture toward PNIPAM chain segment in the PNIPAM hydrogel.

Poly(N‐isopropylacrylamide) (PNIPAM) hydrogels were simply prepared by free radical polymerization in different methanol–water mixture. A scanning electron microscopy study revealed that the freeze‐dried hydrogels were macroporous. The swelling ratios in water at 20°C of the resulting hydrogels followed the order: X0.43>X0.21>X0.76 ≈ X0.57>X0.31>X0.13>X0.06>X0, where Xm denotes a gel prepared in a methanol–water mixture with m mole fraction of methanol (xm). Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with the increase in the temperature. The complete collapse of the PNIPAM chain of all the gels occurred at about 38°C, whereas the same was observed at about 35°C for the conventional gel prepared in water. The swelling ratio values of all the PNIPAM gels in the methanol–water mixtures with different xm values at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X0.43> X0.31> X0.21> X0.57> X0.76 ≈ X0.13> X0.06> X0. The reswelling rates of these hydrogels decreased in the following order: X0> X0.31> X0.06 ≈ X0.13 > X0.76> X0.57> X0.21> X0.43. The release rates of the Tramadol Hydrochloride drug at 37°C from the drug‐loaded hydrogels were almost same for all of the hydrogels. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

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