A novel luminophor and host polymer from fluorene-carbazole derivatives for preparing solution-processed non-doped blue and closed-white light devices

A novel blue light emitting polymer was designed and synthesized via alternative conjugated 9,9-dioctylfluorene and 9-(6-(9H-carbazol-9-yl)hexyl)-9H-carbazole, named PF2Cz. It exhibited high thermal stability, good film morphology and strong deep-blue emission peaks at 408 and 429?nm in film. The triplet energy level of PF2Cz (E_T?=?2.30?eV) was also improved. Non-doped and doped devices were both prepared by solution process to characterize the electroluminescent (EL) properties of PF2Cz. In non-doped devices, PF2Cz acted as blue emitter which exhibited a Commission Internation de L'Eclairage (CIE) coordinate of (0.164, 0.102) and a external quantum efficiency (EQE) values of 1.28%. Moreover, the doped phosphorescent devices utilized PF2Cz as host material obtained a closed-white light emission with a content of 1?wt% dopant. All these results indicated that the fluorene-carbazole derivatives could be a promising molecular design strategy for the synthesis of blue light and host organic semiconductors.     

Resorcinarene‐based ATRP initiators for star polymers

Two novel multifunctional initiators for atom transfer radical polymerization (ATRP) were synthesized by derivatization of tetraethylresorcinarene. The derivatization induced a change in the conformation of the resorcinarene ring, which was confirmed by NMR spectroscopy. The initiators were used in ATRP of tert‐butyl acrylate and methyl methacrylate, producing star polymers with controlled molar masses and low polydispersities. Instead of the expected star polymers with eight arms, polymers with four arms were obtained. Conformational studies on the initiators by rotating‐frame nuclear Overhauser and exchange spectroscopy NMR and molecular modeling suggested that of eight initiator functional groups on tetraethylresorcinarene, four are too close to each other to be able to initiate the chain growth. Starlike poly(tert‐butyl acrylate) macroinitiators were used further in the block copolymerization of methyl methacrylate. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4189–4201, 2004     

Folding Patterns in a Family of Oligoamide Foldamers

A series of small, unsymmetrical pyridine‐2,6‐dicarboxylamide oligoamide foldamers with varying lengths and substituents at the end groups were synthetized to study their conformational properties and folding patterns. The @‐type folding pattern resembled the oxyanion‐hole motifs of enzymes, but several alternative folding patterns could also be characterized. Computational studies revealed several alternative conformers of nearly equal stability. These folding patterns differed from each other in their intramolecular hydrogen‐bonding patterns and aryl–aryl interactions. In the solid state, the foldamers adopted either the globular @‐type fold or the more extended S‐type conformers, which were very similar to those foldamers obtained computationally. In some cases, the same foldamer molecule could even crystallize into two different folding patterns, thus confirming that the different folding patterns are very close in energy in spite of their completely different shapes. Finally, the best match for the observed NOE interactions in the liquid state was a conformation that matched the computationally characterized helix‐type fold.     

Structural Hierarchy and Polymorphic Transformation in Shear‐Induced Shish‐Kebab of Stereocomplex Poly(Lactic Acid)

The realization of hierarchical shish‐kebab structures for stereocomplex poly(lactic acid) (PLA) is achieved by the application of a shear flow (100 s^–1 for 1 s) mimicking what can be expected during polymer processing. Compared to the normal shearing scenarios, this transient and strong shear flow enables the creation of dense shish precursors in time‐ and energy‐saving manner. The distribution of crystal form associated with the hierarchical structure is revealed by 2D Fourier transform infrared spectroscopy imaging, creating a unique visualization for both spatial resolution and polymorphism identification. Interestingly, in the shear stereocomplex chains are preferentially extended and crystallized as stable central cores with weak temperature dependence, whereas the development of lateral kebabs is defined by the distinct relation to the crystallization temperature. Below the melting point of homocrystals, both homo and stereocomplex crystallization are engaged in lamellar packing. Above that, exclusive stereocomplex crystals are organized into ordered lamellae. Combining the direct observations at multiscale, the ordered alignment of stereocomplex chains is recognized as the molecular origin of fibrillar extended chain bundles that constitute the central row‐nuclei. The proposed hypothesis affords elucidation of shish‐kebab formation and unique polymorphism in sheared stereocomplex PLA, which generates opportunities for engendering hierarchically structured PLA with improved performance.

     

Biodegradation of Starch-Based Materials

Abstract

The aim of this study was to compare three different test methods for assaying the biodegradability of starch-based materials. The materials tested included some commercial starch-based materials and thermoplastic starch film prepared by extrusion from native potato starch and glycerol. Enzymatic hydrolysis was performed using excess Bacillus licheniformis α-amylase and Aspergillus niger glucoamylase at 37°C. The degree of degradation was assayed by measuring the dissolved carbohydrates and the weight loss of the samples. The head-space test was based on carbon dioxide evolution using sewage sludge as an inoculum. The composting experiments were carried out in an insulated commercial composter bin. The degradation was evaluated visually at weekly intervals, and the weight loss of the samples was measured after composting. Good correlation was found among the three different test methods.     

Structural studies on lithocholyl-N-(2-aminoethyl)amide in the solid state

The synthetic procedure of lithocholyl-N-(2-aminoethyl)amide yielded a mixture of several forms detected by solid state ¹³C CP/MAS NMR although the solution state NMR unambiguously ascertained that the compound was pure. By recrystallization from various solvents one pure polymorph alongside with four solvates were isolated. The structures of the pure polymorph and the solvates were characterized by ¹³C and ¹⁵N CP/MAS NMR and powder X-ray diffraction (PXRD) methods. Variable contact time and dipolar dephasing experiments were employed to obtain optimized CP parameters and to distinguish various CH _n (n = 0–3) resonances. CSA analyses of spinning side bands at different spinning rates showed small variations in the shielding tensor values of the carbonyl group between the pure polymorph (recrystallized from acetonitrile, tetrahydrofuran and 1,4-dioxane) and p-xylene solvate.     

Miscibility and surface segregation in PVC/polyester blends—The influence of chain architecture and composition

Four poly(butylene adipate) (PBA) polyesters, the structure ranging from linear to highly branched, were synthesized and solution casted with poly(vinyl chloride) (PVC) in 20 or 40 wt % concentrations to evaluate the influence of polyester chain architecture on miscibility, surface segregation, and mechanical properties. The miscibility of PVC and polyesters is based on specific interactions between the carbonyl group in the polyester and PVC. These interactions cause a shift in the carbonyl absorption band in the FTIR spectra. The shifting of the carbonyl absorption band was more significant for all the 40 wt % blends compared with the blends containing 20 wt % of the same polyester. In the 20 wt % blends surface segregation and enrichment of polyester at the blend surface increased as a function of branching. However, all the films containing 40 wt % of polyester had similar surface composition. This is explained by better miscibility and stronger intermolecular interactions in the 40 wt % blends, which counteract the effect of branching on the surface segregation. High degree of branching resulted in poor miscibility with PVC and poor mechanical properties. A linear or slightly branched polyester structure, however, resulted in good miscibility and desirable blend properties. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1552–1563, 2007     

化学模拟唯铁氢化酶研究进展

氢化酶(hydrogenase,简称H2ase)是一类存在于微生物体内的重要生物酶,它可以催化氢的氧化反应,也可以催化还原质子产生氢气.根据氢化酶活性中心金属的不同,可以大致分为三类:Fe-Fe氢化酶,Ni-Fe氢化酶和不含金属的氢化酶.本文主要介绍近年来唯铁(Fe-Fe)氢化酶的结构研究和化学模拟最新进展.     

Phase separation and crystallinity in proton conducting membranes of styrene grafted and sulfonated poly(vinylidene fluoride)

A series of proton exchange membranes have been prepared by the preirradiation grafting method. Styrene was grafted onto a matrix of poly(vinylidene fluoride) (PVDF) after electron beam irradiation. Part of the samples was crosslinked with divinylbenzene (DVB) or bis(vinylphenyl)ethane (BVPE). Subsequent sulfonation gave membranes grafted with poly(styrene sulfonic acid) and marked PVDF‐g‐PSSA. It was found that the intrinsic crystallinity of the matrix decreased in both the grafting and the sulfonation reaction in all the membranes. The graft penetration and the ion conductivity are influenced strongly by the crosslinker. The ion conductivity is considerably lower in crosslinked membranes than in noncrosslinked ones. Generally, the mechanical strength decreases with crosslinking. The membranes show a regular phase separated structure in which the sulfonated grafts are incorporated in the amorphous parts of the matrix polymer. The phase separated domains are small, of the order of magnitude of 100–250 nm. These were resolved on transmission electron micrographs and on atomic force images but could not be resolved with microprobe Raman spectroscopy. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1741–1753, 1999     

Calcium dicaesium silver thio­cyanate dihydrate

The title compound, CaCs₂[Ag₂(SCN)₆]·2H₂O, forms a continuous structure where the Ag atoms form chains with S atoms in the c‐axis direction. The chains are bonded together through Cs and Ca atoms. The crystal water of the structure is bonded to the Ca atoms, which lie on centers of symmetry.