Preparation and Flame Retardancy Properties of Novel PA12 and PE/Layered Titanoniobates Nanocomposites

Summary: We report herein a study performed on a layered titanoniobate KTiNbO₅ modified by octadecylamine to evaluate the fire retardancy properties of this novel hybrid nanofiller dispersed in PA12 and LLDPE, by polymer melt intercalation. The nanocomposites have been characterized using Electron Microscopy techniques to evaluate the degree of exfoliation and the morphologies. Thermogravimetric analyses and cone calorimeter tests have been carried out to assess the fire retardant performances.     

Potentially <Emphasis Type="Italic">K</Emphasis><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript> — <Emphasis Type="Italic">G</Emphasis>-graphical sequences: A survey

The set of all non-increasing nonnegative integer sequences π = (d(v ₁), d(v ₂), …, d(v _n )) is denoted by NS _n . A sequence π ∈ NS _n is said to be graphic if it is the degree sequence of a simple graph G on n vertices, and such a graph G is called a realization of π. The set of all graphic sequences in NS _n is denoted by GS _n . A graphical sequence π is potentially H-graphical if there is a realization of π containing H as a subgraph, while π is forcibly H-graphical if every realization of π contains H as a subgraph. Let K _k denote a complete graph on k vertices. Let K _m −H be the graph obtained from Km by removing the edges set E(H) of the graph H (H is a subgraph of K _m ). This paper summarizes briefly some recent results on potentially K _m −G-graphic sequences and give a useful classification for determining σ (H, n).     

双参数对数正态分布异常数据的检测方法

针对双参数对数正态分布场合下的多个异常数据给出一种新的检测方法。首先由参数的BLUE导出证明了两个检验所用的枢轴量,然后通过蒙特卡罗方法模拟得到枢轴量的样本分位点表,最后用一个例子说明方法是有效可行的。     

New norditerpenoids from Cespitularia hypotentaculata

Four new norditerpenoids, designated as cespihypotins A (1), B (2), C (3) and D (4), were isolated from Cespitularia hypotentaculata Roxas (Xeniidae) that was collected in Taiwan. Compounds 1 and 2 are unprecedented structures having 13- and 14-membered lactone ring, respectively. Their structures were elucidated on the basis of extensive spectroscopic analysis. A plausible biogenetic pathway for compounds 1-4 was also proposed.     

Self-assembly of beta-cyclodextrin in water. Part 1: Cryo-TEM and dynamic and static light scattering

In this article, we report evidence of beta-cyclodextrin (beta-CD) self-aggregation in water. A critical aggregation concentration (cac) between 2 and 3 mM was determined by using dynamic (DLS) and static (SLS) light scattering to investigate the presence of beta-cyclodextrin aggregates. Transmission electron microscopy at cryogenic temperature (Cryo-TEM) was used to detect the structural features of cyclodextrin self-aggregates. The results show the occurrence of polymorphism depending on the beta-CD concentration: polydisperse nearly spherical objects with diameters of about 100 nm are present at lower concentrations, whereas micrometer planar aggregates are predominant at higher concentrations.     

Effect of 2,6-disubstituted aryl groups on acyclic conformation: preference for an antiperiplanar orientation of the geminal and vicinal hydrogens

Multiple X-ray crystallographic and 1H NMR spectroscopic studies demonstrate that 2,6-disubstituted aryl groups exert a strong effect on acyclic conformation, inducing the geminal and vicinal hydrogens on the adjacent sp3-sp3 C-C bond to adopt an antiperiplanar orientation. Twenty-one examples comprising nitrile, ketone, and dithiane aldols are provided. A search of the Cambridge Structural Database uncovered an additional 11 examples of this effect. This preference causes some unanticipated remote effects on acyclic conformations: in anti-nitrile aldols, this effect causes 2,6-disubstituted aryls to generally prefer a gauche, rather than antiperiplanar, relationship to the largest vicinal groups. X-ray crystallography, 1H-1H NOESY spectroscopy, and computation demonstrate that minimization of allylic 1,3-strain and syn-pentane-like interactions work together in establishing this conformational preference.     

Efficient route to 4a-methyltetrahydrofluorenes: a total synthesis of (+/-)-dichroanal B via intramolecular Heck reaction

An efficient new route based on intramolecular Heck cyclization of the diene 11 was developed to prepare the 4a-methyltetrahydrofluorene diterpenoids and utilized for the total synthesis of (+/-)-dichroanal B with significantly improved overall yield.     

High-throughput analysis of bergamot essential oil by fast solid-phase microextraction-capillary gas chromatography-flame ionization detection

The advantages of using a narrow-bore column in headspace solid-phase microextraction-gas chromatographic (HS-SPME-GC) analysis are investigated. An automated rapid HS-SPME-GC method for the determination of volatile compounds in a complex sample (bergamot essential oil) was developed. A low-capacity (7 microm) SPME fibre was employed, enabling a short equilibration time (15 min). The absorbed volatile compounds were then separated in 12.5 min on a 10 m x 0.1 mm I.D. capillary. The fast GC method was characterized by relatively moderate GC parameters (head pressure: 173 kPa; temperature program rate: 12 degrees C/min). The employment of the low-capacity fibre also suited the reduced sample capacity of the capillary employed, hence column overloading was avoided. Analytical repeatibility was determined in terms of retention times (maximum RSD: 0.32%) and peak areas (maximum RSD: 9.80%). The results obtained were compared to those derived from a conventional HS-SPME-GC (a 30 microm SPME fibre and 0.25 mm I.D. capillary were used) application on the same sample. In this respect, a great reduction of analytical time was obtained both with regard to the conventional SPME equilibration and GC run times, which both required 50 min. Peak resolution was altogether comparable in both applications. Although a slight loss in terms of sensitivity was observed in the rapid approach (generally within the 25-50% range), this did not impair the detection of all peaks of interest. Finally, the selectivities of the 30 and 7 microm fibres were evaluated and, as expected, these were in good agreement.     

Morphology of hybrid polystyrene-block-poly(ethylene oxide) micelles: analytical ultracentrifugation and SANS studies

Morphology and structure of aqueous block copolymer solutions based on polystyrene-block-poly(ethylene oxide) (PS-b-PEO) of two different compositions, a cationic surfactant, cetyl pyridinium chloride (CPC), and either platinic acid (H2PtCl6.6H2O) or Pt nanoparticles were studied using a combination of analytical ultracentrifugation (AUC), transmission electron microscopy (TEM), and small angle neutron scattering (SANS). These studies combining methods contributing supplemental and analogous structural information allowed us to comprehensively characterize the complex hybrid systems and to discover an isotope effect when H2O was replaced with D2O. In particular, TEM shows formation of both micelles and larger aggregates after incorporation of platinic acid, yet the amount of aggregates depends on the H2PtCl6.6H2O concentration. AUC reveals the presence of micelles and micellar clusters in the PS-b-PEO block copolymers solution and even larger (supermicellar) aggregates in hybrids (with CPC). Conversely, SANS applied to D2O solutions of the similar species indicates that micelles are spherical and no other micellar species are found in block copolymer solutions. To reconcile the SANS and AUC data, we carried out AUC examination of the corresponding D2O block copolymer solutions. These measurements demonstrate a pronounced isotope effect on micelle aggregation and micelle size, i.e., no micelle aggregation in D2O solutions, revealing good agreement of AUC and SANS data.