Formation of higher cyclic oligomers in polyamide‐4,6

An example of morphology‐steered chemistry of cyclic oligomers with the example of polyamide‐4,6 (PA46) is discussed in this article. The cyclic oligoamide profiles of solid‐state post condensed PA46 show an unusual maximum for intermediate cycles consisting of 10 and 12 amide groups, which are formed in the initial stage of solid state post condensation. This is explained from the short chain length at the start of the post condensation, the preorganization of linear oligomers in the lamellar crystal structure, and the occurrence of amide units in the PA46 lamellar folds. Further the development of the cyclic oligomers up to the cyclic hexadecamide is followed on heating the base polymer in the melt at 310 °C, where it showed to react back to the theoretical Jacobsen and Stockmayer distribution. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of porphyrin‐end‐functionalized polycyclohexane with well‐controlled and defined polymer chain structure

Tetraphenylporphyrin‐end‐functionalized polycyclohexane (H₂TPP‐PCHE) and its metal complexes (MTPP‐PCHE) were synthesized as the first successful example of porphyrin‐end‐functionalized transparent and stable polymers with a well‐controlled and defined polymer chain structure. Chloromethyl‐end‐functionalized poly(1,3‐cyclohexadiene) (CM‐PCHD) was synthesized as prerequisite prepolymer by the postpolymerization reaction of poly(1,3‐cyclohexadienyl)lithium and chloro(chloromethyl)dimethylsilane. CM‐end‐functionalized PCHE (CM‐PCHE) was prepared by the complete hydrogenation of CM‐PCHD with p‐toluenesulfonyl hydrazide. H₂TPP was incorporated onto the polymer chain end by the addition of 5‐(4‐hydroxyphenyl)‐10,15,20‐triphenylporphyrin to CM‐PCHE. The complexation of H₂TPP‐PCHE and Zn(OAc)₂ (or PtCl₂) yielded a zinc (or platinum) complex of H₂TPP‐PCHE. H₂TPP‐PCHE and MTPP‐PCHE were readily soluble in common organic solvents, and PCHE did not inhibit the optical properties of the H₂TPP, ZnTPP, and PtTPP end groups. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation of poly(p‐oxybenzoyl) crystals using direct polymerization of p‐hydroxybenzoic acid in the presence of boronic anhydrides

Poly(p‐oxybenzoyl) (POB) crystals were prepared by reaction‐induced crystallization during direct polymerization of p‐hydroxybenzoic acid in the presence of boronic anhydrides. Polymerizations were carried out at 300 °C in dibenzyltoluene at a concentration of 1% with three kinds of anhydrides of boronic acid such as 3,4,5‐trifluorophenylboronic acid (TFB), 4‐methoxyphenylboronic acid (MPB) and 4‐biphenylboronic acid (BPB). The POB crystals were formed as precipitates in the solution and the morphology was considerably influenced by both the structure of the boronic anhydride and its concentration (c_B). Needle‐like crystals were firmed in the presence of TFB anhydride (TFBA) at c_Bs of 5 and 10 mol % by the spiral growth of lamellae. Spherical aggregates of slab‐like crystals were formed at c_Bs from 50 to 100 mol %. The polymerization with MPB anhydride and BPB anhydride (BPBA) also yielded the needle‐like crystals at c_Bs of 50 and 5 mol %, respectively. The polymerization with TFBA at lower c_B was favorable to prepare the needle‐like crystal. Molecular weight was also influenced by the structure of the boronic anhydride and c_B. M_n increased generally with c_B and BPBA gave the highest M_n of 14.7 × 10³ at c_B of 100 mol %. The loose packing of the molecules in the crystal caused by the bulkiness of the end‐groups made the polymerization in the crystals more efficiently. Morphology and molecular weight of the POB crystals could be controlled by the chemical structure and the content of boronic anhydride. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Economy of proficiency testing: reference versus consensus values

Many proficiency tests are operated with a consensus value derived from the participants’ results. Apart from technical issues, one of the reasons often mentioned is that proficiency tests operated with consensus values would be cheaper than those using reference values obtained from a priori characterisation measurements. The economy of a proficiency test must of course be balanced by the need of the participants, and the quality of the comparison in general. The proficiency tests selected in this study had both a reference value and a consensus value, one of which was used for assessing the performance of the participating laboratories. In this work, both a technical and an economical assessment of how the comparisons were operated is made. From the evaluation, it follows that usually the use of consensus values does not necessarily reduce the costs of a proficiency test. However, frequently it may be observed that the quality of the assessment of the laboratories is better with a reference value. Received: 11 October 2000 Accepted: 3 January 2001     

An analytical method for prohexadione in Chinese cabbage and apple

A residual determination method as a regulatory residue method was developed using HPLC‐UVD for prohexadione residues in Chinese cabbage (Brassica pekinensis) and apple (Malus domestica). The developed method consisted of solid–liquid extraction with acidic acetonitrile and ion‐suppression liquid–liquid partitioning, followed by anion exchange cartridge cleanup. The limits of detection and quantitation for the method were 0.005 and 0.02 mg/kg, respectively. The method gave good linearity in the range of 0.02–2.5 mg/kg. Accuracy and precision ranged from 84.1 to 94.1% and from 2.4 to 6.9%, respectively. Additionally, the confirmative conditions of LC‐MS/MS for prohexadione were set in negative electrospray ionization mode with transitions of m/z 211.4 → 167.5 and m/z 211.4 → 123.5 in the selected reaction monitoring mode. The applicability of the method was demonstrated by analyzing real samples collected from local markets in Seoul, Republic of Korea. This developed method fully deserves consideration in accordance with its sensitivity, accuracy and precision required for residue analysis of prohexadione in Chinese cabbages and apples. Copyright © 2010 John Wiley & Sons, Ltd.     

Impact of average photon-energy coefficient of solar spectrum on the short circuit current of photovoltaic modules

The output energy of photovoltaic (PV) modules is influenced by the spectral irradiance distribution of the solar spectrum under outdoor conditions. To rate the precise output energy of PV modules, the correction of short circuit current (I_SC) based on actual environmental conditions is needed, because I_SC significantly depends on the shape of the spectral irradiance distribution. The average photon energy (APE) is a zero-dimensional index for spectral irradiance distribution, and APE value uniquely describes the shape of a solar spectrum. Thus, APE has an impact on I_SC of PV modules. In this contribution, the relationship between APE coefficient and I_SC of the multi-crystalline silicon, single-crystalline silicon, heterojunction intrinsic thin-layer, back contact, copper indium selenide and cadmium telluride PV modules has explored. It is revealed that APE value changes the I_SC of PV modules which appeared to have immense possibilities of I_SC correction using APE coefficient. This new approach can be very effective for precise rating the output energy of PV modules under actual outdoor conditions.     

Investigation of water absorption in clay-reinforced polypropylene nanocomposites

The behaviour of polypropylene nanocomposites containing different amounts of commercial nanoclay upon exposure to distilled water and sea water at different temperatures was investigated and compared with that of neat polypropylene. In the initial stages, the weight gain (moisture absorption) follows Fick's second law, but at longer times deviations are observed owing to physical degradation and in some cases a loss of mass. Distilled water diffuses more rapidly than sea water. As the nanoclay content increases, both the rate of moisture absorption and the maximum moisture content increase, owing to the hydrophilic nature of the nanoclay and the added compatibilizing agent. Although the moisture absorption decreases the flexural properties of both the nanocomposites and neat PP, because the unexposed (as-moulded) nanocomposites are significantly superior to the neat PP they remain so even after prolonged exposure.     

Evaluation of various fire retardants for use in wood flour-polyethylene composites

Wood-plastic composites represent a growing class of materials used by the residential construction industry and the furniture industry. For some applications in these industries, the fire performance of the material must be known, and in some cases improved. However, the fire performance of wood-plastic composites is not well understood, and there is little information regarding the effectiveness of various fire retardants in the public domain. We used oxygen index and cone calorimeter tests to characterize the fire performance of wood flour-polyethylene composites, and compared the results with unfilled polyethylene and solid wood. We then evaluated the effect of five additive-type fire retardants on fire performance. Generally, magnesium hydroxide and ammonium polyphosphate improved the fire performance of WPCs the most while a bromine-based fire retardant and zinc borate improved fire performance the least.     

Development and Application of Ultra Performance Liquid Chromatography Method to the Quantification of the Biotransformation of Methyl Paraben in Eisenia foetida

A simple and quick ultra performance liquid chromatography method (UPLC) has been developed for determination of methyl paraben (MP) and its major metabolites p‐hydroxybenzoic acid (pHBA) and phenol (Phe), following its biotransformations in Eisenia foetida. After different exposure time to paper contact test, the presence of methyl paraben and his biotransformation products in adult earthworms was monitored. Determination of its metabolites was achieved with a BEH (bridged ethane‐silicon hybrid) C₁₈ column (2.1×50 mm i.d., 1.7 µm particle size), using methanol/water/phosphoric acid as mobile phase, under a gradient elution program, and a PDA (photo‐diode array) detection (quantification with MaxPlot in the range 210–400 nm). The absorption of MP did not exceed 30% and in the first 4–6 h after exposure only minute amounts of pHBA and Phe were detected in the worm homogenates. After 48 h of exposures, almost 70% of absorbed MP was already metabolized to Phe and around 20% could be found as pHBA.