Copolymerization of styrene and ethylene with mononuclear and dinuclear half-titanocenes

With mononuclear half-titanocenes such as CpTiCl₃, IndTiCl₃, and Me₅CpTiCl₃, as well as the constrained geometry catalyst (CGC) and a new dinuclear hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride) (TSDT), the copolymerization of styrene and ethylene was examined. The thermal properties and structure of copolymerization products were investigated with differential scanning calorimetry and ¹³C-nuclear magnetic resonance. In addition, the raw polymer was separated into homopolymer and copolymer with an extraction method and cross fractionation chromatography. With the above analysis, it was concluded that the raw polymer obtained with CpTiCl₃ and IndTiCl₃ was a mixture of syndiotactic polystyrene and polyethylene homopolymers with 10–30 wt % copolymer, whereas that produced by Me₅CpTiCl₃ and TSDT was a homopolymer mixture with a negligible amount of copolymer. Only CGC produced the copolymer of styrene and ethylene perfectly. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2187–2198, 1998     

A new higher-order hybrid-mixed curved beam element

The purpose of this work is to show the successful use of nodeless degrees of freedom in developing a highly accurate, locking free hybrid-mixed C⁰ curved beam element. In the performance evaluation process of the present field-consistent higher-order element, the effect of field consistency and the role of higher-order interpolation on both displacement-type and hybrid-mixed-type elements are carefully examined. Several benchmark tests confirm the superior behaviour of the present element. © 1998 John Wiley & Sons, Ltd.     

Surface reaction on polyvinylidenefluoride (PVDF) irradiated by low energy ion beam in reactive gas environment

Polyvinylidenefluoride (PVDF) was irradiated by a keV Ar⁺ ion in O₂ environment for improving adhesion between PVDF and Pt, and reaction between PVDF and the ion beam has been investigated by X‐ray photoelectron spectroscopy (XPS). The adhesion test between Pt and the modified PVDF was carried out by boiling test, in which the specimens were kept in boiling water for 4 h. Two failure modes (buckling up due to weak adhesion and crack formation due to strong adhesion) of Pt films have been observed in the system. Contact angle of PVDF was reduced to 31 from 75° by the irradiation of 1 × 10¹⁵ Ar⁺ ions/cm² with oxygen flow rate of 8 sccm. The surface of the irradiated PVDF became more rough as ion dose increased. The improved adhesion mechanism and identification of newly formed chemical species have been confirmed by Carbon 1s and Fluorine 1s X‐ray photoelectron core‐level spectra. The main reaction occurred at the irradiated PVDF surface is an ion‐beam‐induced oxidation accompanied with preferential sputtering of fluorine. Newly formed chemical species at interface are regarded as ester and carboxyl groups. Adhesion of the Pt–PVDF interface was improved by ion irradiation in O₂ environment. This improvement is originated from the presence of carbon—oxygen bonds on the irradiated PVDF surface. Comparison of failure modes on the irradiated PVDF at various conditions after the boiling test shows that adhesion of Pt film is largely affected by the product of ion‐assisted reaction. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 41–47, 1999     

Effects of chemical reactions on the properties of polycarbonate/liquid crystalline polymer blends

Effects of chemical reactions on the properties of the polycarbonate (PC)/liquid crystalline polymer (LCP) blends are considered here. Not only thermal and rheological behaviors, but also morphology and molecular weight change are investigated. Reactive blends were prepared in a cylindrical flask at 300°C with varying processing time in the presence of a catalyst by the melt-phase reactions. For comparison, physical blends, in which chemical reactions were minimized, were also prepared at 300°C in a twin-screw extruder. It seems that transesterification and repolymerization did not occur, but depolymerization reaction took place slightly in PC/LCP physical blends. In reactive blends, however, transesterification and repolymerization as well as depolymerization reaction took place simultaneously. The depolymerization reaction occurred mainly at an early stage of processing; whereas, repolymerization reaction becomes especially dominant after some time (more than 30 min) in the presence of the catalyst, which had a great impact on its molecular weight. Also, chemical reactions changed the glass transition temperature and morphology as well as rheological behavior, which resulted in the enhanced miscibility in reactive blends. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2123–2133, 1999     

Effect of dialcohols on properties of poly(ethylene 2,6‐naphthalate) copolymers

Properties of poly(ethylene 2,6‐naphthalate) (PEN) and its copolymers containing diethylene glycol (DEG), propanediol (PD), butanediol (BD), and bisphenol A ethoxylate (BSA) were investigated. The copolymer composition was determined by ¹H‐NMR spectroscopy. It has a higher value than the feed composition due to the high volatility of ethylene glycol (EG). The melting temperature of the copolymers was gradually depressed with the increase of dialcohol in the composition. The complex viscosity of the copolymers did not depend on the molecular weight, but on the chemical structure. The complex viscosity of the copolymers containing 3 mol % of DEG, BD, and 5 mol % of BD was lower than that of PEN, and the mechanical properties were similar with the value of PEN. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2900–2905, 1999     

Korean Red Ginseng Improves Astrocytic Mitochondrial Function by Upregulating HO-1-Mediated AMPKα–PGC-1α–ERRα Circuit after Traumatic Brain Injury

Heme oxygenase-1 (HO-1) exerts beneficial effects, including angiogenesis and energy metabolism via the peroxisome proliferator-activating receptor-γ coactivator-1α (PGC-1α)–estrogen-related receptor α (ERRα) pathway in astrocytes. However, the role of Korean red ginseng extract (KRGE) in HO-1-mediated mitochondrial function in traumatic brain injury (TBI) is not well-elucidated. We found that HO-1 was upregulated in astrocytes located in peri-injured brain regions after a TBI, following exposure to KRGE. Experiments with pharmacological inhibitors and target-specific siRNAs revealed that HO-1 levels highly correlated with increased AMP-activated protein kinase α (AMPKα) activation, which led to the PGC-1α-ERRα axis-induced increases in mitochondrial functions (detected based on expression of cytochrome c oxidase subunit 2 (MTCO2) and cytochrome c as well as O₂ consumption and ATP production). Knockdown of ERRα significantly reduced the p-AMPKα/AMPKα ratio and PGC-1α expression, leading to AMPKα–PGC-1α–ERRα circuit formation. Inactivation of HO by injecting the HO inhibitor Sn(IV) protoporphyrin IX dichloride diminished the expression of p-AMPKα, PGC-1α, ERRα, MTCO2, and cytochrome c in the KRGE-administered peri-injured region of a brain subjected to TBI. These data suggest that KRGE enhanced astrocytic mitochondrial function via a HO-1-mediated AMPKα–PGC-1α–ERRα circuit and consequent oxidative phosphorylation, O₂ consumption, and ATP production. This circuit may play an important role in repairing neurovascular function after TBI in the peri-injured region by stimulating astrocytic mitochondrial biogenesis.     

Continuous glass-fiber reinforced nylon 6 by using a new impregnation die

This paper describes a process for the manufacture of thermoplastic composites reinforced with continuous fibers and the equipment for producing such a product. The process makes it possible to expand and reconsolidate the fibers of rovings by passing them into the impregnation die filled with molten thermoplastic. The die consists of three rollers and numerous pins fixed on the roller surfaces over which the roving is drawn under tension. The material chosen to illustrate the die process is a glass-fiber reinforced nylon-6, PA6. The void content and mechanical properties were measured to investigate the influence of processing variables on properties. These process experiences indicated that poor fiber resin impregnation and fiber damage, due to harsh prepreg fabrication, result in low values for longitudinal tensile strength and impact properties. However, the composites manufactured by this technique show a significant improvement in mechanical properties over conventionally prepared thermoplastic composites.     

A comparative study of the antithrombotic effect through activated endothelium of garlic powder and tomato extracts using a rodent model of collagen and epinephrine induced thrombosis

Food Science and Biotechnology - In this study, garlic powder, tomato extract and a mixture of both were analyzed for anti-thrombotic effects using a collagen and epinephrine induced thrombosis...