Comparison of the Effect of an Organoclay,Triphenylphosphate, and a Mixture of Both on the Degradation and Combustion Behaviour of PC/ABS Blends

Summary: Polycarbonate Acrylonitrile-Butadiene-Styrene blends (PC/ABS) with flame retardants Triphenyl Phosphate (TPP), nanoclay and their mixtures were prepared in a twin- screw extruder. The morphological properties were characterized by X-ray diffractometry (XRD) which showed the intercalated structure of nanoclay in the matrix. Thermal stability of the samples was studied using Thermogravimetric Analysis (TGA), and the degradation kinetic parameters were determined using various methods including Kissinger, Flynn-Wall-Ozawa and Coats-Redfern methods. It was found that the sample containing both TPP and nanoclay has the highest activation energy. The activation energy order of PC/ABS blends with different flame retardant packages, obtained by Kissinger method agrees well with that obtained by Coats-Redfern. Cone calorimetry and limited oxygen index (LOI)/underwriters laboratory 94 (UL94) methods were used to investigate the fire behaviour and flammability of materials. The reduced mass loss rate (MLR), peak heat release rate (PHRR) and enhanced LOI of the composite containing mixture system confirmed a synergistic effect of TPP and nanoclay.     

Prenylated flavonoids from Tephrosia apollinea

In continuation of our chemical investigation on some medicinal plants of the genus Tephrosia,re-investigation of the methylenechloride/methanol(1:1) extract of the air-dried aerial part of Tephrosia apollinea afforded a new prenylated flavonoid 1, in addition to an aromatic ester,a sesquiterpene,a lignan and several known prenylated flavonoids.The structures were established by(~1H NMR,~(13)C NMR,DEPT,~1H-~1H COSY,HMQC,HMBC,NOESY and HRMS).Relative configurations of 9 and 10 were confirmed by X-ray anal...     

On linear vertex-arboricity of complementary graphs

The linear vertex-arboricity ρ(G) of a graph G is defined to be the minimum number of subsets into which the vertex set of G can be partitioned such that each subset induces a linear forest. In this paper, we give the sharp upper and lower bounds for the sum and product of linear vertex-arboricities of a graph and its complement. Specifically, we prove that for any graph G of order p. and for any graph G of order p = (2n + 1)², where n ? Z⁺, 2n + 2 ≦ ρ(G) + ρ(G ).     

Deflated and Augmented Krylov Subspace Techniques

We present a general framework for a number of techniques based on projection methods on ‘augmented Krylov subspaces’. These methods include the deflated GMRES algorithm, an inner–outer FGMRES iteration algorithm, and the class of block Krylov methods. Augmented Krylov subspace methods often show a significant improvement in convergence rate when compared with their standard counterparts using the subspaces of the same dimension. The methods can all be implemented with a variant of the FGMRES algorithm. © 1997 by John Wiley & Sons, Ltd.     

Poly(arylene ether)s from new biphenols containing imidoarylene and dicyanoarylene moieties

Novel poly(arylene ether)s were synthesized from new biphenol monomers 14–16 1 containing imido‐ or dicyanoarylene groups. The syntheses of these polymers were carried out in tetramethylene sulfone in the presence of anhydrous K₂CO_3, by a nucleophilic substitution condensation between the biphenol and activated difluoro compounds to give high molecular weight polymers. All the polymers have high T_g 's and good thermal stability as determined from DSC and TGA analysis. Inherent viscosities of these polymers are in the range of 0.33–0.63 dL/g. They are amorphous and readily soluble in NMP, DMF, and DMSO. The glass‐transition temperatures of the polymers range from 248–295 °C. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1318–1322, 2000     

Mach's Principle and Model for a Broken Symmetric Theory of Gravity

We investigate spontaneous symmetry breaking in a conformally invariant gravitational model. In particular, we use a conformally invariant scalar tensor theory as the vacuum sector of a gravitational model to examine the idea that gravitational coupling may be the result of a spontaneous symmetry breaking. In this model matter is taken to be coupled with a metric which is different but conformally related to the metric appearing explicitly in the vacuum sector. We show that after the spontaneous symmetry breaking the resulting theory is consistent with Mach's principle in the sense that inertial masses of particles have variable configurations in a cosmological context. Moreover, our analysis allows to construct a mechanism in which the resulting large vacuum energy density relaxes during evolution of the universe.     

Nonrelativistic Strong-Field Photoionization without Making the Dipole Approximation

Within the context of the time-reversed S-matrix approach to photoionization, and employing a recently proposed strong-field solution to the Schrödinger equation, analytic expressions for the atomic photoionization rates are obtained here without using the dipole approximation. We show that the absorbed photon momentum shows up as a forward-directed momentum component for the photoelectron. All the expressions reported in this work have the correct limits when the dipole approximation is used.     

Polymer-bound oxathiaphospholane: a solid-phase reagent for regioselective monothiophosphorylation and monophosphorylation of unprotected nucleosides and carbohydrates

Two polymers bound to N,N-diisopropylamino-1,3,2-oxathiaphospholane were reacted with unprotected carbohydrates and nucleosides in the presence of 1H-tetrazole, followed by oxidation with tert-butyl hydroperoxide or sulfurization with Beaucage's reagent. The 1,3,2-oxathiaphospholane ring-opening with 3-hydroxypropionitrile, followed by treatment with DBU, afforded the corresponding monophosphate and monothiophosphate derivatives, respectively, through the elimination of polymer-bound ethylene episulfide. Reactions using this strategy offer the advantages of high regioselectivity, monosubstitution, and facile isolation and recovery of products.     

Selective diphosphorylation, dithiodiphosphorylation, triphosphorylation, and trithiotriphosphorylation of unprotected carbohydrates and nucleosides

[chemical reaction: see text]. Aminomethyl polystyrene resin-bound linkers of p-acetoxybenzyl alcohol were subjected to reactions with diphosphitylating and triphosphitylating reagents to yield the corresponding polymer-bound diphosphitylating and triphosphitylating reagents, respectively. A number of unprotected carbohydrates and nucleosides were reacted with the polymer-bound reagents. Oxidation with tert-butyl hydroperoxide or sulfurization with Beaucage's reagent, followed by removal of cyanoethoxy group with DBU and the acidic cleavage, respectively, afforded only one type of monosubstituted nucleoside and carbohydrate diphosphates, dithiodiphosphates, triphosphates, and trithiotriphosphates with high regioselectivity.