Dynamic mechanical properties of isotactic polypropylene/nitrile rubber blends: Effects of blend ratio,reactive compatibilization,and dynamic vulcanization

The effect of blend ratio and compatibilization on dynamic mechanical properties of PP/NBR blends was investigated at different temperatures. The storage modulus of the blend decreased with increase in rubber content and shows two T_g's indicating the incompatibility of the system. Various composite models have been used to predict the experimental viscoelastic data. The Takayanagi model fit well with the experimental values. The addition of phenolic modified polypropylene (Ph-PP) and maleic modified polypropylene (MA-PP) improved the storage modulus of the blend at lower temperatures. The enhancement in storage modulus was correlated with the change in domain size of dispersed NBR particles. The effect of dynamic vulcanization using sulfur, peroxide, and mixed system on viscoelastic behavior was also studied. Among these peroxide system shows the highest modulus. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2309–2327, 1997     

Intuitionistic fuzzy linear regression analysis

Linear regression analysis in an intuitionistic fuzzy environment using intuitionistic fuzzy linear models with symmetric triangular intuitionistic fuzzy number (STriIFN) coefficients is introduced. The goal of this regression is to find the coefficients of a proposed model for all given input–output data sets. The coefficients of an intuitionistic fuzzy regression (IFR) model are found by solving a linear programming problem (LPP). The objective function of the LPP is to minimize the total fuzziness of the IFR model which is related to the width of IF coefficients. An illustrative example is also presented to depict the solution procedure of the IFR problem by using STriIFNs.     

Microhydration of oxalic acid leading to dissociation

The effect of microhydration on the simplest dicarboxylic acid, namely oxalic acid, leading to the dissociation of its proton, is studied using first principle-based electronic structure calculations. The geometry of the hydrated clusters of oxalic acid considering up to seven water molecules is determined at ωB97X-D/aug-cc-pVDZ level of theory. Solvent stabilisation and interaction energy parameters are calculated applying CCSD(T) level of theory. The calculated free energy of formation shows that the hydrated oxalic acid clusters are stable only at low temperature and pressure. Though the solvent stabilisation energy increases linearly with an increase in the size of the hydrated cluster, the calculated interaction energy, acidic O–H bond dipole moment and hydrogen bond energy show characteristic features of ion pair formation. The spectral manifestation of the weakening hydroxyl bond is observed as red shift in its stretching frequency. A rigid potential energy scan, altering the dissociating O–H bond length of the oxalic acid molecule, shows an energy barrier for acid to water proton transfer in all cases except hepta-hydrate of oxalic acid, where a barrier-less proton transfer occurs. The number of water molecules (n) needed for dissociation of oxalic acid molecule is consistent with the value obtained from recently reported emperical correlation between n and pKa.     

New reagents for the synthesis of depsides Methyl evernate, methyl lecanorate, evernic acid and atranorin

Lichen depsides have now been synthesized by making use of two reagents, dicyclohexyl-carbodiimide (DCC) and trifluoroacetic anhydride. Methyl evernate, methyl lecanorate and evernic acid have been prepared in satisfactory yields. Altranorin has been synthesized for the first time.     

Spatial regimes in the dynamics of polyolefins: collective motion

Molecular simulation is used to characterize the spatial dependence of collective motion in four saturated hydrocarbon polymers. The observable is the distinct intermediate scattering function, as measured in coherent quasielastic neutron scattering experiments. Ranges of 0.01-1000 ps in time and 2-14 A in spatial scale are covered. In this time range, a two-step relaxation, consisting of a fast exponential decay and a slower stretched decay, is observed for all spatial scales. The relaxation times for the fast process are very similar to those obtained by following self motion, with a small modulation of relaxation times near the peak in the static structure factor which is well described by the narrowing picture suggested by de Gennes. For the slow process, self and collective relaxation times have larger numerical differences and follow different scaling with spatial scale. The modulation of slow relaxation times is larger than that observed for the fast process, but is overestimated by the de Gennes prediction, which only works qualitatively.     

Analysis of signal-to-noise enhancement of box-car averagers

The signal-to-noise improvement ratio (SNIR) of a Box-Car averager is calculated for various noise sources such as random white noise, exponentially correlated noise, etc. For a time constant (RC), and a sampling time ε, the quoted value of SNIR as (2RC/ε)^1/2 is shown to be strictly correct only when the noise is white and deviation from this law is expected for other non-white noise sources. The validity of some of the calculated expressions is established by direct measurement of noise output.     

Design and applications of new phosphine-free tetradentate Pd-catalyst: Regioselective C–H activation on 1-substituted 1,2,3-triazoles and indoles(NH-Free)

This article describes the synthesis of a new phosphine free tetradentate Pd catalyst using dl-2,3-diaminopropionic acid. The complex was characterized by Mass, IR, and ¹H NMR. The catalyst is air stable at room temperature and non-hygroscopic. Application of this new catalyst to regioselective C–H activation on 1-substituted 1,2,3-triazole and indoles with aryl iodides to get corresponding C-5 and C-2 arylated products with satisfactory yields. All the products were characterized by spectroscopic studies.