Thermotropic main chain liquid crystalline polyesters containing ferrocene and phosphate units: synthesis and characterization

A new series of liquid crystalline main chain copolyesters were prepared, having ferrocene in the mesogenic segment and a methyl phosphate group along with a methylene spacer. The even numbered methylene groups were varied from two to ten. Liquid crystalline behaviour was investigated on a hot stage optical polarized microscope. Thermal properties of the polymers were analysed by TGA and DSC, revealing that the polymers yield high char products, probably caused by the formation of phosphorus and iron oxides. The glass transition (T_g) temperatures of the polymers were found to be fairly low, the result of the incorporation of bulky phosphorus and ferrocene moieties in the chain. The phase behaviour was analysed and correlated with the structure of the polymers. The liquid crystalline textures of the polymers became more transparent with increasing spacer length. Energy minimized structures for the polymer repeating units reveal that both the ferrocene and phosphorus moieties produce more molecular entanglement, thus reducing the T_g and T_m of the polymers.     

Selecting green suppliers based on GSCM practices: Using fuzzy TOPSIS applied to a Brazilian electronics company

Due to an increased awareness and significant environmental pressures from various stakeholders, companies have begun to realize the significance of incorporating green practices into their daily activities. This paper proposes a framework using Fuzzy TOPSIS to select green suppliers for a Brazilian electronics company; our framework is built on the criteria of green supply chain management (GSCM) practices. An empirical analysis is made, and the data are collected from a set of 12 available suppliers. We use a fuzzy TOPSIS approach to rank the suppliers, and the results of the proposed framework are compared with the ranks obtained by both the geometric mean and the graded mean methods of fuzzy TOPSIS methodology. Then a Spearman rank correlation coefficient is used to find the statistical difference between the ranks obtained by the three methods. Finally, a sensitivity analysis has been performed to examine the influence of the preferences given by the decision makers for the chosen GSCM practices on the selection of green suppliers. Results indicate that the four dominant criteria are Commitment of senior management to GSCM; Product designs that reduce, reuse, recycle, or reclaim materials, components, or energy; Compliance with legal environmental requirements and auditing programs; and Product designs that avoid or reduce toxic or hazardous material use.     

Review of wavelet methods for the solution of reaction–diffusion problems in science and engineering

Wavelet method is a recently developed tool in applied mathematics. Investigation of various wavelet methods, for its capability of analyzing various dynamic phenomena through waves gained more and more attention in engineering research. Starting from ‘offering good solution to differential equations’ to capturing the nonlinearity in the data distribution, wavelets are used as appropriate tools at various places to provide good mathematical model for scientific phenomena, which are usually modeled through linear or nonlinear differential equations. Review shows that the wavelet method is efficient and powerful in solving wide class of linear and nonlinear reaction–diffusion equations. This review intends to provide the great utility of wavelets to science and engineering problems which owes its origin to 1919. Also, future scope and directions involved in developing wavelet algorithm for solving reaction–diffusion equations are addressed.     

Periodic solutions of nonlinear wave equations with damping

A known existence theorem for doubly periodic solutions of nonlinear wave equations with linear damping is being proved in a direct manner by an approach which has been developed by the authors in [5, 6, 7] for hyperbolic problems, when the kernel of the underlying linear operator is infinite dimensional.     

Bis(trimethylphosphine)silver(I) hexafluorophosphate

In the title two‐coordinate silver compound, [Ag(C₃­H₉­P)₂]­PF₆, the cation has crystallographically imposed mirror symmetry, and approximates very closely to m (D_3d) symmetry with fully staggered methyl groups in the solid state. The Ag atom has a nearly linear coordination geometry, with a P—Ag—P angle of 178.70 (4)°. The Ag—P bond lengths are 2.3746 (12) and 2.3783 (12) Å, which are ­significantly longer than the Au—P bond length of 2.304 (1) Å in the analogous two‐coordinate gold cation. The lack of intra­molecular steric effects within the present cations containing tri­methyl­phosphine (cone angle 118°), compared with those in known cations containing trimesityl­phosphine (cone angle 212°), provides a better comparison of M—P distances and thus more conclusive evidence that Au really is smaller than Ag.     

Periodic solutions of semilinear partial differential equations of parabolic type

Summary In this paper we obtain necessary and sufficient conditions for the existence of solutions of a class of periodic-Dirichlet problems for parabolic- partial differential equations. The structure of the solution set and the asymptotic behaviour of the solution is also studied.Entrata in Redazione il 17 giugno 1983.     

Simultaneous best approximation by three polynomials

Let [a, b] be any interval and let p₀, p₁, p_k be any three polynomials of degrees 0, 1, k, respectively, where k 2. A set of necessary and sufficient conditions for the existence of an f in C[a, b] such that p_i is the best approximation to f from the space of all polynomials of degree less than or equal to i, for all i = 0, 1, k, is given.     

Investigation of clay modifier effects on the structure and rheology of supercritical carbon dioxide‐processed polymer nanocomposites

Superior property enhancements in polymer–clay nanocomposites can be achieved if one can significantly enhance the nanoclay dispersion and polymer–clay interactions. Recent studies have shown that nanoclays can be dispersed in polymers using supercritical carbon dioxide (scCO₂). However, there is need for a better understanding of how changing the clay modifier affects the clay dispersability by scCO₂ and the resultant nanocomposite rheology. To address this, the polystyrene (PS)/clay nanocomposites with “weak” interaction (Cloisite 93A clay) and “strong” interaction (Cloisite 15A clay) have been prepared using the supercritical CO₂ method in the presence of a co‐solvent. Transmission electron microscopy images and small‐angle X‐ray diffraction illustrate that composites using 15A and 93A clays show similar magnitude of reduction in the average tactoid size, and dispersion upon processing with scCO₂. When PS and the clays are coprocessed in scCO₂, the “dispersion” of clays appears to be independent of modifier or polymer–clay interaction. However, the low‐frequency storage modulus in the scCO₂‐processed 15A nanocomposites is two orders of magnitude higher than that of 93A nanocomposites. It is postulated that below percolation (solution blended composites), the strength of polymer–clay interaction is not a significant contributor to rheological enhancement. In the scCO₂‐processed nanocomposites the enhanced dispersion passes the percolation threshold and the interactions dictate the reinforcement potential of the clay–polymer–clay network. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 823–831, 2010     

FTIR spectroscopic investigation of thermal effects in semi‐syndiotactic polypropylene

The temperature‐dependent behavior of individual components within metallocene‐catalyzed semisyndiotactic polypropylenes (semi‐sPP) with a wide range of stereoregular content (26 to 96% rr) is studied using Fourier transform infrared (FTIR) spectroscopy and temperature‐modulated differential scanning calorimetry (DSC). Changes in sensitive, high‐resolution absorbance spectra are observed as melt‐slow‐cooled thin films are subjected to stepwise temperature increases. In general, spectral bands previously identified as being sensitive to ordered structures (e.g., conformed chains, crystal morphs) appear to follow overall trends of shifting to lower wavenumbers (energies), broadening, and decreasing in peak area intensity as temperature increases. Peaks that appear due to “splitting” (observed in more stereoregular materials) show a trend toward coalescence as temperature increases; this corresponds to a gradual loss of chain conformational order. Gauche‐gauche‐trans‐trans (ggtt)_n helical and all‐trans (tttt)_n planar zigzag‐conformed chains that participate in the crystalline‐amorphous interfacial region (“mesophase”) appear to be more stable (i.e., they do not lose their conformational order as easily) with increasing temperature in materials with a greater degree of syndiotacticity. Moreover, IR data correspond well with modulated DSC endotherms located near 50 °C and 70 °C. At each transition temperature—thought to represent, respectively, a thermally driven chain conformation from planar zigzags to helices, and a dynamic disorder of helices marked by rapid gauche ? trans isomerization—the IR absorbance ratio, A₉₇₈/A₉₆₃, which represents the relative population of helical chains, undergoes an accelerated decrease. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 439–461, 2005