Synthesis and investigation of the effect of nematic phases on the glass‐transition behavior of novel cycloaliphatic liquid‐crystalline poly(ester amide)s

We designed and developed novel cycloaliphatic liquid‐crystalline (LC) poly(ester amide)s to investigate the effects of nematic LC phases and hydrogen‐bonding interactions on the glass‐transition behavior. Three series of poly(ester amide)s based on commercially important poly(1,4‐cyclohexanedimethylene terephthalate) were synthesized with two new cycloaliphatic diamines {3,8‐bis(aminomethyl)‐tricyclo [5.2.1.0.(2,6)]decane (tricyclic) and 1,3‐cyclohexane bismethylene amine (monocyclic)} and a linear counterpart (1,6‐hexamethylene diamine). The compositions of the ester/amide units in the copolymers were varied up to 50% by the adjustment of the amounts of the diol and diamine in the feed. The structures of the polymers were confirmed with NMR and Fourier transform infrared, and their inherent viscosities were measured at 30 °C with an Ubbelohde viscometer. Thermal analysis revealed that the poly(ester amide)s having less than 25 mol % amide linkages were thermotropic and LC, and threadlike nematic phases were observed under a polarizing microscope. The introduction of nematic, LC phases drastically affected the glass‐transition temperatures of the copolymers, and a plot of the composition versus the glass‐transition temperature passed through a maximum for lower amide incorporation, regardless of the structural differences of the amide units (cyclic or linear). This nonlinear Flory–Fox trend was correlated to the cooperative effect of the strong alignment of polymer chains in the nematic phases and intermolecular packing induced by the hydrogen bonding in the poly(ester amide)s. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5557–5571, 2006     

Electronic and magnetothermal properties of ferromagnetic clusters

The electronic structures and the magnetothermal properties of nickel clusters have been investigated. Their effective magnetic moments and specific heat capacities have been calculated assuming that the clusters undergo superparamagnetic relaxation. The average magnetic moments are computed adopting Friedel's model of ferromagnetic clusters. The surface effect and the cluster size effect on the thermodynamic properties of these clusters have been analysed based on the mean field theory approximation. The specific heat capacity of Ni clusters for N=300, where N is the number of atoms in the cluster, shows the peak value at T=550 K and exhibits a steady increase with N. The effective potentials and energy eigen values of the clusters as a function of the number of atoms and radius of the cluster have also been calculated self-consistently using the local density approximation (LDA) of the density functional theory (DFT); this has been performed within the framework of the spherical jellium background model (SJBM). The results of this study have been compared with the Stern-Gerlach experimental data and other theoretical results already reported in literature     

Microporous polyurethanes: Synthesis and investigation of the mechanism of the pore formation

A new approach for microporous polymeric material is developed utilizing the secondary interactions such as hydrogen bonding in the polymer chains in polyurethane systems at ambient conditions. A new series of highly rigid, thermally stable, and readily soluble cycloaliphatic polyurethanes were designed and synthesized for this purpose, based on new tricyclodecanedimethanol and 1,4‐cyclohexanedimethanol. The hydrogen‐bonding interactions induce phase separation in solution, which leads to polymer‐rich and solvent‐rich domains; subsequent evaporation of the solvent molecules results in micropores. The phase‐separation process in the polyurethane is found to be highly dependent on the chemical structures of the polymer chain backbone. ¹H NMR titration experiments were carried out to understand the mechanism of the micropore formation and its dependence on different structural subunits. The hydrogen‐bonding association constant (K) obtained from the titration experiments revealed that higher the K‐value more the tendency to form micropores. A fully cycloaliphatic polyurethane produces micropores of sizes ranging from 1 to 8 μm, and each pore is separated by 10^?20 μm, whereas the replacement of one of the cyclic unit in the backbone disturbs the entire phase‐separation process and results in nonporous morphology. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1296–1308, 2006     

Higher order fully discrete scheme combined withH 1-Galerkin mixed finite element method for semilinear reaction-diffusion equations

We first apply a first order splitting to a semilinear reaction-diffusion equation and then discretize the resulting system by anH ¹-Galerkin mixed finite element method in space. This semidiscrete method yields a system of differential algebraic equations (DAEs) ofindex one. Apriori error estimates for semidiscrete scheme are derived for both differential as well as algebraic components. For fully discretization, an implicit Runge-Kutta (IRK) methods is applied to the temporal direction and the error estimates are discussed for both components. Finally, we conclude the paper with a numerical example.     

Using Nanoparticle Tracking Analysis (NTA) to Decipher Mucoadhesion Propensity of Curcumin-Containing Chitosan Nanoparticles and Curcumin Release

Real-time nanoparticle tracking analysis (NTA) was used to evaluate the propensity of curcumin-containing chitosan nanoparticles (CUR-CS-NP) to muco adhere and release curcumin under simulated colon conditions. This novel procedure is relatively simple and fast and does not require use of animals, but more importantly, it permits the correlation of physical changes to the CUR-CS-NP with the observed behavior under simulated conditions in realtime. The CUR-CS-NP formed spontaneous aggregates in response to exposure to mucin. This observation correlated with curcumin release from CUR-CS-NP was observed in phosphate buffer (pH 7.4) where, 81% of curcumin was released within 6 hours. Atomic force microscopy imaging CUR-CS-NP exposed to mucin solution revealed a decorated surface of the CUR-CS-NP by mucin, consistent with expected electrostatic interactions between the two. The use of NTA, thus, provided us with a means of ascertaining the performance of the CUR-CS-NP under simulated colonic conditions and we propose that this prototype delivery system could be the basis for an effective colon mucoadhesive drug delivery system.      

Quaternary ammonium hydroxide-functionalized g-C3N4 catalyst for aerobic hydroxylation of arylboronic acids to phenols

A new and efficient metal-free approach toward the synthesis of phenols via an aerobic hydroxylation of arylboronic acids by using a novel quaternary ammonium hydroxide g-C₃N₄ catalyst has been described. The functionalized quaternary ammonium hydroxide (g-C₃N₄-OH) has been prepared from graphitic carbon nitride (g-C₃N₄) scaffold by converting the residual –NH₂ and –NH groups to quaternary methyl ammonium iodide by performing a methylation reaction with methyl iodide followed by ion-exchange with 0.1 N KOH or anion exchange resin Amberlyst A26 (OH- form) by post-synthetic modification. The resultant g-C₃N₄-OH was characterized by XRD, FTIR, field-emission scanning electron microscope (FESEM), high-resolution transmission electron microscope (HRTEM), N₂ adsorption/desorption isotherms, and acid–base titration. Tested as solid-base catalysts, the g-C₃N₄-OH showed excellent catalytic activity in the aerobic hydroxylation reaction by converting a variety of arylboronic acids to the corresponding phenols in high yields. More importantly, the g-C₃N₄-OH solid-base has been successfully reused four times with the minor loss of initial catalytic activity (10.5%).     

Solvent-induced self-organization approach for polymeric architectures of micropores,hexagons and spheres based on polyurethanes prepared via novel melt transurethane methodology

Solvent-induced self-organization approach was developed, for the first time, to produce polyurethane microporous templates and higher ordered morphologies such as micro or nanometer-sized polymeric hexagons and spheres. A novel melt transurethane methodology was designed and developed for synthesizing new class of cycloaliphatic polyurethanes under nonisocyanate and solvent-free conditions. In this new process, a diurethane monomer was polycondensed with equimolar amounts of diol in presence of Ti(OBu)₄ as catalyst with the removal of low boiling alcohol from the equilibrium. The hydrogen bonding of the polyurethanes are very unique to their chemical structure and they undergo selective phase-separation process in solution to produce hexagonally packed microporous templates. The increase of water content in the polymer solution enhances the phase-separation process and the micro pores coalesce to isolate the encapsulated polymer matrix into polymeric hexagons or densely packed solid spheres. The concentration-dependent solution FTIR and ¹H NMR of the polyurethanes revealed that the polymers possessing higher H-bonding association constants (K) have greater tendency to undergo solvent-induced self-organization phenomena. The mechanism of solvent-evaporation process indicated that only microporous polyurethanes have tendency to form higher ordered hexagons and spheres whereas others failed to show any new morphology. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2351–2366, 2007     

2-(Trimethylsilyl)ethanol as a new alcohol equivalent for copper-catalyzed coupling of aryl iodides

2-(Trimethylsilyl)ethanol as a new alcohol equivalent has been employed for copper-catalyzed coupling of aryl iodides. Using mild reaction conditions, it has been observed that substituted phenols and phenols with sensitive functional groups can be readily prepared.     

Micelles of poly(styrene-b-2-vinylpyridine-b-ethylene oxide) with blended polystyrene core and their application to the synthesis of hollow silica nanospheres

Core-shell-corona (CSC) micelles of asymmetric triblock copolymer, poly(styrene-b-2-vinylpyridine-b-ethylene oxide) (PS-PVP-PEO), containing polystyrene homopolymer (homo-PS) in the core were successfully prepared in aqueous media. The influence of homo-PS contents over the formation of the micelles was investigated thoroughly by various techniques such as dynamic light scattering (DLS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fluorescence spectroscopy. It was found that the size of the PS core of the micelle was increased by the addition of homo-PS as observed by DLS and TEM techniques. The SEM and TEM measurements confirm the spherical morphology of the micelles and enlargement of PS core over the addition of homo-PS. The increase in the PS core volume of the PS-PVP-PEO micelles is attributed to the insertion of homo-PS in the PS core. The micelles have also been demonstrated as facile soft templates for synthesis of hollow silica nanospheres. The average diameter of the spherical hollow particles could be tuned between 30.6 and 38.8 nm with cavity sizes ranging from 20.7 to 28.5 nm using tetramethoxysilane as silica precursors under mild acidic conditions. The facile synthesis of hollow silica using the CSC micelles with different homo-PS contents indicates that the hollow void size can be controlled within a range of several nanometers.     

Polyaniline nanoscaffolds for colorimetric sensing of biomolecules via electron transfer process

Biologically important analytes such as cysteine and vitamin-C were detected by electron transfer (ET) via naked eye colorimetric sensing using a tailor-made water-soluble self-doped polyaniline (PSPANa) as a substrate. Monomer (N-3-sulfopropylaniline) was synthesized via ring-opening of propane sultone with excess aniline and polymerized in water using ammonium persulfate to obtain green water-soluble polymer. Vitamin-C (ascorbic acid) and cysteine showed unexpected sharp and instantaneous color change from blue to colorless sensing action. The stoichiometry of the analyte to polymer was determined as 3:2 and 4:1 with association (or binding) constants of K = 2.1 × 10(3) and 1.5 × 10(3) M(-1) for vitamin-C and cysteine, respectively. Efficient electron transfer from vitamin-C (also cysteine) to the quinoid unit of the polyaniline base occurred in solution; as a result, the color of the solution changed from deep blue to colorless. Cyclic voltammetry analysis of PSPANa showed the disappearance of the cathodic peak at -0.21 V upon the addition of analytes (vitamin-C and cysteine) and confirms the electron transfer from the analyte to the polymer backbone. Dynamic light scattering (DLS) and zeta potential techniques were utilized to trace the molecular interactions in the electron transfer process. DLS histograms of the polymer samples confirmed the existence of nanoaggregates of 8-10 nm in diameter. The polymers possessed typical amphiphilic structure to produce micellar aggregates which facilitate the efficient electron transfer occurred between the analyte and polyaniline backbone.