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     

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     

Smart electrochromic windows (SECWs) for energy management

Smart Electrochromic Windows (SECWs) — the windows for future, are the windows, which by dynamically controlling solar and visual properties in response to exterior environmental conditions and interior needs, can offer visual and thermal comfort along with significant amount of energy saving. They play an increasingly important role in high standards of efficient energy usage and management in new building regulations. Their greatest value is generated if they can respond appropriately in terms of dynamic switching speed, color, lifetime and optical properties and if they can be fabricated cost effectively. This paper presents some of the results of our preliminary attempts made in this direction, in terms of the preparation and salient features of the components of the SECWs developed and the performance characteristics of different prototype SECWs fabricated and their comparison. Paper presented at the 2nd International Conference on Ionic Devices, Anna University, Chennai, India, Nov. 28–30, 2003.     

Reactions of vinyl sulfone with α-diazo-β-ketosulfone and Bestmann–Ohira reagent for the regioselective synthesis of highly functionalized pyrazoles

The 1,3-dipolar cycloaddition of diazomethylsulfone anion, generated in situ from α-diazo-β-ketosulfone, with vinyl sulfone proceeds in a regioselective manner to provide sulfonylpyrazoles. Similar reaction of diazomethylphosphonate anion, derived from Bestmann–Ohira reagent, with vinyl sulfone leads to phosphonylpyrazoles. The sulfonyl group of vinyl sulfone undergoes chemoselective elimination in these reactions.     

Conversion of Alkylamines to Thiocarbamoylguanidines

N-Alkyl-, N, N-dialkyl- or N-unsubstituted-N′-(arylthiocarbamoyl)guanidines are prepared in very good yield from amines and 1-(N-arylthiocarbamoyl)-amidino3,5-dimethylpyrazoles.     

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     

Does the TauD Enzyme Always Hydroxylate Alkanes, While an Analogous Synthetic Non-Heme Reagent Always Desaturates Them?

This theoretical work addresses the mechanistic switch between hydroxylase (alcohol formation) and desaturase (olefin formation) activities during alkane oxidation by two non-heme high-valent oxoiron reagents, the enzyme taurine:α-ketoglutarase dioxygenase (TauD) and the synthetic shape-selective catalyst (TpOBzFe), toward cyclohexadiene, cyclohexane, cyclopentane, and ethane. As we show, the desaturase/hydroxylase steps obey unique orbital selection rules, and the mechanistic switch is determined by intrinsic reactivity factors that depend on the ligand-sphere flexibility of the oxoiron species, the substrate, and the spin states of the reaction pathways. Testable predictions are outlined.     

The effect of various complexing agents on the morphology and optoelectronic properties of chemically deposited ZnS thin films: A comparative study

Thin films of ZnS were synthesized on glass substrates by chemical bath deposition technique. The effect of three different complexing agents, viz. hydrazine hydrate (HH), triethanolamine (TEA) and trisodiumcitrate (TSC) on the growth and physical properties of ZnS films has been investigated. The experimental results indicated that the complexing agents affect the structure, lattice strain, surface morphology and optoelectronic properties of ZnS films significantly. X-ray diffraction studies disclosed that all the ZnS layers crystallized in hexagonal form and the predominant orientations of the crystallites differed with complexing agents. Thickness of the films profoundly varied with the complexing agents though the deposition parameters like time, temperature and pH of reaction baths were kept constant. Atomic Force Microscopy revealed the variation in surface topography and roughness of the films. The film with HH as complexing agent exhibited maximum transmittance (87%) in the visible region of electromagnetic spectrum whereas those synthesized using TEA and TSC had a lower transmittance of approximately 60% and 50% respectively. The corresponding values of optical band gap were found to be 3.73, 3.64 and 3.57 eV respectively. The room temperature photoluminescence emission spectra consisted of bright blue emission peaks for all the samples. The intensity of emission peak was found to be maximum for TSC film and minimum for HH film.