Co-curing studies of ethynyl terminated oligoimide and (methyl) nadicimide resins

The paper describes the co-curing studies of ethynyl and ethenyl end-capped imide resins. The effect of composition and chemical structure of ethenyl end-capped resins (nadicimides) on thermal behavior of ethynyl end-capped resins was evaluated using DSC and thermogravimetric analysis. An increase in char yield was observed on co-curing of few resin formulations. A mechanism has been proposed to account for this observation.Paper presented at Intern. Symposium on Macromolecules at Trivandrum, Jan. 11–13, 1995.     

Gravitationally Non-Degenerate Petrov Type–I Cosmological Model Filled with Viscous Fluid in Modified Brans-Dicke Cosmology

Adding the Cosmological term, which is assumed to be variable in Brans-Dicke theory, we have discussed about a cylindrically symmetric cosmological model filled with viscous fluid with free gravitational field of a non-degenerate petrov type-I. The effect of viscosity on various kinematical parameters has been discussed. Finally, this model has been transformed to the original form (1961) of Brans-Dicke theory (including a variable cosmological term).     

Two‐fold Bioorthogonal Derivatization by Different Formylglycine‐Generating Enzymes

Formylglycine‐generating enzymes are of increasing interest in the field of bioconjugation chemistry. They catalyze the site‐specific oxidation of a cysteine residue to the aldehyde‐containing amino acid C^α‐formylglycine (FGly). This non‐canonical residue can be generated within any desired target protein and can subsequently be used for bioorthogonal conjugation reactions. The prototypic formylglycine‐generating enzyme (FGE) and the iron‐sulfur protein AtsB display slight variations in their recognition sequences. We designed specific tags in peptides and proteins that were selectively converted by the different enzymes. Combination of the different tag motifs within a single peptide or recombinant protein enabled the independent and consecutive introduction of two formylglycine residues and the generation of heterobifunctionalized protein conjugates.     

Processing impact on tocopherols and triglycerides composition of soybean oil and its deodorizer distillate evaluated by high-performance liquid chromatography

In the present study, high-performance liquid chromatography (HPLC) was used for the separation of tocopherols and triglycerides of processed soybean oil and deodorizer distillate (DD). The results of normal and reversed-phase modes of HPLC revealed that concentrations of tocopherols and triglycerides content were decreased during the neutralization, bleaching, and deodorization processes. The loss of individual tocopherols ranged between 55.16% and 63.25%. During processing, triglycerides containing stearic-oleic-linoleic (SOL) moieties and palmitic-palmitic-linoleic (PPL) fragments showed greater reduction up to 38.14% and 37.69%, respectively. Among tocopherols and triglycerides; γ-tocopherol and oleic-oleic-oleic (OOO) were found to be in greater concentrations 5.53% and 19.78%, respectively in DD as compared to their counterparts. A maximum reduction of tocopherols was observed in the deodorization step. DD was found to be a rich source of bioactive components; therefore, it could be used for many industrial applications including pharmaceutical formulations, cosmetics, and food industries.     

Thermally amendable tailor‐made functional polymer by RAFT polymerization and “click reaction”

This investigation reports the preparation and characterization of thermally amendable functional polymer bearing furfuryl functionality via reversible‐addition fragmentation and chain transfer (RAFT) polymerization and Diels‐Alder (DA) reaction. In this case, furfuryl methacrylate (FMA) was polymerized using 4‐cyano‐4‐[(dodecylsulfanylthiocarbonyl)sulfanyl] pentanoic acid as RAFT reagent and 4,4′‐azobis(4‐cyanovaleric acid) as thermal initiator. ¹H NMR, ¹³C NMR, and matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry analysis showed that furfuryl group in poly(furfuryl methacrylate) (PFMA) was not affected during RAFT polymerization and the tailor‐made polymer had RAFT end group. The DA reaction was successfully carried out between the reactive furfuryl functionality of PFMA and different bismaleimides. The thermoreversible property of these DA polymers was characterized by FT‐IR and DSC analysis. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3365–3374     

Microbial transformation of the steroidal alkaloid dictyophlebine by Rhizopus stolonifer

The microbial transformation of a steroidal alkaloid, dictyophlebine (1) with Rhizopus stolonifer (ATCC 10404) afforded three oxidized metabolites 2-4. Compound 2 was found to be a new product. These metabolites were structurally characterized on the basis of modern spectroscopic techniques. Their inhibitory activity towards acetyl- and butyrylcholinesterase has been evaluated and the new product 2 has been found to be more potent than the parent compound and other metabolites.     

Synthesis of Polyimide Nanocomposites

A series of polyimide nanocomposite (PINC) films were prepared by using poly(amic acid) and Ba, Sr, Sn, TiO₃ nanoparticles via in-situ polymerization method. Poly(amic acid) was synthesized from benzophenone tetracarboxylic anhydride and diamino diphenyl ether by ring-opening polyaddition reaction. The PINC films were characterized by FTIR spectroscopy. The thermal properties of PINC films were investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) methods. The prepared PINC showed major weight loss in the range of 550–600°C in nitrogen atmosphere. These had char yield in the range of 50–60% at 800°C. The morphological studies of PINC films were carried out using SEM method.     

Synthesis of silicon-containing bisnadiimide

Silicon-containing thermosetting bisnadiimide (BNI) was synthesized using Bis (amino propyl) tetramethyl disiloxane and nadic anhydride, and fluorine-containing thermoplastic polyamic acid (FPA) was synthesized from 4,4′-(hexafluoroisopropylidene) bis phenoxy dianiline and 4,4′-(hexafluoroisopropylidene) dipthalic anhydride [6-FDA]. The semi-interpenetrating network (s-IPN) systems in various ratios were prepared via solution casting of FAA and crosslinkable BNI, and then curing them up to 370 °C in order to achieve an optimum combination to be used for advanced high temperature composite applications. The polyimides and s-IPN were characterized using NMR and FTIR spectroscopy. The thermo-oxidative and water uptake properties of these polyimides and s-IPNs were investigated. The thermogravimetric analysis (TG) showed increase in thermal stability with the increase in thermoplastic polyimide proportion.     

Heat Transfer and Entropy in a Vertical Porous Plate Subjected to Suction Velocity and MHD

This article presents an investigation of heat transfer in a porous medium adjacent to a vertical plate. The porous medium is subjected to a magnetohydrodynamic effect and suction velocity. The governing equations are nondepersonalized and converted into ordinary differential equations. The resulting equations are solved with the help of the finite difference method. The impact of various parameters, such as the Prandtl number, Grashof number, permeability parameter, radiation parameter, Eckert number, viscous dissipation parameter, and magnetic parameter, on fluid flow characteristics inside the porous medium is discussed. Entropy generation in the medium is analyzed with respect to various parameters, including the Brinkman number and Reynolds number. It is noted that the velocity profile decreases in magnitude with respect to the Prandtl number, but increases with the radiation parameter. The Eckert number has a marginal effect on the velocity profile. An increased radiation effect leads to a reduced thermal gradient at the hot surface.