Prathima Kamath

Bio: Prathima Kamath is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Dissociation (chemistry) & Thermal decomposition. The author has an hindex of 1, co-authored 2 publication(s) receiving 5 citation(s).

The kinetics of dissociation of blocked 2,4‐diisocyanatotoluene (tdi) in amines

Abstract: The kinetics of dissociation of blocked diisocyanates based on commercial diisocyanatotoluene (TDI) (80/20 mixture of 2,4- and 2,6- isomers) in the presence of amino compounds was studied by a volumetric method and Fourier Transform IR (FTIR) spectral data. Second-order rate constants for the dissociation of TDI adducts (with phenol, thiophenol and p-chlorophenol) in the presence of amines (dibenzyl, benzyl, cyclohexyl, n-hexyl and di-n-butyl) in cyclohexanone solvent are reported. The relative effects of various blocking agents, basicity of the amines and temperature on the dissociation of blocked TDI have been determined. An FTIR spectroscopic method was used to study the dissociation of blocked TDI (with blocking agents such as phenol, thiophenol, p-chlorophenol,p-nitrophenol,p-cresol, α-naphthol and resorcinol) in the presence of excess triethylamine and in cyclohexanone solvent. Pseudo-first-order rate constants were calculated from NCO concentrations as determined from FTIR spectra.

Blocked isocyanates: from analytical and experimental considerations to non-polyurethane applications

Abstract: In this review we aim to provide an introductory guide to blocked isocyanates, through discussion on different examples of blocking groups, along with experimental considerations for their application. The review brings together updated examples of functionalities used and places specific emphasis on the analytical techniques used for the determination of deblocking temperature, updating previous reviews with the newly applied technique of X-ray photoelectron spectroscopy (XPS). Additionally, we put forward a brief update on the use of blocked isocyanates for other non-traditional polyurethane based polymer applications. We also highlight the importance of matching the analytical technique to the application of the blocked isocyanate, with differences in material state and experimental parameters having a great impact on the deblocking temperature reported.

Dynamic mechanical and underwater acoustic properties of the polyurethane/epoxy resin blend elastomers filled with macroporous poly(vinyl acetate-co-triallyl isocyanurate) resin beads

Abstract: Macroporous poly(vinyl acetate-co-triallyl isocyanurate) resin beads were prepared by suspension polymerization and used as acoustic particles for polyurethane (PU)/epoxy resin (EP) intercrosslinked elastomer matrices. The influences of the beads on the dynamic mechanical and underwater acoustic properties of the matrices were investigated. The results show that the underwater acoustic absorption properties of the matrices were improved by the beads, and this depended on the amount of the beads, the composition ratios of PU to EP, the bead diameters, the matrix thickness, and the water temperature. A comparison of the matrix with a 70/30 composition ratio of PU to EP to one without the beads showed that the average acoustic absorption coefficient of the composite with 5% beads increased from 0.38 to 0.55, and the peak value increased from 0.42 to 0.65, but the composites with 10 and 15% of the beads had lower acoustic absorption coefficients at low frequency and a much higher acoustic absorption coefficient at high frequency. The results also indicate that the beads with smaller diameters had a better enhancing effect on the underwater acoustic properties of the matrices. The results of the dynamic mechanical measurements showed that the damping properties of the composites depended on the composition ratios of PU to EP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.

Successful synthesis of blocked polyisocyanates, using easily cleavable phenols as blocking agents, and their deblocking and cure studies

Abstract: Phenols with electron withdrawing substituents at the 2,4-positions are important for use as blocking agents for isocyanates. Blocked polyisocyanates derived using such blocking agents are attractive for producing heat-cured polyurethane products at relatively low temperatures, i.e., below 160 °C. In this study, a series of blocked polyisocyanates were prepared using phenol, 2,4-dichlorophenol, 2-chloro-4-esterphenol and 2-chloro-4-nitrophenol; their blocking and deblocking kinetics, deblocking temperatures, equilibrium temperatures, equilibrium rate constants and cure-times were studied using a hot-stage FT-IR spectrophotometer, adapting neat conditions. Double Arrhenius plots for these thermally reversible systems were reported with an aim to understanding the relationship between forward and reverse reactions. It was found that the rates of forward and reverse reactions and equilibrium rates increased with increasing the acidity of phenol, except in the case of 2-chloro-4-nitrophenol; correspondingly, the deblocking temperature and cure-time of blocked polyisocyanates decreased. Blocked polyisocyanates obtained using unsubstituted phenol showed equilibrium temperature as a range in the double Arrhenius plot, whereas, in the case of 2,4-dichlorophenol and 2-chloro-4-nitrophenol, the Arrhenius plots showed distinct equilibrium temperatures. The equilibrium temperature range or equilibrium temperature of 2-chloro-4-esterphenol-blocked polyisocyanate was not determined, as extrapolation of its plot was found to extend out of the temperature range studied. Importantly, as expected with strong background, all three di-substituted phenols were found to deblock remarkably below 55–70 °C, compared to unsubstituted phenol, which deblocks at 135 °C. More importantly, 2-chloro-4-nitrophenol deblocks at 65 °C and its blocked polyisocyanate cures with polyol within 25 minutes at 110 °C.

In Situ FT-IR Study on the Blocking Reaction of Isocyanate with Naphthol

Abstract: The blocking reactions of phenyl isocyanate with 1-naphthol and 2-naphthol were investigated with in situ FT-IR. The reaction kinetics was studied and the reaction rates were described by a second-order equation. It was found that there was a remarkable induction period in the reaction. The induction period shortened with increase of temperature, and the induction period of 1-naphthol was obviously longer than that of 2-naphthol. Activation energies and Eyring parameters were also determined for the blocking reaction with 1-naphthol (E a = 55.3 kJ · mol−1, ΔH = 56.9 kJ · mol−1, ΔS = −120.8 J · mol−1 · K−1) and 2-naphthol (E a = 74.2 kJ · mol−1, ΔH = 69.8 kJ · mol−1, ΔS = −79.8 J · mol−1 · K−1), respectively.

Synthese und Kristallstruktur von Ammin(μ3‐L‐glutamato)kupfer(II)

Abstract: Synthesis and Crystal Structure of Ammine(μ3-L-glutamato)copper(II) [Cu(L-Glu)H2O]·H2O reacts with aqueous ammonia to give the ammine complex [Cu(L-Glu)NH3] (1). 1 forms orthorhombic crystals, space group P 21212 with a = 1585,1(1) pm; b = 979,46(7) pm and c = 504,70(5) pm. In the crystal structure of 1 the copper atoms are linked by μ3-glutamate units to give a 2D layer structure. The copper atoms exhibit a square-pyramidal coordination with two N atoms and two O atoms in the base plane and one O atom at the apex of the pyramid. The crystal structure is stabilized by a 3D network of N–H···O hydrogen bridges.