B. Mohamad Ali

Bio: B. Mohamad Ali is an academic researcher from University of Madras. The author has contributed to research in topics: Catalysis & Dendrimer. The author has an hindex of 3, co-authored 4 publications receiving 26 citations.

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.

Elimination of 50% Iodine and Excellent Performance of Dye-Sensitized Solar Cell Enabled by TEMPO Radical Dendrimer-Iodide Dual Redox Systems

Abstract: Detrimental effect of counter electrode corrosion, electrolyte leakage problem, and sublimation of iodine ions affect the performance and stability of dye-sensitized solar cells (DSSCs) based on a liquid redox electrolyte system. TEMPO/TEMPO+ is the most desirable one to replace the existing redox couples in liquid electrolyte owing to its rapid and reversible one electron kinetics, high diffusion coefficient, and electrochemical stability. In the present study, a fifth generation polyurethane dendrimer end-capped with 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) was prepared and employed as an active redox mediator to replace up to 75% of iodine ions in the standard liquid iodide electrolyte system to elucidate the effect of a quick self-exchange reaction in DSSCs. In this concern, quasi-gel type electrolytes were prepared by incorporating different amounts of a newly prepared TEMPO radical dendrimer to a liquid I-/I3- redox system and were used as a dual redox mediator for DSSCs. Blending of 50 wt % of I-/I3- electrolyte with 50 wt % of the radical dendrimer improved the device performance (η) unprecedentedly from 6.56 to 9.54% upon illumination with 1 sun intensity. Thorough electrochemical characterization of cells was carried out and all such parameters authenticated this remarkable enhancement. Stability of the device was also found to be good, which retained its >80% efficiency after 30 days. (Less)

Hydrogenolysis of glycerol to 1, 2-propanediol on MgO/Ni3C catalysts fabricated by a solid-state thermal synthesis

Abstract: In this study, the fabrication of MgO, Ni3C and MgO/Ni3C (1:1, 1:2, & 2:1) catalysts via a one-step solid-state synthesis and the production of 1, 2-propanediol from glycerol (a by-product of the biodiesel industry) on the synthesized catalysts without using any external hydrogen sources were presented. Different physicochemical techniques were used to analyze the synthesized catalysts. The XRD result revealed formation of the composites with MgO/Ni3C pure phase catalyst; 5% amorphous and 95% crystalline nature. The MgO/Ni3C (1:1) catalyst showed a high surface area and pore volume of about 183 m2 g−1 and 0.18 cm3 g−1, respectively. MgO/Ni3C (1:1) showed a superior thermal stability and has a stable regeneration. Catalytic conversion of glycerol to 1, 2-propanediol was investigated under different reaction conditions (180 °C -240 °C, 1–5 h, 25–125 mg of catalyst, 10 wt.% of glycerol, and 600 rpm). Compared to other prepared materials, the MgO/Ni3C (1:1) catalyst showed a superior activity with about 74% of glycerol conversion, 67% of 1, 2-propanediol selectivity, and about 94% of the total product recovery. Its SRR and TOF values were determined as 15.03×10−3 mol g−1 s−1 and 3.01 s−1, respectively. The results demonstrated that MgO/Ni3C (1:1) is a potential candidate for a superior glycerol conversion.

Catalysis of cure reaction of ɛ-caprolactam-blocked polyisocyanate with diol using non-tin catalysts

Abstract: Catalysis of cure reaction of ɛ-caprolactam-blocked polyisocyanate with 1,4-butane diol in the presence of DABCO - a tertiary amine, tin(II) 2-ethylhexanoate and non-tin organometallics like bismut...

Preparation and properties of self-healing cross-linked polyurethanes based on blocking and deblocking reaction

Abstract: Self-healing polyurethane via incorporating reversible bonds obtains great recognition. However, a reasonable design of polyurethane containing reversible bonds with high self-healing efficiency, facile preparing and low costs is still a challenge. Here, we report a novel self-healing polyurethane (Sh-C-PU) containing reversible urethane bonds ( NHCOO ), which was conducted by the reaction of diphenol (tetrabromobisphenol A, TBBPA) and 4, 4′-diphenylmethane diisocyanate (MDI). TBBPA can block the NCO groups in MDI at 60 °C, and NCO groups can be deblocked at the temperature higher than 90 °C, which gave Sh-C-PU self-healing property. FTIR analysis demonstrated thermal reversibility of Sh-C-PU by monitoring the deblocking and reblocking reaction in thermal cycles. In addition, qualitative self-healing phenomenon of cracks was observed under polarizing optical microscopy, and quantitative evaluation of self-healing Sh-C-PU via mechanical properties confirmed the great healing property of Sh-C-PU with healing efficiency by 97.82%, 86.38% and 55.04% for three times self-healing cycles, respectively.