Investigation on the Thermo-Oxidative Degradation of Polyethylene, Poly(vinyl chloride), and Polystyrene Using NiPIm1.5 and NiPIm2 Nanocomposites

In this work, we report the synthesis of two nanoscale composites of nickel, NiPIm_1.5 and NiPIm₂ (NiPIm_1.5 = [Ni(C₃H₄N₂)(H₂O)₅](HPO₄)(H₂O)·0.3(C₃H₄N₂) and NiPIm₂ = [Ni(C₃H₄N₂)(H₂O)₅](HPO₄)(H₂O)·0.4(C₃H₄N₂)·H₂O), characterization by various instrumental methods and the investigation of the thermo-oxidative degradation of polyethylene (PE), poly(vinyl chloride) (PVC), and polystyrene (PS) in the presence of both nanocomposites. All of these polymers are subjected to thermal treatment with and without composites at 353 K for 120 min. The rate of degradation is maximum with NiPIm₂ for all three polymers, PE-13.1522%, PS-13.6152%, and PVC-8.04%, whereas with NiPIm_1.5, PE-7.3128%, PS-11.9837%, and PVC-4.9106%. The percentage of degradation in the presence of composites is much greater than the percentage of degradation without composites. The specific heat capacities of NiPIm_1.5 and NiPIm₂ are -148.42 and -348.64 J kg^-1 K^-1, respectively. The degradation process takes place by free radical mechanism. Thermogravimetric and differential thermal analyses revealed that the temperatures corresponding to the formation of composite materials with NiPIm₂ are 338.76, 331.78, and 354.30 K for PE, PVC, and PS, respectively. The temperatures of formation of the above composites are found to be less than that of NiPIm_1.5. The degraded residues of polymers indicate that ester is formed in each case along with other byproducts containing imidazole. Infrared studies revealed the thermal oxidation of hydroperoxides and the formation of ketone.

Kinetics and Mechanism of the Reaction of Dichlorotetraaquaruthenium(III) and Thiols

The formation of an intermediate ruthenium(iii) thiolate complex by the interaction of thiols, RSH (R = glutathione and l-cysteine) and dichlorotetraaquaruthenium(iii), [RuIIICl2(H2O)4]+, is reported in the temperature range 25–40°C. The kinetics and mechanism of formation of the intermediate complex were studied as a function of [RuIIICl2(H2O)4]+, [RSH], pH, ionic strength and temperature. Reduction of the intermediate complex takes place slowly and results in the corresponding disulfides RSSR and [RuIICl2(H2O)4]+. The results are interpreted in terms of a mechanism involving a rate-determining inner-sphere one-electron transfer from RSH to the oxidant used in the present investigation and a comparison of rate and equilibrium constants is presented with activation parameters.

Kinetics of oxidation of hydrogen peroxide and ascorbic acid by a tribridged manganese(IV,IV) dimer in feebly acidic media

In weakly acidic, aqueous buffer (MeCO2-+ bipy), the complex ion [Mn2IV(μ-O)2(μ-MeCO2)(bipy)2(H2O)2]3+, 1 (bipy = 2,2prime-bipyridine), coexists in rapid equilibrium with its hydrolytic derivatives, [Mn2IV(μ-O)2(bipy)2(H2O)4]4+, 2, and [Mn2IV(μ-O)2(μ-MeCO2)(bipy)(H2O)4]3+, 3. The solution quantitatively oxidizes hydrogen peroxide to oxygen and ascorbic acid to dehydroascorbic acid, itself being reduced to MnII. In the presence of excess reductant, the reactions follow simple first-order kinetics with no evidence for the accumulation of a significant amount of any intermediate manganese complex. The ascorbate anion shows overwhelming kinetic dominance over ascorbic acid, but no evidence is available for deprotonation of hydrogen peroxide. The preferred intimate mechanism for hydrogen peroxide is inner sphere but that for ascorbic acid is uncertain. For both reductants, increased extent of aquation leads to increased kinetic activity in the order: 1 < 2 < 3.Key words: kinetics, manganese, ascorbic acid, hydrogen peroxide, 2,2prime-bipyridine.