Mechanisms of antioxidant action: Mechanochemically bound antioxidants to polyethylene and polypropylene

It is shown that a thiolamide antioxidant, 4-mercaptoacetamido diphenylamine (MADA) can be reacted with both polypropylene and polyethylene in a mechanochemical process. The resulting bound antioxidant concentrates (MADA-B) can be used for the thermal and photostabilisation of the parent polymers. The adduct is very stable to solvent extraction and is also very effective as a high temperature antioxidant for polypropylene subjected to water leaching.The uv stabilising mechanism of MADA-B is believed to be related to the regenerative process involved in the mechanism of stabilisation by hindered nitroxyl radicals.     

Classification and identification of mass spectra of toxic compounds with an inductive rule-building expert system and information theory

An expert system for classifying and identifying low-resolution mass spectra of toxic and related compounds was developed with an expert shell program. The shell system used was an inexpensive, rule-building software package with an implementation of the ID3 algorithm. Seventy-eight target compounds were used to establish classes previously found by SIMCA class modeling. The six classes included nonhalobenzenes; chlorobenzenes; bromoalkanes and bromoalkenes; mono- and di-chloroalkanes and the analogous alkenes; tri-, tetra- and penta-chloroalkanes and the analogous alkenes; and unknowns. Identification modules for the target compounds were forward-chained to the classification modules. An expert system based on binary-encoded mass spectra, with 17 masses selected on the basis of information content, gave 97 and 86% classification accuracy for training and test spectra, respectively. Identification accuracy was 77 and 80%, respectively. An expert system was also developed which was based on ternary encoding of the mass spectra of 108 training compounds using 25 masses. Ternary encoding has many of the advantages of binary encoding, without the disadvantages. This latter system was tested with the spectra of thirty compounds found in field samples or potential air pollutants. The classification accuracy for training and test spectra was 99 and 97%, respectively. The identification accuracy was 96 and 93%, respectively. With proper precautions, the rule-building expert system can be very effective in spectral classification and identification problems.     

The effect of thermal processing on PVC—VI. The role of hydrogen chloride

The reaction between cumene hydroperoxide (CHP) and anhydrous hydrogen chloride under various conditions of temperature and concentration has been studied in an inert solvent (chlorobenzene) and in an oxidisable medium (cumene). The kinetics were first order with respect to each reactant; the energy of activation of the overall second-order reaction was 53.4 kJ mol^?1 K^?1. Competing ionic and free radical mechanisms were found to operate, the latter predominating at relatively high HCl concentrations, leading to rapid pro-oxidation in cumene. The effect of typical organo-tin PVC stabilizers on the pro-oxidant process were examined. It was found that dibutyltin maleate neutralized the HCl thus eliminating the pro-oxidant effect when used in stoichiometric proportions, but had little other effect. Dioctyltin bis(isol-octylthioglycollate) on the other hand not only neutralized the HCl stoichiometrically but gave additional oxidative stabilization over a wide concentration range.     

Mechanisms of antioxidant action: The effect of thermal processing on the antioxidant activity of sulphur compounds

The nickel dithiophosphates and their corresponding disulphides are shown to be more effective uv stabilisers for LDPE than the closely related nickel xanthates and disulphides (dixanthogens). In general, the nickel complexes in both series are more effective uv stabilisers than the disulphides.Evidence is presented to show that the better performance of the dithiophosphates than the xanthates is associated with their higher solubility in the polymer. For the same reason, nickel dithiolates containing long alkyl substituents are more effective uv stabilisers than those containing shorter alkyl substituents.Thermal processing adversely affects the photo-stabilising performance of nickel dithiolates whereas the performance of the less efficient disulphides is enhanced under the same conditions. In the former case, the uv stability of the polymer is shown to be directly proportional to the amount of the nickel complex left after processing. In the case of the disulphides, on the other hand, the evidence suggests that increasing the severity of their processing increases the extent of oxidation to products which are more effective uv stabilisers than the parent disulphides.     

The uniqueness of the adjoint operation I

Let H be a complex, infinite-dimensional Hilbert space. Let B(H) denote the set of bounded linear operators on H. This paper contains a nonlinear characterization of the adjoint operation on B(H). The statement of this result is:THEOREM:Let h: B(H) B(H)be a function such that h(I)0.Then h(ST)=h(T)h(S)and h(S)S0for all elements Sand Tof B(H)if and only if h(S)=S^* for all S B(H).     

Direct dynamics trajectory study of the reaction of formaldehyde cation with D2: vibrational and zero-point energy effects on quasiclassical trajectories

Quasiclassical, direct dynamics trajectories have been used to study the reaction of formaldehyde cation with molecular hydrogen, simulating the conditions in an experimental study of H2CO+ vibrational effects on this reaction. Effects of five different H2CO+ modes were probed, and we also examined different approaches to treating zero-point energy in quasiclassical trajectories. The calculated absolute cross-sections are in excellent agreement with experiments, and the results provide insight into the reaction mechanism, product scattering behavior, and energy disposal, and how they vary with impact parameter and reactant state. The reaction is sharply orientation-dependent, even at high collision energies, and both trajectories and experiment find that H2CO+ vibration inhibits reaction. On the other hand, the trajectories do not reproduce the anomalously strong effect of nu2(+) (the CO stretch). The origin of the discrepancy and approaches for minimizing such problems in quasiclassical trajectories are discussed.     

Heteroatom transfer to alkenes by N-protected-oxaziridines: new reaction pathways and products

N-Alkoxycarbonyl- and N-carboxamido-oxaziridines are shown to react with aromatic alkenes to give epoxide, aziridine or hydro-oxidation products, in ratios depending on the oxaziridine structure. Chiral oxaziridines can effect epoxidation and hydro-oxidation with promising levels of asymmetric induction.