L. A. Shibaev

Antiwear Effect of Fullerene C60 Additives to Lubricating Oils

The protective film (≤1000 Å thick) formed on the copper foil surface upon friction of a steel roller lubricated with industrial oil containing 5% fullerene C60 was studied by optical and electron microscopy, X-ray diffraction (XRD) analysis, hardness measurements, and mass spectrometry. This protective film is probably a fullerene-polymer network formed by fullerene C60 and covalently bound fragments of hydrocarbon chains released in the course of mechanochemical degradation of the lubricating oil. The film exhibits elevated hardness and antiwear properties, and increases the load-carrying power of the tribotechnical unit. Chemical mechanisms of tribopolymerization were analyzed.

Influence of C60 Fullerene on the Oxidative Degradation of a Free Radical Poly(Methyl Methacrylate)

The results of studies of thermal and oxidative degradation of a free-radical poly(methyl methacrylate) (PMMA) and the influence of a fullerene C60 on these processes are considered. The best characteristic of the change of the thermal stability is the temperature shift of the entire thermal gravimetric (TG) curve (or the middle part of it), but not the shift of onset or the starting temperature of the mass loss. During oxidative degradation in air of PMMA, three processes occur practically simultaneously: thermal degradation, or scission of chains; oxidation, or insertion of oxygen atoms in the polymer chains and in products of the degradation; and a sublimation of degradation products. The competition between exothermic and endothermic processes results in sharp changes in the balance of heat energy in the system and the sign of the total heat effect. In accord with these changes all of the process of PMMA oxidative degradation can conditionally be divided into three stages. The introducing of small quantities of C60 in a system results in replacement of oxygen by a fullerene or to a partial avoidance of oxidation, as a result of which, at the first stage, a smaller quantity of degradation products is formed and oxidized. There is a “transfer” of degradation products and heat generation from the first, lowest temperature stage, to the third, highest one. Simultaneous application of DSC and TG techniques has shown that during oxidative degradation of PMMA, especially in the presence of a fullerene, there is a latent degradation manifested in exothermal effects on DSC curves without mass losses on the TG curves. The introducing of C60 results in narrowing of the peaks (by ∼1.5 times) on DTG and MTA curves that may be explained by the narrowing of a set of possible degradation reactions. The C60 molecules are divided during oxidative degradation of PMMA into two groups: linked (∼20%) and nonlinked with macroradicals of PMMA. The nonlinked molecules of C60, in turn, are subdivided into oxidized and volatilizing without oxidation and degradation. The inhibiting effect of C60 on the thermal oxidative degradation reduces basically to two processes: to formation of fullerene-containing chains of PMMA and to nonchain inhibition. The matrix of PMMA also has a significant influence on the thermal behavior of C60.

Thermal and tribological properties of fullerene-containing composite systems. Part 2. Formation of tribo-polymer films during boundary sliding friction in the presence of fullerene C60

The techniques of mass‐spectrometric thermal analysis, wide‐angle X‐ray diffraction, scanning and transmission electron microscopy, light microscopy, and hardness and tribological measurements were used for study of formation and properties of protective—anti‐wear and friction‐reducing—tribo‐polymer film forming on metal surfaces during sliding boundary friction, in the presence of fullerene C60 used as an additive to some mineral lubricating oils and greases. A possible mechanism of formation of tribo‐polymer film was proposed based on the idea of attachment of paraffin and naphthenic oligomers of the lubricants to C60 molecules, which in turn are polymerized and form a hard fullerene network with attached polyolefin chains. A fullerene network provides a high wear resistance while polyolefin chains provide some decrease in the friction coefficient and widening of the working intervals of friction joints.

Effect of Fullerene C60 on Thermal Oxidative Degradation of Polymethyl Methacrylate Prepared by Radical Polymerization

The influence of small C60 additions on thermal and thermal oxidative degradation of polymethyl methacrylate prepared by radical polymerization was studied by differential scanning calorimetry, thermo- gravimetric analysis, differential thermogravimetric analysis, and mass spectrometry.

Mass-spectrometric investigation of the thermal stability of polymethyl methacrylate in the presence of C60 fullerene

The thermal degradation of polymethyl methacrylate, synthesized by the method of free-radical polymerization, in a mixture with C60 fullerene has been investigated by mass-spectrometric thermal analysis. C60 suppresses the first two, low-temperature, stages in the thermal degradation of polymethyl methacrylate and thereby increases its thermal stability.

Effect of C60 on the thermal stability of polyethylene glycol grafted to it

The thermal degradation of regular polymer networks, cross-linked by C60 molecules along the end groups of polyethylene glycol, has been investigated by mass-spectrometric thermal analysis for the example of polyethylene glycol grafted to fullerene C60. The character of the thermal degradation of the networks is substantially different from that of free polyethylene glycol and other polymer systems investigated earlier. The grafting to C60 increases the thermal stability of polyethylene glycol.

The effect of fullerene C60 on the thermooxidative degradation of a free-radical PMMA studied by thermogravimetry and calorimetry

Thermogravimetric and calorimetric study of the effect of fullerene C60 on the thermooxidative degradation of free-radical poly(methyl methacrylate) revealed three stages in the process.

Influence of fullerene C60 on the kinetics of toluene evaporation

The kinetic dependences of the relative weight loss of the solvent from dilute solutions of fullerene C60 in toluene under ambient conditions were determined. Evaporation of the pure solvent is slower than that of the same solvent from dilute solutions (≤0.01%).

Synthesis and spectral characteristics of silicon-containing poly(salicylidene azomethines) derived from aromatic di- and tetraamines

New silicon-containing poly(salicylidene azomethines) were prepared by polycondensation of di-or tetrasalicylidene derivatives of aromatic di- or tetraamines. The spectral data suggest the occurrence of noncovalent transannular donor-acceptor interaction N→Si providing “nonclassical” conjugation.

Thermal and Tribological Properties of Fullerene‐Containing Composite Systems. Part 3. Features of the Mechanism of Thermal Degradation of Poly‐(N‐Vinyl‐Pyrrolidone) and Its Compositions with Fullerene C60

By mass‐spectrometric thermal analysis (MTA) the thermochemical features of poly(N‐vinyl pyrrolidone) (PVP) and its compositions with fullerene C60 were studied. The mechanism of PVP thermal degradation was investigated; in particular the nature of the low‐temperature degradation (between 75 and 300°C) accompanied by output of pyrrolidone was explained as well as the influence of fullerene C60 on this mechanism. It was shown that during thermal degradation of copolymer PVP‐C60, there is a disappearance of the low‐temperature peaks of the output of pyrrolidone that is interpreted as an increase of the thermal stability of N‐vinyl‐pyrrolidone fragments in this product in comparison with their thermal stability in pure PVP.