The modification recently developed for polyethylene, based on the thermolysis of peroxyketals and peroxy esters in the molten polymer, was applied to atactic and isotactic polypropylene. The grafting of an ester function onto the backbone of these polyolefins was much less efficient in this case than for the former. The thermal decomposition of such peroxides in polyethylene and isotactic and atactic polypropylenes was analyzed by DSC. These studies showed that the physical state of the polyolefin cannot account for the difference encountered in the functionalization yields. The analysis of the reaction products, generated in the thermolysis of a cyclic peroxy ketal, was realized on the extracts by GC and on the bulk by 1H NMR and DOSY spectroscopies. This led one to conclude that the difference in efficiencies in the chemical modification of the various polyolefins is related to the chemical reactivity of the hydrogens toward 1,1-dimethylethyloxy radicals. Surprisingly, it was found that hydrogen abstraction hardly occurs with polypropylene (either isotactic or atactic) despite the presence of thermodynamically more labile tertiary hydrogen atoms than the ones present in polyethylene. This was attributed to the steric hindrance of the methyl present on the backbone of this polyolefin.

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ABSTRACT:The functionalization of polyethylene was realized by the thermal decomposition of peroxyesters in molten polymer in the absence of any other additive. Ester and acid functions were introduced onto the polymer operating with various peroxyesters. This grafting resulted from the combination of a polymer radical, generated in the abstraction of a hydrogen from polyethylene by an alkoxy radical, with an acyloxy or carbon-centered radical arising from the perester. A complete methodology was set up to identify and to titrate the functions present onto the polyethylene and to determine the extent of crosslinked polymer.

In this article, a dynamical force microscopy study of self-assembled monolayers of organosilanes, grafted on a silica support, is reported. Organosilanes, terminated either with a functional group (ethylene glycol) or with a methyl group, were used. The influence of the reaction time and the solvent composition on the grafting was investigated to improve the homogeneity of the self-assembled monolayers. Numerical simulations of approach-retract curves, obtained in the tapping mode, were performed and compared to experimental ones.Informations, such as mechanical response and height of the grafted organic layers, have been obtained.

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This paper presents unenhanced Raman spectra of self-assembled monolayers [2-(22-trichlorosilanyldocosoxy)ethyl acetate], grafted on to silicon dioxide wafers, obtained by using a confocal Raman microscope. The quality of monolayer formation, at the micrometer scale, was monitored by drawing maps of a few square micrometers and homogeneous monolayers were obtained using a detergent cleaning procedure. The results are in good agreement with those obtained previously by atomic force microscopy studies.

This paper presents the successful use of ruthenium nanoparticles, stabilized in water by ammonium surfactants, in the selective hydrogenation of -pinene and the first industrially reported scale-up of this catalyst on a multigram-scale. After designing the nanocatalyst at the lab scale, operational parameters (substrate/metal ratio, pressure and temperature) were identified and optimized in the scale-up. The -pinene hydrogenation process was operated with a 200 g batch, under 30 bar H 2 and at 110°C, with a complete conversion and a selectivity of 98% into cis-pinane within 4 h. The catalyst was easily recycled through a liquid-liquid biphasic approach for 5 reaction cycles to achieve a total turnover number (TTON) of 14000.