Hydrolyzable functional silanes are used as silicone elastomer crosslinkers. The hydrolysis, triggered by air moisture, leads to crosslinking of linear polymer chains to three-dimensional networks. The properties of these elastomers depend on the silane structure. The in uence of the structure has been studied for RSi(OR 0 ) 3 silanes with R D Me, Et, Pr, Bu, Pentyl (Pe), Vinyl (Vi) and Phenyl (Ph) for hydrolyzable acetoxy or oximino groups.Reactivity differences have been observed. The cure kinetics follows the order Vi > Ph » Me > Et > Pr > Bu > Pe leading to a decrease in surface curing rate from Vi to Pe. The cure thermodynamics, i.e. completeness of cure, follows the order Me > Et > Pr > Bu > Pe and Vi > Ph leading to a decrease in the crosslink density from Me to Pe. The lower degrees of cure are related to steric and inductive effects of the functional groups.Oximinosilanes showed a lower reactivity compared to acetoxysilanes, because of a Si ON bond being more stable than a Si OAc bond. This also leads to slower surface cure and lower crosslink density.Organometallic tin used for the catalysis of oximinosilane systems gave results similar to organometallic titanium. For acetoxysilane systems, the titanium system was found to be more ef cient.Silicone materials tailored to speci c requirements can be designed. So the cure rate, release and mechanical properties can be adjusted with the selection of appropriate silanes.

-In this paper, a comparison of the biofuels barrier properties of PolyAmide 6 (PA6) and High Density PolyEthylene (HDPE) is presented. Model fuels were prepared as mixtures of toluene, isooctane and ethanol, the ethanol volume fraction varying between 0% and 100%. Barrier properties were determined at 40°C by gravimetric techniques or gas chromatography measurements, and it was shown that polyamide 6 permeability is lower than that of polyethylene on a wide range of ethanol contents up to 85% of ethanol (E85) in the biofuel, permeability of PA6 being 100 times lower than that of HDPE for low ethanol content fuels (E5, E0). The time-lags were also compared, and on the whole range of ethanol contents, HDPE permeation kinetics appears to be much faster than that of PA6, the time lag for a 1 mm thick specimens in presence of E10 being 50 days for PA6 and 0.5 days for HDPE. The compositions of the solvent fluxes were analyzed by FID (Flame Ionization Detector) gas chromatography, and it turned out that the solvent flux was mainly made up of ethanol (minimum 95%) in the case of PA6, whereas in the case of HDPE, solvent flux was mainly made up of hydrocarbons. The implication of this difference in the solvent flux composition is discussed in the present article, and a side effect called the "fuel exhaustion process" is presented. The influence of the sample thickness was then studied, and for the different biofuels compositions, the pervaporation kinetics of polyamide 6 appeared to evolve with the square of the thickness, a long transitory regime being highlighted in the case of PA6. This result implies that the time needed to characterize the steady state permeability of thick PA6 parts such as fuel tanks can be very long (one year or more), this duration being far superior to the Euros 5 or Euro 6 standard emission measurements time scale. The influence of temperature on the permeability was finally assessed, and the activation energy that is the signature of the temperature dependence of the barrier property turned out to be similar for the different biofuels compositions.Re´sume´-Proprie´te´s barrie`re aux bio essences du polyamide 6 (PA6) et du polye´thyle`ne haute densite´(PEHD) -Dans cet article, les proprie´te´s barrie`re aux bio essences du PolyAmide 6 (PA6) sont compare´es a`celles du PolyEthyle`ne Haute Densite´(PEHD). Des essences mode`les sont pre´pare´es en faisant varier entre 0 et 100 % la fraction volumique d'e´thanol dans des me´langes ternaires e´thanol/tolue`ne/isooctane. Les proprie´te´s barrie`re aux bio essences sont caracte´rise´es a`40°C par gravime´trie ou par des mesures de chromatographie en phase gaz, et il est montre´que la perme´abilite´du PA6 est plus faible que celle du PEHD sur une grande gamme de compositions d'essences contenant jusque 85% d'e´thanol, le ratio de performance atteignant un facteur 100 pour les essences faiblement alcoolise´es (E5, E0). Les temps d'induction ont aussi e´te´compare´s, et pour toutes les compositions d'essences e´value´es, il apparait que la ci...