The coadsorption of water and preadsorbed oxygen on Ru͕0001͒ was studied by synchrotron-based highresolution x-ray photoelectron spectroscopy. A dramatic change was observed in the interaction of water with oxygen between low and high oxygen precoverages. Low oxygen coverages below 0.18 ML induce partial dissociation, which leads to an adsorbed layer of H 2 O and OH. Around half the oxygen atoms take part in this reaction. All OH recombines upon heating to 200 K and desorbs together with H 2 O. Oxygen coverages between 0.20 and 0.50 ML inhibit dissociation, instead a highly stable intact water species is observed, which desorbs at 220 K. This species is significantly more stable than intact water on the clean surface. The stabilization is most likely due to the formation of hydrogen bonds with neighboring oxygen atoms. For intermediate oxygen coverages around 0.18 ML, the dissociation behavior depends on the preparation conditions, which points toward possible mechanisms and pathways for partial dissociation of water on Ru͕0001͖.

S P O P M BThe thermal stabilities of polybutadienyllithium, polyisoprenyllithium, and polystyryllithium solutions have been determined in hydrocarbon solvents. Kinetic analysis indicated that a complex mechanism was involved in the thermolysis of polybutadienyllithium. The thermal stability was observed to increase with increasing lithium concentration, suggesting the presence of competitive reactions in addition to the expected elimination of lithium hydride. The thermal stability of the three systems studied was consistent with their reported degrees of association: dimeric polystyryllithium was less stable than tetrameric polyisoprenyllithium or hexameric polybutadienyllithium.

A method for simultaneously determining the molecular weight averages, molecular weight distribution, hydroxyl equivalent weight, functionality averages, and functionality distribution of hydroxyl‐terminated polybutadienes using GPC has been developed. The method is based on the preparation of a UV absorbing derivative of the hydroxyl group and GPC analysis using dual differential refractive index and UV detectors. In order to determine the hydroxyl equivalent weight, quantitative derivatization of the hydroxyl group is required. If the equivalent weight can be determined by an independent method, the derivatization reaction can be less than quantitative if sufficient UV absorptivity can be obtained. The procedure used for calibrating the GPC columns and UV detector are presented. Equations for calculating number‐ and weight‐average functionalities from GPC data were also developed. The number‐average functionality is independent of the functionality distribution, but the weight‐average functionality is dependent upon the distribution of functionality. The ratio of the weight‐average to number‐average functionality is indicative of how the functionality is skewed as a function of molecular weight.

SynopsisThe functionality averages, functionality distribution, hydroxyl equivalent weight, molecular weight averages, and molecular weight distribution of three commercial hydroxyl terminated polybutadienes have been determined using a dual-detector GPC method used to analyze the polymers before and after derivatization with phenyl isocyanate. The values of these parameters are compared with existing literature data. The determined number-average functionalities were in reasonable agreement with previously published values. However, the distribution of functionality as a function of molecular weight differs from distribution data obtained by column fractionation techniques. Our distribution data appears to be generally consistent with the distribution expected from the polymerization mechanisms. The differences in the variation of hydroxyl content with molecular weight obtained from the dual-detector GPC method and the column fractionation procedures should be resolved since a combination of these procedures could provide additional information regarding the actual amounts of mono-, di-, and polyfunctional polymer and their molecular weight distributions. The dual-detector GPC method should be applicable for the determination of the distribution of a variety of functional groups provided a selective derivatization reaction is available or a second detector which can directly and accurately determine the concentration of the functional group is available.

SynopsisA method for determining the distribution of olefinic bonds in elastomers has been developed using dual detector GPC analysis of the polymer after derivatixation with 2,4-dinitrobenzenesulfenyl chloride. The method is particularly useful for determining the distribution of olefinic bonds in hydrocarbon copolymers having small levels of unsaturation.