Compositional analysis serves to show the effect of process separations on petroleum residua as well as its dependence on the type of crude being used. Consistency of the asphalt residua first depends upon the separation cut-point and the crude type used. Distillation controls this by slicing off the lowest boiling fractions while concentrating the highest boiling fractions in the residuum. Solvent separations using propane to heptane cut deeper into the residua, preferentially removing the most saturated hydrocarbons first and then those of low molecular weight. This concentrates the most aromatic and highest molecular weight components in the raffinate or precipitated fraction. Propane precipitates a mixture of asphaltenes, polar-aromatics and naphthene-aromatics, pentane a mixture of asphaltenes and polar-aromatic, while heptane yields only asphaltenes by definition. Whereas propane has been used for many years in separating residua, the asphalt technologist might find the pentane precipitate to be more useful as a blending component for paving asphalt.

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of the aprotie solvent. The influence of the steric structure of the last monomeric unit of the growing chain may indeed play a role in the steric regulation of this radical polymerization process. Solution polymerization in a nonpolar solvent, such as n-CgFig, gives a high proportion of 1,4-polymeriza-

the grafting medium, the outermost shell is swollen, and swelling continues along a gradient to the middle of the fiber. As a result of the strong swelling forces involved, some of the tie molecules are broken, producing free radicals as observed. This gradient swelling condition can exist until the fiber has equilibrated with the medium. Since this medium contains a monomer capable of adding with the free radicals formed, the gradient swelling condition can be maintained for a considerably longer period of time which would ordinarily be determined only by diffusion rates of the molecules involved. In fact, as grafting proceeds, the swelling agent probably changes from water, which is a good swelling agent for the Presented at the Division of Polymer Chemistry, 162nd Meeting, ACS, Washington, DC, September 1971. We thank the Camille and Henry Dreyfus Foundation for generous support of this work.

Die Reaktionen des Schwefels mit schweren Erdölfraktionen und mit reinen Kohlenwasserstoffen (als Modellverbindungen) werden untersucht und die Reaktionsprodukte nach densimetrischen Methoden analysiert.