T h e vapor-phase radiolysis o f cyclohexane and benzene-cyclohexane mixtures has been studied with isotopic tracer techniques using CsDlr and CGDG. Benzene does not quench the molecular detachment o f hydrogen, CGDI? D! +. CGDIo, but interacts with the secondorder processes giving I-ID in CGD1?-Cr,H1? mixtures. T h~s ~nteraction is not H-atom scavenging and an ionic mechanism is preferred. T h e radiolysis o f all these systenls is very different from their liquid-phase radiolysis.'The low radiolytic yields in liquid benzene-cyclohexane mixtures are a classic example of 'protection'. T h e interactions causing these low yields are physical; they do not involve the ma1;ing or breaking of chemical bonds. This has been shown in two ways: by complete product analysis (1) and by techniques using isotopically labelled hydrocarbons (2). These isotopic techniques have revealed similar interactions in alkane mixtures (3) which are, however, absent in the vapor phase (4). As a result, we expect the vapor-phase radiolysis of benzene-cyclohexane inixtures to show marked differences froin the liquid-phase radiolysis.We have applied our isotopic techniques t o the vapor-phase radiolysis. In the liquid, benzene quenches both the first-order process, which gives D2 by molecular detachment from CGDl?, and the second-order processes which give HD in C G H~~-C G D~~ mixtures. I n the vapor, however, the D2 yield is reduced much more sloivly than would be expected if I-I-atom scavenging were occurring and so we favor an ionic mechanism for this interaction. Physical interactions quenching the first-order processes are absent. 1;isher 'Spectranalyzed' cyclohesane and benzene and Merck benzene-dG and benzene-free cyclohexane-d,z were used as received. T o minimize air contamination the sa~nple vessels (volume about 330 m l ) were evacuated t o 5x10-"mm Hg at 500' C for at least 24 hours before being filled and irradiated. Even so, the gaseous radiolytic products contained about 3% air. T h e vessels were sealed t o a grease-and mercury-free preparation line; the sample (about 2 1111 o f liquid) was degassed b y repeated freezing, pumping, and thawing and was then distilled into the irradiation vessel. During irradiation in our Co60 source, t h e vessels were kept at a constant temperature ( 2~2 ' C ) in a n electric furnace. Using the techniques already described ( 4 ) , we found t h e dose rate t o be 4.S7XlOL6 ev/sec g cyclohexane; the dose in most experiments was 3.61 X 101%v/g organic vapor.After
A sample of poly(butadiene‐co‐styrene), SBR, was divided into twelve fractions by precipitation from a dilute benzene solution. The intrinsic viscosities [η] and weights of all the fractions were measured, and the sedimentation coefficients s0 were determined for the nine fractions of highest molecular weight. From the values of [η] and s0 the number of crosslinks per molecule m, was calculated for each fraction. The results indicated that only the four fractions of highest molecular weight contained crosslinked molecules. The number of crosslinks per weight‐average primary (prior to crosslinking) molecule for the entire sample, δ0, was obtained from the weights of the fractions and the values of m. By use of various theories, values of δ0 of 0.78, 0.56, and 0.38 were obtained. From the values obtained for [η] and s0 and the pycnometric partial specific volume of the polymer in benzene, the molecular weights M of the nine fractions of highest [η] were calculated. The molecular weights of the remaining fractions were calculated from the relation between M and [η] obtained by others. A molecular weight distribution curve was established and used to obtain δ0 ≤ 0.36.
Using Verwey and Overbeek's theory and Stokes' law the paths of two charged particles undergoing interaction have been calculated. Brownian motion and inertial effects are assumed to be negligible; the particles are spherical and nonswelling and the flow is laminar. From the calculated paths and the collision frequency the concentration dependence of the viscosity has been theoretically derived for a suspension of spherical, charged, nonswelling particles. At high ionic strength the theory agrees well with previously described experiments on sulfonated polystyrene latex, but at low ionic strength the theory overestimates the Huggins coefficient, k', particularly at low shear rates.
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