摘要：

The sedimentation and diffusion constants of twelve fractions and of a very highly unfractionated sample of nitrated cotton cellulose have been studied. The nitrogen content of all samples was about 13.8%. Between the viscosity number in acetone at 20°C. and the ultracentrifuge molecular weight the relation [η] = 2.8 times; 10 3 M 1.00 S,D in cm. 3 g. 1 is obtained at the gradient 0. Recalculating Jullander's ultracentrifuge measurements to our nitrogen content and the measurements of Newman, Loeb, and Conrad in ethyl acetate to acetone gives a very good agreement for the three ultracentrifuge measurements. On the other hand, the light scattering molecular weights M LS are higher at the same viscosity number throughout: perhaps this may be accounted for by the standard used or by some impurities of the solutions. The coil diameters are calculated from [η], M , and the friction factor f according to Debye-Bueche-Peterlin. As M LS is considerably higher than M S,D , the coil radii as a function of molecular weight obtained by the different methods cannot be compared. However, the light scattering coil diameters ( r ) 1/2 agree satisfactorily with the calculated values. All molecular weights are found to be, to a good approximation, proportional to M 1.34 instead of M 1.00 for an ideal coil. Thus the very stiff cellulose molecule shows a non-ideal behavior in solution. The relation ( r 2 ) M is not valid, and we do not find any indication of its validity as a limiting law for extremely high and no longer measurable molecular weights. The relation for cellulose nitrates is similar to the relation previously found for polymethyl methacrylate in acetone, only the effects are more marked in the present case. An exponent > 1/2 for the viscosity-molecular weight relation is parallel to a second virial coefficient >0 and to an increase of the Kuhn statistical chain element with increasing molecular weight.

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