New automatic instrument for the determination of viscosity-average molecular weight

DNA isolated from Coli bacteriophage T1 was irradiated in 0.165 ᴍ NaCl with γ-rays. The molecular weight was determined by measurement of the sedimentation coefficient and viscosity. An analysis of the boundary permits the determination of the sedimentation distribution. The distribution of sedimentation coefficients obtained at various DNA concentrations were extrapolated to zero concentration and were transformed into molecular weight distributions. These were used to calculate the weight average molecular weight Mw and the number average molecular weight Mn.The molecular weight of T1-DNA was found to be 32· 106. After irradiation at a concentration of 200 μg/ml, double breaks as well as intermolecular crosslinks could be determined. The number of double breaks showed a rise with dose that can best be described as composed of a linear and a quadratic term. At low doses the crosslinks increase linearly, the rate being approximately half of that for the linear part of the double breaks. After higher doses, where most of the molecules are degraded, apparently no additional crosslinks are produced. No crosslinks were seen in DNA degraded by DNase. The influence of the DNA concentration on the degradation and the formation of crosslinks is discussed.

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Prediction of the swelling behaviour of amphiphilic hydrogels and the determination of average molecular weight between cross-links

Computational and Theoretical Polymer Science ◽

10.1016/s1089-3156(00)00030-1 ◽

2001 ◽

Vol 11 (6) ◽

pp. 475-482 ◽

Cited By ~ 10

Author(s):

M Şen ◽

O Güven

Keyword(s):

Molecular Weight ◽

Average Molecular Weight ◽

Swelling Behaviour ◽

Cross Links

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Molecular Weights and Intrinsic Viscosities of Polyisobutylenes

Rubber Chemistry and Technology ◽

10.5254/1.3540135 ◽

1943 ◽

Vol 16 (3) ◽

pp. 493-508

Author(s):

Paul J. Flory

Keyword(s):

Molecular Weight ◽

Intrinsic Viscosity ◽

Average Molecular Weight ◽

Chain Structure ◽

Molecular Weight Range ◽

Molecular Weights ◽

Satisfactory Precision ◽

Heterogeneous Polymers ◽

Definition Of

Abstract Experimental methods for fractionating polyisobutylene and for determining osmotic pressures have been described. The ratio π/c of osmotic pressure to concentration has been found in the case of cyclohexane solutions of polyisobutylene to vary nonlinearly with concentration, contrary to recent theories advanced by Huggins and the writer. The slope of this relationship appears to be independent of molecular weight. Reliable methods for extrapolating π/c to c=0 have been established, enabling the determination of absolute molecular weights with satisfactory precision up to values of about 1,000,000. Molecular weights of polyisobutylenes calculated from Staudinger's equation are too low; the discrepancy is more than ten-fold at high molecular weights. On the basis of data for carefully fractionated samples covering a two-hundred-fold molecular weight range, the intrinsic viscosity is found to be proportional to the 0.64 power of the molecular weight. This decided deviation from Staudinger's “law”cannot in this instance be attributed to nonlinear chain structure, as Staudinger has sought to do in other cases. This dependence of molecular weight on intrinsic viscosity leads to the definition of a “viscosity average”molecular weight which is obtained when the relationship is applied to heterogeneous polymers. The viscosity average is less than the weight average molecular weight, which would be obtained if Staudinger's equation were applicable, and greater than the number average obtained by osmotic or cryoscopic methods.

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