142 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1952 



response to mechanical shocks of very short duration. The lowest fre- 

 quency configurational relaxation is spread over a wide spectrum of 

 relaxation times in pure liquids. 



Measurements" of these and other chains in various solvents have 

 also been made and the results are discussed, from a chemical point of 

 view, in a companion paper by W. O. Baker and J. H. Heiss. It is shown 

 that the stifTnesses vary with the polymer chain and the solvent used. 



IV. MEASUREMENTS OF PURE LIQUID POLYMERS 



A. Shear Wave Measurements in Liquid Polymers 



Similar shear wave measurements have been made for pure polyiso- 

 butylene liciuids of molecular weights from 904 to 10,380 (i.e. from 16 

 chain elements to 186 chain elements), by the techniques described in 

 Section 11. Some of these results have been discussed in reference (8) 

 but the much more comprehensive measurements made since require 

 some revisions of the original conclusions. 



The easiest data to interpret are the high-frequency data obtained by 

 the shear wave reflectance method. The data of Table I give measure- 

 ments of 8 liquids varying m average molecular weight from 900 to 

 10,380, at three frequencies and four temperatures. If we plot for ex- 

 ample the Maxwell shear stiffness and viscosity for the three frequencies 

 and for 25°C as a function of the number of chain elements (here a chain 

 element is taken as two adjacent carbon atoms one of which has two 

 methyl groups attached and the other two hydrogens) the 4.5-mc meas- 

 urements are shown by the triangles of Fig. 15. The 14 megacycle 

 measurements are shown by the circles and the 24-mc measurements by 

 the squares. 



An attempt was made to fit these measurements with a two relaxa- 

 tion mechanism shown by the figure with two stiffnesses which are taken 

 to be independent of the molecular weight and equal respectively to 

 1.2 X 10* dynes/cm^ and 6 X 10* dynes /cm^ The best fit is obtained by 

 taking the two viscosities rji and 772 equal and these are adjusted for the 

 different molecular weights in such a manner as to best fit the experi- 

 mental curve. A fair agreement is obtained except for the range from 60 

 to 90 chain elements where the two relaxation model gives too rapid an 

 increase of stiffness with increase in the number of chain elements and 

 at the high molecular weight viscosity range where the viscosity shows 

 a dispersion in values but the model does not. The sum of the two vis- 



'1 These results on the mechanical impedance of long chain molecules in sol- 

 vents have been presented at the Xllth International Congress of Pure and 

 Applied Chemistry by W. O. Baker, W. P. Mason and J. H. Heiss, Sept. 13, 1951. 



