Interaction of Polymers and Mechanical 



Waves 



BY W. O. BAKER AND J. H. HEISS 



(Manuscript received October 19, 1951) 



New techniques of Mason, McSkimin, Hopkins and co-workers for gener- 

 ation of shear waves over the frequency range 2 X 10 to 2.4 X 10 cps 

 have been used to study mechanical properties of chain polymers. Polymer 

 solids, melts and dilute solutions, representing the main states in which 

 plastics and rubbers are fabricated or used, were explored to find the char- 

 acteristic relaxation times, rigidities and viscosities of various chemical 

 structures. Polyisobutylene, hevea rubber, polydimethyl siloxane, vinyl chlo- 

 ride-acetate copolymers and plasticized nitrocellulose were compared with 

 polyethylene and polyamides as examples of the range of solid properties 

 encountered. 



As melts, several polyisobutylene s, polybutadiene, polypropylene, poly- 

 propylene sebacate and poly-a-methyl styrene were investigated as models 

 for varying degrees of chain substitution. Chain rigidity in, for instance, 

 polyisobutylene, seemed to reflect visco-elastic over-all configurational changes 

 up through the kilocycle range, but nearest neighbor interactions took over in 

 the megacycle region, leading to fnodidi of 10 dynes/ cm even for syrupy 

 fluids. 



In dilute solution, polyisobutylene, polystyrene, natural rubber and poly- 

 butadiene microgel exhibited characteristic dynamic viscosities and rigidi- 

 ties depending linearly on concentration. Presumably, this reflects mechan- 

 ical properties of isolated chains. Some possible models were suggested for 

 the frequency dependence of such properties. 



INTRODUCTION 



The "equilibrium" mechanics of polymers, the giant molecules of 

 plastics and rubbers, have been quite elegantly de\'eloped in the range 

 of high strains ("kinetic theory" of elasticity — Meyer, et al.). However, 

 the molecular displacements as these strains, and, indeed, much smaller 

 ones, occur, are little understood. Nevertheless, it is essential to know 

 about detailed motions in connecting chemical structure with physical 

 properties. Only in this way can there be obtained from the chemical 

 industry compositions which will serve properly in telephone apparatus. 



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