354 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1952 



CONCLUSIONS 



To leave some impression of the elemental chemical structures which 

 move around when wood, rubber, plastics, textiles and finishes are used 

 mechanically — that has been the aim of this study. Polymer \'iscosities 

 have been found in a variety of "solids"; rigidities have been demon- 

 strated for very fluid "liquids" and solutions. Studies of these solid and 

 licjuid extremes have given some chemical reality to the classical sprhig 

 and dashpot models. 



Existence of compressional viscosity has been shown for polymer 

 liquids and sohds. It may comprise a new quality for mvestigation of 

 polymer structure. At present, too little is known of its origin to mter- 

 pret further the effects of mtense ultrasonic Eradiation of polymer solu- 

 tions. Experiments of Schmid and co-workers'" early indicated degrada- 

 tion of molecular weight of polystyrene, so irradiated, but whether this 

 is chemical, from local heating m the solvent, or actual physical coupling 

 with the wave field, is still unsettled. However, these workers also con- 

 sidered a compressional stiffness of the polj^mer molecules m the solu- 

 tions, and showed that if there was coupling, it was not mertial (by 

 dissolving polystyrene in solvents of exactly the same density, no reduc- 

 tion in effect was observed). A point of general interest arises here; 

 impact fractures of plastics presumably actually fracture some primary 

 valence bonds. This is certamly true for many therm oset materials, and 

 probably for cham compounds. Hence, if the detailed mechanism of how 

 compressional waves move and perhaps rupture pohTner segments were 

 known, information on the baflflmg problems of ultimate strength would 

 be gained. The observations above on dependence of X and X' on molec- 

 ular weight and structure provide only the barest start on this but a 

 new goal is in view. Too, basic questions of how rapidlj" molecules being 

 formed in a polymerization equilibrate in temperature with then* sur- 

 roundings are elucidated by compressional wave propagation constants. 

 For mstance, absolute rate measurements on velocity of chain growth 

 cannot be said to be isothermal if they seem to be faster than the ther- 

 mal relaxation time§ which the ultrasonic measurements indicate can be 

 '-'lO"'^ to 10~^ sec. 



Likewise, more thorough understanding of velocity and dispersion of 

 compressional waves in polymer solutions would clear up anomalies in 

 velocity measurements for a wide variety of pohoners," some of which 

 have been tentatively attributed to cham branching. 



