INTKRAC'TION OF I'OL^MKKS AM) M lOCHANICAL WAVKS 'M)7 



(^tlior studies have treated one way of getting at these mecliaiiisnis l)y 

 relatiiit>; stress rehixation, creep, viscosity, etc. to a dislrihnt ion of 

 molecular I'elnxatioii lini(\s (;ui(l cn('ru;\' hni'riers), as oriuiiiatcd \)\ 

 Kuhii."' Anotiier approach is to sti'ain pt»lyniers with pci'io(hc \va\'es 

 o\'er a \-ei\v wi(h> spectrum of \\a\'elen>>;ths, exciitually j2;oinj>; to fre- 

 (|uencies conijiai'ahle with those of the thei'mal xihrations of si<i;nificant 

 groups or s(>j>;meiits in \\\v macromolecailes. The result iiifz; dispei'sion or 

 resonance phenomena can then l)e examined. Hence a mechanical radi- 

 ation ti(>ld can interact with the masses of elementary structural units, 

 as the usual elect romafz;netic field interacts with atomic and f^roup 

 charges. In genei-al, direct int(M-i)retations of this kind must be done 

 witii shear wa\'es, and, at least, not onlji with loii<),itu(liiial or ultrasoni(' 

 waves. 



This kind of study is now proceeding using waves generated and fol- 

 h)W(Hl by piezoelectric crystals connected in as actual electromechanical 

 circuit elements (A. M. Nicolson, 1919). Recent schemes of Mason and 

 co-workers cover the frequency range from 10 X 10 to 60 X 10 cps, 

 as reported m the paper by Mason and McSkimin in the last issue, 

 while a tuning fork method used by I. L. Hopkins has been applied to 

 "soft" polymers (rubbers) over the range 10" to 10 cps (the general 

 range of J. D. Ferry's work at Wisconsin on concentrated polymer 

 solutions). 



The relation of these studies to the scientific and technical exploita- 

 tion of plastics and rubbers is in knowing what a particular chemical 

 composition does to strength, stiffness, ease of molding, impact tough- 

 ness, etc. That is, are there qualities of the interaction of saturated 

 aliphatic groups that make polyethylene or polyisobutylene have some 

 glass-like as well as liquid-like, or rubbery, nature even at room tem- 

 perature? If so, conditions causing brittle failures must be watched for. 

 How is the storage of molecular strains in injection molded plastics re- 

 duced by increasing molding temperature (when the kinetic theory stiff- 

 ness per chain actually increases)? These and many similar problems 

 may be generalized under the headings below; in each case the chemical 

 structure of the macromolecule appears to be reflected in relaxation 

 times which combine in different ways to give flow^ or rigidity, toughness 

 or brittleness. 



Extrusion and Mohlituj 



Non-Newtonian flow leading to "fi'ozen-in" stresses, subseciuent dis- 

 tortion and irregular shapes of plastics and rul)bers, implies energy 



