IXTEHACTIOX OF roLVMKKS AND MKCIIAMCAL WAVKS 817 



tratos some values for Butyl compouncls. Tlio .swelling ratio (SR) for 

 tiie coinpouiid eontaining 28/) wt. per ceiil filler has di-opped to 3.2, 

 implying also considerable I'cduclions in .1/,. (since tlicoiclicnlly 



{I SR.y'^ = 77- — 2hMc^'^). Thus, the apparent ciiain segment between 

 M c 



cross-links is shorter than in tlie nnfilled stock (the two wei'e cui-ed to 

 give closely similar degrees of primaiy valence cross-linkage) and corre- 

 spondingly the steady-pull modulus is higher. Yet, the internal friction, 

 while also higher, seems to reflect iuav relaxations from intei'aclion with 

 th(> tiller, and total shock-absoi'bing power has declined. 



MicrocrystaUine Polymers 



The i)receding studies at comparatively low frec}uencies indicated (1) 

 magnitudes of shear rigidity and internal viscosity characterizing rub- 

 bers and soft plastics. By familiar shifts of temperature oi- frequency, 

 the}' would also apply to polymers known as hard, amorphous plastics 

 at room temperature such as polystyrene and polymethyl methacrylate. 

 (2) Dispersion of /x and m' ^^ith frequency affirm that the intrinsic or 

 fine structure relaxations have times <10~ to 10^ sec, and so refer to 

 chemical luiits much smaller than the average molecules in the usual 

 technical rubbers and plastics. A way to get at what sizes and habits 

 these units might have will be by investigation of low molecular weight 

 polymer liquids. But, while still in the section on solids, it is recalled 

 that microcrystalline polymers such as polyethylene, polyesters (Teryl- 

 ene), polyamides (nylons), cellulose esters, polyvinylidene chloride, poly- 

 acrylonitrile etc., have mechanical properties dominated by their crystal- 

 line-amorphous ratios. ' ' ' The amorphous \-olumes are clearly those 

 which donate the flexibility, toughness and shock-resistance of these 

 plastics and textile fibers. ' An interesthig point is, how "viscous" are 

 the disordered chain segments? In an over-all sense, all kinds of dissipa- 

 tion including crystallite friction, analogous to grain friction in metals, 

 scattering of longitudinal waves, and stiffening by low temperatures can 

 occui- in these polyphase systems. Thus, effects of chain orientation as 

 well as lateral order (crystallinity) have been detected in dynamics 

 studies.' ' ' The intrinsically li(iuid-like or amorphous components of 

 this behaviour — and the things which will correlate most simply with 

 dipole concentration and other chemical features — arc most accessible 

 to study at very high fretiuencics. For, in these polymer solids, unlike 

 tiie essentially continuous and homogeneous amoiphous ones first dis- 

 c-ussed, the mechanics reflect small regions lun'ing widely di\'ergent 

 properties. Thus, methods developed by H. J. AlcSkimin of Bell Tele- 



