RESINOGRAPHY 



Fig. 2. A fanciful map to chart the relationships in the world of plastic materials. 



High polymers also differ from metals in 

 that the molecules of high polymers are huge 

 and may vary in effective sizes, assumed 

 shapes and internal configurations and con- 

 formations. High polymers differ from waxes 

 in that the former may be of much higher 

 degree of polymerization and/or they are 

 not always predominantly crystallized. High 

 polymers can be of only one phase or state 

 and yet be plastic; mastics and plasters are 

 plastic only while solid particles are moving 

 around in a second, liquid phase. 



Solid metals are always crystalline and 

 waxes are essentially crystalline. In metals 

 the crystalline grain is the primary unit 

 involved in fabrication, use, fatigue and 

 failure. For example : One speaks of inter- or 

 intra- granular diffusion, corrosion or frac- 

 ture; precipitation may be along grain 

 boundaries; deformation takes place in each 

 grain according to its own crystallographic 

 orientation. On the other hand, in polymeric 



materials at least four types of units appear 

 (9) to be at play in the construction and 

 behavior as indicated in Table 1. 



Type I. By classical definition, the smallest 

 descriptive and functional unit which is 

 characteristic of a material phase is the mole- 

 cule. In resins such as rosin, when the mole- 

 cules are monomeric or nearly so, they are 

 far from visible in the electron-lens micro- 

 scope; in low polymers there are macro- 

 molecules, but even these are too small to 

 be resolved. In some high polymers heter- 

 ogeneities of macromolecular order are 

 revealed, e.g., as spheroids (Figure 4), ellips- 

 oids or fibrils near the limit of visibility.* 

 The dimensions are small, generally varying 

 between the lower microscopical limit (10 or 

 20 A) to 100 or 200 A, but precision of 

 measurement is hampered by relatively 

 broad, fuzzy boundaries. Details such as the 



* "Visibility" pertains to both resolution and 

 contrast. 



526 



