320 



THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1952 



teresting to see what are the simplest structures (particularly in terms 

 of molecular weight) yielding these effects. In other words, what kind of 

 liquid really exhibits "polymer mechanics?" No detailed answer to this 

 can be given l^elow, but results on some polymer lic|uids of low average 

 molecular weight will indicate that the mechanisms in rubbers and plas- 

 tics are probably more general than previously supposed. 



POLYMER LIQUID MECHANICS 



By techniques described in detail elsewhere,-^ -^ a series of polyisobutyl- 

 ene liquids have been investigated. These polymers were made by ionic 

 catalyzed mass polymerization at reduced, but not very low, tempera- 

 tiu'es. While no great care to purify the monomer was used, such poly- 

 merizations require fair purity to go at all. Seemingly, the resulting lici- 

 uids do represent a polymer homologous series, although head-to-tail 

 setiuence of the monomer units, some single ethyl rather than paired 

 methyl side groups, etc., may differ slightly from the higher molecular 

 weight forms in Butyl rubber and polyisobutylene gum. Whatever are 

 these details, it appears that the polymers represent a linear hydro- 

 carbon chain, with essentially two methyl groups on every other chain 

 atom: 



CH, 



-CH. • C 



CH3 



CH, 



CH2-C- 



CH. 



3JDP-1 



By contrast, polyethylene, with the nominal chain 

 CH2 — and to a lesser extent polystyrene, 



— CH2CH— , 



-CH2CH2CH0. 



have chains in which rotation about the bonds is less sterically hindered. 

 The final section, on isolated polymer chains (in dilute solution), will 

 consider this aspect further. However, some results will be reported be- 

 low on a low molecular weight poly-a-methyl styrene, which may be 

 considered structurally a cross between the rubber, polyisobutylene, and 



