Glassy polystyrene, molecular

The free radical concentration is quite small relative to the number of chains present. Also, the number of crosslinks formed are sufficient to gel the network, which could lead only to a decrease in creep rate. Finally, the crosslinks exceed the scissions, and the latter could not reduce the molecular weight sufficiently—even temporarily—to yield the significant increases in creep noted in the glassy polystyrene. Recombination of chain scission radicals has also been neglected. 

J Schaefer, MD Sefcik, EO Stejskal, RA McKay, WT Dixon, RE Cais. Molecular motion in glassy polystyrenes. Macromolecules 17 1107-1118, 1984. 

Fig. 37. The rubbery-solvent interface (S), the glassy-rubbery interface (R), and the gel layer thickness (S-R) as a function of dissolution time. The polystyrene molecular weight was M = 52 000...

The polystyrene molecular weight was Mn = 52,000. The position = 0 is the glassy/rubbery interface. The time increment starting from the first curve on the right is At = 3600 s. 

A series of polystyrene molecular weight standards available from the Pressure Chemical Company have been studied by Keinath et al. via thermomechanical analysis. AflYs ranged from nominal molecular weight 2,200 up to 7,200,000. Smooth glassy samples, contained in DSC pans, were prepared by fusing the as-received powdered samples. Tlje weighted probe of the DuPont 943 TMA unit was placed onto the surface of the sample and the entire assembly was heated at S C/min from room temperamre up to a point where the probe had penetrated through the whole thickness of the sample. 

Molecular Motion in amorphous atactic polystyrene (PS) is more complicated and a number of relaxation processes, a through 5 have been detected by various techniques as reviewed recently by Sillescu74). Of course, motions above and below the glass transition temperature Tg have to be treated separately, as well as chain and side group mobility, respectively. Motion well above Tg as well as phenyl motion in the glassy state, involving rapid 180° jumps around their axes to the backbone has been discussed in detail in Ref.17). Here we will concentrate on chain mobility in the vicinity of the glass transition. 

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