Molecular Motion in Glassy Polystyrenes

JACOB SCHAEFER, M. D. SEFCIK, E. O. STEJSKAL, and R. A. MCKAY—Monsanto Company, Physical Sciences Center, St. Louis, MO 63167 

DIXON —Department of Chemistry, Washington University, St. Louis, MO 63130 R. E. CAIS—Bell Telephone Laboratories, Murray Hill, NJ 07974 

The amplitudes of ring- and main-chain motions of a variety of polystyrenes have been established from the NMR magic-angle spinning sideband patterns of dipolar and chemical shift tensors. The frequencies of the same motions have been determined by Ti(C) and Tip(C) experiments. The most prevalent motion in these polymers is restricted phenyl rotation with an average total displacement of about 40°. Both the amplitude and frequency of this motion vary from one substituted polystyrene to another, and from site to site within the same polystyrene. A simple theory correlates the observed ring dipolar patterns with Tip(C) s. 

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

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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