Relaxation phenomena in high polymers

Abstract

AbstractThe principles of the nuclear magnetic resonance, NMR, and dynamic mechanical methods and their use for the investigation of segmental motion in high polymers are briefly discussed. Mechanical loss‐temperature data have been obtained from 4.2°K. at audiofrequencies for various addition type high polymers along with NMR line‐width or second moment and NMR spin‐lattice relaxation time, T1, data from 77°K. The examples include a linear polymer, polyethylene, PE, four polymers with mono‐substituted repeat units, polypropylene, poly(4 methyl pentene‐1), poly(ethylacrylate) and polystyrene (PS), and three polymers with disubstituted repeat units, poly(methyl methitcrylate), poly(ethyl methacrylate) and poly(alpha methyl styrene). For all but PE and PS NMR line narrowing processes and T1 minima, attributed to methyl group reorientations, are found at low temperatures. Molecular motion, usually occurring above room temperature as a consequence of the glass to rubber transformation, leads to the appearance of a mechanical loss maximum, further NMR line narrowing, and a T1 minimum. Mechanical loss maxima, possibly due in some cases to side‐chain (other than methyl) reorientations and in other cases to main chain oscillations are also evident.