Atactic polypropylene at high pressure. II. Methyl group and segmental motion from deuteron NMR spectra and relaxation times

Abstract Deuteron NMR spectra and relaxation times have been used in an investigation of the effect of high pressure (up to 5000 bar) on the molecular motion in atactic deuterated polypropylene, below and above its glass-transition temperature Tg. Fast axial reorientation of the methyl groups is found, which is neither affected by the glass transition, nor by the application of high pressure. Small-angle motion of the main-chain segments is observed. This motion is identified with the mechanical β-relaxation process. In the glass the character of this process is maintained up to the glass-transition temperature found at each pressure value, while its pressure dependence is very weak. Above Tg this process is strongly pressure-dependent while its character is mainly determined by the distance to Tg.