SUB-TG DYNAMIC PROCESSES IN AMORPHOUS SOLIDS - A DEUTERIUM AND C-13 NMR-STUDY OF POLY(PHENYLENE SULFIDE)

Deuterium NMR spectroscopy shows that the aromatic rings in deuterated amorphous poly-(phenylene sulfide) (PPS) undergo rapid 180-degrees flips at room temperature. Detailed analysis of the deuterium NMR spectrum shows that any subsidiary motion that accompanies ring flipping involves ring reorientation of no more than 20-degrees. There is a distribution in the natural logarithm of the flipping rates of 6.8 at 205 K and 3.9 at 350 K. The distribution of flipping rates corresponds to a distribution of activation energies centered about 11.0 kcal/mol. The signals in the C-13 NMR spectrum of amorphous PPS are exceptionally broad, reflecting a wide range of local conformations for the polymer chains that are imposed by the local packing of the chains. The range of local packing environments presumably accounts for the distribution of activation energies.