Molecular basis of Beta-transition in polysulfones.

The molecular basis for the beta-relaxation in polysulfones has been established by deuterium NMR studies on specifically deuterated polysulfones. The primary mode of motion of the aromatic rings in these polymers is 180D phenylene ring flips. These flips occur with a broad distribution of characteristic frequencies. Added antiplasticizers decrease the magnitude of the beta-relaxation and lead to a significant loss in ductile mechanical properties. Antiplasticizers also markedly reduce the rate of phenyl ring flips, thereby establishing this type of phenyl motion as a molecular-level process responsible for the beta-relaxation. Other details of motion in these polymers are also addressed.