Dynamics of phenylene rings in engineering thermoplastics. A quasielastic neutron scattering study

By using quasielastic neutron scattering we have contributed to the long-standing question of the molecular motions behind the secondary relaxations in engineering thermoplastics. The phenylene Hydrogen motions in polyethersulfone and bisphenol-A polysulfone, polycarbonate and phenoxy have been studied by combining time of flight and backscattering techniques in the time range from about 0.1 ps to 1ns. After vibrations and fast processes below 2 ps, the Hydrogen motions reveal relatively fast oscillations and 180$^{\circ}$ flips of the rings in all cases. Polycarbonate phenylene groups additionally show rotations of about 90$^{\circ}$. Relationships among the microscopically observed motions and the secondary relaxations as followed by mechanical and/or dielectric spectroscopy are established.