SynopsisThe dynamic mechanical properties of molded and cast polyacrylonitrile and copolymers have been measured by an automatic Rheovihron. The transitions are described for the amorphous, "paracrystalline," and crystalline phases. Based upon a number of polymer theories of multiple phases in polymeric systems, the transitions have been assigned to specific polymer motions. Three transitions are defined for the alpha transition region. The mechanical response is compared to x-ray diffraction and infrared to ascertain the transition assignments in decreasing order beginning with the highest temperature transition as (1) the main transition for the amorphous phase ( T I ) , (2) dipole-dipole interaction which is related to the "paracrystalline phase" (T2), and (3) secondary transition for the amorphous phase (7'3).

The direct reading dynamic viscoelastometer DDV-I1 (Rheovibron) has been completely automated to provide continuous measure of stress, strain, phase angle, temperature, and elongation of sample. The tension on the sample is automatically controlled to permit measurements under constant strain or to maintain sufficient tension to prevent sagging during the cycling operation. The sensitivity has been greatly increased, which permits extension of mechanical properties far beyond the Tg More accurate locations of the relaxations are possible so that minor transitions can be detected over the temperature range of -160 to 250°C. The tan 6 has been measured to +0.001.Stress and strain can be maintained at constant values over an extended time. Data are processed on an off-line computer to give printout of storage modulus, loss modulus and tan 6 as a function of temperature. Measurements have been made on many types of polymer films and fibers.