Mechanical relaxation processes in polyacrylonitrile polymers and copolymers

Abstract

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).

Dynamic mechanical thermal and infrared analyses of polyacrylonitrile ?electrografted? onto a metal

“…These data agree completely with previous observations for a commerElectrochemistry cially available PAN 13 or for PAN fibers, 11 according to which the lowest transition temperaIn this study, a newly designed electrochemical cell was used in order to accommodate a copper ture (in the 80-100ЊC range) is characteristic of a paracrystalline phase transition and a second cathode of a larger size (required by the DMTA experiments) compared with the experiments pretransition (ca. 150-170ЊC) corresponds to the glass transition temperature of the amorphous viously conducted by some of us.…”

“…The DMTA re-D1250) has been observed to be proportional to sponse (Fig. 8c) is thus the superposition of the the content of the isotactic triads as determined responses for a ''grafted'' PAN film and a solvent by 13 C NMR spectroscopy. Figure 9 compares the cast film of a commercially available PAN (Fig.…”

“…sonic irradiation. It was dried in a vacuum oven Later on, Kenyon and Rayford 13 reported from for 12 h at 100ЊC. Just before use, the superficial tan d curves three transitions for a commercially oxide layer was electrochemically reduced by available PAN.…”

Fouling resistant, high flux nanofiltration membranes from polyacrylonitrile-graft-poly(ethylene oxide)

“…A large glass transition was observed at approximately −49 • C. This value is consistent with the glass transition temperature of low molecular weight, non-crystalline PEO [32], and indicates the presence of a separate PEO phase. There is a second transition observed at approximately 70 • C. This value corresponds to the second amorphous relaxation observed for PAN cast from DMF [33], indicating the presence of a separate PAN phase. Finally, a third transition is observed at 153 • C, which corresponds to backbone rotation in PAN [33].…”

Empregados na Indústria

“…Pode-se, então, imaginar a macromolécula de PAN como uma estrutura torcida semi-rígida dentro de um cilindro ou haste. Vários autores sugerem que a PAN é um sistema polimérico heterogêneo que pode conter até três regiões de transição térmica antes da sua temperatura de início da ciclização, a saber, fase amorfa, fase paracristalina, e fase cristalina [10][11][12] . Por modelagem molecular, Hu [13] conclui que as interações de Van der Waals são um fator dominante na conformação da cadeia afetando a energia potencial dessas moléculas.…”