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synopsisThe effect of molecular organization (crystallinity, orientation) on the internal friction of poly(ethy1ene terephthalate) was studied by means of dynamic mechanical measurements a t temperatures from 300 to 4.2OK, with a free-oscillating torsion pendulum at 1 Hz. It was found that crystallinity decreases the intensity of the composite y relaxation at 21OOK and gives rise to an additional loss maximum B at 26°K. TJniaxial orientation broadens the y relaxation and gives rise to an additional loss peak 6, at 46'K. The 6 and e losses are dependent on molecular organization, occurring only in samples containing aligned, taut chain segments and crystalline structures, respectively. They have a common activation energy of 4 kcal/mole. All three low-temperature relaxations in oriented specimens show pronounced directioiial anisotropy, which, in the y loss, may be due to the preferred orientation of noncrystalline chain segments, while in the 6 and e losses, may be associated with the direction of defect structures. On the basis of the observed behavior of the 6 and e relaxations it is suggested that they may involve motions of defect structures and may thus participate in stress-transfer mechanisms at large deformations.

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The growth of cultured calf aortic smooth muscle cells on cardiovascular biomaterials was investigated, using native and oxidized polyacrylonitrile (orlon) fabrics, dacron velour, and Parylene-C coated polypropylene microfabric as substrates. By light microscopic evaluation, surface cell coverage was most complete on microfabric, followed by native orlon, dacron velour, and oxidized orlon. Native orlon supported the greatest total cell growth, as determined by chemically extractable protein, followed by oxidized orlon, dacron velour, and the microfabric. The observed differences appear to be related to the pore size and fiber thickness of the different substrates.