No abstract

Uniaxially oriented commercial films of isotactic polypropylene were strained with ends keeping fixed and subjected to the heat treatment at temperatures from 50 to 2008C. The rigidity of annealed samples was characterized by the value of tangent modulus, E t , determined graphically at the initial portions of stress-strain curves. The structural changes in the samples were studied with the help of the IR and low-frequency Raman spectroscopies. The smallest E t values were obtained for the low-strained films, while the tangent moduli measured for highly strained samples exceeded the value for the original (untreated) film. The most prominent positive effect was achieved after annealing the samples at 908C.

The crystalline phase in gels and solid gel-derived samples of ultrahigh molecular weight polyethylene was studied using the infrared spectroscopy, low-frequency Raman spectroscopy and wideangle X-ray scattering methods. The spectroscopic data evidence the presence in gels of tiny crystallites whose thickness (3-5 nm) depends on the sort of the solvent used and it is insensitive neither to the concentration of the diluted solution, nor to the molecular weight of the polymer. After removal of the solvent, there appear crystalline clusters composed of closely attached folded platelets. The total thickness of these stacked entities is about 10-20 nm while their transverse size reaches ∼50 nm. In addition, the crystalline domains in the gelled material exhibit a kind of mosaic structure which is much more pronounced in solid xerogels than in wet gels.