Pseudohexagonal crystallinity and thermal and tensile properties of ethene-propene copolymers

Structural (X-ray diffraction), melting (differential scanning calorimetry) , as well as mechanical (tensile tests) characterizations on uncrosslinked ethene-propene copolymer samples, obtained using a metallocene-based cataly tic system and having an ethene content in the range 80-50% by mel, are rep orted. Samples with an ethene content in the range 80-60% by mol present a disordered pseudohexagonal crystalline phase, whose melting moves from appr oximate to 40 degrees C down to approximate to -20 degrees C as the ethene content is reduced. The dramatic influence of the crystalline phase on tens ile properties of uncrosslinked ethene-propene copolymers is shown. In part icular, highest elongation at break values are obtained for samples being e ssentially amorphous in the unstretched state and partially crystallizing u nder stretching. On the other hand, lowest tension set values (most elastic behavior) are observed for samples presenting, already in the unstretched state, microcrystalline domains acting as physical crosslinks in a prevaili ng amorphous phase. (C) 1999 John Wiley & Sons, Inc.