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 catalytic system and having an ethene content in the range 80-50% by mel, are reported. Samples with an ethene content in the range 80-60% by mol present a disordered pseudohexagonal crystalline phase, whose melting moves from approximate 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 tensile properties of uncrosslinked ethene-propene copolymers is shown. In particular, highest elongation at break values are obtained for samples being essentially amorphous in the unstretched state and partially crystallizing under 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 prevailing amorphous phase. (C) 1999 John Wiley & Sons, Inc.