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Ferrara, Italy

De Rosa C.,University of Naples Federico II | Ruiz De Ballesteros O.,University of Naples Federico II | Auriemma F.,University of Naples Federico II | Di Girolamo R.,University of Naples Federico II | And 6 more authors.
Macromolecules | Year: 2014

A study of the crystallization behavior and mechanical properties of random isotactic butene-ethylene copolymers prepared with a metallocene catalyst is presented. The use of the metallocene catalysis ensures a fine control over the molecular structure with low concentration of rr stereodefects (0.8%), negligible amount of regiodefects, and random and uniform distribution of ethylene constitutional defects. This molecular characteristic has allowed evidencing the only effect of the presence of ethylene units on the polymorphic behavior and mechanical properties of isotactic polybutene (iPB). The presence of ethylene accelerates the transition of form II into form I at room temperature and at concentration of nearly 6 mol % favors the direct crystallization from the melt of the stable form I. The presence of ethylene also affects the mechanical behavior of iPB and produces increase of flexibility and ductility with increasing ethylene content. A significant modification of the properties of iPB is observed for ethylene concentration higher than 8 mol %, with development of elastomeric properties, never observed for the iPB homopolymer prepared with Ziegler-Natta catalysts and not observed in the iPB homopolymer with similar content of stereo defects. In these samples, elastomeric properties are due to the low degree of crystallinity that develops upon aging at room temperature by direct crystallization of form I′ from the amorphous phase. © 2014 American Chemical Society.

De Rosa C.,University of Naples Federico II | Auriemma F.,University of Naples Federico II | Vollaro P.,University of Naples Federico II | Resconi L.,Centro Ricerche G Natta | And 3 more authors.
Macromolecules | Year: 2011

A structural characterization of samples of isotactic propylene-butene copolymers (iPPBu), synthesized with a metallocene catalyst, is reported. The copolymers crystallize in the entire range of comonomer compositions, and α and γ forms of isotactic polypropylene (iPP) crystallize in propene-rich copolymers, whereas form I of isotactic polybutene (iPB) crystallizes in butene-rich samples. Butene and propene comonomeric units are included incrystals of iPP and iPB, respectively, as indicated by the change of the unit cell parameters of copolymer crystals with changing comonomer composition. The trigonal form of iPP, recently found in propylene-hexene and propylene-pentene copolymers, does not crystallize in asprepared or melt-crystallized samples of iPPBu copolymers, but it has been obtained in oriented fibers of copolymers. In fact, in copolymers with butene concentrations lower than 10-15 mol %, crystals of α or γ forms present in the melt-crystallized compression-molded samples transform by stretching at high deformations into the mesomorphic form of iPP, whereas in samples with butene concentration of around 50%, crystals of α form of iPP transform into the trigonal form of iPP by stretching. This is the first evidence of the crystallization of the trigonal form of iPP in iPPBu copolymers. © 2011 American Chemical Society.

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