Influence of constitutional defects on the crystallization properties of isotactic polypropylene: A tool to predict the polymorphic behavior

PMSE 213

Claudio De Rosa, claudio.derosa@unina.it, Finizia Auriemma, finizia.auriemma@unina.it, Odda Ruiz de Ballesteros, and Giovanni Talarico, talarico@unina.it. Dipartimento di Chimica, Università di Napoli Federico II, Complesso Monte S.Angelo, Via Cintia, Napoli, 80126, Italy
Isotactic propylene-ethylene (iPPEt), propylene-butene (iPPBu) and propylen-hexene (iPPHe) copolymers have been prepared with different metallocene catalysts. The influences of stereodefects and constitutional defects on the crystallization behavior of isotactic polypropylene (iPP) have been discriminated. All copolymers crystallize from the melt as mixtures of alpha and gamma forms. The amount of gamma form increases with increasing crystallization temperature, comonomer concentration and content of rr stereodefects. Ethylene comonomeric units and rr stereodefects exert a similar effect in inducing crystallization of gamma form. Butene and hexene units, instead, favor crystallization of gamma form at low concentrations and of alpha form at high concentrations. These data indicate that the crystallization of gamma form of iPP is not only related to the value of the average length of the regular fully isotactic propylene sequences but is also related to the inclusion of defects in the crystals of iPP. In the case of iPPEt copolymers, ethylene and rr stereodefects are more easily included in crystals of gamma form and, hence, favor crystallization of gamma form. In the case of iPPBu copolymers, butene units are included indifferently in crystals of alpha and gamma form, but at concentrations higher than 10 mol% the effect of inclusion in crystals of alpha form prevails, producing a decrease of the amount of gamma form. Hexene units are instead more easily included in crystals of alpha form, producing an increase of crystal density up to a critical value that produces crystallization of the trigonal form. The preferred inclusion of hexene in the alpha form, driven by the tendency to increase the density, produces decrease of the amount of gamma form at high hexene concentration.
 

50 Years after the Discovery of Polymer Single Crystals: A Look Back, Current Discoveries and Future Opportunities
1:30 PM-4:45 PM, Tuesday, August 21, 2007 Westin Boston Waterfront -- Alcott, Oral

Division of Polymeric Materials: Science & Engineering

The 234th ACS National Meeting, Boston, MA, August 19-23, 2007