A set of Ziegler-Natta copolymers of iPP with ethylene or with 1-butene, and terpolymers with both counits have been characterized, devoting special attention to the effect of composition and processing conditions on the crystal structure and on the final properties.DSC and X-ray diffraction is used to study the polymorphism of copolymers and terpolymers.Comonomer insertion interrupts the isotactic sequences, acting as a structural defect, and the formation of  form is enhanced in the interval of studied compositions. Moreover, crystallinity decreases and crystal structure is modified. Comonomer type and concentration determine the extent of these modifications, resulting on important changes in macroscopicproperties. An important aspect to be considered is the higher ability of 1-butene units to be incorporated in the iPP crystals in relation to ethylene counits. From the balance of different properties, possible applications are suggested for the various types of samples. For instance, the excellent optical properties of the analyzed terpolymers make them very attractive for applications such as transparent film or packaging.

The competition between a, b, and c polymorphs has been studied in several random copolymers and terpolymers of propylene, by performing X-ray diffraction and differential scanning calorimetry experiments. Formation of b-crystals, achieved by the addition of a b-nucleating agent, was found to be highly dependent on comonomer type and crystallization conditions. Additionally, the mechanical properties have been evaluated from stress-strain, microhardness and dynamicmechanical thermal analyses.

Molecular microstructure, thermal properties and morphology of three polypropylene heterophasic copolymers (PHC) with similar comonomer content were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), analytical and preparative temperature rising elution fractionation (TREF), scanning electron microscopy (SEM), and carbon nuclear magnetic resonance spectroscopy ( 13 C NMR). These results indicate that there are no differences in solution and thermal properties between unfractionated copolymers. Nevertheless, a physical fractionation by crystallization of these copolymers was developed to carry out a detailed study. Four fractions at different temperatures were collected. The results showed that the PHC's copolymers are composed by polypropylene, ethylene-propylene rubber (EPR) and, crystallisable sequences with different propylene and/or ethylene comonomers distribution. Despite the similar thermo-chemical properties shown by the raw PHC's copolymers, the characterization of fractions displayed significant differences between them. These results suggest that the fractionation by crystallization allows the different components in which the PHC's copolymers are based to be distinguished clearly, and obtain a more comprehensive sense of the molecular structure characterization.