The mesophase structuring has been studied by fast scanning calorimetry in a series of random propylene-co-1-pentene copolymers, up to 7.9 mol % of 1-pentene units. It was found that the formation rate of the mesophase can be easily tailored in a wide range covering 2 orders of magnitude, in such a way that the rates involved in the copolymer with highest comonomer content can be also analyzed by conventional techniques, namely DSC and real-time X-ray diffraction employing synchrotron radiation. The advantage from the standpoint of easiness on the study of mesophase structuring is, therefore, well evident. The penalty to pay is the decrease on the overall degree of order attained in the copolymers.

A metallocene copolymer of isotactic propene and 1-pentene was subjected to different crystallization conditions with 13 mol% of 1-pentene counits, aiming to enhance the formation of a new trigonal modification of iPP. Since it was not possible to obtain a diffractogram for the amorphous sample of cPPe13 at room temperature, the X-ray crystallinity was determined using the profile of the molten polymer, extrapolated to room temperature according to the resulting temperature coefficients. The X-ray diffraction results indicate a very interesting polymorphism in this copolymer; when crystallized from solution, amazingly high degrees of crystallinity -as high as 65% -are obtained, and this value is similar to those obtained for the iPP homopolymer. Further, the enthalpy of melting for a 100% crystalline sample of the trigonal modification was estimated from those crystallinities and the actual enthalpies of melting.

Terpolymers based on propylene with 1‐pentene and 1‐hexene as comonomeric units are satisfactorily synthesized using a metallocene catalyst. Thus, several terpolymers are prepared with distinct overall compositions in comonomers as well as three different 1‐pentene/1‐hexene ratios at a given composition to evaluate the influence on polymerization activity, intrinsic viscosity, and microstructural details. The new trigonal δ polymorph is observed in those quenched terpolymers with a global content in comonomers of about 14 mol %, independently of the ratio between both comonomers. However, preliminary results indicate a profound influence of that ratio on the crystallization rate. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3251–3259

Nanocomposites based on polypropylene have been prepared by in situ polymerization of propene in presence of mesoporous SBA-15 silica. Synthetic reactions were carried out with a zirconocene catalyst under either homogenous or supported conditions, the SBA-15 particles being used as carriers, and testing the immobilization of the catalytic system by several approaches. The existence of polypropylene able to crystallize within the mesoporous channels in the resulting materials is initially figured out from the appearance of a small endothermic process on heating calorimetric experiments, located at around 100 ºC. The presence of polypropylene crystallites confined within the SBA-15 mesostructure is thereafter confirmed by SAXS measurements through the intensity variation of the SBA-15 first order reflection, this change being dependent on composition. Accordingly, polypropylene chains can grow up either outside or inside the SBA-15 channels during polymerization and the mesoporous particles maintain their ordered hexagonal arrangement. Mechanical response, as deduced from indentation measurements, improves with SBA-15 incorporation (without varying the final processing temperature). Thus, stiffness increases and deformability is reduced in the nanocomposites as the SBA-15 content rises. Simultaneously, polypropylene amount within channels is enlarged. Amount of SBA-15 is, then, the most important variable.

The main objective of this research is the study of different nanocomposites based on isotactic polypropylene (iPP) and mesoporous SBA-15 silica prepared by melt extrusion, analyzing the possible effect of this filler on the polymorphic behavior of iPP and the eventual observation of confinement effects. Thus, simultaneous Small Angle X-ray Scattering/Wide Angle X-ray Diffraction (SAXS/WAXD) synchrotron experiments at variable temperature have been performed on several iPP nanocomposites with different contents of SBA-15 mesoporous particles. Real-time variable-temperature SAXS measurements turned out a very useful tool to analyze the confinement of iPP crystallites within SBA-15 channels, and also to determine the most probable long spacing of chains located outside the SBA-15 nanospaces. Importance of these structural features is assessed by changes in the mechanical response of the final materials, finding that the presence of mesoporous particles leads to a reinforcing effect and contribute to improve the final dimensional stability.