Nucleation and Crystallization of Low Isotatic Polypropylenes with Statistically Distributed Stereoerrors

Abstract

The time dependent crystallization of a low isotactic polypropylene with statistically incorporated stereoerrors was investigated by the combination of differential scanning calorimetry (DSC), wideangle X-ray scattering (WAXS) and scanning force microscopy (SFM). Owing to Scanning force microscopy (SFM) and WAXS experiments the crystallization of the sample in mixed =-form aggregates can be proposed. The nucleation and growth processes of crystallization in thin polypropylene films in real time were visualized with nanometer resolution by using SFM at variable temperature. During the isothermal crystallization from the melt initially crystals of the -form were developed. These lamellae act as nuclei for the further crystallization of -and mixed =-lamellae, which can be observed at longer crystallization times. Time dependent SFM and WAXS experiments showed that due to the low amount of crystallizable, regular sequences and its statistical distribution only slow crystallization rates can be observed. These results form the basis for a better understanding of the crystallization of low crystallinity polypropylenes. The investigations clearly show that the distribution of the regular isotactic segments influences the crystallization properties of propene based TEP's. This opens the possibility to tailor not only the mechanical but also the thermal properties of elastomeric polypropylenes by changing the polymer microstructure.

Fourier transform infrared spectroscopy and wide‐angle X‐ray scattering: Investigations on polypropylene–vapor‐grown carbon nanofiber composites

“…Such conditions could appear during the processing of the polymer–filler mixture and, consequently, were not directly connected to the presence of the VGCNFs. The exceptional thermal conductivity of the VGCNFs could have also played an important role in the dissipation of heat during processing. The combined crystallization of the α and γ phases was reported in PP with statistically distributed stereo errors, which for our samples, could be generated during the processing step 26 …”

“…The combined crystallization of the α and γ phases was reported in PP with statistically distributed stereo errors, which for our samples, could be generated during the processing step 26…”

“…The combined crystallization of the a and c phases was reported in PP with statistically distributed stereo errors, which for our samples, could be generated during the processing step. 26 There is a tendency in the literature on polymerbased composites [21][22][23][24][25][26][27][28] to consider that nanometersized fillers have a complex behavior, acting as nucleating agents, reducing the induction time, 28 decreasing the crystallization temperature, lowering the enthalpy of fusion, increasing the crystallization speed, resulting in larger crystallites, and leading to a higher degree of crystallinity. Such indiscriminate and often not properly subtantiated conclusions should be discussed and analyzed with more caution.…”

Designing polymer crystallinity: An industrial perspective

“…Stereodefects decrease the crystallization temperature . Besides the total content of such defects, their distribution is also relevant to change the crystallization kinetics in particular for polymers produced by Ziegler‐Natta catalysts. In this case, stereodefects related to specific catalytic sites, are typically distributed nonhomogeneously inside the chains .…”

Molecular and Thermal Characterization of a Nearly Perfect Isotactic Poly(propylene)

“…The crystallization behavior of isotactic poly(propylene) (iPP) is strongly influenced by different types of microstructural defects in the macromolecular chain, e.g., stereo‐defects, regio‐defects, and comonomers, in addition to molecular parameters such as molecular weight or molecular weight distribution . All these parameters together play a role in determining the crystallization behavior of iPP, which in turn affects the crystal structure(s) obtained and the related final properties …”