Cover: Varying normalized concentrations of hydrogen and external electron donors affect the mmmm pentads of polypropylene made with a 4th generation heterogeneous Ziegler–Natta catalyst. These experimental results agree well with Monte Carlo simulations, including the transformation of non‐specific sites to stereoselective sites via donor complexation and hydrogen transfer reactions to 2‐1 “dormant” sites. Further details can be found in the article by João Soares http://doi.wiley.com/10.1002/mren.201400028.

Heterogeneous Ziegler-Natta catalysts are still the most important catalysts for the industrial production of polyolefins, despite the discovery of high-activity metallocene systems in the eighties. Despite of their huge commercial importance, several aspects of Ziegler-Natta catalysts are still poorly understood from both qualitative and quantitative points of view. Especially for polypropylene, a very important factor controlling product quality is the effect of the electron donor used to modify the catalyst. In this manuscript we present, for the first time, a quantitative mathematical model that describes the effect of electron donors on the tacticity of polypropylene made with multiple-site type catalysts.

Apparent kinetic rate constants and activation energies for catalyst activation, deactivation, and propylene propagation with a 4th‐generation Ziegler‐Natta catalyst are estimated. The rate of polymerization in the presence of donor and hydrogen is higher than in their absence. Catalyst activation and propagation rate constants increase with the addition of hydrogen, likely because hydrogen frees 2–1‐terminated dormant sites. The deactivation term was the highest without electron donor, presumably because the nonspecific sites deactivate faster than the specific sites. Apparent activation energies for catalyst activation, deactivation, and propagation are not significantly influenced by the presence of hydrogen or external donor, indicating that they do not affect these mechanisms substantially.

This paper presents the results of a detailed investigation on propylene polymerization kinetics and microstructural characterization of polypropylene samples made with a 4th generation Ziegler–Natta catalyst under varying hydrogen pressures, external donor concentrations, and polymerization temperatures. Hydrogen had a positive effect on the mmmm pentad fraction at low donor concentrations, in agreement with our previous Monte Carlo model. Estimated activation energies for activation, propagation, and deactivation were very close to the values previously reported by our group for a narrower set of experiments with the same catalyst.

Ethylene polymerization was done to form polyethylene nano-composite with nanoaluminum nitride using zirconocene catalysts. Results show that the catalytic activity is maximum at a filler loading of 15 mg nanoaluminum nitride. Differential scanning calorimeter (DSC) and X-ray diffraction (XRD) results show that percentage crystallinity was also marginally higher at this amount of filler. Thermal behavior of polyethylene nanocomposites (0, 15, 30, and 45) mg was studied by DSC and thermal gravimetric analyzer (TGA). Morphology of the component with 15 mg aluminium nitride is more fibrous as compared to 0 mg aluminium nitride and higher filler loading as shown by SEM images. In order to understand combustibility behavior, tests were performed on microcalorimeter. Its results showed decrease in combustibility in polyethylene nanocomposites as the filler loading increases.