No abstract

Cover: The cover shows a scanning electron microscopy image of a cross-section through a polymer particle with catalyst fragments in the early stage of polymerization. Further details can be found in the Communication by X. Zheng, M. S. Pimplapure, G. Weickert and J. Loos* on page 15.

Polypropylene (PP) composites containing nanosized (φ ∼ 10 nm) spherical silica particles were prepared in situ utilizing a 1-L slurry-phase polymerization reactor containing a MgCl2-supported Ziegler−Natta (fourth-generation) catalyst. Composites were prepared with variable filler sizes ranging from the nano- to microsize domain. The surface of the silica particles was modified with a silane coupling agent to prevent catalyst deactivation and to achieve better polymer/filler synergy by decreasing the hydrophobicity surrounding the bulk particle surface. The feasibility of the process was tested with low loading additions (∼3 wt % for each sample) of (nano)silica. The effect of the filler on the crystal structure and crystallite size of PP was studied with differential scanning calorimetry and wide-angle X-ray diffraction. The reaction kinetics of the nanocomposite (∼10 nm) was studied and compared with samples containing larger microsized particles. It was demonstrated that the former did not decrease the catalyst activity when compared with the latter; comparisons were also made with pure PP. The particle size influenced the reactivity of the catalyst, and the addition of silica influenced the degree of crystallinity of the PP.