The role of alkoxysilanes in propylene polymerization catalysis. A study of model Ti( O i ‐C 3 H 7 ) 4 ‐Al( C 2 H 5 ) 2 Cl /Mg( C 4 H 9 ) 2 catalyst system

The article describes the modifying effect of methylcyclohexyldimethoxysilane (CH 3 )( cyclo ‐C 6 H 11 )Si(OCH 3 ) 2 in propylene polymerization reactions with a pseudo‐homogeneous catalyst system: Ti(O i‐ C 3 H 7 ) 4 ‐Al(C 2 H 5 ) 2 Cl/Mg(C 4 H 9 ) 2 . This catalyst system is a convenient model for the analysis of modifier effects (effects of ‘external donors’) in supported Ziegler–Natta polymerization catalysts of the fourth generation. A combination of chromatographic, spectroscopic and calorimetric data for crystalline and amorphous fractions of polypropylene prepared in the presence of the silane shows that it has a dual modification effect: (i) the silane is a potent poison of stereo‐aspecific active centers in the catalyst (the centers producing amorphous polypropylene fraction) and (ii) silane molecules coordinate at isospecific centers in the catalyst and changes their nature: the centers produce isotactic polypropylene of higher molecular weight and a higher isotacticity level. © 2023 Society of Industrial Chemistry.