Adv Polym Sci (2013) 258: 43–116
DOI: 10.1007/12_2013_220
# Springer-Verlag Berlin Heidelberg 2013
Published online: 26 September 2013
Syndiotactic Polypropylene: Discovery,
Development, and Industrialization via
Bridged Metallocene Catalysts
Abbas Razavi
Abstract This chapter covers the discovery that enabled, for the first time, the
manufacturing of high molecular weight, highly stereoregular syndiotactic polypropylene polymers with narrow molecular weight distribution via the new class of
metallocene molecules with bridged cyclopentadienyl-fluorenyl ligands. First, the
salient crystal structural features of the neutral metallocene molecules and the crystal
structure of the corresponding mono-alkyl-zirconocenium cation is introduced. Then,
by employing the structural and geometrical data, a realistic working model for the
active site precursor is developed and presented. The stereochemistry of the catalytic
propylene poly-insertion reaction and the formation of syndiotactic polypropylene
according to the enantiomorphic site control mechanism at the enantiotopic cationic
active sites, formed after the activation of the prochiral metallocene dichloride with
methylaluminoxane, MAO, is reviewed and further delineated. In the following
sections, the impact of the introduction of substituents with proper size and composition at some selected positions of the ligand is discussed and the methods for
increasing the molecular weight and stereoregularity of syndiotactic polypropylene
polymers are elaborated. With the aid of computational calculations on real and
hypothetical catalyst systems with substitutionally altered ligand structures, it is
shown that the degree of enantioselectivity of syndiospecific catalyst systems can be
determined and/or predicted for these systems quantitatively and with high precision.
The calculations confirm that the introduction of substituent(s) reinforcing the
preferential conformational orientation of the polymer chain enhances the overall
enantioselectivity of the active site, and to certain extends stereoselectivity in general,
by affecting the site epimerization processes. The computational calculations reveal
that to account correctly for the frequency of the site epimerization-dependent m-type
stereo-errors it is essential to include the counter-ion, as an integrated part of the
A. Razavi (*)
35 Domaine de la Brisee, 7034 Obourg, Belgium
e-mail: abbasrazavi@skynet.be
DOI: 10.1007/12_2013_220
# Springer-Verlag Berlin Heidelberg 2013
Published online: 26 September 2013
Syndiotactic Polypropylene: Discovery,
Development, and Industrialization via
Bridged Metallocene Catalysts
Abbas Razavi
Abstract This chapter covers the discovery that enabled, for the first time, the
manufacturing of high molecular weight, highly stereoregular syndiotactic polypropylene polymers with narrow molecular weight distribution via the new class of
metallocene molecules with bridged cyclopentadienyl-fluorenyl ligands. First, the
salient crystal structural features of the neutral metallocene molecules and the crystal
structure of the corresponding mono-alkyl-zirconocenium cation is introduced. Then,
by employing the structural and geometrical data, a realistic working model for the
active site precursor is developed and presented. The stereochemistry of the catalytic
propylene poly-insertion reaction and the formation of syndiotactic polypropylene
according to the enantiomorphic site control mechanism at the enantiotopic cationic
active sites, formed after the activation of the prochiral metallocene dichloride with
methylaluminoxane, MAO, is reviewed and further delineated. In the following
sections, the impact of the introduction of substituents with proper size and composition at some selected positions of the ligand is discussed and the methods for
increasing the molecular weight and stereoregularity of syndiotactic polypropylene
polymers are elaborated. With the aid of computational calculations on real and
hypothetical catalyst systems with substitutionally altered ligand structures, it is
shown that the degree of enantioselectivity of syndiospecific catalyst systems can be
determined and/or predicted for these systems quantitatively and with high precision.
The calculations confirm that the introduction of substituent(s) reinforcing the
preferential conformational orientation of the polymer chain enhances the overall
enantioselectivity of the active site, and to certain extends stereoselectivity in general,
by affecting the site epimerization processes. The computational calculations reveal
that to account correctly for the frequency of the site epimerization-dependent m-type
stereo-errors it is essential to include the counter-ion, as an integrated part of the
A. Razavi (*)
35 Domaine de la Brisee, 7034 Obourg, Belgium
e-mail: abbasrazavi@skynet.be