Premium
Modeling of isospecific Ti sites in MgCl 2 supported heterogeneous Ziegler‐Natta catalysts
Author(s) -
Barino Luisa,
Scordamaglia Raimondo
Publication year - 1998
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/(sici)1521-3919(19980701)7:4<407::aid-mats407>3.0.co;2-d
Subject(s) - steric effects , chemistry , molecule , polymerization , lewis acids and bases , natta , chirality (physics) , closeness , catalysis , stereochemistry , polymer , organic chemistry , mathematics , physics , nambu–jona lasinio model , chiral symmetry breaking , mathematical analysis , quantum mechanics , quark
New models for the steric environment of Ti isospecific polymerization sites for poly(propylene) on MgCl 2 microcrystals are proposed. They directly involve a donor molecule in order to obtain isospecific activable Ti atoms otherwise belonging to isolated adsorbed TiCl 4 molecules or Ti 2 Cl 8 dimers which are lacking of the required chirality for stereocontrol. The donor molecules able to attain at best this effect keep to some peculiar conformational rules settled by the authors in a previous theoretical‐correlative study on highly active Lewis bases. The new 1,3‐dimethoxypropane series suggested by the authors and recently patented by Montell has been examined in detail. Essentially three different types of closeness between Ti atoms and donor molecules can take place, in which different moieties of the diether compound help to build the ‘right’ steric environment in the site's neighbouring. In the three proposed models S1, S2, S3 the stereocontrol is attained through, respectively, one of the methoxy moieties, one of the methyls, and one of the central carbon atom substituents. New hypotheses on the role of Lewis bases in the preparation of isospecific heterogeneous Ziegler‐Natta catalysts are discussed.