Temperature dependence of stereospecificity of active sites in heterogeneous catalysts for propylene polymerization

✍ Scribed by L.A. Rishina; E.I. Vizen; F.S. Dyachkovsky

• Publisher: Elsevier Science
• Year: 1979
• Tongue: English
• Weight: 346 KB
• Volume: 15
• Category: Article
• ISSN: 0014-3057
• DOI: 10.1016/0014-3057(79)90255-6

✦ Synopsis

A~traet--Temperature dependences of the stereoregularity parameters of the most stereospecific active centres of =-TiCI3:AIEt 3 catalytic system from -25 to 120 and of VCI3--AIEt 3 catalytic system from -15: to 90 c have been measured. It was found that this temperature dependence could be represented by a curve with a minimum at 20-50. The results could be explained by a two-step mechanism of isotactic chain growth (propagationt with preliminary co-ordination of monomer on the active centres.

Study of the temperature dependence of the stereospecificity active sites is important for understanding the mechanism of stereoregulation in olefin polymerization on heterogeneous complex catalysts. Significant efforts have been made to elucidate this dependence (see reviews I-1,2]), but these studies were mainly concerned with examining the fractional compositions of propylene polymers obtained with various catalysts, assuming that all polypropylene fractions with the same solubility have the same stereoregularity. In particular, polymer fractions insoluble in boiling n-heptane were regarded as completely isotactic. The main result of these studies was that the stereospecificity of heterogeneous complex catalysts based on TiCI a decreased with rising temperature, due to deterioration of the crystal lattice on the catalyst surface [2], and that maximum stereoregularity for the polymers occurred at 0-30 c.

This approach cannot be regarded as conclusive: all stereoregularity parameters of total polymer products (if measured by any physical method)