Comparison of the solvents n-hexane, tert-butyl benzene and toluene in the polymerization of 1,3-butadiene with the ziegler catalyst system neodymium versatate/diisobutylaluminum hydride/ethylaluminum sesquichloride

摘要

The influence of the solvents n-hexane, tert-butyl benzene (TBB) and toluene on the Nd-catalyzed polymerization of butadiene was studied. Special emphasis was placed on polymerization kinetics and on the evolution of molar masses and molar mass distributions with monomer conversion. Distinct differences were found between the three solvents. From the polymerization kinetics there is evidence which supports Porri's view on the competitive coordination between aromatic solvents and butadiene to active Nd-sites. In addition, there are indications for the irreversible transfer of benzyl-H-atoms from toluene to active allyl-anionic polymer chains. The evolution of molar mass distributions with monomer conversion provides evidence for the existence of two active catalyst species which are present in all three solvents. One of these two species is highly reactive ("hot") and short-lived. This species generates BR with high molar mass. The second species has a low reactivity and lives throughout the entire course of the polymerization. In n-hexane the "hot", short-lived species is present only at the start of the polymerization, whereas in TBB and toluene, the short-lived species becomes evident at monomer conversion >10% and is constantly ( re) generated. Cis-1,4-contents determined at final monomer conversion are not in line with other available studies in this field.