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In NJV-dimethylaniline the ionic complexes [Cp*,MMe(THT)]+[BPhJ (M = Zr, Hf) oligomerize propene to low molecular weight oligomers. At room temperature for M = Zr a rather broad molecular weight distribution is obtained (c6 to C%), whereas for M = Hf only one dimer (4methyl-l-pentene) and one trimer (4,6-dimethyl-l-heptene) are formed. With an increase in reaction temperature the product composition shifts to lower molecular weights, but the specific formation of head-to-tail oligomers is retained. The oligomers are formed by &Me transfer from the growing oligopropene alkyl chain to the metal center. The molecular weight distributions of the oligomers produced at temperature between 5 and 45 OC are satisfactorily described by the Flory-Schulz theory. This allows the calculation of ratios of rate coefficients for propagation (k,) and termination (kJ. Values for (AG* -AG*t)298~ were calculated as -1.9 (3) and

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The structure of organoaluminum(halide) complexes, used as cocatalysts in Ziegler−Natta catalysis, is investigated by experimental far-infrared spectroscopy and by quantum simulations. Experimental and calculated far-infrared spectra agree very well, holding promise for the employed far-infrared/quantum simulation approach to reveal more detail on the catalytically active site in Ziegler−Natta catalysis. Whereas the species preferably form dinuclear aluminum complexes when the bridge can be formed by chlorine, on the basis of the calculated total energies and the observed infrared spectra, alkyl-bridged dimers are found to be much less stable.

SYNOPSISIn the oxidative coupling polymerization, catalyzed by copper-amine complexes, the oxidation rates of 2,6-dimethylphenol (DMP) and its C-0-coupled dimer [ 4-(2',6'-dimethylphenoxy ) -2,6-dimethylphenol] and trimer [ 4-( -4'-(2",6"-dimethylphenoxy ) -2',6'-dimethylphenoxy ) ) -2,6-dimethylphenol] have been determined. The DMP concentration dependence shows a Michaelis-Menten-type behavior. On the other hand, the dimer and trimer showed a first-order rate-dependence in the respective phenol concentrations. This indicates that the slow reaction step, following an equilibrium complex formation between DMP and copper complex, is relatively fast for both the dimer and the trimer. Therefore, coordination of dimer or trimer to the copper complex appears to be rate-determining. Furthermore, the dimer and trimer gave overall reaction rates approximately eight times higher than found for DMP. Following the Flory principle of equal reactivity for functional groups of oligomers in polycondensations, all PPO oligomers can be assumed to have equally high oxidation rates as the dimer and trimer. The yield of undesired DPQ side product is strongly reduced when starting with the dimer (0.18%), or trimer (0.17%), compared to 3.3% for DMP. This is not unexpected, since DPQ can only be formed from two monomeric DMP residues. In fact, using a 1/10 molar mixture of dimer/DMP already results in a DPQ yield of only 1.7%. Furthermore, when starting from DMP, it has been observed that DPQ was predominantly formed during the first 30% conversion. Starting from dimer (or trimer) DPQ was formed at an almost constant very low rate during the whole course of the reaction. From these experiments it can be concluded that the most important polymerization reaction involves oxidation of copper-coordinated DMP anion to its corresponding cations, followed by coupling with a copper coordinated PPO chain. Keywords: oxidative coupling polymerization poly(2,6-dimethyl-1,4-phenylene)oxide 2,6-dimethylphenol PPO-dimer PPO-trimer specificity reactivity flory principle of equal reactivity * See Ref. 1 for previous paper in this series. Present address: GE Plastics,