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Propylene polymerization was investigated with the TiCl 4 /MgCl 4 supported catalyst with the stereoregulating donor pair dibutylphtalate (DBPH)/triethoxyphenylsilane (TEPS) in heptane with AlEt 3 as cocatalyst in the presence of hydrogen. It was shown that there is an activation effect by the influence of hydrogen. The removal of hydrogen from the polymerization medium results in an immediate disappearance of activation. However, the deactivation of the system is reversible, and it is possible to repeat the activation effect by hydrogen more than once. It was found that the value of the activation energy is the same in the presence of hydrogen and without it and is equal to 11 kcal/mol. From the experimental results it is concluded that the maximum number of active centres is realized in the catalytic system in the presence of hydrogen, but a value of the propagation rate constant is not changed. It was also found that in the presence of hydrogen the system's decay follows the bimolecular law of active centres deactivation.

The effect of CS 2 on the catalytic system TiCl 4 /MgCl 2 /DBPH-AlEt 3 /TEPS in propylene polymerization in the presence and absence of hydrogen was studied. It was shown that CS 2 poisons active centres in both cases by a similar way. The yield of polypropylene decreases with the CS 2 effect, but the isotactic centres poison to the greatest degree. Results obtained by the study of polymerization kinetics, fractional comosition and molecular mass distribution of polymers permit a conclusion that there is not any differentiation between initial and “hydrogen” centres, i.e. these centres have the same nature. An observed hydrogen activation effect is explained by the revival of “dormant” centres, resulting from 2-1 propylene insertion in the polymer chain in the chain transfer reaction with H 2 . Seemingly the competition between the polymerization rate retarding by irregular monomer insertion and the activation by hydrogen takes place. It leads to non-stationary kinetics of propylene polymerization in the presence of hydrogen.

Temperature dependences of the stereoregularity parameters of the most stereospecific active centres of α-TiCl3-AlEt3 catalytic system from −25 to 120 and of VCl3-AlEt3 catalytic system from −15° to 90° 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 (propagation) with preliminary co-ordination of monomer on the active centres.

It has been shown that replacement of Cl atoms by I and Br atoms leads to decrease in the activity of the catalytis systems TiCl 3 -AlEt 3 owing to decrease in the number of active centres. This decrease is probably due to the fact that a group of titanium atoms bound by halogen bridges, and not a single atom, is involved in the catalytis act. The most effective way of enhancing the isospecificity of the active centre is to induce the iodine-containing compound to act upon the TiCl 3 crystal surface. However, no simple correlation between the stereospecificity of the catalytis systems, ion radii of the anions and distances M-M and M-X was found.

A fractional poisoning method has shown that all groups of Ziegler catalyst centres, both stereospecific and non-stereospecific, have a similar distribution of propagation rate constants. The most regular and highly molecular isotactic fraction is quite uniform by stereoregularity. Most of the poison-resistable part of active centres in δTiCl 3 -AlEt 3 systems have properties similar to those of initial system TiCl 3 -AlEt 2 Cl, which may be caused by different adsorption abilities of co-catalysts AlEt 3 and AlEt 2 Cl at TiCl 3 surface. Values n p and k p have been estimated for δTiCl 3 (TAC)-AlEt 3 system.

A study was made of the effect of NEt 3 as a donor additive on the centres of different stereospecificities of the catalytic system δ-TiCl 3 (TAC)-AlEt 3 . It is shown that the addition of amine, both in a free form (D) and as part of the complex NEt 3 -AlEt 3 (C), produces a poisoning action on the catalytic centres. In the former case (D), the isospecific centres are also partially poisoned, leading to a drop in the system activity and a decrease in the M v value of the polypropylene iso-fraction. In the latter case (C), at C/TiCl 3 = 5, one can observe the effect of system modification which shows up in increasing the molecular weight and amount of the iso-fraction and also in improving its stereoregularity parameters with the general catalyst activity remaining unchanged. The effect of the modifying additive is explained by the increase of iso-addition propagation constant.

From a study of the products of the reaction between TiCl 4 and AlR 2 Cl the conclusion is drawn that oligomerization of propylene with this system at ratios of Al : Ti

The i.r. spectra of C3H6C3D6 copolymers obtained with an isospecific catalyst have been studied. An estimate is given of the minimum length of regular helix sequences sufficient for the appearance of helix bands and regularity bands in the spectra of isotactic polypropylene and its deuterated analogue.

Stereoregularity parameters are measured by different i.r. methods for samples of polypropylene, obtained with catalytic systems MCl 3 AlEt 3 (M  Ti, V, Cr and Fe). The degree of stereoregularity of the fractions of these polymers insoluble in boiling n -heptane and n -octane decreases in the order α -TiCl 3 ≅ δ -TiCl 3 > CrCl 3 > VCl 3 > FeCl 3 which is close to the order of the decrease of MCl and MM distances in the MCl 3 lattices.