The effect of Ti content on the activity of titanium-magnesium catalysts (TMC) and molecular weight distribution (MWD) of polyethylene (PE) produced has been studied. It was found that the activity enhances sharply as Ti content decreases from 0.6 to 0.07 wt %, and shows no significant changes in the Ti content range of 0.6-5.0 wt %. The maximum activity (36 kg PE/mmol Ti  h  bar C 2 H 4 ) was observed for TMC with the lowest Ti content. The catalyst with low titanium content ($ 0.1 wt % of Ti) produced PE with narrower MWD (M w /M n ¼ 3.1-3.5) as compared to catalysts with higher titanium content (3-5 wt % of Ti; M w /M n ¼ 4.8-5.0). New data on the effect of hydrogen on MWD of PE have been found. Increasing hydrogen concentration results in broadening the MWD of PE, especially in the case of TMC with high titanium content. The data presented indicate the heterogeneity of active centers of TMC in the reaction of chain transfer with hydrogen. The data on the ethylenehexene-1 copolymerization over TMC with different titanium content are presented. Comonomer reactivity ratios were shown to be independent of the Ti content in TMC. Presumably the difference in activity of these catalysts is mainly caused by the difference in the number of active centers.

Supported titanium–magnesium catalysts (TMC) comprising isolated and clustered titanium ions in different oxidation states, which are obtained using titanium compounds of different composition (TiCl4, TiCl3•nDBE (DBE – dibutyl ether), [η6–BenzeneTiAl2Cl8]), were synthesized and tested in ethylene polymerization. The state of titanium ions was studied by the ESR method both for the procatalysts and after their interaction with triisobutilaluminum. For identification of ESR‐silent Ti3+ ions and Ti2+ ions, special procedures of additional catalyst treatment with pyridine, water, and chloropentafluorobenzene were used to obtain Ti3+ ions that are observable in ESR spectra. In distinction to numerous earlier works performed with the TiCl4/MgCl2 catalyst comprising after the interaction with AlR3 the Ti3+ surface compounds both as isolated ions and clusters (ESR‐silent), this work considers the [η6–BenzeneTiAl2Cl8]/MgCl2 catalyst (TMC‐3) comprising mainly the isolated Ti2+ ions and a new catalyst TMC‐4 obtained by treating the TMC‐3 with chloropentafluorobenzene. This catalyst comprises only the isolated Ti3+ ions both before and after the interaction with triisobutylaluminum. It was shown that in spite of sharp distinctions between the catalysts under consideration concerning titanium oxidation state and the ratio of isolated Ti3+ ions to clustered ones, all these catalysts produce polyethylenes with similar molecular weights and molecular‐weight distributions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6362–6372, 2009

ABSTRACT:The data on the effects of polymerization duration, cocatalyst, and monomer concentrations upon ethylene polymerization in the absence of hydrogen, and the effect of an additional chain transfer agent (hydrogen) on the molecular weight (MW), molecular weight distribution (MWD), and content of vinyl terminal groups for polyethylene (PE) produced over the supported titanium-magnesium catalyst (TMC) are obtained. The effects of these parameters on nonuniformity of active sites for different chain transfer reactions are analyzed by deconvolution of the experimental MWD curves into Flory components. It has been shown that the polymer MW grows, the MWD becomes narrower and the content of vinyl terminal groups in PE increases with increasing polymerization duration. It is assumed to occur due to the reduction of the rate of chain transfer with AlEt 3 with increasing polymerization duration. The polydispersity of PE is found to rise with increasing AlEt 3 concentration and decreasing monomer concentration due to the emergence of additional low molecular weight Flory components. The ratios of the individual rate constants of chain transfer with AlEt 3 , monomer and hydrogen to the propagation rate constant have been calculated.

Electron spin resonance (ESR) studies reveal a high yield of isolated Ti3+ compounds (30–70% of the total titanium content) that form in superactive supported titanium–magnesium catalysts (TMCs) of composition TiCl4/MgCl2 with a low titanium content (≤0.1 wt%) after their interaction with different aluminum trialkyls (AlR3). These catalysts strongly differ from conventional TMCs with titanium contents of 1–3 wt%, which produce a set of isolated or associated Ti(II) and Ti(III) species after the interaction with the AlR3. A correlation is found between the content of the isolated Ti(III) ions and the activity in ethylene polymerization. According to temperature rising elution fractionation (TREF) data, the catalysts with a low titanium content (isolated Ti(III) ions) mainly produce polypropylene with a very high atactic‐fraction content. Organic products formed on the interaction of AlEt3 and AlMe3 with TMC are identified. The data obtained allow a scheme of Ti3+ and Ti2+ compounds formed in these catalysts to be proposed.

Heterogeneity of active centers (AC) of titanium-magnesium catalysts (TMC) and vanadium-magnesium catalyst (VMC) in ethylene-hexene-1 copolymerization has been studied on the base of data of polymer molecular weight distribution (MWD) deconvolution technique and copolymer fractionation onto narrow fractions. It was found that 3 and 4 Flory components (groups of active centers) are required to describe experimental MWD curves of copolymers produced over TMC with different Ti content. In the case of VMC MWD of homopolymer and copolymer are characterized by set of 5 Flory components (5 groups of AC). Different character of inter-relationship between MW and short chain branching (SCB) was found for ethylene-hexene-1 copolymers produced over different catalysts: heterogeneous type in the case of TMC and more uniform for copolymer prepared over VMC. The content of Ti affects on the slope of that profile in copolymers produced over TMC. The results indicated that TMC and VMC are different greatly on the heterogeneity of active centers to the formation of polymers with different molecular weights and to formation of copolymers with different inter-relationship between MW and short chain branching. TMC produces polymers with more narrow MWD but it contains highly heterogeneous centers regarding comonomer reactivity ratios. VMC produces polymers with broad and bimodal MWD but it contains more homogeneous centers regarding comonomer reactivity ratios.