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.

A detailed study of the effect of reaction temperature, time, and cocatalyst composition on the ethylene polymerization performance of 2-[1-(2,6-dibenzhydryl-4-chlorophenylimino)­ethyl]-6-(1-mesityliminoethyl)­pyridyliron dichloride (1) is reported. In the presence of modified methylaluminoxane (MMAO), 1 behaves like a highly active, “multisite-like” ethylene polymerization catalyst, with the resulting polyethylenes having time-dependent bimodal-like molecular-weight distributions and featuring saturated (n-propyl- and i-butyl-terminated) chain ends. To readily distinguish between bimodal and bimodal-like molecular-weight distributions, we have proposed the use of the dN f/(d log M) – log M representation further to the mainstream dW f/(d log M) – log M one. The consensus mechanism of chain transfer and chain-end formation in the presence of MMAO has been proposed, which explains the composition and amount of terminal alkyl groups in the polymer, and the apparent “multisite-like” nature of the iron catalyst. A comparison between the catalytic behaviors of the “multisite-like” 1/MMAO catalyst system and the truly multisite catalyst system based on Brookhart’s symmetrical bis­(imino)­pyridine iron catalyst 2 is given.

Summary: Method of polymerization inhibition by radioactive carbon monoxide (14CO) has been used to determine the number of active centers (CP) and propagation rate constant (kP) for ethylene polymerization with homogeneous complex 2,6‐(2,6‐(Me)2C6H3NCMe)2C5H3NFeCl2 (LFeCl2), activated with methylalumoxane (MAO) or Al(i‐Bu)3. With both activators the rate profile of polymerization was unstable: high activity [0.8 × 103–1.5 × 103 kg PE per (molFe · h · atm) at 35 °C] of the initial period sharply decreases (sevenfold in 10 min). In the beginning of polymerization with the catalysts LFeCl2/MAO and LFeCl2/Al(i‐Bu)3, the CP values were found to be 8 and 41% of total Fe‐complex content in catalysts, respectively, and decreased 1.5–2‐fold in 9 min. As polymerization proceeds, the kP value for LFeCl2/MAO system decreases from 5 × 104 to 1.5 × 104 L · (mol · s)−1 LFeCl2/MAO, and for LFeCl2/Al(i‐Bu)3 system from 2.6 × 104 to 0.82 × 104 L · (mol · s)−1. Data on the effect of polymerization time on polyethylene molar mass distribution are presented. Basing on the obtained results it was suggested that highly reactive, but unstable centers, dominating at short polymerization times, produce low‐molar‐mass polyethylene, while polyethylene with higher molar mass is produced by less active (low kP) and more stable centers.Data showing change in molar mass distribution of polyethylene with polymerization time.magnified imageData showing change in molar mass distribution of polyethylene with polymerization time.

The article reports on the noncatalytic transformation of a polybutadiene (number‐average molecular weight = 128,000) into a functionalized liquid rubber via the carboxidation of the polymer CC bonds by nitrous oxide. The reaction was conducted in a benzene solution at 160–230 °C and a pressure of 3–6 MPa. The carboxidation mechanism was determined. The main route (95%) of the reaction proceeded without cleavage of CC bonds and led to the formation of ketone groups in the polymer backbone. A minor route (5%) of the reaction proceeded with the cleavage of CC bonds, yielding two smaller fragments containing aldehyde and vinyl end groups. The availability of the cleavage route could lead to a dramatic decrease in the molecular weight, which, depending on the carboxidation degree, could be 1–2 orders of magnitude less than that of the initial material. Thus, the carboxidation of more than 15% of the polybutadiene CC bonds transformed it into a CO‐functionalized liquid rubber with a narrow molecular weight distribution. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2510–2520, 2006

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.