Реферат: The combination of the method for measuring of the number of active centers by quenching of polymerization by radioactive carbon monoxide with fractionation of polymers obtained by TREF method (temperature rising elution fractionation) to the separate fractions with different isotacticity has been used for determination of the number of active centers with different isospecificity (Cpi) responsible for the formation of Fi fractions as well as for calculation of propagation rate constants (kpi) for these centers. Data on the effect of catalyst composition on the Cpi and kpi values have been obtained for the first time for polymerization with three types of titanium-magnesium catalysts with different internal stereoregulating donors (di-n-butyl phthalate – TMC-D, 2,3-diisobutyl-diethyl succinate – TMC-S, 9,9-bis(methoxymethyl)-fluorene – TMC-F) and for catalytic system TMC-D with external stereoregulating donor – cyclohexylmethyl(dimethoxy)silane (ED). It was found that upon propylene polymerization without ED, non-stereospecific active centers AS constitute the maximum portion (38–46%) of active centers in all the catalysts under study. Catalysts TMC-D and TMC-S have a similar distribution of active centers AS, IS1, IS2, and IS3 with different stereospecificity, while catalyst TMC-F differs from them: it contains a much smaller portion of active centers IS1 with low stereospecificity and a higher portion of isospecific centers IS2 and highly isospecific centers IS3. The portion of non-stereospecific active centers AS and centers with low stereospecificity IS1 is significantly reduced upon polymerization over catalyst TMC-D in the presence of ED, while the portions of stereospecific centers IS2 and highly stereospecific centers IS3 increase noticeably. The rate constants of chain propagation reaction (kpi) on these centers were calculated using data on the number of active centers with different stereospecificity (Cpi) under conditions of the minimum content of «dormant» centers (10 vol. % H2), formed due to the 2,1-insertion of the propylene molecule into the polymer chain. For all the catalysts studied, kpi was found to increase in the set of active centers AS ˂ IS1 ˂ IS2 ˂ IS3. The possible structures of active centers with different isospecificity are discussed on the base of experimental data obtained on the Cpi and kpi values.

Библиографическая ссылка: Barabanov A.A. , Vereykina V. , Matsko M.A. , Zakharov V.A.
Propylene Polymerization over Titanium-Magnesium Catalysts: Effect of Stereoregulating Donors on the Number and Reactivity of Active Centers with Different Stereospecificity
Asian Polyolefin Workshop 2021 20-21 Dec 2021