Butadiene Insertion and Constitutional Units in Ethene Copolymerizations by C₂-Symmetric Metallocenes

Abstract

Copolymerizations of ethylene with 1,3-butadiene in the presence of catalytic systems based on some C 2-symmetric zirconocenes (rac-[CH2(3-R-1-indenyl)2]ZrCl2 where R = −C(CH3)3 (1), −CH(CH3)2 (2), −CH2CH3 (3), −CH3 (4), and −H (5)) are compared. The chemical nature and the relative amount of constitutional comonomer units from butadiene are strongly affected by the bulkiness of the substituent in positions 3 and 3‘. DFT calculations indicate that the observed dependence of constitutional units from butadiene on the bulkiness of the alkyl ligand substituent can be easily rationalized by the occurrence of an unusual insertion mechanism for butadiene. This mechanism, involving butadiene η2 primary coordination followed by its primary vinyl insertion, becomes largely predominant for catalytic systems based on the zirconocenes (1−4), which present R ≥ CH3. This kind of butadiene insertion mechanism is also able to account for the high stereoregularity which is observed for adjacent methylene-1,2-cyclopropane units.

Synthesis of Ethylene or Propylene/1,3-Butadiene Copolymers Possessing Pendant Vinyl Groups with Virtually No Internal Olefins

“…Chemical shifts were referenced to the residual solvent peak (δ1H = 7.15 ppm). Quantity of the vinyl groups Equation (7) and the internal olefins Equation (8) in ethylene/butadiene copolymers were quantified as per 1000 Carbon in accordance with the following Equations (7) and (8) C-NMR spectra of the propylene/butadiene copolymers were recorded on an ECA500 spectrometer (125 MHz) from Japan Electron Optics Laboratory Co. Ltd. (JEOL, Tokyo, Japan), using 1,1,2,2-tetrachloroethane-d2 as a solvent at 140 °C. Chemical shifts were referenced to the residual solvent peak (δ13C = 72.4 ppm).…”

“…Chemical shifts were referenced to the residual solvent peak (δ13C = 72.4 ppm). The spectrum was analyzed with reference to the chemical shifts of the signals assigned to the vinyl groups, the cyclopropane skeleton, the methylcyclopentane skeleton [19], the 1,4-addition units and the 1,3-addition units in the propylene/butadiene copolymers which were described in previous papers [8,10,11]. The determination of the butadiene content (Equation (9)) and the vinyl groups content (Equation (10)), the cyclopropane skeleton content (Equation (11)), the methylcyclopentane skeleton content (Equation (12)), the 1,4-addition units content (Equation (13)), the 1,3-addition units content (Equation (14)), and the hydrogenated 1,4-addition units content (Equation (15)) relative to all the butadiene-derived structural units was performed in accordance with the following Equations (9) to (15).…”

“…η2 primary coordination of butadiene leads to formation of vinyl groups or rings through a primary vinyl insertion, whereas η2 secondary and η4-cis coordination of butadiene leads to trans and cis 1,4-butadiene units through the formation of a syn-η3-coordinated growing chain and an anti-η3-coordinated growing chain, respectively [6][7][8][9]. Until now, reports on olefin/butadiene copolymerization, where the insertion reaction of the 1,3-butadiene proceeds via 1,2-insertion preferentially to form a vinyl group, are scarce.…”

“…Bu) in that η2 primary coordination of butadiene is energetically favorable compared to η2 secondary coordination and the η4-cis coordination of butadiene [8]. In addition, the relative amount of constitutional monomer units derived from butadiene are affected by the bulkiness of the substituent.…”

Synthesis of polyethene–graft–polystyrene copolymers from linear polyethene-containing cyclopropane rings

“…[2][3][4][5][6][7] As it has been reported in the literature, PEs containing controlled amounts of methylene-1,2-cyclopropane and methylene-1,2-cyclopentane units (hereafter called E-C3) can be obtained by the polymerization of ethene with 1,3-butadiene using rac-[CH 2 (3-tert-butyl-1-indenyl) 2 ]ZrCl 2 activated by methylalluminoxane as a catalyst. [8][9][10][11][12] These PEs are technologically relevant because the presence of reactive cyclopropane rings in the chains discloses the possibility to obtain polymers with different properties. 13,14 For example, in a recent study by our group, we showed that it is possible to produce crosslinked PE by simple thermal treatments of E-C3 copolymers in the temperature range of 160-200 1C.…”