E Stereoregular 1,1 and 1,3 Constitutional Units from 1,3-Butadiene in Copolymerizations Catalyzed by a Highly Hindered C₂ Symmetric Metallocene

Abstract

Unprecedented 1,1 and 1,3 constitutional units from 1,3-butadiene, both presenting only the E configuration of the double bond, have been achieved by copolymerization with ethene, conducted at high temperature and low ethene concentration, when catalyzed by a highly hindered C(2) symmetric metallocene. Ethene/butadiene copolymerizations by this catalyst generally lead to prevailing methylene-1,2-cyclopropane units from butadiene. Polymer microstructures obtained for different comonomer concentrations clearly indicate that the rate-determining step leading to cyclopropanation involves ethene, while that leading to 1,1 and 1,3 constitutional units does not. A general copolymerization scheme and a molecular modeling study of the cyclopropanation reaction are presented. Molecular modeling also indicates that the E stereoselectivity for 1,1 and 1,3 constitutional units can be rationalized, in the assumption that an allyl isomerization of the terminal of the growing chain would occur.

New Group IV Metallocene Systems Active in the Copolymerization of α‐Olefins and Conjugated Dienes

“…E. Probably, catalysts (2) and (3) , the ethene insertion becomes very fast and it usually competes with the D ! G rearrangement, leading to F. [2,3] But, as for catalysts (2) and (3), the D ! F reaction is anyway slowed down by the high steric hindrance of the substituents and the main products, both at high and at low [E], come from the D !…”

“…Recently, we have shown that copolymerization of 1,3-butadiene with ethene, catalyzed by the isospecific catalytic system based on the C 2 symmetric zirconocene rac-[CH 2 -(3-tert-butyl-1-indenyl) 2 ]ZrCl 2 , activated by MAO, leads to polyethenes containing methylene-1,2-cyclopropane Copolymerization performed utilizing 13 C-labeled butadiene [5] and molecular modeling calculations [2][3][4] contributed to rationalize the observed behavior for copolymerizations catalyzed by these C 2 symmetric metallocene complexes. For all the considered metallocene complexes having substituents in positions 3 and 3 0 , minimum energy coordination intermediates and insertion transition states have been located for the primary Z 2 coordination of butadiene, which leads through a primary vinyl insertion to a s-coordinated growing chain (step A !…”

“…The formation of 1,2-cyclopropane, 1,1, and 1,3 constitutional units has been rationalized by the reactions sketched in Scheme 1. [3] According to this reaction scheme, all these new kinds of butadiene constitutional units would be obtained by rearrangements of the same intermediate (D in Scheme 1), whereas the formation of 1,2-cyclopentane would arise from insertion of ethene on intermediate B in Scheme 1, followed by coordination and insertion of pendant double bond into metal-polymer s bond. As recently reported by Choo and Waymouth, [6] cyclopolymerization of butadiene can be also achieved in the presence of (CH 3 ) 2 -Si(Flu) 2 ZrCl 2 (where Flu ¼ 9-fluorenyl); however, only a low amount of cyclopropane, as well as cyclopentane rings are obtained, because butadiene mainly inserts forming 1,4-trans units.…”

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

“…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.…”

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.…”