1,2 Enriched polymerization of isoprene by cobalt complex carrying aminophosphory fused (PN³) ligand

Abstract

Metal‐catalyzed selective isoprene polymerization has been a major entry toward cis‐1,4, trans‐1,4, and 3,4 isomers of polyisoprene, however, 1,2 selective polymerization of isoprene has not yet been achieved due to the steric problem. In this work, difluoro cobalt complexes carrying aminophosphory (‐HN‐P(=O) tBu2‐) fused pyrazol‐pyridine ligand has been prepared and characterized. In combination with Mgn‐Bu2, the formed catalyst unprecedentedly converts isoprene to polyisoprene with 1,2 enchainment up to 50 mol% in a molecular weight controlled polymerization mode. The resultant polymers are fully characterized by NMR, IR, DSC, and GPC. The 1,2 incorporation of polyisoprene is weakly dependent on feeding of Mgn‐Bu2 and reaction temperature. The weak affinity between Mg2+ and allylic terminal of propagating chain is possible for the unique 1,2 irregular insertion and non‐irreversible chain transfer and termination reactions throughout the chain propagation. The ability of current catalyst demonstrates a big advantage for application in the development of 1,2 selective polymerization of isoprene, and a potential for access to a new family of polyisoprene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2286–2293

Anionic Polymerization in Porous Organic Frameworks: A Strategy to Fabricate Anchored Polymers and Copolymers

“…DSC runs of nanocomposites exhibited glass transition temperatures ( T g ) at 12 °C for the PAFMe‐PI and at 110 °C for the PAFMe‐PMMA (Supporting Information, Figures S16 and S17), providing the selective detection of external anchored‐polymers. The relatively high T g of PI suggests a lower flexibility of the polymer chains owing to the lower content of 1,4‐ cis monomer units, as detected by 13 C MAS NMR [41] . Indeed, 13 C MAS NMR spectra of PAFMe‐PI showed a polymer with a high vinyl content and a microstructure with monomer unit distribution of 3,4 (14 % mol), 1,2 (35 % mol), 1,4‐ cis (36 % mol), and 1,4‐ trans (15 %; Supporting Information, Figure S15).…”

Controlled isoprene polymerization mediated by iminopyridine‐iron (II) acetylacetonate pre‐catalysts

“…The polymer obtained by title iron catalysts being different from the previously reported iron chloride catalyzed isoprene polymerization, indicates a different activation process thus lead to different counterions. Upon activation with MAO, a heterobimetallic intermediate I or II (Scheme S1) would form during the activation process: two metals centers (Fe and Al species) connected through acetylacetone in which one oxygen atom of acetylacetone coordinated to iron center and remaining oxygen atom bonded to aluminum center . The type of monomer insertion and subsequent monomer enchainment are the key steps that determine the end structural properties of the polymer.…”

“…Upon activation with MAO, a heterobimetallic intermediate I or II (Scheme S1) would form during the activation process: two metals centers (Fe and Al species) connected through acetylacetone in which one oxygen atom of acetylacetone coordinated to iron center and remaining oxygen atom bonded to aluminum center. [10] The type of monomer insertion and subsequent monomer enchainment are the key steps that determine the end structural properties of the polymer. Following the initial coordination of monomer at vacant site of iron center either through cis-η 4 or trans-η 4 coordination (III and IV in Scheme S1) and insertion of coordinated monomer to Fe-alkyl bond leading to the formation of anti-η 3 or syn-η 3 allyl-Fe intermediates (V and VI in Scheme S1) respectively, and then multiple coordination-insertion steps proceed leading to chain growth (propagation step).…”

“…Compared to the early transition metal catalysts or conventional Ziegler-Natta catalysts, few studies are found in which late transition metal complexes used as catalysts for the isoprene polymerization. [8][9][10] The discovery of α-diimine-Pd (II)−/-Ni (II) [11][12][13][14][15][16][17][18][19][20][21][22][23] and bis (phenylimino)pyridine-Co (II)/Fe (II) based catalysts [24][25][26][27] for the polymerization of olefins were found as instrumental in the development in the late transition based catalyst for olefin polymerization. Since then, the well-defined late transition metal complex began to attract attention from scientific researcher in academia as well as from industrial community to use these complexes as catalysts for olefin polymerization, due to their expedient preparation, high reactivity, single catalytic behavior and controlled stereoselectivity.…”

“…For the isoprene polymerization, titanium, lithium and rare earth metal based catalysts have been extensively studied in academia as well as in industry. Compared to the early transition metal catalysts or conventional Ziegler‐Natta catalysts, few studies are found in which late transition metal complexes used as catalysts for the isoprene polymerization …”