Chain Growth Polymerization of Isoprene and Stereoselective Isoprene–Styrene Copolymerization Promoted by an ansa-Bis(indenyl)allyl–Yttrium Complex

Abstract

The ability of rac-[{Me2C(Ind)2}Y(1,3-(SiMe3)2C3H3)] (Ind = 9-indenyl) (1) to catalyze isoprene polymerization, either as a single-site component or in combination with an alkyl–metal as a chain transfer agent (CTA) via coordinative chain transfer polymerization (CCTP), has been investigated. Complex 1 alone catalyzes the highly 1,4-trans-stereoselective polymerization of isoprene with moderate activity. The addition of ZnEt2 provides an efficient catalytic system for the reversible CCTP of isoprene with retention of the 1,4-trans stereoselectivity. By contrast, in the presence of Mg(nBu)2, with increasing amounts of CTA, the 1,4-trans specificity gradually decreases at the advantage of the 3,4-polymer. The copolymerization between isoprene and styrene has been also studied, resulting in the formation of materials with unprecedented architecture. Simultaneous copolymerization of isoprene and styrene with 1 provides copolymers with a wide range of compositions (χS = 0.30–0.98) and a stereospecific blocky distribution of the monomers in the copolymer chain. The reactivity ratios (average values: r 1,Ip = 2 and r 2,St = 18) determined by NMR spectroscopy confirmed the propensity to form multiblock materials. Microstructural 13C NMR analysis showed the presence of stereoregular 1,4-trans-polyisoprene and isotactic polystyrene segments. The copolymerization via sequential monomer addition allowed the synthesis of well-defined 1,4-trans-polyisoprene-block-isotactic polystyrene, which contains two crystalline blocks. The authenticity of these new di- or multiblock copolymer materials was assessed by combined NMR, GPC, and DSC characterizations.

Alkaline-Earth Metal Complexes in Homogeneous Polymerization Catalysis

“…By adjusting the amount of Mg(nBu) 2 , up to 200 polymer chains can be generated per metal center, and good control of the molecular weight features enables the tailoring of low to medium molecular weight polymers. The same system proved effective also for the CGP of isoprene and isoprene-styrene, yet with the 1,4-trans specificity gradually decreasing in favor of the 3,4-polymer with increasing amounts of Mg(nBu) 2 [20]. Finally, it is noteworthy that, in contrast to Mg(PE) 2 species, the isolation and further manipulation of the Mg(polystyryl) 2 and Mg(polydienyl) 2 species generated in these Ln-Mg-mediated CGP processes remains to be demonstrated.…”

“…In the global context of sustainable development stigmatized by the depletion of the reserves of fossil fuel and the ever-increasing prices of oil-derived materials, linear (19) by Gibson and coworkers [38] and related bis(pyridylamine) magnesium isopropyl complexes (20) by Carpentier and coworkers [39] for the polymerization of MMA Alkaline-Earth Metal Complexes in Homogeneous Polymerization Catalysisaliphatic poly(ester)s and poly(carbonate)s prepared by ROP of cyclic (di)esters and carbonates are attracting growing attention as both commodity and specialty materials. They are often biocompatible and biodegradable, and offer thermal, physical, and mechanical properties which are complementary or comparable to those of some oil-based polymers [40][41][42][43][44][45].…”

Recent Advances in Rare Earth Complexes Bearing Allyl Ligands and Their Reactivity towards Conjugated Dienes and Styrene Polymerization

“…The ansa-lanthanidocene allyl rac-{Me2C(Ind)2}Y[ 3 -1,3-(SiMe3)2C3H3] (9Y) (Ind = 2-indenyl) was assessed for the polymerization of isoprene [32]. This compound was synthesized previously and initially evaluated for styrene polymerization as single-component catalyst [31].…”

“…By adjusting the amount of Mg( n Bu) 2 , up to 200 polymer chains can be generated per RE center. Complex 9 Y was previously shown to be active as a single-component catalyst [32], but the dispersity was improved in the presence of excess Mg( n Bu) 2 . Mechanistic investigations, also confirmed by the support of theoretical studies, demonstrated that the initiation of the polymerization resulted from the insertion of styrene into the RE-allyl (single component) or RE-alkyl (chain transfer) moiety, and that an enantiomorphic site control mechanism (ECM) was operative to account for the isoselectivity observed [39].…”

Precisely Controlled Polymerization of Styrene and Conjugated Dienes by Group 3 Single‐Site Catalysts

“…Yttrium complex 47 bearing a C 2 ‐symmetric rac ‐Me 2 C(Ind) 2 ligand could obtain trans ‐1,4‐PIP‐ co ‐iPS diblock or multiblock copolymers via either sequential or simultaneous copolymerization method. Typical plastic properties of well‐defined trans ‐1,4‐PIP‐ b ‐iPS diblock copolymers were featured because of their two crystalline chain segments …”