Chain‐Shuttling Polymerization at Two Different Scandium Sites: Regio‐ and Stereospecific “One‐Pot” Block Copolymerization of Styrene, Isoprene, and Butadiene

Abstract

The development of new generations of polymerization catalysts and technology for efficient, selective synthesis of novel polymer materials having well-controlled microstructures and desired properties has been a long-standing research subject of both academic and industrial scientists. In this endeavor, exploring the potential of untapped elements is an important strategy. Recently, the chainshuttling copolymerization of two different monomers by two Group 4 metal catalysts that show different monomer selectivities has emerged as a powerful technology for the preparation of olefin block copolymers with different segments. [1] In contrast, the potential of rare-earth catalysts in such chain-shuttling copolymerization has remained unexplored to date. [2,3] Moreover, the success of chain-shuttling copolymerization reported to date has been limited mostly to the copolymerization of ethylene and propylene (or 1-hexene), while the chain-shuttling copolymerization of styrene and a conjugated diene such as isoprene or butadiene has not been reported.We report herein the first example of chain-shuttling copolymerization of styrene, isoprene, and butadiene by two different scandium catalysts. In the presence of scandium catalyst 1 (Scheme 1), which shows high activity and high selectivity for the syndiotactic polymerization of styrene but low activity and low selectivity for isoprene, [4a-c] and scandium catalyst 2, which shows high activity and high cis-1,4selectivity for the polymerization of isoprene [4c] but low activity and low selectivity for styrene, together with a chainshuttling agent, the copolymerization of styrene and isoprene has been achieved regio-and stereoselectively at each monomer, affording for the first time block copolymers with perfect syndiotactic polystyrene (sPS) and highly regulated cis-1,4-polyisoprene (PIP) blocks. In a similar manner, the terpolymerization of styrene, isoprene, and butadiene has also been achieved for the first time to give terpolymers containing perfect sPS, highly regulated cis-1,4-PIP and highly regulated cis-1,4-PBD blocks. By replacement of the catalyst 2 with a catalyst 3, [4d] which showed high 3,4-selectivity for the polymerization of isoprene in the chain-shuttling polymerization of styrene and isoprene, novel styrene-isoprene block copolymers with sPS and 3,4-PIP blocks have been obtained for the first time.Some representative results of the polymerization and copolymerization of styrene and isoprene by three different Sc catalysts 1, 2, and 3 (Scheme 1) under various conditions are summarized in Table 1. As reported, the half-sandwich scandium dialkyl complex 1 bearing the sterically demanding C 5 Me 4 SiMe 3 ligand in combination with [Ph 3 C][B(C 6 F 5 ) 4 ] showed high activity and high syndiospecific selectivity (rrrr > 99 %) for the polymerization of styrene (Table 1, run 1), [4a] but low activity and poor regio-and stereoselectivity for the polymerization of isoprene (Table 1, run 4). [4b,c] The smaller C 5 H 5 -bound Sc analogue 2 exhibited much lower ...

Isolation and Characterization of Precise Dye/Dendrimer Ratios

“…3 The polybutadiene block shows a glass transition temperature below room temperature, providing the elastomeric character or soft block, while polystyrene with a T g above room temperature acts as the cross‐link or hard block. Di‐ and triblock copolymers are formed by anionic polymerization,1 while multiblock microstructures of homopolymers can be obtained by chain shuttling copolymerization (see below) 4d. These blocky structures show well‐defined transition temperatures ( T g or melting temperature of the homopolymers) that cannot be tuned, which restricts their fields of application.…”

Simultaneous Chain‐Growth and Step‐Growth Polymerization of Methoxystyrenes by Rare‐Earth Catalysts

“…However, the polymerization of amethoxystyrene monomer in astep-growth fashion has not been reported previously.W eh ave previously shown that half-sandwich rare-earth alkyl complexes serve as efficient catalysts for the chain-growth polymerization and copolymerization of awide range of monomers,i ncluding styrenes,t hrough continuous C = Cbond insertion. [7,8] Very recently,wefound that the same type of half-sandwich rare-earth catalyst can also catalyze the step-growth copolymerization of 1,4-dimethoxybenzene with 1,4-divinylbenzene by intermolecular CÀHp olyaddition of the anisyl unit to the vinyl group of the styrene moiety. [9] These findings invoked much interest in the polymerization behaviors of methoxystyrenes,w hich have both an anisyl group and as tyrene unit in one molecule,w ith the halfsandwich rare-earth catalysts.Inprinciple,ifthe activation of an ortho-CÀHbond of the anisole unit by the rare-earth alkyl species and subsequent addition of the resulting rare-earth metal anisyl species to the C=Cd ouble bond of the styrene unit could take place,t he step-growth polymerization of amethoxystyrene monomer would be possible (Scheme 1b).…”

A novel synthetic strategy for styrene–butadiene–styrene tri-block copolymer with high cis -1,4 units via changing catalytic active centres

“…Hou et al . [23–25] and Cui et al . [26] synthesized a series of styrene–butadiene/isoprene di-block or tri-block copolymers with a high percentage of cis -1,4 units ( cis -1,4 > 95%) and a high conversion rate using cationic alkyl rare-earth metal catalysts.…”