Changguang Yao

Highly isoselective coordination polymerization of ortho-methoxystyrene with β-diketiminato rare-earth-metal precursors.

Stereoselective coordination/insertion polymerization of the polar ortho-methoxystyrene has been achieved for the first time by using the cationic β-diketiminato rare-earth-metal species. High activity and excellent isoselectivity (mmmm>99 %) were acheived. The unmasked Lewis-basic methoxy group does not poison the Lewis-acidic metal center, but instead activates the polymerization through σ-π chelation to the active species together with the vinyl group, thus lower the coordination and activation energies as compared with those of styrene derivatives lacking the methoxy group.

Highly cis-1,4-selective coordination polymerization of polar 2-(4-methoxyphenyl)-1,3-butadiene and copolymerization with isoprene using a β-diketiminato yttrium bis(alkyl) complex

The unprecedented highly cis-1,4 selective (>99%) coordination–insertion polymerization of the polar monomer 2-(4-methoxyphenyl)-1,3-butadiene (2-MOPB) has been achieved using a β-diketiminato yttrium bis(alkyl) complex to afford a hydrophilic plastic polymer P(2-MOPB) with a water contact angle of 87.7° and glass transition temperature of 34.2 °C. The copolymerization of polar 2-MOPB and non-polar isoprene has also been successfully realized for the first time to produce a type of highly modified cis-1,4 polyisoprene with a wide range of 2-MOPB content (8.2%–88.5%). The composition was adjusted by regulating the monomer feed ratio according to the copolymerization kinetics. Hydrogenation of P(2-MOPB) provided an unusual alternating copolymer, poly(4-methoxystyrene-alt-ethylene) that could not be obtained via any other methods.

Rare-earth metal alkyl complexes bearing an alkoxy N-heterocyclic carbene ligand: synthesis, characterization, catalysis for isoprene polymerization

Treatment of imidazolium iodide [R-NHC-CH2CH(nBu)OH]I (1a (R = methyl), 1b (R = isopropyl)) and benzimidazole iodide [R-NHC(C6H4)-CH2CH(nBu)OH]I (2a (R = methyl), 2b (R = isopropyl)), respectively, with ((trimethylsilyl)methyl)lithium (LiCH2SiMe3) followed by rare-earth metal tris(alkyl)s (Ln(CH2SiMe3)3(THF)2) (Ln = Sc, Y, Lu) afforded the alkoxy-modified N-heterocyclic carbene ligated rare-earth metal bis(alkyl) complexes {[R-NHC-CH2CH(nBu)OLn(CH2SiMe3)2]2 (3a (R = methyl, Ln = Sc), 3b (R = methyl, Ln = Lu), 4a (R = isopropyl, Ln = Y), 4b (R = isopropyl, Ln = Lu)) and [(CH3)2CH-NHC(C6H4)-CH2CH(nBu)OY(CH2SiMe3)2]2 (5)} via double-deprotonation reactions. All complexes were characterized by NMR spectroscopy, elemental analysis and X-ray crystallography. They are dimers in which two rare-earth metal ions are bridged by two μ2-O atoms. Under the activation of an organoborate, complex 3a showed cis-1,4 enriched regioselectivity for isoprene polymerization (84.3%).

Neutral lutetium complex/polyamine mediated immortal ring-opening polymerization of rac-lactide: facile synthesis of well-defined hydroxyl-end and amide-core stereoregular star polylactide

A highly efficient strategy for synthesizing hydroxyl-end and amide-core, highly stereoregular, star-shaped polylactide was established by employing a lutetium complex via immortal ROP of rac-lactide with a polyamine as the chain transfer agent.

Synthesis of Ultraviolet Absorption Polylactide via Immortal Polymerization of Rac -Lactide Initiated by a Salan-Yttrium Catalyst

A highly efficient strategy for the synthesis of polylactide with the UV absorption ability was established by employing a Salan-yttrium complex (acting as a fast runing catalyst) combined with large excess hydroxyl functionalized benzophenone, BP′-OH. During polymerization, BP′-OH, acting as the chain transfer agent, attached to the active rare-earth metal catalyst via a rapid-reversible exchange reaction to initiate the polymerization. Thus, more polyester chains appeared to grow from one active metal species, and the UV absorption fragments were incorporated into the polymer chains at specific sites, in situ. A high productivity up to 1000 molLA/mol(Salan-Y) was successfully achieved and 100 BP′-labeled PLA chains grew from each active metal center.

Highly cis-1,4 Selective Living Polymerization of Unmasked Polar 2-(2-Methylidenebut-3-enyl)Furan and Diels-Alder Addition

The polymerization of a new polar diene-based monomer 2-(2-methylidenebut-3-enyl)furan (MBEF) without masking is achieved by using the bis(phosphino)carbazoleide-ligated yttrium (Y) alkyl complex upon the activation of [Ph3 C][B(C6 F5 )4 ]. Under mild conditions, the polymerizations under the monomer-to-Y ratios ranging from 100:1 to 500:1 perform fluently in high yields. The afforded polydienes bearing pendant terminal furan groups have high cis-1,4-regularity up to 98.6% and molecular weights close to the theoretic values and narrow polymer dispersity index(PDI) (1.13-1.17) suggesting a livingness polymerization mode. In addition, this novel polydiene is an excellent building block for preparing functional rubber materials. For example, via Diels-Alder addition of furan groups under mild conditions, hydroxyl groups are successfully introduced on the side chains efficiently in a 75% conversion. Furthermore, the copolymerization of polar MBEF and nonpolar isoprene is also successfully realized by the bis(phosphino) carbazoleide-ligated scandium analog to access furan-modified cis-1,4 (>97%) polyisoprene with different MBEF contents (5.3%, 8.7%).