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Chemoselective terpolymerization can produce polymer materials with diverse compositions and sequential structures, and thus have attracted considerable attention in the field of polymer synthesis. However, the intrinsic complexity of three‐component system also brings great chanllenge, in regard to the reactivity and selectivity of different monomers. Herein, we report the terpolymerization of CO2/epoxide/anhydride by a binary organocatalytic C3N3‐Py‐P3/TEB (triethylborane) system. Both the activity and chemoselectivity were highly dependent upon the molar ratio of C3N3‐Py‐P3 to TEB, and sequence‐controlled poly(ester‐carbonate) copolymers were readily synthesized through one‐pot/one‐step methodology by tuning the stoichiometric ratio of phosphazene/TEB. In particular, C3N3‐Py‐P3/TEB with a molar ratio of 1/0.5 exhibited an unprecedentedly high chemoselectivity for ring‐opening alternating copolymerization (ROAC) of cyclohexene oxide (CHO) and phthalic anhydride (PA) first and then ROAC of CO2/CHO. Thus, well‐defined triblock polycarbonate‐b‐polyester‐b‐polycarbonate copolymers can be produced from the mixture of CO2, CHO and PA using a bifunctional initiator. With C3N3‐Py‐P3/TEB=1/1, tapered copolymers were obtained, while random copolymers with high content of polycarbonate (PC) were synthesized with further increasing the amount of TEB. The mechanism of the unexpected chemoselectivity was further investigated by DFT calculations. [ABSTRACT FROM AUTHOR]

Organophosphazenes combined with triethylborane (TEB) were selected as binary organocatalyts for the copolymerization of CO2 and epoxides. Both the activity and selectivity were highly dependent on the nature of phosphazenes. 2,4,6‐Tris[tri(1‐pyrrolidinyl)‐iminophosphorane]‐1,3,5‐triazine (C3N3‐Py‐P3) with a relatively low basicity (pKa=26.5 in CD3CN) and a bulky molecular size (φ=1.3 nm) exhibited an unprecedented efficiency (TON up to 12240) and selectivity (>99 % polymer selectivity and >99 % carbonate linkages) toward copolymerization of CO2 and cyclohexene oxide (CHO), and produced CO2‐based polycarbonates (CO2‐PCs) with high molar masses (Mn up to 275.5 kDa) at 1 MPa of CO2 and 80 °C. Surprisingly, this binary catalytic system achieved efficient CO2/CHO copolymerization with TOF up to 95 h−1 at 1 atm pressure and room temperature. [ABSTRACT FROM AUTHOR]

ABSTRACT: The random copolymers poly(LA‐ran‐CL) have improved properties of degradability, mechanical strength, elasticity, and permeability over the PLA and PCL homopolymers. However, the synthesis of such copolymers is still a great challenge in polymer chemistry. In this contribution, we develop a simple but well‐designed phenoxyimine Al complex (4) with bulky Ph2CH groups, which achieves controlled random copolymerization of rac‐LA and ɛ‐CL in a living manner (Ð = 1.06–1.09). The reactivity ratios of rac‐LA and ɛ‐CL (rLA and rCL) are 1.09 and 1.05 and the average sequence lengths of the lactidyl unit (LLA) and the caproyl unit (LCL) are in the range of 1.9–2.0 at different stages of conversion. In marked contrast, Al complexes (1–3) having less bulky substituents on the ligands only produce gradient copolymers. Furthermore, this strategy of catalyst design would be readily extended to other catalytic systems including β‐ketiminato Al complex (5). © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 611–617 [ABSTRACT FROM AUTHOR]

Ultrahigh molecular weight polyethylene (UHMWPE) is a class of high-performance engineering plastics, exhibiting a unique set of properties and applications. Although many advances have been achieved in recent years, the synthesis of UHMWPE is still a great challenge. In this contribution, a series of zirconium and hafnium complexes, [2,6-(R1)2-4-R2-C6H2-N-C(camphyl)=C(camphyl)-N-2,6-(R1)2-4-R2-C6H2]MMe2(THF) (1-Zr: R1 = Me, R2 = H, M = Zr; 2-Zr: R1 = Me, R2 = Me, M = Zr; 1-Hf: R1 = Me, R2 = H, M = Hf; 2-Hf: R1 = Me, R2 = Me, M = Hf), bearing bidentate NN ligands with the bulky camphyl backbone were synthesized by the stoichiometric reactions of α-diimine ligands with MMe4 (M = Hf or Zr). All Zr and Hf metal complexes were analyzed using 1H and 13C NMR spectroscopy, and the molecular structures of complexes 1-Zr and 1-Hf were determined by single-crystal X-ray diffraction, revealing that the original α-diimine ligand was selectively reduced into the ene-diamido form and generated an 1,3-diaza-2-metallocyclopentene ring in the metal complexes. Zr complexes 1-Zr and 2-Zr showed moderate activity (up to 388 kg(PE)·mol−1(M)·h−1), poor copolymerization ability, but unprecedented molecular weight capability toward ethylene/1-octene copolymerization. Therefore, copolymers with ultrahigh molecular weights (>600 or 337 × 104 g∙mol−1) were successfully synthesized by 1-Zr or 2-Zr, respectively, with the borate cocatalyst [Ph3C][B(C6F5)4]. Surprisingly, Hf complexes 1-Hf and 2-Hf showed negligible activity under otherwise identical conditions, revealing the great influence of metal centers on catalytic performances. [ABSTRACT FROM AUTHOR]